Optical properties of polymer capped gold nanoparticles of various sizes (diameter 3-6 nm) have been studied. We present a new scheme to extract size dependent variation of total dielectric function of gold nanoparticles from measured UV-Vis absorption data. The new scheme can also be used, in principle, for other related systems as well. We show how quantum effect, surface atomic co - ordination and polymer - nanoparticle interface morphology leads to a systematic variation in inter band part of the dielectric function of gold nanoparticles, obtained from the analysis using our new scheme. Careful analysis enables identification of the possible changes to the electronic band structure in such nanoparticles.
We studied the magnetic and transport properties of Co nanoparticles (NPs) being capped with varying amounts of Pt. Beside field and temperature dependent magnetization measurements we performed delta-M measurements to study the magnetic interactions between the Co NPs. We observe a transition from demagnetizing towards magnetizing interactions between the particles for an increasing amount of Pt capping. Resistivity measurements show a crossover from giant magnetoresistance towards anisotropic magnetoresistance.
We report on the effect of organic acid capping on the behavior of magnetite nanoparticles. The nanoparticles of magnetite were obtained using microwave activated process, and the magnetic properties as well as the electron magnetic resonance behavior were studied for the Fe3O4 nanoparticles capped with alginic acid. The capped nanoparticles exhibit improved crystalline structure of the surface which leads to an enhanced magnetization. The saturation magnetization Ms increases to ~75% of the bulk magnetization. The improved structure also facilitates quantization of spin-wave spectrum in the f…
We propose a new type of surfactants, namely, tetrazole derivatives which can be controllably removed from the nanoparticle surface. Tetrazoles are a peculiar class of heterocyclic compounds. The presence of four nitrogen atoms in the tetrazole ring determines their interesting physical and chemical properties. Tetrazoles show high thermal stability below 200C while decomposing at higher temperature with formation of gaseous products and no or very little solid residue. Moreover, the tetrazole group is known as an important ligand in coordination chemistry. Its donor nitrogen atoms can bind to…
When the particle size of a metal is reduced, it is expected that an energy gap will open due to the quantum size effect. However, the energy gap in platinum (Pt) metal nanoparticles has not been observed directly by nuclear magnetic resonance (NMR). To investigate the particle size dependence of the electronic state of Pt nanoparticles, we performed 195Pt NMR experiments on thiol-capped Pt nanoparticles with three different average diameters of less than 3 nm. For the nanoparticles with a diameter of 2.8 nm, we observed usual metallic behavior with a smaller density of states than that of the…
Gold nanoclusters encapsulated with organic molecules are of great interest for its possible applications in the fields of molecular electronics, catalysis and medical science. Here we demonstrate that monolayer and bilayer films of thiol-capped gold nanoclusters can exhibit diode-like properties provided controlled spatial asymmetry exist between two tunnel junctions used to connect a thiol capped gold nanoclusters. Current-voltage characteristics of this rectifier were obtained from conducting probe atomic force microscopy measurements and also from conventional two probe resistance measurem…
The technology problems of fabricating different, nanometers sized gold particles in the layered composites like light-sensitive chalcogenide glass/gold nanoparticles/transparent substrate or titanium/titanium oxide/gold nanoparticles were investigated in our work. Combination of ion implantation, plasma deposition with annealing processes results physical routes for creation of gold nanoparticles in the mentioned structures, which possess plasmon effects. These functionalized structures are planned to use for investigations of optical recording processes, biocompatibility of titanium implants…
This paper is devoted to present the results of creation of gold nanoparticles on titanium surface. We focused on the problem how to create gold nanoparticles on the titanium surface with defined particle size and distribution, which could be interesting for several applications (e.g. providing well-defined substrates for biomedical research, etc.). To do that the sample is affected by the complex physical rout of gold nanoparticles formation: by gold ion implantation, thin Au layer deposition and thermal annealing. The effect of the technology, influence on the surface structure and its param…
