Influence of Cu nanoparticle size on the photo-electrochemical response from Cu-multiwall carbon nanotube composites

We show that Cu metal nanoparticle-multiwall carbon nanotube (MWCNT) assemblies can act as a new hybrid photoactive layer in photo-electrochemical devices. The carbon nanotube (CNT) composites were formed by a controlled thermal deposition of copper which produced crystalline metal nanoparticles localized on the carbon tube outer walls. The photoresponse evaluated in terms of IPCE (incident photon-to-charge carrier generation efficiency) varied for different sized-Cu-MWCNT samples across all the visible and near ultraviolet photon energy range with respect to the response of bare MWCNTs. In the case of 0.2 nm Cu nominal thickness, the IPCE increased, reaching 15%, a value 2.5 times higher than that measured for bare MWCNTs. As the Cu nominal coverage thickened, the IPCE started to decrease and become totally ineffective after 1 nm deposited Cu. The IPCE increase found was interpreted as being the result of a remarkable charge transfer between the Cu metal nanoparticles and the CNTs due to the formation of a strong ionic bond at their interface. The results obtained prove that the metal nanoparticle-CNT composites have optical, electrical and structural properties that can be applied in a variety of nanoscale architectures for novel photo-electrochemical devices.     

Utilizing the thermodynamic nanoparticle size effects for low temperature Pb-free solder

Development of a Pb-free Sn nanosolder paste with an initial melting temperature near or below the melting temperature of eutectic Sn-Pb solder (183 °C) has been investigated using the size-dependent melting behavior of small particles. Three to five nanometer Sn nanoparticles were fabricated by sonochemical reduction and observed to melt at temperatures near or below 183 °C. Prototype nanosolder pastes were produced by combining the nanoparticles with flux and were characterized by differential scanning calorimetry (DSC) in terms of their melting, solidification, coalescence, and metal particle loading properties. The results indicate that, although target melting temperatures were achieved, nanoparticle coalescence was limited by low volume loading of the metal, due in part to the capping layer (an organic layer adsorbed on the metal surface during chemical synthesis).     

Freeze cast carbon nanotube-alumina nanoparticle green composites

CNT-Al₂O₃ nanoparticle suspensions without and with sodium dodecyl sulfate (SDS) were freeze-cast into green samples. SDS drastically improves Carbon nanotube (CNT) dispersion and CNT-Al₂O₃ nanocomposite homogeneity. Green density of the CNT-Al₂O₃ nanocomposites decreases with CNT addition. Green strength of the CNT-Al₂O₃ nanocomposites increases with the CNT content when CNTs are well separated. The CNT-Al₂O₃ nanocomposites show medium energy fracture mode during equibiaxial flexural strength testing and change color in response to CNT content and distribution in the Al₂O₃ nanoparticle matrix.     

Epoxy based photoresist/carbon nanoparticle composites

We have fabricated composites of SU-8 polymer and three different types of carbon nanoparticles (NPs) using ultrasonic mixing. Structures of composite thin films have been patterned on a characterization chip with standard UV photolithography. Using a four-point bending probe, a well defined stress is applied to the composite thin film and we have demonstrated that the composites are piezoresistive. Stable gauge factors of 5–9 have been measured, but we have also observed piezoresistive responses with gauge factors as high as 50. As SU-8 is much softer than silicon and the gauge factor of the composite material is relatively high, carbon nanoparticle doped SU-8 is a valid candidate for the piezoresistive readout in polymer based cantilever sensors, with potentially higher sensitivity than silicon based cantilevers.     

Modelling of size effects on strengthening of multiphase Al based composites

A new multilevel mechanical model for multiphase metal matrix composite is proposed, accounting for size distribution effects. The matrix is considered as a micropolar elastic plastic Cosserat material and the hardening phases – as pure elastic ones. A two-steps homogenization procedure is applied to obtain the overall properties of the composite. A variational approach is used to evaluate the equivalent stress on macro level at the transition from micro to macro scale. The model is developed using information provided by microstructural investigations and EDX analysis. The elastic–plastic behaviour of rapidly solidified Al based Fe Si enriched alloys is considered. Due to fast cooling the material can be regarded as “natural” (in situ) composite, containing intermetallic and non-intermetallic compounds of different shapes, sizes, mechanical properties and volume fractions. The multistage modelling of bulk material manufacturing process is simulated using the FEM. The model is implemented as user defined subroutines into the FE code MARC. The influence of the microstructural size parameters on the hardening behaviour of the overall material is discussed.     

White light emission from co-precipitated organic nanoparticle composites

Co-precipitation of 1,4-bis(2-phenyl-1-propen-1-yl)benzene (1) and 2-(4-(2-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)ethynyl)benzylidene) malononitrile (2) that individually form blue-emitting and orange-emitting nanoparticles, respectively, results in the formation of composite fluorescent organic nanoparticles that emit white light. The two components likely align in the head-to-tail fashion in nanoparticles, creating two parallel and strongly coupled transition dipoles. The emission characteristics of the composite was dependent upon the concentration of 1 and 2, and a pure white-light emission (CIE chromaticity coordinates of 0.34, 0.35) was achieved from the composite that was prepared by employing 12 parts of 1 and 1 part of 2.     

