Explaining the Frequency Dependence of the DC-Biased Dielectric Response of Polar Nanoregions by Field-Enhanced Correlation Length.

Understanding the effects of polar nanoregions (PNRs) dynamics on dielectric properties is a complex question of essential importance for both fundamental studies of relaxor ferroelectrics and their applications to electro-optic devices. The frequency dependence of dielectric response to the bias electric field opens a brand new window for the study of this problem. A novel model from mesoscopic to macroscopic, revealing the relationship between the dielectric permittivity to the applied electric field, temperature, and PNRs, was established based on mean field approximation and the theory of continuum percolation, and not only validates the field-induced percolation and the relaxation time divergency at the freezing temperature, but also predicts the frequency dependence of dielectric response. Unexpectedly, the model reveals the field-enhanced correlation length results in the nonmonotonic behavior of dielectric response, and implies that the increased orientation consistency of dipolar clusters and coercive fields originated from inherent inhomogeneity slow down the relaxation time of PNR reorientation. Considering the multi-scale heterogeneity of PNRs in relaxor, we found that the increased heterogeneity degree reduces the dielectric permittivity, but changes the slope of dielectric response to the bias electric field.

Cu2O-Au nanowire field-effect phototransistor for hot carrier transfer enhanced photodetection.

In metal-semiconductor hybrid nanostructures, metal absorbs incident photons and generates hot carriers. The hot carriers are injected into the adjacent semiconductor and subsequently contribute to photocurrent. This process increases the conversion efficiency of optoelectronic devices and provides a new path of photodetectors. In this work, we report an enhanced photodetector by hot holes transfer, which is based on Au nanoparticles decorated p-type Cu2O nanowires. The photodetector achieves an enhanced photo-responsivity up to 0.314 A W-1, a higher detectivity of 3.7 × 1010 Jones. The response time and external quantum efficiency of the Cu2O-Au nanowires photodetector are 3.7 times faster and 18.2 times higher than that of the Cu2O nanowires, respectively. The findings indicate that Cu2O-Au nanowires would be a promising candidate in developing novel plasmonic hot carrier devices.

[Determination of six progesterones in milk by on-line cleanup liquid chromatography-tandem mass spectrometry].

A new method using TurboFlow on-line cleanup liquid chromatography combined with tandem mass spectrometry (MS/MS) has been developed for simultaneous determination of six progesterones including 19-norethindrone, 17alpha-hydroxyprogesterone, medroxyprogesterone, megestrol acetate, progesterone and melengestrol acetate in milk. Samples were extracted by acetonitrile. The analytes in extract were on-line purified directly on Cyclone-P purification column where the sample matrices were washed away. Subsequently, the analytes which were eluted from the extraction column onto Phenyl-Hexyl column were separated with a gradient elution, and detected with electrospray ionization mass spectrometry in the positive scan mode using multiple reaction monitoring (MRM). The isotope internal standards were employed for quantification. As a result, the linearities were satisfactory with the correlation coefficients of > 0.999 at concentrations ranging from 0.1 microg/L to 50 microg/L. Based on the repeated analysis of a known blank sample, the limit of quantification (LOQ) is 0.5 microg/kg. Average recoveries of the analytes fortified at three levels (1, 5 and 25 microg/kg) ranged from 90.8% to 107.5%, and the relative standard deviations (RSDs) ranged from 6.3% to 11.8%. This proposed method is simple, rapid, sensitive and highly selective, and can be applied to simultaneous identification an quantification of the six progesterones in milk.