Correlating electron tomography and plasmon spectroscopy of single noble metal core-shell nanoparticles

The 3D structure reconstruction of gold core-silver shell nanoparticles by electron tomography is combined with optical dark-field spectroscopy. Electron tomography allows segmentation of the particles into core and shell subvolumes and facilitates avoiding Bragg diffraction artifacts inherent in 2D images. This advantage proves essential for accurate correlation of plasmon spectra and structure. We find that for the nanoparticles of near-spherical shape studied here the plasmon resonances depend on the relative size of the core and shell, rather than on their exact shapes and concentricity. A remarkable dependence of the spectral shape on the permittivity of the surrounding medium is also demonstrated, suggesting that core-shell nanoparticles can be used as ratiometric sensors with a very high dynamic range.     

Synthesis of core-shell nanoparticles using organic surface-functionalized gold and Au@SiO2 nanoparticles as multifunctional initiators in atom transfer radical polymerization

Gold and Au@SiO2 nanoparticles were synthesized and surface-functionalized by initiators for atom transfer radical polymerization (ATRP), either using a thiol or a trialkoxysilane anchor group for the immobilization of the initiating functionality. The thus obtained initiator-capped gold systems were applied in polymerizations of various monomers, such as styrene, methacrylic acid trimethyloxysilyl propylester and isoprene and copolymers thereof. The final inorganic-organic core-shell nanoparticles were characterized applying different techniques such as electron microscopy and light scattering. Kinetic studies of the polymerizations revealed that they were highly controlled and therefore the thickness of the polymer shell could be easily adjusted. The obtained nanoparticles formed stable suspensions in various organic solvents and can therefore be used as building blocks for polymer nanocomposites.     

A compact model for multi-island single electron transistors

Multi-island single electron transistor is an important kind of the single electron transistor, which is convenient to realize the controllable room temperature operation. A novel semi-empirical compact model for the Multi-island single electron transistor is proposed. The new approach combines the orthodox theory of the single electron tunneling through single coulomb island and a novel empirical analysis procedure for the chain of multi coulomb islands to solve the current of the whole multi-island single electron transistor. The tunneling rates are calculated based on the orthodox theory for the single electron tunneling. The tunneling currents representing the first splitted peaks in the coulomb oscillation curves are calculated according to the assumption that the currents through all the coulomb islands are equal to each other at the stable states, while the currents representing the other splitted peaks are constructed and merged together according to the empirical analysis. The model is verified by the traditional SET simulator SIMON and shows much faster calculation speed than SIMON. Therefore, the novel compact model is suitable for the large scale MISET circuit simulation.     

Three-dimensional simulation of realistic single electron transistors

We present an approach, and its implementation in a computer program, for the three-dimensional (3-D) simulation of realistic single electron transistor (SET) structures, in which subregions with different degrees of quantum confinement are simultaneously considered. The proposed approach is based on the self-consistent solution of the many body Schrodinger equation with density functional theory and on the computation of the conductance of tunnel constrictions through the solution of the 3-D Schrodinger equation with open boundary conditions. We have developed an efficient code (ViDES) based on such an approach. As examples of addressable SET structures, we present the simulation of a SET, one defined by metal gates on an AlGaAs/GaAs heterostructures, and of a SET defined by etching and oxidation on the silicon-on-insulator material system. Since SETs represent prototypical nanoscale devices, the code may be a valuable tool for the investigation and optimization of a broad range of nanoelectronic solid-state devices.     

Few electron limit of n-type metal oxide semiconductor single electron transistors

We report the electronic transport on n-type silicon single electron transistors (SETs) fabricated in complementary metal oxide semiconductor (CMOS) technology. The n-type metal oxide silicon SETs (n-MOSSETs) are built within a pre-industrial fully depleted silicon on insulator (FDSOI) technology with a silicon thickness down to 10 nm on 200 mm wafers. The nominal channel size of 20 × 20 nm(2) is obtained by employing electron beam lithography for active and gate level patterning. The Coulomb blockade stability diagram is precisely resolved at 4.2 K and it exhibits large addition energies of tens of meV. The confinement of the electrons in the quantum dot has been modeled by using a current spin density functional theory (CS-DFT) method. CMOS technology enables massive production of SETs for ultimate nanoelectronic and quantum variable based devices.     