We demonstrate an organic memory-transistor device based on a pentacene-gold nanoparticles active layer. Gold (Au) nanoparticles are immobilized on the gate dielectric (silicon dioxide) of a pentacene transistor by an amino-terminated self-assembled monolayer. Under the application of writing and erasing pulses on the gate, large threshold voltage shift (22 V) and on/off drain current ratio of ~3E4 are obtained. The hole field-effect mobility of the transistor is similar in the on and off states (less than a factor 2). Charge retention times up to 4500 s are observed. The memory effect is main…
In metal nanoparticles (NPs) supracrystals, the metallic core provides some key properties, e.g. magnetization, plasmonic response or conductivity, with the ligand molecules giving rise to others like solubility, assembly or interaction with biomolecules. The formation of these supracrystals depends on a complex interplay between many forces, some stemming from the core, some from the ligands. At present, there is no known approach to characterize the local order of ligand molecules or their dynamics with atomic spatial resolution. Here, we develop a methodology based on small-angle ultrafast …
We report the first direct observation of ferromagnetic spin polarization of Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold magnetization is explored. Magnetization of gold atoms estimated by XMCD shows a good agreement with the results obtained by conventional magnetometry. This result is evidence of intrinsic spin polarization in nano-sized gold.
In this paper, we have tried to find out the origin of magnetism in Gold nanoparticles (Au- NPs). We observe that upon incorporating Gold nanoparticles (Au-NPs) in Fe3O4 nanoparticle medium the net magnetisation increases compared to the pure Fe3O4 nanoparticle medium. This increase of magnetization can be attributed to the large orbital magnetic moment formation at the Au/magnetic particle interface indicating that magnetism observed in Au-NPs is an interfacial effect. This interfacial effect has been supported by the observation of sudden transition from positive saturated magnetisation to a…
Films of close-packed Au nanoparticles are coupled electrodynamically through their collective plasmon resonances. This collective optical response results in enhanced light-matter interactions, which can be exploited in various applications. Here, we demonstrate their application in sensing volatile organic compounds, using methanol as a test-case. Ordered films over several cm2 were obtained by interfacial self-assembly of colloidal Au nanoparticles (~10 nm diameter) through controlled evaporation of the solvent. Even though isolated nanoparticles of this size are inherently non-scattering, …
Single-walled carbon nanotubes (SWNTs) have been coated with gold and platinum nanoparticles either by microwave treatment or by the click reaction and the Raman spectra of these SWNT-metal nanoparticle composites have been investigated. Analysis of the G bands in the Raman spectra shows an increase in the proportion of metallic SWNTs on attachment with metal nanoparticles. This conclusion is also supported by the changes observed in the RBM bands. Ab-initio calculations reveal that semiconductor-metal transition occurs in SWNTs due to Columbic charge transfer between the metal nanoparticles a…
The optical and morphological properties of hollow gold nanoparticles (HGNPs) can be finely modified by employing Poly-L-Lysine hydrobromide (PLL), an homo poly aminoacid of the L-lysine, used as reducer and stabilizer. We investigate locally the plasmonic response of these nanostructures by electron energy loss spectroscopy (EELS). The plasmon excitations are interpreted by discrete dipolar approximation (DDA) simulations. We demonstrate that this controlled top-down morphological modification a fine tuning of the optical response is possible. Unlike the traditional lithographic techniques, t…
The factors controlling the size and morphology of nanoparticles have so far been poorly understood. Data-driven techniques are an exciting avenue to explore this field through the identification of trends and correlations in data. However, for these techniques to be utilized, large datasets annotated with the structural attributes of nanoparticles are required. While experimental SEM/TEM images collected from controlled experiments are reliable sources of this information, large-scale collection of these images across a variety of experimental conditions is expensive and infeasible. Published…
