Influence of surface ligands on the electronic structure of Fe-Pt clusters: A density functional theory study

The geometrical and electronic structures of a chemically disordered face-centered-cubic- (fcc) FePt cluster capped with various organic ligands, including propanoic acid, propylamine, and propanethiol, were investigated by means of density functional theory (DFT) calculations within a generalized gradient approximation (GGA). Detailed analysis of the electronic structure revealed that (1) Fe atoms are the favored adsorption sites of the ligands on the surface of the FePt cluster; however, for propanethiol, adsorption can also occur at Pt sites. (2) The spin magnetic moment of Fe atoms at adsorption sites in the clusters containing adsorbed ligands decreases slightly compared to that in the bare cluster on the adsorption of the ligand, and it does not depend on the length of hydrocarbon chain of the ligand. The decrease in the magnetic moment originates from the interplay between the strong hybridization of the majority d states of Fe atoms with majority p states of O, N, and S atoms and the electron transfer between the ligands and Fe atoms on the surface of the clusters involving d, p, and s states of the Fe atoms, as well as from the high symmetry of the surface Fe atoms on adsorption of a ligand

Chemical Synthesis of Blue-emitting Metallic Zinc Nano-hexagons

We report a new ligand directed chemical synthesis of hexagonal shaped zinc nanoplates. The produced nano-hexagons (NHex)s display a thickness of about 20–40 nm and diameter ranging from about 200–350 nm, exhibiting a high aspect ratio. While zinc is traditionally highly susceptible to oxidation, these high surface area NHexs possess a remarkable resistance to atmospheric oxidation, owing to their unique surface crystalline faces and the fact that these particles are protected by organic surface ligands. The zinc NHexs size, morphology and chemical properties were characterized using transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy, among other techniques. Photoluminescence spectroscopy analysis revealed blue photoluminescence emission, making these NHexs potentially ideal for optics, optoelectronics or security printing

One-pot synthesis and characterization of well defined core–shell structure of FePt@CdSe nanoparticles

Magnetic fluorescent FePt@CdSe core–shell nanoparticles were directly synthesized by sequential addition of precursors and using tetraethylene glycol as a solvent and a reducing agent. The core–shell NPs were successfully formed over a wide range of temperature (240–300 °C). The size and composition of the FePt core were tuned by changing the ratio of surfactant (oleic acid and oleylamine) to metal precursors [Fe_3(CO)_ and Pt(acac)_2] and the feeding ratio of the precursors, respectively. The CdSe shell thickness also could be varied from 1 to 8.5 nm by rational control of the total amount of Cd and Se precursors. FePt@CdSe core–shell NPs with a core size of about 4.3 nm and shell thickness of about 2.5 nm displayed a fluorescence emission around 600 nm. They exhibited superparamagnetic behaviour at room temperature and the blocking temperature was about 55 K, which was almost the same as uncoated FePt NPs, while the coercivity decreased from 400 Oe for the FePt NPs to 200 Oe. Detailed characterization of intermediates and synthesized FePt@CdSe NPs revealed the fine structure and formation mechanism

Assembly of Ag@Au Nanoparticles Using Complementary Stranded DNA Molecules and Their Detection Using UV-Vis and Raman Spectroscopic Techniques

Silver nanoparticles coated by a layer of gold (Ag@Au) have received much attentionbecause of their potential application as ultra sensitive probes for the detection of biologicallyimportant molecules such as DNA, proteins, amino acids and many others. However, the abilityto control the size, shape, and monodispersity of the Ag@Au structure has met with limitedsuccess. In our own research we have addressed this challenge by creating an aqueous wetchemical synthesis technique towards size and shape controllable Ag@Au nanoparticles. Thesematerials are highly interesting because of the tunable silver core size, and the tunable gold shellthickness, opening many avenues to the modification of the particle properties in terms of biomolecularsensing. The resulting nanoparticle probes were functionalized with twocomplementary stranded DNA oligonucleotides. When combined, the complementary strandshybridized, causing the Ag@Au nanoparticles to assemble into large nano-structures. Thepresence of the oligonucleotide was confirmed through a series of techniques including UV-Visand Raman spectroscopy, as well as TEM, XPS, DLS, and many others. The results reflect therole that the nanoparticle physical properties play in the detection of the bio-molecules, as wellas elucidate the characteristics of the bio-molecule/nanoparticle interaction

Aqueous Synthesis and Characterization of Ag and Ag-Au Nanoparticles: Addressing Challenges in Size, Monodispersity, and Structure

In this paper we demonstrate the synthesis of monodispersed silver nanoparticles (NPs) of controlled size (20.5 ± 3.3 nm) in aqueous phase from a silver hydroxide precursor with sodium acrylate as dual reducing–capping agent. We then coat these NPs in a layer of gold with controllable thickness through a reduction–deposition process. The materials are characterized using several techniques including HR-TEM, UV-Vis, XRD, XPS, etc. The results show that we were able to synthesize not only monodispersed Ag NPs but also core–shell Ag–Au NPs with a discrete structure, which is significant because of the challenges associated with the creation of such materials, namely the propensity of metallic Ag to be oxidized by the presence of ionic Au. The NPs are of interest for use in a wide range of potential applications including bio-medical diagnostics and bio-molecular detection as well as many others

