Assembly Of Nanoclusters Research Articles

Atomistic modeling of the directed-assembly of bimetallic Pt-Ru nanoclusters on Ru(0001)-supported monolayer graphene

The formation of Pt-Ru nanoclusters (NCs) by sequential deposition of Pt and Ru on a periodically rumpled graphene sheet supported on Ru(0001) is analyzed by atomistic-level modeling and kinetic Monte Carlo simulations. The "coarse-scale" periodic variation of the adsorption energy of metal adatoms across the graphene sheet directs the assembly of NCs to a periodic array of thermodynamically preferred locations. The modeling describes not only just the NC densities and size distributions, but also the composition distribution for mixed NCs. A strong dependence of these quantities on the deposition order is primarily related to different effective mobilities of Pt and Ru on the supported graphene.

Starting Point of Cluster-Derived Silicon Nanowires

The assembly of medium-sized silicon nanoclusters was simulated to study the starting point of the formation of cluster-derived silicon nanowires (CDSiNWs). Hydrogen-terminated clusters were found repulsing each other and inter-connecting through the hydrogen bonds, thus could not form a stable silicon nanowire (SiNW). Between the pristine silicon clusters without hydrogen saturation, the assembly takes place automatically. An orientation priority in cluster assembly is obtained, as silicon clusters Si29 are more possibly adhered along direction than the other directions. Such an assembly may be the starting point of the SiNW growth along direction. Moreover, it indicates the possibility of silicon tetrapods or zigzag wires formation, besides straight SiNWs.

Tuning Hierarchical Cluster Assembly in Pulsed Laser Deposition of Al-doped ZnO

ABSTRACTThe synthesis of hierarchically assembled Al-doped ZnO layers by Pulsed Laser Deposition (PLD) at room temperature was investigated. PLD was performed in a background pressure of 100 Pa O2 to deposit clusters in a low energy regime and obtain nano- and mesostructures resulting from a hierarchical assembly of nanoclusters. We here analyzed the effects of varying the gas flow rate on mesoscale morphology, mass density and optical properties. The variation of the target-to-substrate distance was also investigated, identifying its effects on mass density and film morphology. The optimization of optical properties in terms of transparency and light scattering capability is of potential interest for photovoltaic applications.

Plasmonic Mode Engineering with Templated Self-Assembled Nanoclusters

Plasmonic nanoparticle assemblies are a materials platform in which optical modes, resonant frequencies, and near-field intensities can be specified by the number and position of nanoparticles in a cluster. A current challenge is to achieve clusters with higher yields and new types of shapes. In this Letter, we show that a broad range of plasmonic nanoshell nanoclusters can be assembled onto a lithographically defined elastomeric substrate with relatively high yields using templated assembly. We assemble and measure the optical properties of three cluster types: Fano-resonant heptamers, linear chains, and rings of nanoparticles. The yield of heptamer clusters is measured to be over 30%. The assembly of plasmonic nanoclusters on an elastomer paves the way for new classes of plasmonic nanocircuits and colloidal metamaterials that can be transfer-printed onto various substrate media.

Directed assembly of Ru nanoclusters on Ru(0001)-supported graphene: STM studies and atomistic modeling

Directed assembly of an array of Ru nanoclusters (NCs) is achieved by deposition of Ru at around room temperature on a single layer of graphene supported on Ru(0001). In this system, directed assembly is guided by the periodic moire structure of the buckled graphene sheet. Behavior is analyzed utilizing both scanning tunneling microscopy and atomistic lattice-gas modeling together with kinetic Monte Carlo simulation. We elucidate the kinetics of NC nucleation and growth, specifically assessing the coverage dependence of the NC density and height distribution. In addition, we provide a detailed characterization of the development of short-range spatial order within the NC array, identifying a tendency for row formation.

DNA-Directed Assembly of Asymmetric Nanoclusters Using Janus Nanoparticles

Asymmetric assembly of nanomaterials has attracted broad interests because of their unique anisotropic properties that are different from those based on the more widely reported symmetric assemblies. Despite the potential advantages, programmable fabrication of asymmetric structure in nanoscale remains a challenge. We report here a DNA-directed approach for the assembly of asymmetric nanoclusters using Janus nanoparticles as building blocks. DNA-functionalized spherical gold nanoparticles (AuNSs) can be selectively attached onto two different hemispheres of DNA-functionalized Janus nanoparticle (JNP) through DNA hybridization. Complementary and invasive DNA strands have been used to control the degree and reversibility of the assembly process through programmable base-pairing interactions, resulting in a series of modular and asymmetric nanostructures that allow systematic study of the size-dependent assembly process. We have also shown that the attachment of the AuNSs onto the gold surface of the Janus nanoparticle results in red shifting of the UV-vis and plasmon resonance spectra.

