Core-shell Nanoclusters Research Articles

Unusual behavior in magnesium-copper cluster matter produced by helium droplet mediated deposition.

We demonstrate the ability to produce core-shell nanoclusters of materials that typically undergo intermetallic reactions using helium droplet mediated deposition. Composite structures of magnesium and copper were produced by sequential condensation of metal vapors inside the 0.4 K helium droplet baths and then gently deposited onto a substrate for analysis. Upon deposition, the individual clusters, with diameters ∼5 nm, form a cluster material which was subsequently characterized using scanning and transmission electron microscopies. Results of this analysis reveal the following about the deposited cluster material: it is in the un-alloyed chemical state, it maintains a stable core-shell 5 nm structure at sub-monolayer quantities, and it aggregates into unreacted structures of ∼75 nm during further deposition. Surprisingly, high angle annular dark field scanning transmission electron microscopy images revealed that the copper appears to displace the magnesium at the core of the composite cluster despite magnesium being the initially condensed species within the droplet. This phenomenon was studied further using preliminary density functional theory which revealed that copper atoms, when added sequentially to magnesium clusters, penetrate into the magnesium cores.

Luminescent Cu(0)@Cu(I)–TGA core–shell nanoclusters via self-assembly

Antioxidation has always been a challenge in synthesis and application of high luminescence of copper nanoclusters. In this work, Cu(0)@Cu(I)–mercaptoacetic acid (TGA) core–shell structure is developed by well-defined assemblies in aqueous-based solution, which is formed by multilayer shell Cu(I)–TGA and Cu(0) core of 5 atoms. The core–shell structure shows intrinsic green photoluminescence with stability of over two months. The developed structure has been systematically characterized by Fourier-transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electrospray ionization mass spectrometry (ESI-MS), dynamic light scattering (DLS), and photoluminescence (PL) spectroscopy.

Computational cogitation of Cn@Al12 clusters.

A variety of novel Cn Al12 core-shell nanoclusters have been investigated using density functional calculations. A series of Cn cores (n=1-4) have been encapsulated by icosahedral Al12 , with characteristic physical properties (energetics and stabilities, ionisation energies, electron affinities) calculated for each cluster. Other isomers, with the Cn moiety bound externally to the Al12 shell, have also been studied. For both series, a peak in stability was found for n(C)=2, a characteristic that appears to be inextricably linked with the relaxation of the constituent parts upon dissociation. Analysis of trends for ionisation energies and electron affinities includes evaluation of contributions from the carbon and aluminium components, which highlights the effects of composition and morphology on cluster properties.

Raman Scattering Surface Signal Enhancement: Induced by Au@SiO2 core-shell nanoclusters and nanorods

Surface-enhanced Raman scattering (SERS) is a powerful technique that has been widely applied in different fields to identify molecular structures and characterize atomic interactions. In this article, we introduce the theory and instrumentation relevant to SERS induced by silicon dioxide (SiO 2 )-coated shell isolated gold nanoparticles (Au@SiO 2 ) core-shell nanoclusters (NCs) and nanorods (NRs). We explain the synthetic methods used to generate Au@SiO 2 core-shell NCs and NRs and show how they can be manipulated for SERS applications, including their use in biosensors that are able to quantitatively analyze small molecules and their roles in the structural identification of -amorphous ultrathin solid-state film materials and in elucidating the interphase reactions between the electrode and electrolyte in lithium-ion (Li-ion) batteries. Our findings support the view that SERS techniques, used in conjunction with metallic NCs or NRs, can reduce the detection limits for target molecules and are, thus, applicable to future studies of nanoscale materials.

A new spectroelectrochemical cell for in situ measurement of Pt and Au K-edge X-ray absorption fine structure.

A new spectroelectrochemical cell to investigate the structure of Pt/Au nanoclusters using Pt and Au K-edge X-ray absorption fine structure (XAFS) measurements under the electrochemical conditions is developed. K-edge XAFS measurements for Pt and Au require a sample as thick as 1-2 cm, which prevents homogeneous potential distribution. We can measure in situ Pt and Au K-edge XAFS spectra and determine reasonable electrochemical surface areas using our developed spectroelectrochemical cell. This work provides a new approach to analyze Pt/Au core-shell nanoclusters. The new cell is designed to be applied to both spectra with high absorption-edge energies such as the K-edge of Pt and Au and those with low absorption-edge energy such as Pt L-edge.

