X.Z. Cao

Formation of Cu precipitates in a high-energy-particle-irradiated and thermally aged Fe-0.6%Cu alloy

The stability of Cu precipitates in thermally aged Fe-Cu alloys after high-energy particle irradiation was investigated using a mono-energetic positron beam apparatus. The S-parameters did not change with increasing incident positron energy above 15 keV, which means positron annihilation at the surface does not influence the Doppler broadening (DB) spectra. In a non-aged sample, the S-parameter increased, while the W-parameter did not change upon ion irradiation at above 10 keV. By contrast, in the thermally aged sample, the S-parameter increased, while the W-parameter decreased upon ion irradiation. The DB spectra of thermally aged and non-aged samples have nealy the same shape after high-energy particle irradiation. In both thermally aged and non-aged samples, almost all positrons annihilate with electrons in Cu, and vacancy clusters covered with Cu atoms are formed upon neutron irradiation. This agrees with the results of previous studies. However, the defect growth process may be different in aged and non-aged samples.

Cu Precipitates in Fe Ion Irradiated Fe-Cu Alloys Studied Using Positron Techniques

In this paper, we summarized our recent experimental results on Fe-Cu model alloys irradiated by Fe ion. Two kinds of Fe-Cu alloys with 0.3%Cu and 0.6%Cu were prepared and irradiated by 2.5 MeV Fe ion at 573 K. Irradiation dose is 0.1 dpa and 1.2 dpa for each type alloy respectively. Positron annihilation techniques of slow positron beam were used to investigate the irradiation induced defects. Results show that the S parameters are higher in the specimens with high irradiation dose, but the intensity of Cu peaks of CDB is lower. It indicates that the precipitation of Cu atoms formed easily as lower irradiation dose.

DNA nanostructure-based fluorescence thermometer with silver nanoclusters

DNA nanostructure-based fluorescence thermometers were fabricated by linking fluorescent silver nanoclusters (AgNCs) and guanine-rich（G-rich）DNA chains via a thermally sensitive DNA stem-loop at terminals 5 and 3. Variations of temperature alter the distance between the AgNCs and G-rich DNA chain, affecting the interaction between them. As a result, the intensity of fluorescence emission from the AgNCs at 636 nm can be sensitively modulated. It was found that the intensity of such red emission is more temperature sensitive than the equivalent green emission at 543 nm; sensitivity of -3.6%/°C was achieved. Through variation of the melting temperature of the DNA stem-loop, the response temperature range of the thermometers could be readily adjusted. Novel DNA nanostructure-based fluorescence thermometers as described in this work are anticipated to be able to measure the temperature of biological systems at small scales-even a single cell.

The ability of the Coincidence Doppler Broadening Spectroscopy to characterize polymers containing different chemical elements

Hydrocarbon polymers, O-containing, F-containing and Cl-containing polymers are comprehensively studied by Coincidence Doppler Broadening Spectroscopy (CDBS). It is shown that for polymers with different chemical structure, CDBS results can effectively distinguish polar groups CO, CCl, and CF. For polymers with similar chemical structure, the intensity of the element-specific peak in the CDBS ratio curve is dependent not only on the fraction of free positrons, but also on the content of characteristic atom in polymer repeated unit, and the polarity of the polymer molecule. For polymers containing several different polar groups, such as PCTFE (CF & CCl) and PFA (CF & CO), whether the element-specific peak appears or not depends on the amount of the polar groups and its positron capture ability. This work may provide insights into potential applications of CDBS for studying complex polymer systems.

Single Silicon Nanowire-Based Fluorescent Sensor for Endogenous Hypochlorite in an Individual Cell

As a prototype of a single‐cell detecting technique, a single silicon nanowire‐based (SiNW‐based) fluorescent sensor for endogenous hypochlorite in a macrophage is constructed. The fluorescent sensor for hypochlorite is prepared by decorating a near‐infrared dye, IR780 onto the surface of SiNWs. The sensor exhibits high sensitivity and linear dependence of the fluorescence intensities on the hypochlorite concentrations. With the help of micromanipulation and laser scanning confocal microscopy, detection of endogenous hypochlorite in a single macrophage is realized by penetrating the single SiNW‐based sensor into individual cells. The current SiNW‐based sensor will possess potential value in revealing the role of hypochlorite in physiology and pathology. Such single‐cell detecting techniques can be expanded to other fields. This work will open a new door to a variety of novel studies by combining the strengths of single‐cell detecting techniques with biology.

Silver Nanowire-Based Fluorescence Thermometer for a Single Cell

A fluorescence thermometer based on silver nanowires (AgNWs) is realized by assembling Texas Red (TR)-marked thermal-sensitive DNA stem-loops (TR-DNA stem-loop) on the surface of AgNWs. Temperature configures the structure of the TR-DNA stem-loop and resultantly adjusts the energy transfer between TR and the AgNWs, which could sensitively control the fluorescence intensity of the thermometer. The thermometer is sensitive to the temperature ranging from 30 to 40 °C with the sensitivity of 2.6%/°C. Under the assistance of laser confocal microscopy, a temperature change within a single cell was observed by the monofilament AgNW-based thermometer.