We show that, when a gold nanoparticle is coated by a thin layer of nematic liquid crystal, the deformation produced by the nanoparticle surface can enhance the splitting of the nanoparticle surface plasmon. We consider three plausible liquid crystal director configurations in zero electric field: boojum pair (north-south pole configuration), baseball (tetrahedral), and homogeneous. From a calculation using the Discrete Dipole Approximation, we find that the surface plasmon splitting is largest for the boojum pair, intermediate for the homogeneous, and smallest for the baseball configuration. …
We report a simple, rapid, and quantitative wide-field technique to measure the optical extinction $σ_{\rm ext}$ and scattering $σ_{\rm sca}$ cross-section of single nanoparticles using wide-field microscopy enabling simultaneous acquisition of hundreds of nanoparticles for statistical analysis. As a proof of principle, we measured nominally spherical gold nanoparticles of 40\,nm and 100\,nm diameter and found mean values and standard deviations of $σ_{\rm ext}$ and $σ_{\rm sca}$ consistent with previous literature. Switching from unpolarized to linearly polarized excitation, we measured $σ_{\…
Gold nanoparticles are highly desired for a range of technological applications due to their tunable properties, which are dictated by the size and shape of the constituent particles. Many heuristic methods for controlling the morphological characteristics of gold nanoparticles are well known. However, the underlying mechanisms controlling their size and shape remain poorly understood, partly due to the immense range of possible combinations of synthesis parameters. Data-driven methods can offer insight to help guide understanding of these underlying mechanisms, so long as sufficient synthesis…
With photothermal efficiency higher than traditionally used reduced graphene oxide, while simultaneously being water dispersible, we propose biocompatible Molybdenum Nanoribbons - gold Nanoparticles (MoS2 NR-Au NPs) system for synergistically enhanced photo-thermal ablation of cancerous cells (100% fatality) using NIR radiation (808nm), owing to commendable temperature rise above 70oC at a much faster rate.
The practical use of nanoparticle superlattices (NPSLs) which are of great interest as materials with designed functionalities is often limited by their lack of structural stability under various utilization conditions. Here, we report a new method for directly synthesizing NPSL fully embedded in hierarchically porous silica which provides exceptional stability and efficient pathways for reactant molecules, making the NPSL highly efficient catalyst. The superlattices made of 12 nm gold nanoparticles exhibit exceptionally high catalytic activity for CO oxidation at low temperature, showing high…
Rare-earth-doped optical materials are important for light sources in optoelectronics, as well as for efficient optical amplification elements and other elements of photonics. On the basis of the previously developed method of anhydrous, low-temperature synthesis of Er/Yb oxides from their chlorides we fabricated proper nanoparticles with defined parameters and used them for the development of optically transparent, luminescent polymer nanocomposite with low optical scattering, suitable for direct, light-induced formation of photonic elements. Introduction of preformed gold nanoparticles in su…
The final performance of a molecular electronic device is determined by the chemical structure of the molecular wires used in its assembly. Molecular place-exchange was used to incorporate di-thioacetate terminated molecules into ordered arrays of dodecanethiol capped gold nanoparticles. X-ray photoelectron spectroscopy confirmed successful molecular replacement. Room-temperature molecular conductance of a statistically large number of devices reveals that conductance is enhanced by up to two orders of magnitude for the di-thioacetate terminated molecules. Density functional theory transport c…
In this article, a practical procedure for absolute intensity calibration for SAXS studies on liquid microjets is established, using a gold nanoparticle suspension as standard so that the intercept at $Q=0$ of the SAXS scattering curve would provide a scaling reference. In order to get the most precise extrapolation at $Q=0$, we used an extension to the Guinier approximation, with a second-order term in the fit that adapts to a larger $Q$-range.