Oxide shell reduction and magnetic property changes in core-shell Fe nanoclusters under ion irradiation

Ion irradiation effects are studied on the Fe-based core-shell nanocluster (NC) films with core as Fe and shell as Fe3O4/Fe3N. These NC films were deposited on Si substrates to thickness of ∼0.5 μm using a NC deposition system. The films were irradiated at room temperature with 5.5 MeV Si2+ ions to ion fluences of 1015 and 1016 ions/cm2. It is found that the irradiation induces grain growth, Fe valence reduction in the shell, and crystallization or growth of Fe3N. The film retained its Fe-core and its ferromagnetic properties after irradiation. The nature and mechanism of oxide shell reduction and composition dependence after irradiation were studied by synthesizing additional NC films of Fe3O4 and FeO + Fe3N and irradiating them under the same conditions. The presence of nanocrystalline Fe is found to be a major factor for the oxide shell reduction. The surface morphologies of these films show dramatic changes in the microstructures due to cluster growth and agglomeration as a result of ion irradiation.

The search for the good Pd-based catalyst for oxygen reduction reaction: core–shell M4@Pd20 nanowires

The dissociation barriers of O2 and the adsorption energies of atomic O on the icosahedron M@Pd12, double icosahedron M2@Pd17 core–shell nanoclusters, and the M@Pd (M = Mn, Fe, Co, Ni, Cu, Pd) nanowires (NWs) are studied. It is found that the M@Pd NWs can probably serve as good catalysts for oxygen reduction reaction with both small O2 dissociation energy (0.10–0.23 eV) and O adsorption energy (1.19–1.28 eV). The reasons for the advantage of the M@Pd NWs are discussed in detail.

Theoretical Investigation of the Mechanism of the Water–Gas Shift Reaction on Cobalt@Gold Core–Shell Nanocluster

We studied the mechanism of the water–gas shift reaction (WGSR; CO + H2O → CO2 + H2) catalyzed by Co6@Au32 core–shell nanoalloy using density-functional theory (DFT) calculations to investigate the bimetallic effects on the catalytic activation. The molecular structures and adsorbate/substrate interaction energies were predicted, along with the potential energy surface constructed using the nudged elastic band (NEB) method. Our results indicated that the energetic barriers of the two hydrogen dissociation reactions are lower on the core–shell nanoalloy than on Au38. Furthermore, all of the related chemical species of the WGSR can adsorb stably on Co6@Au32 to allow the reactions to take place under ambient pressure. To gain insight into the synergistic effect in the catalytic activity of the Co6@Au32 nanoalloy, the nature of the interaction between the adsorbate and substrate was analyzed by detailed electronic local densities of states (LDOS) as well as molecular structures.

Evidence for core–shell nanoclusters in oxygen dispersion strengthened steels measured using X-ray absorption spectroscopy

Nanostructured ferritic alloys (NFA) dispersion strengthened by an ultra high density of Y–Ti–O enriched nano-features (NF) exhibit superior creep strength and the potential for high resistance to radiation damage. However, the detailed character of the NF, that precipitate from solid solution during hot consolidation of metallic powders mechanically alloyed with Y2O3, are not well understood. In order to clarify the nature of the NF, X-ray absorption spectroscopy (XAS) technique, including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were used to characterize the local structure of the Ti and Y atoms in both NFA powders and consolidated alloys. The powders were characterized in the as-received, as-milled and after annealing milled powders at 850, 1000 and 1150°C. The consolidated alloys included powders hot isostatic pressed (HIPed) at 1150°C and commercial vendor alloys, MA957 and J12YWT. The NFA XAS data were compared various Ti and Y-oxide standards. The XANES and EXAFS spectra for the annealed and HIPed powders are similar and show high temperature heat treatments shift the Y and Ti to more oxidized states that are consistent with combinations of Y2Ti2O7 and, especially, TiO. However, the MA957 and J12YWT and annealed–consolidated powder data differ. The commercial vendor alloys results more closely resemble the as-milled powder data and all show that a significant fraction of substitutional Ti remains dissolved in the (BCC) ferrite matrix.

Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties

A cluster deposition method was used to produce films of loosely aggregated nanoclusters (NCs) of Fe core-Fe3O4 shell or fully oxidized Fe3O4. Films of these NC on Si(100) or MgO(100)/Fe3O4(100) were irradiated to 1016 Si2+/cm2 near room temperature using an ion accelerator. Ion irradiation creates structural change in the NC film with corresponding chemical and magnetic changes which depend on the initial oxidation state of the cluster. Films were characterized using magnetometry (hysteresis, first order reversal curves), microscopy (transmission electron, helium ion), and x-ray diffraction. In all cases, the particle sizes increased due to ion irradiation, and when a core of Fe is present, irradiation reduces the oxide shells to lower valent Fe species. These results show that ion irradiated behavior of the NC films depends strongly on the initial nanostructure and chemistry, but in general saturation magnetization decreases slightly.

