On the surface of silicon nanowires (SiNWs) synthesized by gold (Au)-catalyzed chemical vapor deposition (CVD), Au particles 5-20 nm in diameter are formed if the growth conditions are within a specific range. We studied the mechanism of Au particle formation by growing SiNWs under different conditions, specifically by dynamically changing the growth parameters during the growth process. We show that insufficient supply of Si source to the Au-Si eutectic on top of the SiNWs enhances the migration of Au atoms on the surface of SiNWs in the form of Au-Si eutectic, which is precipitated on the surface as Au particles during cooling. We also show that using Au-Si eutectic on the surface of SiNWs as a catalyst enables one-step growth of branched SiNWs. 相似文献
The distribution of electrically active B concentration in single SiNWs (nanowires) grown by a vapor-liquid-solid (VLS) process was studied by analyzing Fano resonance in Raman spectra. We found a gradient of active B concentration along the growth direction; the B concentration was the largest at the substrate side and the smallest at the catalyst side. The observed concentration gradient suggests the conformal growth of a high B concentration layer during a VLS process. To confirm this effect, we grew SiNWs with controlled impurity profiles, that is, p-type/intrinsic ( p-i) and intrinsic/ p-type ( i-p) SiNWs, by controlling the supply of B source during SiNWs growth. We found that p-i SiNWs can be grown by just stopping the supply of B source in the middle of the growth, while i-p SiNWs were not realized; that is, the whole region of nominal " i-p" SiNWs was B-doped even if we started the supply of B source in the middle of the growth. These results confirm the above doping model. We also found that the distribution of active B concentration was significantly modified by high temperature annealing. By annealing at 1100 degrees C for 1 min, B concentration became almost uniform along 10 mum long SiNWs irrespective of initial B profiles. This suggests very efficient diffusion of B atoms in a defective high B concentration surface layer of SiNWs. 相似文献
We have developed a conceptually and methodologically novel self‐assembled multilayer nickel nanoparticle (NP) catalyst – sulfur‐modified gold‐supported Ni NPs (SANi) – for organic synthesis. The SANi catalyst was easily prepared through a three‐step procedure involving simultaneous in situ metal NP and nanospace organization. This unique method does not require any conventional preformed template for immobilizing and stabilizing NPs. SANi catalyzes carbon‐carbon bond‐forming cross‐coupling, Kumada coupling, and Negishi coupling reactions under ligand‐free conditions and can be used repeatedly for these reactions. Physical analysis of SANi showed that the active species in these reactions are self‐assembled multilayer zerovalent Ni NPs with a size of ∼3 nm.
We injection molded a plastic ferrule for a single-mode optical fiber connector. We used liquid crystalline polymer (LCP) as the molding material because of its fine mold replication ability and introduced an eccentricity control mechanism into the ferrule mold. As a result, we succeeded in molding plastic ferrules whose eccentricity was less than 1 μm by optimizing the eccentricity control conditions. The connection loss of these low eccentricity plastic ferrules was around 0.2 dB and they exhibited an excellent reflection characteristic of 52.5 dB. These initial results were maintained during mating tests and temperature and humidity cycling tests 相似文献
In this study, resonant ultrasound spectroscopy (RUS) for determining residual stress in small size spherical balls was examined. Natural frequencies of spherical balls with residual stress were analysed by finite element method. Resonant frequencies of spherical balls were experimentally measured by a RUS system. Both natural frequencies in the analysis and the resonant frequencies measured in the experiment decreased as the compressive circumferential stress at the ball surface increased. It was concluded, on the basis of both analytical and experimental results, that the measurement of the resonant frequency by the RUS system along with the analysis of natural frequency are effective for determining the values and distributions of unknown residual stress in spheres. 相似文献
The dynamics preceding the spatial separation of a charged soliton pair after photoexcitation in trans-polyacetylene was successfully investigated by using ultrafast spectroscopy with a 6.2 fs pulse laser. It was directly verified that after photoexcitation, the electron–hole pair relaxes with a breather mode (i.e. multi-quanta vibronic states), as theory predicts, with an electron–hole pair lifetime of 33–50 fs. By applying spectrogram analysis to the time trace of the absorbance change, the ultrafast amplitude and frequency modulations of CC and CC stretching modes, induced by breathers and lasting no longer than 100 fs, can be observed simultaneously for the first time. The frequency shifts of both modes were in good agreement with a simulation based on the Su–Schrieffer–Heeger model. It was found that the intensities of transition dipoles changed due to breathers, whereas transition energies were dominantly modulated by CC stretching modes as recent theoretical work predicted. 相似文献