Long—Range Effects on the Pyroelectric Coefficient of Ferroelectric Superlattice

Long-range effects on the pyroelectric coefficient of a ferroelectric superlattice consisting of two different ferroelectric materials are investigated based on the transverse Ising model.The effects of the interfacial coupling and the thickness of one period on the pyroelectric coefficient of the ferroelectric superlattics are studied by taking into account the long-range interaction.It is found that with the increase of the strength of the long-range interaction,the pyroelectric coefficient decreases when the temperature is lower than the phase transition temperature;the mumber of the pyroelectric peaks decreases gradually and the phase transition temperature increases,It is also found that with the decrease of the interfacial coupling and the thickness of one period.the phase transition temperature and the number of the pyroelectric peaks decrease.     

A New Method of Measuring Electron Emission Induced by Low Energy Ions from Solids

A new mathematical method of measuring electron emission induced by low energy ions from solids is described and used to calculate secondary electron emission according to the recorded pulse-height spectra of ions and ultraviolet （UV） photons. Using the UV single secondary electron spectra, we predict the shape of many secondary electron distributions under consideration of detection efficiency of MCP detector. These calculated distributions allow us to characterize the secondary electrons yield, and to give a secondary electron distribution for measured data. It seems rather feasible to determine secondary electron yield emitted by low energy ions at very low ion uxes.     

Mechanism of Low Threshold Lasing of Dye Solution Embedding in Nanoparticle Fractal Aggregates

We study the single-photon and two-photon induced emission properties of dye solution embedded with nanoparticle fractal aggreagates.The spectral and temporal experimental results show that the lasing threshold of single photon absorption of a neat dye solution;while that of two-photon absorption does not.These experimental results imply that this low threshold single-photon absorption lasing mainly results from the mechanism of random walking,instead of Anderson localization.unless somthing about two-photon induced emission is unknown.     

Measurement of D(d,p) T Reaction Cross Sections in Sm Metal in Low Energy Region (10≤Ed≤20keV)

To study the screening effect of nuclear reactions in metallic environments, the thick target yields, the cross sections and the experimental S(E) factors of the D(d,p)T reaction have been measured on deuterons implanted in Sm metal at 133.2K for beam energies ranging from 10 to 20keV. The thick target yields of protons emitted in the D(d,p) T reaction are measured and compared with those data extrapolated from cross sections and stopping power data at higher energies. The screening potential in Sm metal at 133.2K is deduced tobe 520±56eV. As compared with the value achieved in the gas target, thecalculated screening potential values are much larger. This screening potential cannot be simply interpreted only by the electron screening. Energy dependences of the cross section σ(E) and the experimental S(E) factor for D(d,p)T reaction in Sm metal at 133.2K are obtained, respectively.     

Kinetics and Mechanism of Nanostructures in Oxidation of Si1—xGex Alloys

We investigate the oxidation behaviour of Si1-xGex alloys(x=0.05,0.15,and 0.25),The oxidation of SiGe films with different compositions was carried out in O2(dry)atmosphere at 800,900 and 1000℃,respectively,for various lengths of time,The thickness and property of the nanoparticle and nanolayer in oxide films and germanium segregation in oxidation of SiGe alloys are measured by using a high precision ellipsometer.The results are in good agreement with the Rutherford backscattering spectrometry,profile dektak instrument and high-resolution scanning transmission electron microscopy.We found that the Ge content in the oxide layer increases with the Ge content in SiGe alloys,and that the Ge content in the oxide film decreases with the increasing oxidation temperature and time,Rejection of Ge results in Piling up of Ge at the interface etween the growing SiO2 and the remaining SiGe,which forms a nanometre Ge-rich layer.Substantial interdiffusion of Si and Ge takes place in the remaining SiGe,which leads to the complicated distribution of Ge segregation.We find a nanometre cap layer over the oxide film after fast oxidation,in which there are many Ge nanoparticles,We analyse the kinetics and mechanism of the nanostructure of the oxide and Ge segregation in oxidation of Si1-xGex alloys.     

Bi—dimension Position Sensitive Detector Used in the Study of Fusion Fission of Heavy Ions at the Sub—Coulomb Barrier Energy Region

The structure,operation principle and performance of the bi—dimension position sensitive avalanche chamber (BPAC) used in the study of fusion fission induced by heavy ions at the near and sub-Coulomb barrier energy region are describerd.
The fold angle distribution of fragments in different angle region for 84MeV(E_cm)¹⁶O+²³²Th reaction system was obtained by using BPAC,from which the angle distribution of transfer—fission fragments has been distinguished from that of compound mucleus fission fragments.It is thereby certified that transfer—fission is not the reason of anomalous anisotropies of fragment angle distribution.Meanwhile experimental results supported the preequilibrium fission model,in frame of which the anomalous anisotropies of fragment distribution was explained.     

Elemental Analyzer-Quadrupole MS Coupling—A Low Cost Equipment for the Simultaneous Determination of Carbon/13C and Nitrogen/15N in Isotopically Enriched Soil and Plant Samples

Abstract

Since the end of the 80s elemental analyzer-isotope ratio mass spectrometer connections have been used for the fast, automatic and highly precise determination of carbon and nitrogen content as well as their isotopic composition in one run. But for artificially enriched stable isotopes as tracer in biological processes and since these processes have a high biological variability anyway (e.g. soil processes) the use of these highly precise but also sophisticated and expensive instruments is not required. In this case the use of a quadrupole mass spectrometer connected with an elemental analyzer can offer a low cost alternative. As shown, such coupling is suitable for automatic simultaneous routine analysis of total nitrogen and carbon and their isotopic enrichment (¹⁵N, ¹³C) in plant material and soils. The relative standard deviation for ¹⁵N and ¹³C determination is 2% To meet this precision a careful sample homogenization by grinding is very important. The duration of one measurement is 6–8 min. depending on whether nitrogen alone or both nitrogen and carbon are determined. This enables a high sample throughput.