Designed Fabrication of Unique Eccentric Mesoporous Silica Nanocluster-Based Core–Shell Nanostructures for pH-Responsive Drug Delivery

A novel and facile strategy using poly(acrylic acid) (PAA) as a nanoreactor and template has been proposed and applied for the first time to fabricate a novel and unique class of multifunctional eccentric Fe3O4@PAA/SiO2 core-shell nanoclusters (NCs) consisting of a single Fe3O4 nanoparticle (NP), PAA, and eccentric SiO2 NCs that are composed of a large number of small fluorescent SiO2 NPs. Interestingly, the resulting eccentric PAA shell around Fe3O4 NPs as a high water-absorbent polymer is like a "reservoir" to absorb and retain water molecules inside its net structure to confine the growth of small SiO2 NPs inside the PAA networks, resulting in the formation of an eccentric SiO2 NC with aggregated pores. The thicknesses of uniform and well-dispersed SiO2 NCs can also be precisely controlled by varying the amount of tetraethyl orthosilicate (TEOS). Importantly, the synthetic method has been confirmed to be universal and extended to other functional NPs with different compositions and shapes as eccentric cores. Furthermore, the as-prepared multifunctional eccentric Fe3O4@PAA/SiO2 core-shell NCs combined fluorescence imaging, ultrahigh drug loading capacity (1.13 mg doxorubicin/mg eccentric NCs), and pH-responsive drug release into one were taken as an example to study the applications in simultaneous fluorescence imaging and pH responsive drug delivery into prostate cancer PC3M cells.

Exchange bias in core-shell iron-iron oxide nanoclusters

An exchange bias study has been performed on core-shell iron-iron oxide (Fe-Fe3O4) nanoclusters (NCs) of sizes 11 nm and 14 nm carrying a different core to shell ratio. NCs show complicated behaviors due to competition between interfacial exchange and Zeeman energy in the presence of magnetic field during cooling. These behaviors are accompanied by the evolution of size-dependent cluster structures in the ferromagnetic-core/ferri- or antiferro-magnetic-shell. Smaller clusters have larger coercive field, exchange bias field, and vertical magnetization shift due to the greater contribution from frozen spins of shell/interfaces and magnetic frustration by the defects and voids present at the interface. These smaller clusters thus also show more dramatic changes with the training effect. Both sizes of clusters display an additional anomaly of the upper part of the hysteresis loop at 10 K under low cooling field (0.1 kOe). This anomaly decreases with number of loop cycles with same field, and disappears with large cooling field (>0.1 kOe). It may be caused by the competition between the magnetization reversal and the magnetostatic interactions.

Experimental Investigation on Core Shell Nanocomposite of Cr<sub>1-x</sub>V<sub>x</sub>S<sub>2</sub>

Electrical and optical character of nanostructured Cr1-xVxS2 is studied here. This sulphide based nanoClusters (NC) was developed through chemical sol-gel route using (NH4)2Cr2O7 and NH4VO3 as active reagent and biopolymer gum acacia is used as capping agent. Core-shell NC has developed with sequential addition of active reagents in sulphation process. It is also possible to develop another type of core shell NC by reversal of the sequence of added reagents, i.e. interchanging the core and shell part. Experimental investigation including UV-VIS spectroscopy, dc current-voltage characteristics (CVC) have carried on. The results of CVC at room temperature (RT) show the distinctive features of localized energy levels. UV-VIS spectroscopic analysis shows absorption peak is blue shifted due to quantum confinement of nanoparticles. Overall appearance of optical absorption curve is completely different for two NCs. Peak positions are different for two types of core shell NC which confirms that the constituent materials of core and shell of two NC s has interchanged.

Au@Pd core–shell nanoclusters growing on nitrogen-doped mildly reduced graphene oxide with enhanced catalytic performance for hydrogen generation from formic acid

Here we report a green and facile strategy for the direct nucleation and growth of ultrafine (1.8 nm) and well dispersed Au@Pd core–shell nanoclusters on nitrogen-doped mildly reduced graphene oxide (Au@Pd/N–mrGO) without any surfactant and additional reducing agent. During the synthesis, N–mrGO acts as both the reducing agent and support by taking advantage of its moderate reducing and high dispersing capacities. Unexpectedly, the as-prepared Au@Pd/N–mrGO hybrid exhibits much greater activity than its alloy or monometallic counterparts toward hydrogen generation from formic acid aqueous solution without using any additive at room temperature.