Lamellar Assembly of Cadmium Selenide Nanoclusters into Quantum Belts

Here, we elucidate a double-lamellar-template pathway for the formation of CdSe quantum belts. The lamellar templates form initially by dissolution of the CdX(2) precursors in the n-octylamine solvent. Exposure of the precursor templates to selenourea at room temperature ultimately affords (CdSe)(13) nanoclusters entrained within the double-lamellar templates. Upon heating, the nanoclusters are transformed to CdSe quantum belts having widths, lengths, and thicknesses that are predetermined by the dimensions within the templates. This template synthesis is responsible for the excellent optical properties exhibited by the quantum belts. We propose that the templated-growth pathway is responsible for the formation of the various flat, colloidal nanocrystals recently discovered, including nanoribbons, nanoplatelets, nanosheets, and nanodisks.

Thermally driven isotropic crystallinity breaking of nanocrystals: Insight into the assembly of EuS nanoclusters and nanorods with oleate ligands

Clusters of EuS nanocrystals formed through the thermal assembly of 2.5 nm nanocrystal monomers by varying the annealing temperature from 300 to 340 °C. Below 310 °C, oleate ligands stabilized on the surface of the EuS nanocrystals, giving rise to their low solubility in triethanolamine while facilitating monomer–monomer oriented attachment into short-chain structures. Above 320 °C, the oleate ligands thermally detached from the surface and were replaced by oleyamine. This reaction mechanism was a multilevel oriented attachment, based on calculations of the nanocrystal growth kinetics, whose evolution gave rise to the formation of EuS nanorods at 340 °C.

In situ formation and ordered assembly of gold nanoclusters to nano-ribbons at the oil/water interface

Ordered assembly of ultra-small nanoparticles or nanoclusters remains a challenge due to their large surface energy induced ripening and isotropic aggregation. In this communication, an in situ formation and assembly of ultra-small gold nanoclusters at the oil/water interface was developed to assemble gold nanoclusters into well-defined nano-ribbon structures. The resulting nano-ribbons exhibited enhanced optical properties and larger Stokes's shift than those of random dispersed gold nanoclusters.

Controlled Assembly of Biodegradable Plasmonic Nanoclusters for Near-Infrared Imaging and Therapeutic Applications

Metal nanoparticles with surface plasmon resonance (SPR) in the near-infrared region (NIR) are of great interest for imaging and therapy. Presently, gold nanoparticles with NIR absorbance are typically larger than 50 nm, above the threshold size of approximately 5 nm required for efficient renal clearance. As these nanoparticles are not biodegradable, concerns about long-term toxicity have restricted their translation into the clinic. Here, we address this problem by developing a flexible platform for the kinetically controlled assembly of sub-5 nm ligand-coated gold particles to produce metal/polymer biodegradable nanoclusters smaller than 100 nm with strong NIR absorbance for multimodal application. A key novel feature of the proposed synthesis is the use of weakly adsorbing biodegradable polymers that allows tight control of nanocluster size and, in addition, results in nanoclusters with unprecedented metal loadings and thus optical functionality. Over time, the biodegradable polymer stabilizer degrades under physiological conditions that leads to disassembly of the nanoclusters into sub-5 nm primary gold particles which are favorable for efficient body clearance. This synthesis of polymer/inorganic nanoclusters combines the imaging contrast and therapeutic capabilities afforded by the NIR-active nanoparticle assembly with the biodegradability of a polymer stabilizer.

Computational study on tuning the 2D self assembly of metallic nanoclusters

We discuss the size selection of metallic 2D clusters in cases where the growth proceeds on flat or wedged surfaces. The growth of nanoclusters is modelled using reaction kinetic model rate equations, where the kinetics are described by size dependent attachment and detachment rates, and the energetics are described through the free energy difference of the clusters. The model describes how the optimum stationary size and small size dispersion are reached, and what are the properties of the stationary size distribution. In addition to the geometrical factors, it is shown that the deposition flux can also be used to tune the size distribution towards the desired property.