Chemical stabilization of gold coated by silver core-shell nanoparticles via electron transfer

Silver nanoparticles are notoriously susceptible to oxidation, yet gold nanoparticles coated in silver exhibit a unique electronic interaction that occurs at the interface of the two metals, leading to enhanced stability properties for the silver shell. In order to probe the phenomenon, the stability of gold nanoparticles coated by silver was studied in the presence of various chloride-containing electrolytes. It was found that a critical silver shell thickness of approximately 1 nm exists that cannot be oxidatively etched from the particle surface: this is in contrast to the observation of complete oxidative etching for monometallic silver nanoparticles. The results are discussed in terms of particle composition, structure and morphology before and after exposing the particles to the electrolytes. Raman analysis of the reporter molecule 3-amino-1,2,4-triazole-5-thiol adsorbed on the particle surface illustrates the feasibility of using gold coated by silver nanoparticle probes in sensing applications that require the presence of high levels of salt. The results provide insight into the manipulation of the electronic and stability properties for gold- and silver-based nanoparticles.     

Advances in the modeling of single electron transistors for the design of integrated circuit

Single electron transistor (SET) has become a promising candidate for the key device of logic circuit in the near future. The advances of recent 5 years in the modeling of SETs are reviewed for the simulation of SET/hybrid CMOS-SET integrated circuit. Three dominating SET models, Monte Carlo model, master equation model and macro model, are analyzed, tested and compared on their principles, characteristics, applicability and development trend. The Monte Carlo model is suitable for SET structure research and simulation of small scale SET circuit, while the analytical model based on combination with master equation and macro model is suitable to simulate the SET circuit at balanceable efficiency and accuracy.     

Effects of strong correlations in single electron traps in field-effect transistors

We study effects of strong electron-electron and electron-phonon correlations in single electron traps in metal-oxide-semiconductor field effect transistors (FETs). In order to explain the strong suppression of single electron tunneling in the trap, we introduce a model in which the excess charge of the trap couples to a local lattice deformation. By using nonperturbative techniques, we derive an effective low-energy action for the system. The behavior of the system is characterized by simultaneous polaron tunneling (corresponding to the charging and discharging of the trap) and Kondo screening of the trap spin in the singly occupied state. Hence, the obtained state of the system is a hybrid between the Kondo regime, typically associated with single electron occupancy, and the mixed valence regime, associated with large charge fluctuations. In the presence of a strong magnetic field, we demonstrate that the system is equivalent to a two-level system coupled to an Ohmic bath, with a bias controlled by the applied magnetic field. Due to the Kondo screening, the effect of the magnetic field is significantly suppressed in the singly occupied state. We claim that this suppression can be responsible for the experimentally observed anomalous magnetic field dependence of the average trap occupancy in Si-Si0/sub 2/ FETs.     

Magnetic and phonon transport properties of two-dimensional room-temperature ferromagnet VSe2

Journal of Materials Science - The room-temperature intrinsic ferromagnetism of monolayer VSe2 with a van der Waals gap provides an exciting opportunity for both the fundamental studies and future...     

Monodisperse Ag@SiO2 core-shell nanoparticles as active inhibitors for marine anticorrosion applications

Monodisperse Ag@SiO2 core-shell structured nanoparticles were firstly utilized as a novel corrosion inhibitor for marine anticorrosion applications. The related marine anticorrosion properties were evaluated with an electrochemical noise (ECN) analysis during 2 weeks of accelerated immersion tests in natural seawater with the addition of various inorganic salts and nutriments. The experimental results indicate that the corrosion activity is markedly reduced by nearly 1-3 orders of magnitude owing to the introduction of Ag@SiO2 core-shell nanoparticles into coating. The inhibition efficiency of corrosion can reach as high as about 99%. More importantly, such a coating exhibits an excellent long-term sustained marine anticorrosion effect. So it could be reasonably inferred that silver cores as active inhibitors effectively prevent the corrosion damage from microorganisms, while silica shells act as a good protection for silver nanoparticles, delay the release of silver ions, and also function as the corrosion inhibiting action for inorganic salts. Therefore, this would make monodisperse Ag@SiO2 core-shell nanoparticles a potential and promising corrosion inhibitor for developing future advanced multifunctional coatings.     