From Aggregation-Induced Emission of Au(I)–Thiolate Complexes to Ultrabright Au(0)@Au(I)–Thiolate Core–Shell Nanoclusters

A fundamental understanding of the luminescence of Au-thiolate nanoclusters (NCs), such as the origin of emission and the size effect in luminescence, is pivotal to the development of efficient synthesis routes for highly luminescent Au NCs. This paper reports an interesting finding of Au(I)-thiolate complexes: strong luminescence emission by the mechanism of aggregation-induced emission (AIE). The AIE property of the complexes was then used to develop a simple one-pot synthesis of highly luminescent Au-thiolate NCs with a quantum yield of ~15%. Our key strategy was to induce the controlled aggregation of Au(I)-thiolate complexes on in situ generated Au(0) cores to form Au(0)@Au(I)-thiolate core-shell NCs where strong luminescence was generated by the AIE of Au(I)-thiolate complexes on the NC surface. We were able to extend the synthetic strategy to other thiolate ligands with added functionalities (in the form of custom-designed peptides). The discovery (e.g., identifying the source of emission and the size effect in luminescence) and the synthesis protocols in this study can contribute significantly to better understanding of these new luminescence probes and the development of new synthetic routes.

High Stability and Reactivity of Pt-Based Core–Shell Nanoparticles for Oxygen Reduction Reaction

Structural stability and catalytic reactivity of M@Pt12 core–shell nanoclusters with different core atom (M) are systematically investigated using ab initio density functional theory calculations with the generalized gradient approximation. We found that the pure D5h-Pt13 cluster is venerable to reactants and may loss its activity in reaction conditions. The insertion of Fe, Co, Tc, Ru, Rh, Re, Os, or Ir into its core, forming D5h M@Pt12 core–shell nanoclusters, may significantly enhance the structural stability and may also further improve its catalytic activity. Our findings provide useful insights for the design of robust bimetallic nanocatalysts.

Theoretical Calculations on the Oxidation of CO on Au55, Ag13Au42, Au13Ag42, and Ag55 Clusters of Nanometer Size

Using density-functional theory (DFT), we investigated the oxidation of CO on Au55, Ag13Au42, Au13Ag42, and Ag55 metal clusters of nm size. The structures of oxidation intermediates and at the transition states on the potential-energy surfaces were derived with the nudged-elastic-band (NEB) method. According to our results, the coupling of CO and O2 molecules to form intermediate OCOO has the least energy barrier (0.13 eV) on the Ag13Au42 core–shell nanocluster, whereas the dissociation of the O–O bond of OCOO to form CO2 and O on the Au13Ag42 core–shell nanocluster is the easiest process with a 0.15 eV barrier height. To understand the electronic property of these nanocluster catalysts and their interactions with the adsorbates, we calculated the electron localization functions, Bader charges, and local densities of states; the results were consistent and explicable.

Intercluster Interaction and Magnetic Interaction between Iron Core and Iron Oxide Shell in Core-Shell Nanoclusters

ABSTRACTThe intercluster interactions of iron/iron oxide core shell nanoclusters have been investigated, and their dependence on cluster size (d) has been discussed. A cluster deposition system is used to prepare core-shell nanoclusters with different d, varying from 9 to 14 nm.Transmission Electron Microscopy has been used for physical characterization, and Vibrating Sample Magnetometer for magnetic study. The cluster – cluster interactions have been investigated by field dependent isothermal remanent magnetization (IRM) and dc demagnetization (DCD) measurements at room temperature. Henkel plot shows more negative deviation from non- interacting case for bigger size nanoclusters than smaller size clusters.

Assembly of a luminescent core–shell nanocluster featuring a Ag34S26 shell and a W6O216− polyoxoanion core

Bridging between silver clusters and polyoxoanion clusters, the first 1D assembly, [Ag(34)(S(t)Bu)(26)(W(6)O(21))(CF(3)COO)](CF(3)COO)·Et(3)N·20CH(3)OH (1), based on POM-templated silver-thiolate nanoclusters featuring a [Ag(34)(S(t)Bu)(26)(CF(3)COO)](7+) shell and a [W(6)O(21)](6-) core is reported. This novel core-shell nanocluster possesses nanoscopic morphology, displays intense deep-blue emission in solution under ambient conditions and also shows special electrochemical properties.

Optical properties of pure and core-shell noble-metal nanoclusters from TDDFT: The influence of the atomic structure

Optical properties of pure and core-shell noble-metal nanoclusters from TDDFT: The influence of the atomic structure