Effect of the TiO2 nanoparticle size on the decomposition behaviors in aluminum matrix composites

The decomposition behaviors and the effect of particle size on the kinetic rate are studied for Al–3 vol.% titanium dioxide (TiO₂) composites by using three different types of TiO₂ particles (15, 50, and 300 nm). Thermal analysis shows that the reaction is stepwise with the first reaction starting before the melting temperature of Al. Since the high chemical potential of nanoparticles enhances reactivity, the TiO, Al₃Ti, and α-Al₂O₃ phases are found to be formed during the first reaction regardless of particle size. Based on observations of microstructure, the formation mechanism of Al₃Ti and α-Al₂O₃ is understood to be solution precipitation. Non-isothermal kinetic analysis reveals that the reaction mechanism is closely related to the three-dimensional continuous nucleation and the growth limited by diffusion. Particle size is found to be having considerable effect on the kinetic rate. As the particle size decreases, the rate constant increases, while the pre-exponential factor and the activation energy decreases. A non-linear relationship between the rate constant and the reciprocal of the size is found and evaluated.     

Small-angle neutron scattering measurement of silicon nanoparticle size

We have determined the particle size distribution profiles of octane-terminated silicon nanoparticle suspensions, produced using the sonication of electrochemically etched Si wafers. Small-angle neutron scattering data was analyzed separately in high (0.4?nm(-1)相似文献   

Role of proteins in controlling selenium nanoparticle size

This work investigates the potential for harnessing the association of bacterial proteins to biogenic selenium nanoparticles (SeNPs) to control the size distribution and the morphology of the resultant SeNPs. We conducted a proteomic study and compared proteins associated with biogenic SeNPs produced by E.?coli to chemically synthesized SeNPs as well as magnetite nanoparticles. We identified four proteins (AdhP, Idh, OmpC, AceA) that bound specifically to SeNPs and observed a narrower size distribution as well as more spherical morphology when the particles were synthesized chemically in the presence of proteins. A more detailed study of AdhP (alcohol dehydrogenase propanol-preferring) confirmed the strong affinity of this protein for the SeNP surface and revealed that this protein controlled the size distribution of the SeNPs and yielded a narrow size distribution with a three-fold decrease in the median size. These results support the assertion that protein may become an important tool in the industrial-scale synthesis of SeNPs of uniform size and properties.     

Effect of particle size on iron nanoparticle oxidation state

Selecting catalyst particles is a very important part of carbon nanotube growth, although the properties of these nanoscale particles are unclear. In this article iron nanoparticles are analyzed through the use of atomic force microscopy and x-ray photoelectron spectroscopy in order to understand how the size affects the chemical composition of nanoparticles and thus their physical structure. Initially, atomic force microscopy was used to confirm the presence of iron particles, and to determine the average size of the particles. Next an analytical model was developed to estimate particle size as a function of deposition time using inputs from atomic force microscopy measurement. X-ray photoelectron spectroscopy analysis was then performed with a focus on the spectra relating to the 2p Fe electrons to study the chemical state of the particles as a function of time. It was shown that as the size of nanoparticles decreased, the oxidation state of the particles changed due to a high proportion of atoms on the surface.     

表面活性剂对纳米氧化锌粒径和形貌的影响研究

以尿素和硝酸锌为原料,采用均匀沉淀法制备纳米氧化锌(ZnO),加入不同的表面活性剂以及同种表面活性剂不同剂量对纳米ZnO的粒径和形貌有不同的影响.实验结果表明:在液相法制备纳米ZnO时,复合型表面活性剂以及阴离子型表面活性剂的分散性能优于非离子表面活性剂.添加浓度为3.2×10-3 mol/L的表面活性剂十二烷基苯磺酸钠时,沉淀物的分散活性好,能够较好的控制ZnO的粒度;油酸钠和聚乙二醇1000复合型表面活性剂浓度分别为1.0×10-4 mol/L和1.6×10-3 mol/L时,分散效果最好,能制得粒径为10～50 nm的纳米ZnO.     

Controlling semiconductor nanoparticle size distributions with tailored ultrashort pulses

The laser generation of size-controlled semiconductor nanoparticle formation under gas phase conditions is investigated. It is shown that the size distribution can be changed if picosecond pulse sequences of tailored ultra short laser pulses (<200?fs) are employed. By delivering the laser energy in small packages, a temporal energy flux control at the target surface is achieved, which results in the control of the thermodynamic pathway the material takes. The concept is tested with silicon and germanium, both materials with a predictable response to double pulse sequences, which allows deduction of the materials' response to complicated pulse sequences. An automatic, adaptive learning algorithm was employed to demonstrate a future strategy that enables the definition of more complex optimization targets such as particle size on materials less predictable than semiconductors.     

Well-defined Au/ZnO nanoparticle composites exhibiting enhanced photocatalytic activities

Well-defined Au/ZnO nanoparticle composites were prepared by modifying ZnO with preformed Au nanoparticles protected with bifunctional glutathione ligand. In this approach, the Au nanoparticles were highly monodisperse and their loading on ZnO surface could be precisely controlled by the anchoring conditions. Steady-state and time-resolved photoluminescence of the composites revealed the ability of the Au nanoparticles to efficiently extract conduction band electrons from the photoexcited ZnO. The composites exhibited strongly enhanced photocatalytic activity without requiring thermal activation process in degrading organic substrates in both oxidative and reductive pathways. A clear correlation between the photocatalytic activity and the Au loading was found for both oxidative and reductive photocatalytic reactions. These results demonstrate that thiolate-protected AuNPs can significantly enhance the charge separation by extracting electrons from the photoexcited ZnO and consequently improve the photocatalytic activity of the composites.