Xianfang Zhu

Interaction of defects and metals with nanocavities in silicon

Abstract Ion implantation of H or He into silicon, followed by annealing can create a band of nanocavities. Such nanocavities can exhibit a range of interesting and often non-equilibrium interactions with defects and metals during subsequent implantation and annealing. This paper gives an overview of such interactions, concentrating on cavities produced by H-implantation. The evolution of cavities during annealing is briefly treated, followed by illustrations of the very efficient gettering ability of cavities for fast diffusing metals. For low metal concentrations introduced into the near-surface by implantation, the metal atoms decorate the cavity walls during annealing but can be displaced by oxygen under certain conditions. At high metal concentrations, precipitation and second phase (silicide) formation can occur at cavities but silicide formation and dissolution are found to be controlled by the availability or removal of silicon interstitials, leading to non-equilibrium behaviour. When silicon that contains cavities is irradiated with silicon ions, irradiation-induced defects interact with cavities, leading to preferential amorphisation at certain temperatures. Continued irradiation leads to cavity shrinkage during bombardment, which is most efficient when the region around the cavities is amorphised.

Antiphotocorrosive photocatalysts containing CdS nanoparticles and exfoliated TiO2 nanosheets

Australian Research Council [DP0666345, DP0773490]; China Ministry of Science and Technology (MOST) International Sci & Tech Cooperation and Exchange [2008DFA51230]; National Key Basic Science Research Program [2007CB936603]

Direct observation of irradiation-induced nanocavity shrinkage in Si

Nanocavities in Si substrates, formed by conventional H implantation and thermal annealing, are shown to evolve in size during subsequent Si irradiation. Both ex situ and in situ analytical techniques were used to demonstrate that the mean nanocavity diameter decreases as a function of Si irradiation dose in both the crystalline and amorphous phases. Potential mechanisms for this irradiation-induced nanocavity evolution are discussed. In the crystalline phase, the observed decrease in diameter is attributed to the gettering of interstitials. When the matrix surrounding the cavities is amorphized, cavity shrinkage may be mediated by one of two processes: nanocavities can supply vacancies into the amorphous phase and/or the amorphous phase may flow plastically into the nanocavities. Both processes yield the necessary decrease in density of the amorphous phase relative to crystalline material.

Stable damping associated with linear viscous motion of the interface in a multiphase Al‐Zn alloy

In the present paper, the characteristics of low‐frequency stable damping are studied in a multiphase eutectoid Al‐Zn alloy. Experimental results show that, within a low‐temperature and low‐strain‐amplitude range, the damping evidently manifests itself by linear viscous characteristics, namely, it obeys a law Q−1=(B/fn)exp(−nH/kT), where H is the real process activation energy, B and n (=0.21) are two experimental parameters, and k is the Boltzmann constant. A value of H=0.74 eV is obtained, which is closely related to the viscosity during interface motion. Accordingly, a linear viscous interface motion mode is put forward and can explain the experimental results as well.

Shrinkage of nanocavities in silicon during electron beam irradiation

An internal shrinkage of nanocavity in silicon was in situ observed under irradiation of energetic electron on electron transmission microscopy. Because there is no addition of any external materials to cavity site, a predicted nanosize effect on the shrinkage was observed. At the same time, because there is no ion cascade effect as encountered in the previous ion irradiation-induced nanocavity shrinkage experiment, the electron irradiation-induced instability of nanocavity also provides a further more convincing evidence to demonstrate the predicted irradiation-induced athermal activation effect.

VLS growth of SiOx nanowires with a stepwise nonuniformity in diameter

China-MOST [2008DFA51230]; National Key Basic Science Research Program (973 Project) [2007CB936603]; NSFC [60776007, 11074207]; China Ministry of Education [20100121110023]; SRF for ROCS, SEM

Effect of chromium interlayer thickness on optical properties of Au-Ag nanoparticle array

The effect of chromium interlayer thickness on optical properties of array of hybrid Au-Ag triangular nanoparticles is systematically investigated. The optical spectrum simulated by discrete dipole approximation (DDA) numerical method shows that with increase of the chromium interlayer thickness both refractive index sensitivity (RIS) and figure of merit (FOM) of localized surface plasmon resonance from the hybrid nanostructures experience remarkable change and the intensity of the extinction efficiency decreases. The nanosphere lithography (NSL) is used to fabricate the hybrid nanostructure arrays with different chromium interlayer thicknesses. The experiment demonstrates that the spectrum as measured from the as-fabricated hybrid nanostructure arrays is essentially in agreement with the simulated results.

Precise linear internal friction expression for a freely decaying vibrational system

From a linear motion equation, the precise linear internal friction expression for the free decay method has been deduced for the first time. A detailed comparison between the newly deduced expression and the currently used approximation has also been addressed.

Atom Diffusion and Evaporation of Free-Ended Amorphous SiOx Nanowires: Nanocurvature Effect and Beam-Induced Athermal Activation Effect

Arresting effects of nanocurvature and electron beam-induced athermal activation on the structure changes at nanoscale of free-ended amorphous SiOx nanowire were demonstrated. It was observed that under in situ uniform electron beam irradiation in transmission electron microscope, the near surface atoms at the most curved free end of the nanowire preferentially vaporized or diffused to the less curved wire sidewall. The processing resulted in an intriguing axial shrinkage and an abnormal radial expansion of the wire. It was also observed that with the beam energy deposition rate being lowered, although both the diffusion and the evaporation slowed down, the processing transferred from an evaporation-dominated status to a diffusion-dominated status. These results are crucial not only to the fundamental understanding but also to the technical controlling of the electron beam-induced structure change at nanoscale or nanoprocessing of low dimensional nanostructures.

Electrical properties of chemical-doped and ion-implanted polyacetylene films

Abstract The electrical properties of chemical-doped and ion-implanted polyacetylene films are studied. Large increases in p-type conductivity upon chemical doping using FeCl 3 and K + ion-implanted samples in n-type conductivity are observed. A method of combining chemical doping with low energy ion implantation (30 keV K + ) makes it possible to fabricate a stable diode-like PA at the near-surface region. The current density of the polymeric diode can be raised as high as 600 mA/cm 2 at 3 V, and the backward-to-forward ratio of current can be 500. As for the conductivity enhancement mechanism in ion-implanted PA films, conductive dangling bond and free radical formation by the implantation induced defects are discussed.