Solution-phase synthesis of germanium nanoclusters using sulfur

Sulfur is used to promote the formation of germanium nanocrystals from the robust organometallic precursor, triphenylgermanium chloride, at elevated temperatures (300?°C) in the surfactant/solvent hexadecylamine. Transmission electron microscopy shows that 8?nm germanium nanocrystals are produced that self-assemble into uniform-sized 60?nm germanium nanoclusters after purification. Electron diffraction studies show that the germanium nanoclusters have a diamond germanium crystal structure and energy dispersive x-ray spectroscopy shows that the nanoclusters are primarily composed of pure germanium.     

Interaction between multiply charged manganese nanoclusters and sulfur atoms in silicon

We have studied the interaction of manganese nanoclusters with sulfur atoms in silicon. The results indicate that both simultaneous and sequential codoping with manganese and sulfur has little effect on the electrical properties (resistivity, carrier mobility, and conductivity type) of silicon. There is no extrinsic photoconductivity in the IR spectral region, and the material has only a small positive magnetoresistance. According to electron paramagnetic resonance data, the material contains only atomic manganese. Sulfur atoms in the silicon lattice are assumed to facilitate the capture of doubly charged manganese interstitials (Mn²⁺) at negatively charged vacancies, resulting in the formation of a multicomponent impurity cluster of composition Si₂S²⁺Mn²⁻ in the silicon lattice throughout the crystal. The optimal thermal annealing conditions for the formation of such clusters are determined. The ability to produce Si₂S²⁺Mn²⁻ clusters with controlled concentration allows one to tailor the main fundamental parameters of silicon and opens up new possibilities for such materials in nano- and microelectronic device development.     

Observation of giant exchange anisotropy

Exchange anisotropy, an interface phenomena in layered magnetic films that produces a hysteresis loop centered at a finite field, has been observed in multilayered films of GdCo/sub 2/ and Co. It is found that the effective bias field diverges at the compensation temperature of the film. The data reported were for films with single-layer thicknesses of 35 AA. Multilayered films are deposited at room temperature and are, therefore, highly disordered or amorphous. To induce exchange anisotropy in these films, they were heated rapidly (<1 min) to 500 degrees C, well above the ordering temperature of the GdCo/sub 2/, and allowed to cool quickly (<3 min to 200 degrees C). The resulting hysteresis loop is shown. Even in the absence of an applied field, this annealing induces exchange anisotropy, presumably due to the presence of a stray magnetic field.<>     

On the mechanism of carbon monoxide oxidation on the surface of gold nanoclusters supported on titanium oxide

The process of carbon monoxide (CO) oxidation on the surface of a system comprising nanodimensional gold clusters deposited onto thin films of titanium oxide of variable stoichiometry formed on a Re(1000) single crystal surface has been studied by methods of thermodesorption, IR, and X-ray photoelectron spectroscopy. It is established that oxygen contained in titanium oxide plays an important role in the conversion of CO into CO₂. The efficiency of this process on the Au/TiO _x (x < 2) system surface is significantly higher that that on the Au/TiO₂ system.     

Mass spectrometry and dynamics of gold adatoms observed on the surface of size-selected Au nanoclusters

We report the imaging, mass spectrum, and dynamical behavior of adatoms and small clusters observed on the surface facets of size-selected, truncated octahedral gold clusters, Au(N) (N = 923 ± 23), via aberration-corrected scanning transmission electron microscopy. Our quantitative atom counting measurements show that most (~70%) of the species on the surface are single Au adatoms. Such species are now proposed as key elements of the atomic structure of both monolayer-protected nanoclusters (nanoparticles) and self-assembled monolayers and may also play a role in gold nanocatalysis. The adatoms are found on both {100} and {111} facets with similar probabilities.     

Microwave-assisted rapid synthesis of platinum nanoclusters with high surface area

Synthesis of platinum nanoclusters (PNCs), with its advantages of high surface area and reduced materials costs, represents a greatly interesting class of nanomaterials. In this paper, a one-step, rapid and efficient aqueous-phase reaction to straightforwardly produce PNCs in high yield is proposed without the need for any organic solvent, template or ion replacement, which is carried out simply by microwave-assisted heat-treatment of an aqueous solution containing K2PtCl4 and 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonicacid (HEPES) within 12 s. As-prepared platinum nanoclusters are porous interconnected nanostructures and possess very high surface area (41 m2 g(-1)). The combination of high surface area with the nanoarchitectures consisting of pores of the product is advantageous for catalytic applications.     