We demonstrate here that the gold nanoparticles (AuNPs) obtained in micellar solutions are susceptible to the precursor complex nature and specific counterion effects controlling the reaction kinetics, particles size and shape. The tested approach consisted in reducing the HAuCl4 complex with ascorbic acid or citric acid in dodecyltrimethylammonium (DTA) solutions, at 318 K, in the presence of bromide (Br), methanesulfonate (Ms), trifluoroacetate (TFA) or trifluoromethanesulfonate (Tf) ions. Bromide ions replaced the chloride ions in the precursor gold complex, and no nanoparticle formation co…
The present paper deals with the systematic growth of plasmonic gold nanoparticles (Au NPs) on molybdenum disulphide (MoS$_2$) nanosheets as well as the effect of Au NPs on the optical and magnetic properties. The crystalline nature of the nanocomposites is confirmed by X-ray diffraction and transmission electron microscopic techniques. The optical properties are characterized using absorption and Raman spectroscopic techniques. The electron paramagnetic resonance technique is used to study the magnetic response of the nanocomposites. The paper attempts to gain a fundamental understanding of t…
In this report we present systematic magnetic studies of pure iron oxide nanoparticles and gold iron oxide nanocomposite with increasing Au particle size/content. For the magnetic studies of these samples we have measured: (1) zero field cooled (ZFC) and field cooled (FC) magnetization, (2) ac susceptibility, (3) magnetization vs field at various temperatures, (4) thermoremanant magnetization relaxation (TRM) and zero field cooled magnetization relaxation (ZFCM) at fixed temperature for various wait times tw for studying the aging effect, (5) magnetization memory effect and (6) exchange bias a…
We present a numerical model allowing to determine the electron and lattice temperature dynamics in a gold nanoparticle under subpicosecond pulsed excitation, as well as that of the surrounding medium. For this, we have used the electron-phonon coupling equation in the particle with a source term linked with the laser pulse, and the ballistic-diffusive equations for heat conduction in the host medium. Our results show that the heat transfer rate from the particle to the matrix is significantly smaller than the prediction of Fourier's law. Consequently, the particle temperature rise is much lar…
We report the studies of ultrafast electron nanocrystallography on size-selected Au nanoparticles (2-20 nm) supported on a molecular interface. Reversible surface melting, melting, and recrystallization were investigated with dynamical full-profile radial distribution functions determined with sub-picosecond and picometer accuracies. In an ultrafast photoinduced melting, the nanoparticles are driven to a non-equilibrium transformation, characterized by the initial lattice deformations, nonequilibrium electron-phonon coupling, and upon melting, the collective bonding and debonding, transforming…
Bio-conjugated nanomaterials play a promising role in the development of novel supramolecular structures, molecular machines, and biosensing devices. In this study, lipid-conjugated gold nanoparticles were synthesized and allowed to form a self-assembled monolayer structure. The nanoparticles were prepared by a phase transfer method, which involved the reduction of potassium tetrachloroaurate (III) by sodium citrate in an aqueous solution and the simultaneous transfer of the reduced species to an organic medium containing DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine). The gold nanoparticl…
We use density functional theory (DFT) to investigate the electronic structure and chemical properties of gold nanoparticles. Different structural families of clusters are compared. For up to 60 atoms we optimize structures using DFT-based simulated annealing. Cluster geometries are found to distort considerably, creating large band gaps at the Fermi level. For up to 200 atoms we consider structures generated with a simple EMT potential and clusters based on cuboctahedra and icosahedra. All types of cluster geometry exhibit jellium-like electronic shell structure. We calculate adsorption energ…
Multi-electron transfer processes, such as hydrogen and oxygen evolution reactions, are crucially important in energy and biological science but require favorable catalysts to achieve fast kinetics. Nanostructuring catalysts can dramatically improve their properties, which can be difficult to understand due to strain and size dependent thermodynamics, the influence of defects, and substrate dependent activities. Here, we report 3D imaging of single gold nanoparticles during catalysis of ascorbic acid decomposition using Bragg coherent diffractive imaging (BCDI) as a route to eliminate ensemble…