Synthesis of Size and Shape Controlled Silver Nanoparticles Coated by a Thin Layer of Gold and Their Use as Ultrasensitive Biomolecular Probes

Silver nanoparticles coated by a layer of gold (Ag@Au) have received much attentionbecause of their potential application as ultra sensitive probes for the detection of biologicallyimportant molecules such as DNA, proteins, amino acids and many others. However, the abilityto control the size, shape, and monodispersity of the Ag@Au structure has met with limitedsuccess. In our own research we have addressed this challenge by creating an aqueous wetchemical synthesis technique towards size and shape controllable Ag@Au nanoparticles. Thesematerials are highly interesting because of the tunable silver core size, and the tunable gold shellthickness, opening many avenues to the modification of the particle properties in terms of biomolecularsensing. The resulting nanoparticle probes were functionalized with twocomplementary stranded DNA oligonucleotides. When combined, the complementary strandshybridized, causing the Ag@Au nanoparticles to assemble into large nano-structures. Thepresence of the oligonucleotide was confirmed through a series of techniques including UV-Visand RAMAN spectroscopy, as well as HR-TEM, XPS, DLS, and many others. The resultsreflect the role that the nanoparticle physical properties play in the detection of the bio-molecules,as well as elucidate the characteristics of the bio-molecule/nanoparticle interaction

Study on Formation Mechanism and Ligand-directed Architectural Control of Nanoparticles Composed of Bi, Sb and Te: Toward One-pot Synthesis of Ternary (Bi,Sb)2Te3 Nanobuilding Blocks

This paper reports a study on the formation mechanism of nanoparticles (NPs) composed of bismuth, antimony and tellurium for thermoelectric materials using a modified polyol synthetic route. Our one-pot synthesis technique has proven highly versatile in creating a wide range of different anisotropic NPs such as nanowires (NWs), nanodiscs (NDs), nanoribbons and nanospines (NDs studded on NWs) simply by modifying the capping species or elemental precursor feeding ratio used in the synthesis. However, an independent control of morphology and composition is still hugely challenging and the facile synthesis of (Bi,Sb)_2Te_3 solid solution NPs is not a trivial task, reflecting the complex nature of this multicomponent system. To achieve this goal, it is imperative to understand the formation mechanism based on a systematic investigation of mono- and binary elemental NP systems. Our study clearly shows the different actions of oleylamine (OAM) and decanethiol (DT) capping ligands in our synthesis reaction. In the case of DT capping system, Te NDs are first formed, and then, Bi and Sb are separately incorporated into the Te ND structure via catalytic decomposition of Bi-DT and Sb-DT complexes on the Te ND surfaces. Therefore, the resulting NPs are phase segregated into Te, Bi_2Te_3 and Sb_2Te_3. On the other hand, in the case of the OAM capping system, Te NWs and Bi-Sb solid solution NPs are formed separately, and then, parts of Te NWs are transformed into (Bi,Sb)_2Te_3 phase via oriented attachment of Bi-Sb NPs and Te NWs. These findings are crucially important towards the one-pot synthesis of uniform (Bi,Sb)_2Te_3 nanobuilding blocks with controllable characteristics for highly efficient thermoelectric materials

Development of magnetic separation system of magnetoliposomes

The magnetic separation technology using sub-microsized ferromagnetic particle is indispensable in many areas of medical biosciences. For example, ferromagnetic particles (200-500 nm) are widely used for cell sorting in stem cell research with the use of cell surface-specific antigens. Nanosized ferromagnetic particles (10-20 nm) have been suggested as more suitable in drug delivery studies given their efficiency of tissue penetration, however, the magnetic separation method for them has not been established. One of the major reasons is that magnetic force acting on the object particles decreases drastically as a particle diameter becomes small. In this study, magnetic force acting on the targets was enhanced by the combination of superconducting magnet and the filter consisting of ferromagnetic particle. By doing so, we confirmed that FeO of 20 nm in diameter was trapped in the magnetic filter under an external magnetic field of 0.5 T. FeO encapsulated with phospholipid liposomes of 200 nm in diameter was also shown to be trapped as external magnetic field of 1.5 T, but not of 0.5 T. We also showed the result of particle trajectory calculation which emulated well the experimental data

Spectroscopic study on the charge redistribution between Au and Ag in Au@Ag core-shell nanoparticles

Charge transfer in Au nanoparticles (NPs) and Au@Ag core-shell NPs synthesized with a wet-chemical reduction method was investigated by X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) techniques. The electron depletion of Au 5d state in the Au@Ag_x NPs compared to Au NPs was ascertained by the XANES analysis in Au L_-edges though the Ag thickness (x nm), which affected the hole density of Au 5d states. The order of Au 5d-state hole density was confirmed as Au foil ≅ Au NPs < Au@Ag_x NPs. The positive and negative shifts in the Au 4f and Ag 3d binding energies in XPS spectra of Au@Ag_x NPs compared to Au or Ag NPs suggested that the Ag shell formation strongly contributes to the electron depletion of 5d state in Au atoms of the Au core. According to these results, we concluded that the electron transfer from Au to Ag in the Au@Ag heteromeric NPs followed the charge compensation mechanism