Rapid room-temperature synthesis of a porphyrinic MOF for encapsulating metal nanoparticles

While metal nanoparticles(NPs)have shown great promising applications as heterogeneous catalysts,their agglomeration caused by thermodynamic instability is detrimental to the catalytic performance.To tackle this hurdle,we successfully prepared a functional and stable porphyrinic metal-organic framework(MOF),PCN-224-RT,as a host for encapsulating metal nanoparticles by direct stirring at room temperature.As a result,Pt@PCN-224-RT composites with well-dispersed Pt NPs can be constructed by introducing pre-synthesized Pt NPs into the precursor solution of PCN-224-RT.Of note,the rapid and simple stirring method in this work is more in line with the requirements of environmental friendly and industrialization compared with traditional solvothermal methods.     

Fabrication and properties of flower-shaped Pt@TiO2 core-shell nanoparticles

Flower-shaped core-shell Pt@TiO₂ nanoparticles have been synthesized successfully by a simple hydrothermal route using TiF₄ as precursor. Morphology of the product was investigated by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction technique. It has been revealed that the TiO₂ shells of core-shell Pt@TiO₂ nanoparticles are constructed by multiple wedge-shaped petals of TiO₂ crystals with anatase-type crystalline phase. The SAED pattern of TiO₂ shells reflecting the formation of wedge-shaped TiO₂ petals is because of the preferential growth of (004) crystal planes surrounded by (101) facets of TiO₂ crystal planes. The high phototocatalytic performance of flower-shaped core-shell Pt@TiO₂ nanoparticles is also largely attributed to the high Schottky energical barrier within Pt-TiO₂ hetero-interface and the interaction between synchronously vibrated electrons within Pt and electrons in valence band of TiO₂ crystals.     

具有核壳结构的纳米CaCO3@SiO2的制备与表征

采用简单的溶胶-沉淀法制备了具有核壳结构的纳米CaCO3@SiO2复合产物。用X-射线衍射、电子扫描显微镜、X-射线能谱以及耐酸性测试等方法对粒子的包覆效果、化学组成等做了分析和表征。结果表明,用硬脂酸改性后的碳酸钙比较容易包覆无机的SiO2,SiO2在CaCO3表面包覆后形成了CaCO3为核,SiO2为壳的核壳结构。     

Synthesis of beta-cyclodextrin-modified water-dispersible Ag-TiO2 core-shell nanoparticles and their photocatalytic activity

The beta-cyclodextrin-modified Ag-TiO2 core-shell nanoparticles were prepared by sodium borohydrate reduction of AgNO3 and the subsequent hydrolysis of the tetraisopropyl orthotitanate in an aqueous medium. Inversely in the preparation of beta-cyclodextrin-modified TiO2-Ag core-shell nanoparticles, first hydrolysis and then following reduction were carried out. The synthesized spherical core-shell nanoparticles were highly water-dispersible and had an average diameter in the range of 9 to 12 nm. A significant shifting of surface plasmon band was observed for the synthesized Ag-TiO2 and TiO2-Ag core-shell nanoparticles. On a model reaction, namely, the photodegradation of phenol by the UV light irradiation, the photocatalytic property of TiO2 nanoparticles was enhanced, when the Ag nanoparticle was embedded in the core of TiO2 nanoparticles but TiO2 nanoparticles coated by Ag shell decreased the photocatalytic property of TiO2 nanoparticles. The mechanism is ascribed to the surface plasmon characteristics of Ag in the core of the TiO2 nanoparticles under the acceleration by host-guest inclusion characteristics.     

Assembly of silica nanoparticles for two-dimensional nanomaterials

To realize the great potential of nanoparticles as new materials for biomedical applications, the nanoparticles will have to be assembled in such a way that the newly created assembly will have unique properties that conventional materials do not possess. This will enable nanomaterials to be used for many novel applications. We have attempted to assemble silica nanoparticles to create a two-dimensional nanomaterial, which might be useful for biosensor and biochip production. The silica nanoparticles are synthesized and assembled in a monolayer fashion through the use of halogenated silanes. Photolithography techniques are used to pattern the glass surface prior to nanoparticle attachment. The concentration of the silica nanoparticles in the solution controls the surface coverage of nanoparticles on the glass surface. Different patterned silica arrays can be made with controlled surface coverage. The nanoparticle-covered surface is successfully tested for surface-enhanced enzymatic reactivity for the detection of a neurotransmitter, glutamate. This report demonstrates the feasibility of assembling nanoparticles for biosensor development.     