Penta-twinned gold nanoparticles under pressure: a comprehensive study
Université de Genève（日内瓦大学）；University of Cantabria（坎塔布里亚大学）；CSIC-UPV/EHU（西班牙国家研究委员会-巴斯克地区大学）；Synchrotron SOLEIL（SOLEIL同步辐射中心）；CIC biomaGUNE（CIC生物医学研究中心）；Ikerbasque, Basque Foundation for Science（伊克尔巴斯科，巴斯克科学基金会）
High surface area graphene sheets were obtained by electrochemical exfoliation of graphite in an acid media under constant potential conditions. Filtration and centrifugation processes played an important role in order to obtain stable dispersions in water. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging revealed highly exfoliated crystalline samples of ~5(\mum). Raman, FT-IR and XPS spectroscopy further confirmed the high quality of the exfoliated material. The electrochemically exfoliated graphene (EEG) was decorated with gold nanoparticles (AuNP) using …
We report on a photoconductive gain effect in two-dimensional arrays of gold nanoparticles, in which alkane molecules are inserted. The nanoparticle arrays are formed by a self-assembly process from alkanethiol-coated gold nanoparticles, and subsequently they are patterned on a Si/SiO2 chip by a microcontact printing technique. We find that the photoconductance of the arrays is strongly enhanced at the frequency of the surface plasmon of the nanoparticles. We interpret the observation as a bolometric enhancement of the conductance of the nanoparticle arrays upon excitation of the surface plasm…
In this work, the structural and magnetic properties of the gold-coated FePt nanoparticles synthesized from high-temperature solution phase are presented. The amount of gold was optimized to obtain most of the FePt particles coated. The particle diameter increases from 4 to 10 nm as observed by TEM. The magnetic properties are largely affected by the coating. At low temperature, the coercive field Hc of the coated nanoparticles decreases about three times respect to the uncoated and the blocking temperature reduces to the half. The changes of the magnetic behavior are discussed in terms of the…
Except serving as an excellent gift on proper occasions, gold finds applications in life sciences, particularly in diagnostics and therapeutics. These applications were made possible by gold nanoparticles, which differ drastically from macroscopic gold. Versatile surface chemistry of gold nanoparticles allows coating with small molecules, polymers, biological recognition molecules. Theoretical investigation of nanoscale gold is not trivial, because of numerous metastable states in these systems. Unlike elsewhere, this work obtains equilibrium structures using annealing simulations within the r…
We report here an original single-step process for synthesis and self-organization of gold colloids by simply incorporating gold salts into a solution prepared with Polystyrene (PS) - Polymethylmethacrylate (PMMA) copolymer, thiolated PS and Propylene Glycol Methyl Ether Acetate (PGMEA) as solvent. The spin-coating and annealing of this solution allows then the formation of PS domains. Depending on the polymer concentration of the as-prepared solution, there can be either one or several gold nanoparticles (NPs) per PS domains. For high concentration of gold nanoparticles in PS domains, the cou…
In this work we present the magnetic properties of gold coated FePt nanoparticles and the study of stable aqueous dispersions of FePt@Au and FePt synthesized after ligand exchange with mercaptoundecanoic acid. The particle size determined from TEM micrographs goes from 4 nm for the uncoated nanoparticles to a maximum of 10 nm for the gold coated ones indicating that the thickness of the shell ranges from 1 to 3 nm. The magnetic characterization consists in hysteresis cycles at 10 and 300 K. The results show that, at low field and room temperature, the magnetic behavior of uncoated and coated n…
We present a computational study for the equilibrium shape of gold nanoparticles. By linking extensive quantum-mechanical calculations, based on Density-Functional Theory (DFT) to Wulff construction, we predict equilibrium shapes that are in good agreement with experimental observa- tions. We discuss the effect of the interactions between a nanoparticle and the encapsulating material on the equilibrium shape. As an example, we calculate adsorption of CO on several different Au(hkl) and use the results to explain the experimentally observed shape change of Au nanoparticles.