Ag纳米颗粒表面等离子体共振吸收峰的红移现象

采用MEVVA源(metal vapor vacuum arcion source)引出的强束流脉冲Ag离子注入到SiO2玻璃,通过电镜观察和分析纳米颗粒的形貌和结构,从电镜照片可知样品中形成了大致呈球形的Ag纳米颗粒.将样品在氧化(空气)和还原(80%N2+20%H2)气氛下退火,由所测光谱曲线看出随着退火温度的升高,共振吸收峰的峰强渐渐减弱,峰位发生红移.根据Drude-Sommerfeld自由电子气模型,并考虑电子带间转换对介电函数的贡献,运用Maxwell-Granett有效媒质理论模拟吸收率与入射波之间的关系.     

Experimental investigation of the film condensation of sulfur hexafluoride on a finned overhead surface

The results of investigating the film condensation of sulfur hexafluoride on a finned overhead surface are presented. An experimental apparatus with controlled heat removal is described. The negative influence of noncondensing impurities in the condensible gas and subcooling of the condensation surface on the rate of the process is demonstrated. Methods of eliminating these effects are considered.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 2, pp. 199–205, February, 1987.     

Fabrication of surface magnetic nanoclusters using low energy ion implantation and electron beam annealing

Magnetic nanoclusters have novel applications as magnetic sensors, spintronic and biomedical devices, as well as applications in more traditional materials such as high-density magnetic storage media and high performance permanent magnets. We describe a new synthesis protocol which combines the advantages of ion implantation and electron beam annealing (EBA) to produce surface iron nanoclusters. We compare the structure, composition and magnetic properties of iron nanoclusters fabricated by low dose 15 keV Fe implantation into SiO(2) followed by 1000?°C EBA or furnace annealing. Atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) images together with superconducting quantum interference device (SQUID) magnetometry measurements show that only EBA leads to the rapid formation of surface crystalline Fe spherical nanoclusters, showing magnetic moments per Fe atom comparable to that of bulk bcc Fe and superparamagnetic properties. We propose a fabrication mechanism which includes e-beam enhanced desorption of SiO(2). This method has potential for fabricating nanoscale magnetic sensors integrated in microelectronic devices.     

Room temperature deposition of self-assembled Al nanoclusters on stepped sapphire (0001) surface and subsequent nitridation

Self-assembled growth and nitridation of ultrathin Al nanoclusters on a stepped sapphire (0001) surface were studied by high-resolution X-ray photoemission spectroscopy, atomic force microscopy and low-energy electron diffraction (LEED). Upon room temperature deposition, in the coverage range of ∼ 0.79 to 2.3 monolayer (ML), Al nanoclusters were uniformly nucleated over the entire surface of defect-free atomically smooth terraces as well as step edges. Subsequent nitridation at elevated temperatures by ammonia did not alter the morphology of the nanoclusters. The global morphology of the stepped sapphire (0001) surface such as terrace width, step height and facet orientation had no obvious influence on the nucleation morphology of the nanoclusters in the given Al coverage range. However, local structural defects at the joints of short facets and step edges played a noticeable role on the local morphology of the nanoclusters and subsequently the nitridation chemistry. The Al nanoclusters were uniformly nitridated from surface and downwards through the 3D structures. The LEED pattern indicated a certain degree of crystallinity on the nitridated surface at a nominal Al coverage less than 2 ML, whereas at 2.3 ML Al coverage, the nitridated surface became amorphous. Thus there is a critical coverage for good surface order.     

Structural and electronic properties of 0.5 ML sulfur adsorbed on the GaP(001) surface

The structural and electronic properties of 0.5 ML S adsorption on the Ga- and P-terminated GaP(001) (1 × 2) surfaces were studied by first-principles total-energy calculations. Sulfur adsorbates prefer to occupy the bridge sites on the Ga-terminated surface, consistent with the experimental results. Electronic analysis shows that the surface state around the Fermi energy (E _f) vanishes for S-adsorbed P-terminated surface at the substitution site. In the case of S-adsorbed Ga-terminated surface at the bridge site, the surface state at E _f is tremendously lowered but not completely diminish, which is in good agreement with the experiments. The S-induced work-function changes on the Ga- and P-terminated surfaces are 1.44 and 0.45 eV, respectively, indicating that some charge is transferred from the substrate to the S adsorbate. The Ga-S stretching vibrational frequency is calculated to be 37.61 meV.     

Effect of protein adsorption on the fluorescence of ultrasmall gold nanoclusters

The interaction of proteins with ultrasmall gold nanoclusters (Au NCs) is investigated. Upon protein association, the fluorescence of Au NCs is significantly enhanced and, concomitantly, their luminescence lifetime is prolonged. The results stress the importance of investigating the behavior of fluorescent metal NCs in complex biological environment for advancing their bio-nanotechnology applications.     