Conversion of a Bi nanowire array to an array of Bi-Bi2O3 core-shell nanowires and Bi2O3 nanotubes

A template-based heat-treatment method has been developed to convert metal nanowire arrays into arrays of metal-metal oxide core-shell nanowires and single-crystalline metal oxide nanotubes. This process is demonstrated by kinetically controlling the conversion of single-crystalline Bi nanowires to Bi-Bi(2)O(3) core-shell nanowires via a multistep, slow oxidation method, and then controlling their further conversion to a single-crystalline Bi(2)O(3) nanotube array via fast oxidation. This process can conveniently be extended to fabricate a free-standing, easily oxidized metal-metal oxide nanowire and metal oxide nanotube array, which may have future applications in nanoscale optics, electronics, and magnetics.     

Silicon single electron transistors with SOI and MOSFET structures: the role of access resistances

Coulomb blockade has been widely reported in silicon and metallic structures without intentional tunnel barriers. In particular, a simple constriction in silicon-on-insulator (SOI) allows to build a three-terminal silicon single-electron transistor (SET) operating at moderate temperature. The key parameters are the access resistances confining the electrons and the size of the gate-channel overlap, which sets the Coulomb energy. Thin films of doped silicon with sheet resistance of a few tens of h/e/sup 2/ are well suited for fabricating optimized access resistances. Low doped extensions with typical resistivity 1000 /spl Omega//spl mu/m (at 300 K) are also good candidates. We illustrate this MOS-SET principle in SOI constriction and standard MOSFET of similar size. Although relying on different concepts, the ultimate MOSFET and MOS-SET are shown to be technologically close, differing mostly by the ratio between the channel resistance over the access resistance. Because this ratio is decreasing as the gate length shrinks, single electron effects should become more and more important at high temperature in the subthreshold regime of standard field effect transistor devices.     

External-force-driven solution epitaxy of large-area 2D organic single crystals for high-performance field-effect transistors

Nano Research - Growth of two-dimensional (2D) organic single crystals (2DOSCs) on water surface has attracted increasing attention, because it can serve as a molecularly flat and defect-free...     

CoFe_2O_4@FeCo纳米核壳颗粒的制备与磁性研究

利用化学共沉淀法合成Co Fe2O4纳米颗粒,并在氢气气氛下还原获得Co Fe2O4@Fe Co核壳结构磁性纳米颗粒。用XRD和TEM对所得样品进行结构分析,用SQUID测量样品在300 K时的磁滞回线,发现随着壳厚度的增加,核壳结构样品的矫顽力呈现先增加后减小的趋势,而其饱和磁化强度表现出逐渐增加的趋势。为了探究所制备样品的核壳磁性层之间的交换相互作用,还测量了M-T曲线以及T=5 K时的零磁场冷却(ZFC)和带磁场冷却(FC)磁滞回线。     

Ru-Pt core-shell nanoparticles for preferential oxidation of carbon monoxide in hydrogen

Most of the world's hydrogen supply is currently obtained by reforming hydrocarbons. 'Reformate' hydrogen contains significant quantities of CO that poison current hydrogen fuel-cell devices. Catalysts are needed to remove CO from hydrogen through selective oxidation. Here, we report first-principles-guided synthesis of a nanoparticle catalyst comprising a Ru core covered with an approximately 1-2-monolayer-thick shell of Pt atoms. The distinct catalytic properties of these well-characterized core-shell nanoparticles were demonstrated for preferential CO oxidation in hydrogen feeds and subsequent hydrogen light-off. For H2 streams containing 1,000 p.p.m. CO, H2 light-off is complete by 30 (composite function)C, which is significantly better than for traditional PtRu nano-alloys (85 (composite function)C), monometallic mixtures of nanoparticles (93 (composite function)C) and pure Pt particles (170 ( composite function)C). Density functional theory studies suggest that the enhanced catalytic activity for the core-shell nanoparticle originates from a combination of an increased availability of CO-free Pt surface sites on the Ru@Pt nanoparticles and a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.