Single crystal PbTe thin films have been grown on BaF2 （111） by using solid source molecular beam epitaxy. The studies of evolution of the surface morphology with the increasing growth temperature from 375 to 525℃ ...Single crystal PbTe thin films have been grown on BaF2 （111） by using solid source molecular beam epitaxy. The studies of evolution of the surface morphology with the increasing growth temperature from 375 to 525℃ by AFM show that PbTe epilayers exhibit smooth surface morphologies with atomic layer scale roughness and are crack free. It is found that for PbTe grown at 475℃, the morphology is dominated by triangles and the rms roughness is 3.987nm. Compared to the rms roughnesses of 0.432nm and 0.759nm for the samples grown at 375 and 525℃ respectively, the surface of the PbTe layer grown at 475℃ is much rougher. This roughening transition is due to the interaction between the elastic relaxation and the plastic relaxation during the strain relaxation process. In contrast to the result of the morphology that the PbTe epitaxial layer grown at 375℃ has most smooth surface, as observed from the line width of x-ray diffraction curves at higher growth temperature improves the crystal quality of the single-crystalline Pb Te layer.展开更多
A BaF2（Barium Fluoride） detector array is designed to precisely measure the（n, γ） cross section at the CSNS-WNS（white neutron source at China Spallation Neutron Source）. It is a 4π solid angle-shaped detector ...A BaF2（Barium Fluoride） detector array is designed to precisely measure the（n, γ） cross section at the CSNS-WNS（white neutron source at China Spallation Neutron Source）. It is a 4π solid angle-shaped detector array consisting of 92 BaF2 crystal elements. To discriminate signals from the BaF2 detector, a pulse shape discrimination method is used, supported by a waveform digitization technique. There are 92 channels for digitizing. The precision and synchronization of clock distribution restricts the performance of waveform digitizing. In this paper, a clock prototype for the BaF2 readout electronics at CSNS-WNS is introduced. It is based on the PXIe platform and has a twin-stage tree topology. In the first stage, clock is synchronously distributed from the tree root to each PXIe crate through a coaxial cable over a long distance, while in the second stage, the clock is further distributed to each electronic module through a PXIe dedicated differential star bus. With the help of this topology, each tree node can fan out up to 20 clocks with 3U size. Test results show the clock jitter is less than 20 ps, which meets the requirements of the BaF2 readout electronics. Besides, this clock system has the advantages of high density, simplicity, scalability and cost saving, so it can be useful for other clock distribution applications.展开更多
The BaF2 （barium fluoride） spectrometer is one of the experiment facilities at the CSNS-WNS（White Neutron Source at China Spallation Neutron Source）, currently under construction. It is designed to precisely measu...The BaF2 （barium fluoride） spectrometer is one of the experiment facilities at the CSNS-WNS（White Neutron Source at China Spallation Neutron Source）, currently under construction. It is designed to precisely measure the（n, γ） cross section, with 92 crystal elements and complete 4π steradian coverage. In order to improve the precision of measurement, in this paper, a new precise digitization and readout method is proposed. Waveform digitizing with 1 GSps sampling rate and 12-bit resolution is used to precisely capture the detector signal. To solve the problem of massive data readout and processing, the readout electronics is designed as a distributed architecture with 4 PXIe crates. The digitized signal is concentrated to the PXIe crate controller through a PCIe bus on the backplane and transmitted to the data acquisition system over gigabit Ethernet in parallel. Besides, the clock and trigger can be fanned out synchronously to every electronic channel over a high-precision distribution network. Test results show that the prototype of the readout electronics can achieve good performance and meet the requirements of the CSNS-WNS BaF2 spectrometer.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 10434090.
文摘Single crystal PbTe thin films have been grown on BaF2 （111） by using solid source molecular beam epitaxy. The studies of evolution of the surface morphology with the increasing growth temperature from 375 to 525℃ by AFM show that PbTe epilayers exhibit smooth surface morphologies with atomic layer scale roughness and are crack free. It is found that for PbTe grown at 475℃, the morphology is dominated by triangles and the rms roughness is 3.987nm. Compared to the rms roughnesses of 0.432nm and 0.759nm for the samples grown at 375 and 525℃ respectively, the surface of the PbTe layer grown at 475℃ is much rougher. This roughening transition is due to the interaction between the elastic relaxation and the plastic relaxation during the strain relaxation process. In contrast to the result of the morphology that the PbTe epitaxial layer grown at 375℃ has most smooth surface, as observed from the line width of x-ray diffraction curves at higher growth temperature improves the crystal quality of the single-crystalline Pb Te layer.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50672087 and 60778039, the National Basic Research Programme of China under Grant No 2006CB806007, the National High-Tech Research and Development Programme of China under Grant No 2006AA03Z304, and the Programme for Changjiang Scholars and Innovative Research Team in University （IRT0651）.
基金Supported by National Research and Development plan(2016 YFA0401602)NSAF(U1530111)National Natural Science Foundation of China(11005107)
文摘A BaF2（Barium Fluoride） detector array is designed to precisely measure the（n, γ） cross section at the CSNS-WNS（white neutron source at China Spallation Neutron Source）. It is a 4π solid angle-shaped detector array consisting of 92 BaF2 crystal elements. To discriminate signals from the BaF2 detector, a pulse shape discrimination method is used, supported by a waveform digitization technique. There are 92 channels for digitizing. The precision and synchronization of clock distribution restricts the performance of waveform digitizing. In this paper, a clock prototype for the BaF2 readout electronics at CSNS-WNS is introduced. It is based on the PXIe platform and has a twin-stage tree topology. In the first stage, clock is synchronously distributed from the tree root to each PXIe crate through a coaxial cable over a long distance, while in the second stage, the clock is further distributed to each electronic module through a PXIe dedicated differential star bus. With the help of this topology, each tree node can fan out up to 20 clocks with 3U size. Test results show the clock jitter is less than 20 ps, which meets the requirements of the BaF2 readout electronics. Besides, this clock system has the advantages of high density, simplicity, scalability and cost saving, so it can be useful for other clock distribution applications.
基金Supported by National Research and Development plan(2016YFA0401602)NSAF(U1530111)
文摘The BaF2 （barium fluoride） spectrometer is one of the experiment facilities at the CSNS-WNS（White Neutron Source at China Spallation Neutron Source）, currently under construction. It is designed to precisely measure the（n, γ） cross section, with 92 crystal elements and complete 4π steradian coverage. In order to improve the precision of measurement, in this paper, a new precise digitization and readout method is proposed. Waveform digitizing with 1 GSps sampling rate and 12-bit resolution is used to precisely capture the detector signal. To solve the problem of massive data readout and processing, the readout electronics is designed as a distributed architecture with 4 PXIe crates. The digitized signal is concentrated to the PXIe crate controller through a PCIe bus on the backplane and transmitted to the data acquisition system over gigabit Ethernet in parallel. Besides, the clock and trigger can be fanned out synchronously to every electronic channel over a high-precision distribution network. Test results show that the prototype of the readout electronics can achieve good performance and meet the requirements of the CSNS-WNS BaF2 spectrometer.