The near-field scanning optical microscopic (NSOM) imaging of Au nanoparticles with size in the sub-wavelength limit (<wavelength/2N.A.) is reported. The NSOM imaging technique can resolve the objects which is beyond the scope of optical microscope using visible light (wavelength=500 nm) with objectives having a numerical aperture (N.A.) close to unity. The role of evanescent waves which is an exponentially decaying field with higher momenta i.e., lower wavelengths compared to that of normal light, in the metal dielectric interface is realized for imaging of noble metal nanostructures with sub…
We demonstrate that highly-ordered two-dimensional crystals of ligand-capped gold nanoparticles display a local photo-mechanical stiffness as high as that of solids such as graphite. In out-of equilibrium electron diffraction experiments, a strong temperature jump is induced in a thin film with a femtosecond laser pulse. The initial electronic excitation transfers energy to the underlying structural degrees of freedom, with a rate generally proportional to the stiffness of the material. With femtosecond small-angle electron diffraction, we observe the temporal evolution of the diffraction feat…
Origin of the rich polymorphism of gold in penta-twinned nanoparticles
Université de Genève（日内瓦大学）；University of Cantabria（坎塔布里亚大学）；Centro de Física de Materiales (CSIC-UPV/EHU)（材料物理中心（西班牙科学研究中心-巴斯克国立大学））；Synchrotron SOLEIL（SOLEIL同步辐射中心）；CIC biomaGUNE（CIC生物医学研究中心）；Ikerbasque, Basque Foundation for Science（伊克拉巴斯科，巴斯克科学基金会）
A differential interference contrast microscopy technique, which employs a photonic crystal fiber as a white-light source, is used to measure both the real and imaginary parts of the complex dielectric constant of single 10 and 15 nm gold nanoparticles over a wavelength range of 480 to 610 nm. Noticeable deviations from bulk gold measurements are observed at short wavelengths and for individual particles even after taking into account finite-size surface damping effects.
The radiative heat transfer between gold nanoparticle layers is presented using the coupled dipole method. Gold nanoparticles are modelled as effective electric and magnetic dipoles interacting via electromagnetic fluctuations. The effect of higher-order multipoles is implemented in the expression of electric polarizability to calculate the interactions at short distances. Our findings show that the near-field radiation reduces as the radius of the nanoparticles is increased. Also, the magnetic dipole contribution to the heat exchange becomes more important for larger particles. When one layer…
We compare the light extinction spectra of elongated gold nanoparticles with different shapes (cylinder, spherocylinder and ellipsoid) and sizes of 10 to 100~nm. We argue that the equivalence of the various moments of mass distribution is the natural comparison criterion -rather than the length-to-diameter (aspect) ratio generally used in the literature- and that it leads to better spectral correspondence between the various shapes.