Thermodynamic properties of silver nanoclusters

Icosahedral models of magic number silver clusters have been constructed using molecular dynamics simulations with the Doyama-Kogure potential. We have calculated the energy, heat capacity, entropy, Gibbs energy change, and excess surface energy as functions of cluster size and temperature. The vibrational contributions to the heat capacity and entropy are weak functions of cluster size (N), and the statistical degeneracy is lifted starting at 250–300 K. The surface energy density of the silver clusters is size-independent down to N = 13. The saturated vapor pressure over the clusters has been estimated. The calculated thermodynamic properties of fcc silver agree well with standard thermodynamic data.     

Observation of stimulated emission of surface plasmon polaritons

We report a direct experimental evidence of stimulated emission of surface plasmon polaritons (SPPs) at telecom wavelengths (1532 nm) with erbium doped glass as a gain medium. We observe an increase in the propagation length of signal surface plasmons when erbium ions are excited optically using pump SPP. The design, fabrication, and characterization of SPP waveguides, thin gold metal strips, embedded in erbium (Er) doped phosphate glass is presented. Such systems can be suitable as integrated devices coupling electronic and photonic data transmissions as well as SPP amplifiers and SPP lasers.     

Observation of the process of dust accumulation on a rigid ceramic filter surface and the mechanism of cleaning dust from the filter surface

The accumulation process of captured particles on the surface of a rigid filter element is experimentally studied by measuring the pressure drop. It is then related to the packing density of the dust layer. The process of the release of dust from filter surface is also studied through the changes in the pressure difference across the filter and the movement of the released dust after clean air is injected. As a result, for a given filtration condition, dust forms the densest layer at the initial and the loosest at the middle stage of the filtration, and forms a uniform layer at the final stage. The cleaning efficiency of the dust layer is found to depend upon the layer structure, i.e, it decreases as dust forms a denser layer, even if the accumulated mass per unit filter surface area is the same. The release velocity of dust from the surface is also found to become slower as the porosity of the layer decreases.     

Modeling the relaxed cohesive energy of metallic nanoclusters

A model is developed to calculate the cohesive energy of metallic nanoclusters with relaxed structure. It is found that the relaxed cohesive energy is higher than that of the un-relaxed one due to relaxation process decreasing the total energy. The relaxed nanoclusters in present model are more close to real ones, and the efficiency of the model is confirmed by molecular dynamics results on Cu nanoclusters.     

Dependence on temperature and energy of the heteroepitaxy of small metallic nanoclusters

Deposition at different energies and temperatures of small metallic nanoclusters on metallic substrates is studied by molecular-dynamics simulations. Small-, Co/Cu(001), and large-misfit, Cu/Au(001) and Au/Cu(001), systems are considered. The rise in temperature improves the epitaxial order, although its effect is smaller in large-misfit systems. Thus, by increasing this parameter, non-epitaxial clusters can turn their structure into epitaxial in the case of Co/Cu(001), into aligned in Cu/Au(001), and into layered in Au/Cu(001). Therefore, the characteristics of the alignment are determined by the properties of the material. In addition, the influence of the initial structure is more marked in Co and Cu clusters, since they can reproduce locally other phases. Epitaxy can also be improved if the deposition energy is increased, although the deposited cluster loses its original shape progressively. Its effect is different depending mainly on the degree of misfit. An increase in energy (of up to 0.75 eV/atom) produces similar effects, but more noticeable, as a rise in temperature.     

Developing a millifluidic platform for the synthesis of ultrasmall nanoclusters: ultrasmall copper nanoclusters as a case study

The future of lab-on-a-chip devices for the synthesis of nanomaterials hinges on the successful development of high-throughput methods with better control over their size. While significant effort in this direction mainly focuses on developing "difficult to fabricate" complex microfluidic reactors, scant attention has been paid to the "easy to fabricate" and simple millifluidic systems that could provide the required control as well as high throughput. By utilizing numerical simulation of fluids within the millifluidic space at different flow rates, the results presented here show velocity profiles and residence time distributions similar to the case of microfluidics. By significantly reducing the residence time and residence time distribution, a continuous flow synthesis of ultrasmall copper nanoclusters (UCNCs) with exceptional colloidal stability is achieved. In-situ synchrotron-radiation-based X-ray absorption spectroscopy (XAS) reveal that the as-prepared clusters are about 1 nm, which is further supported by transmission electron microscopy and UV-vis spectroscopy studies. The clusters reported here are the smallest ever produced using a lab-on-a-chip platform. When supported on silica, they are found to efficiently catalyze C-H oxidation reactions, hitherto unknown to be catalyzed by Cu. This work suggests that a millifluidic platform can be an inexpensive, versatile, easy-to-use, and powerful tool for nanoparticle synthesis in general, and more specifically for ultrasmall nanoclusters (UNCs).