Nanocluster Model of Intermetallic Compounds with Giant Unit Cells: β, β′-Mg2Al3 Polymorphs

A novel method for the computational description of intermetallics as an assembly of nanoclusters was improved and applied to extremely complicated crystal structures of beta, beta'-Mg(2)Al(3) polymorphs. Using the TOPOS program package that implements the method, we separated two types of two-shell primary nanoclusters A, A1, A2, and B consisting of 57-63 atoms that completely compose the structures of the polymorphs. The nanocluster model interprets structural disordering in beta-Mg(2)Al(3): the disordered atoms form the inner shell of the nanocluster A, while the outer shells of all nanoclusters are preserved. The self-assembly of the beta, beta'-Mg(2)Al(3) crystal structures was considered within the hierarchical scheme: 0D primary polyhedral clusters (coordination polyhedra) --> 0D two-shell primary nanoclusters A, A1, A2, or B --> 0D supracluster-precursor AB(2) --> 1D primary chain --> 2D microlayer --> 3D microframework. The self-assembly scheme proves the similarity of beta, beta'-Mg(2)Al(3) to other extremely complicated Samson's phases, NaCd(2) and ZrZn(22); the spatial arrangement of the centers of nanoclusters in these structures as well as the topology of the corresponding network conform to the Laves phase MgCu(2). Using the TOPOS procedure of searching for finite fragments in infinite nets we found that nanocluster B is a typical fragment of intermetallic compounds: it exists in intermetallics belonging to 42 Pearson classes. The nanocluster A was found only in two Pearson classes: cF464 and hP238, while the nanoclusters A1 and A2 occur in beta'-Mg(2)Al(3) only. Thus, the nanoclusters A, A1, and A2 can be considered as "determinants" of the corresponding structures.

Precise positioning and assembly of metallic nanoclusters as building blocks of nanostructures: A molecular dynamics study

Molecular dynamics simulations are used to study the manipulation of metallic nanoclusters. These particles are assumed as potential building blocks for bottom-up manufacturing of nanoscale structures. One of the key factors in the assembly of nanoclusters is the precise positioning of them by a manipulation system. Prediction of the corresponding behavior under the influence of working conditions is of crucial importance for planning of controlled positioning and assembly of nanoclusters. The focus of the present research is on ultra-fine metallic nanoclusters. The effects of material type and manipulation strategy on the success of the process have been investigated by molecular dynamics. Such qualitative simulation studies can evaluate the chance of success of a certain nanopositioning scenario regarding different working conditions before consuming high experimental expenses.

Short- and long-term clinical outcomes of diabetics and nondiabetics receiving bare-metal stents versus drug-eluting stents

We describe phase transitions in microfilm assemblies of octanethiol (OT)-capped 2–4 nm-diameter Ag nanoclusters prepared from solutions with OT/Ag+ ratios of ∼50. Using DSC we observe two melting/crystallization-type reversible phase transitions: one at ∼61 °C due to interdigiated unattached octanethiol, and the other at ∼125 °C due to the phase comprised of the assembly of OT-capped nanoclusters. Increased thermal fluctuations weaken the inter-chain hydrophobic interactions between interdigitated OT molecules, leading to both phase transitions. The thiolate bond of OT-molecules bound to Ag nanoclusters are more rigid, thereby requiring a higher temperature to increase the flexibility of the alkyl chain of OT, and to melt the nanocluster assembly. The mobility of the nanoclusters in the melt is limited, and morphological features of the original assemblies are retained during recrystallization. No observable mass loss is detected up to ∼180 °C, above which OT molecules desorb from the Ag nanoclusters.

Stepwise surface encoding for high-throughput assembly of nanoclusters

Self-assembly offers a promising method to organize functional nanoscale objects into two-dimensional (2D) and 3D superstructures for exploiting their collective effects. On the other hand, many unique phenomena emerge after arranging a few nanoscale objects into clusters, the so-called artificial molecules. The strategy of using biomolecular linkers between nanoparticles has proven especially useful for construction of such nanoclusters. However, conventional solution-based reactions typically yield a broad population of multimers or isomers of clusters; furthermore, the efficiency of fabrication is often limited. Here, we describe a novel high-throughput method for designing and fabricating clusters using DNA-encoded nanoparticles assembled on a solid support in a stepwise manner. This method efficiently imparts particles with anisotropy during their assembly and disassembly at a surface, generating remarkably high yields of well-defined dimer clusters and Janus (two-faced) nanoparticles. The method is scalable and modular, assuring large quantities of clusters of designated sizes and compositions.