We present here an original process combining top-down and bottom-up approaches by annealing a thin gold film evaporated onto a hole template made by etching a PS-PMMA copolymer film. Such process allows a better control of the gold nanoparticle size distribution which provides a sharper localized surface plasmon resonance. This makes such route appealing for sensing applications since the figure of merit of the Au nanoparticles obtained after thermal evaporation is more than doubled. Such process could besides allow tuning the localized surface plasmon resonance by using copolymer with variou…
The simulation and analysis of the thermal stability of nanoparticles, a stepping stone towards their application in technological devices, require fast and accurate force fields, in conjunction with effective characterisation methods. In this work, we develop efficient, transferable, and interpretable machine learning force fields for gold nanoparticles based on data gathered from Density Functional Theory calculations. We use them to investigate the thermodynamic stability of gold nanoparticles of different sizes (1 to 6 nm), containing up to 6266 atoms, concerning a solid-liquid phase chang…
We present theoretical calculations for the absorption properties of protein-coated gold nanoparticles on graphene and graphite substrates. As the substrate is far away from nanoparticles, numerical results show that the number of protein bovine serum molecules molecules aggregating on gold surfaces can be quantitatively determined for gold nanoparticles with arbitrary size by means of the Mie theory and the absorption spectra. The presence of graphitic substrate near protein-conjugated gold nanoparticles substantially enhances the red shift of the surface plasmon resonances of the nanoparticl…
The ability to partially oxidize methane at low temperatures and pressures would have important environmental and economic applications. Although methane oxidation on gold nanoparticles has been observed experimentally, our density functional theory (DFT) calculations indicate neither CH4, CH3, nor H adsorb on a neutral gold nanoparticle. However, by positively charging gold nanoparticles, e.g. through charge transfer to the TiO2 substrate, CH4 binding increases while O2 binding remains relatively unchanged. We demonstrate that CH4 adsorption is via bonding with the metal s levels. This holds …
We suggest that the size effect in heterogeneous catalysis on gold nanoparticles (GNP) of ~1.3 - 9 nm size can be related to spontaneous terahertz (THz) emission of GNPs in the process of channeling the energy of longitudinal phonons therein into THz electromagnetic radiation. Since rotational and vibrational energy levels of molecules adsorbed on the GNP surface are in the THz range, the irradiation by self-induced THz photons would engage the molecules' swing and twisting, which in its turn would weaken or break the intramolecular bonds, facilitating their entering a chemical reaction on the…
Morphology, structure and magnetic properties of nanocomposites of magnetite (Fe3O4) nanoparticles and alginic acid (AA) are studied. Magnetite Fe3O4 nanoparticles and the nanoparticles capped with alginic acid exhibit very distinct properties. The chemical bonding between alginic acid and surface of magnetite nanoparticles results in recovery of surface magnetization. On the other hand, it also leads to enhanced surface spin disorder and unconventional behavior of magnetization observed in Fe3O4-AA nanocomposites at low temperatures.
The dependence of the surface plasmons resonance (SPR) frequency on the size of gold nanoparticles (GNPs) is experimentally studied. The measured data for the SPR frequency by UV-Vis spectroscopy and GNPs diameter by Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) are collected in the course of classical citrate GNPs synthesis. The relationship between the GNPs size and the blue shift of the light absorption is presented. They are fitted by an equation with a single free parameter, the dielectric permittivity of the surrounding media. Th…
UV-Vis absorption spectroscopy is frequently used to characterize the size and shape of gold nanoparticles. We present a full-spectrum model that yields reliable results for the commonly encountered case of mixtures of spheres and rods in varying proportions. We determine the volume fractions of the two populations, the aspect ratio distribution of the nanorods (average value and variance) and the interface damping parameter. We validate the model by checking the fit results against small-angle X-ray scattering and transmission electron microscopy data and show that correctly accounting for th…
In this study nanoscale structure and associated energy dissipation behavior of nanoparticulates of tungsten disulphide (WS2) and nanoparticles of gold (Au) were investigated by advanced scanning probe and electron microscopy techniques. WS2 nanoparticulates were deposited on silicon substrate by van der Waals adhesion transfer-deposition mechanisms. The templates of three size variants of Au nanoparticles, close packed (4-6nm), well dispersed (120-150nm) and clusters of (120-150 nm) nanoparticles were prepared on silicon substrates. Nano-microstructure, morphology, topography and phase shift …
We use molecular dynamics simulations to study the melting of gold icosahedral clusters of a few thousand atoms. We pay particular attention to the behavior of surface atoms, and to the equilibrium shape of the cluster. We find that although the surface of the cluster remains ordered up to the melting T_m, the increasing mobility of vertex and edge atoms significantly soften the surface structure, leading to inter- and intra-layer diffusion, and shrinking of the average facet size, so that the average shape of the cluster is nearly spherical at melting.