Aligning one-dimensional arrays of nanoclusters on a thin film of Al 2O 3 grown on vicinal NiAl surfaces

We present a self-organised approach for the synthesis of one-dimensional (1D) arrays of supported nanoclusters. By oxidising NiAl surfaces vicinal to the (1 0 0) plane tilted along the crystallographic direction [0 1 0], we produced ordered thin films of θ-Al 2O 3 that exhibit uniform protrusion stripes propagating uniquely along direction [0 0 1] of the NiAl. These protrusions are preferential centres for nucleation of metal deposited from a vapour; the nanoclusters grown from such metal are aligned and form massive 1D cluster arrays along direction [0 0 1]. The arrays of Co nanoclusters exhibit a diameter as small as 3 nm and length exceeding a micrometer. The results imply prospective applications for which a patterned assembly of nanoclusters is desired.

Qualitative study of nanocluster positioning process: Planar molecular dynamics simulations

One of the key factors in the assembly of nanoclusters is the precise positioning of them by a manipulation system. Currently the size of clusters used as building blocks is shrinking down to a few nanometers. In such cases, the particle nature of matter plays an important role in the manipulator/cluster/substrate interactions. Having a deeper insight to the aforementioned nano-scale interactions is crucial for prediction and understanding of the behavior of nanoclusters during the positioning process. In the present research, 2D molecular dynamics simulations have been used to investigate such behaviors. Performing planar simulations can provide a fairly acceptable qualitative tool for our purpose while the computation time is greatly reduced in comparison to 3D simulations. The system consists of a tip, cluster and substrate. The focus of the present research is on ultra-fine metallic nanoclusters. To perform this research, Nose–Hoover dynamics and Sutton–Chen interatomic potential will be used to investigate the behavior of the above system which is made from different transition metals. The effects of material type, tip form and manipulation strategy on the success of the process have been investigated by planar molecular dynamics. Such qualitative simulation studies can evaluate the chance of success of a certain nanopositioning scenario regarding different working conditions before consuming large-scale computation time or high experimental expenses.

Synthesis of Beta/MCM-41 composite molecular sieve with high hydrothermal stability in static and stirred condition

Beta/MCM-41 micro/mesoporous composite materials have been prepared through assembly of zeolite Beta nanoclusters and their hydrolysis products in the presence of CTAB under static or stirred conditions. The resulting materials were characterized by powder XRD, TEM and nitrogen adsorption–desorption. Hydrothermal stability of the obtained Beta/MCM-41 composites was evaluated by boiling in distilled water for different periods of time under refluxing. All materials exhibit very high hydrothermal stability.

Monochromatic photoluminescence obtained from embedded ZnO nanodots in an ultrahard diamond-like carbon matrix

At room temperature, we observe the self assembly of nanoclusters in an amorphous matrix using a vacuum deposition technique. Self-assembled ZnO nanoclusters embedded in hard diamond-like amorphous carbon thin films, deposited by high vacuum Filtered Cathodic Vacuum Arc (FCVA) technique at room temperature without post-processing, have been observed. A selective self assembly of metal and oxygen ions in a 3-element plasma was observed. XPS distinctly showed presence of ZnO and DLC-mixture in 5, 7 and 10 at.% Zn (in target) films while maintaining high sp 3 content. This in turn improved the Young's modulus value of the ZnO nanoclusters embedded in DLC film (~ 220 GPa) compared to bulk ZnO (~ 110 GPa). Films with ZnO detected were observed to exhibit absorption edge at 377 nm monochromatic UV light emissions. This corresponded to a band gap value of about 3.30 eV. The emission with greatest intensity (after normalization) was detected from 10 at.% Zn (in target) film where presence of ZnO nanoclusters (~ 40 nm) in DLC matrix were confirmed by TEM. This showed that well-defined crystalline ZnO nanoclusters contributed to strong PL signal. Strong monochromatic emissions detected hinted that no defect states were present.

Synthesis, characterization, and catalytic properties of hydrothermally stable macro–meso–micro-porous composite materials synthesized via in situ assembly of preformed zeolite Y nanoclusters on kaolin

Hydrothermally stable composite materials with hierarchical macro–meso–micro-porous structure were successfully synthesized via in situ assembly of preformed zeolite Y nanoclusters on kaolin using cetyltrimethylammonium bromide as template under alkaline conditions. The characterization results show that the mesophase in the composite contains primary and secondary structural building units of zeolite Y. The building units contribute micropores in the composite with acidity similar to that of zeolite Y, whereas the macroporous kaolin substrate contributes macropores. This hierarchical macro–meso–micro-porous structure increases the accessibility of the active sites in the composite to reactants and thus confers superior catalytic performance on the resulting catalyst in cracking heavy crude oil. The present work demonstrates that the in situ assembly of zeolitic nanoclusters on substrates (e.g., kaolin) can provide a novel route for fabricating composite materials with hierarchical pore structure.