High-purity germanium(HPGe)detectors,which are used for direct dark matter detection,have the advantages of a low threshold and excellent energy resolution.The surface passivation of HPGe has become crucial for achiev...High-purity germanium(HPGe)detectors,which are used for direct dark matter detection,have the advantages of a low threshold and excellent energy resolution.The surface passivation of HPGe has become crucial for achieving an extremely low energy threshold.In this study,first-principles simulations,passivation film preparation,and metal oxide semiconductor(MOS)capacitor characterization were combined to study surface passivation.Theoretical calculations of the energy band structure of the -H,-OH,and -NH_(2) passivation groups on the surface of Ge were performed,and the interface state density and potential with five different passivation groups with N/O atomic ratios were accurately analyzed to obtain a stable surface state.Based on the theoretical calculation results,the surface passivation layers of the Ge_(2)ON_(2) film were prepared via magnetron sputtering in accordance with the optimum atomic ratio structure.The microstructure,C-V,and I-V electrical properties of the layers,and the passivation effect of the Al/Ge_(2)ON_(2)/Ge MOS were characterized to test the interface state density.The mean interface state density obtained by the Terman method was 8.4×10^(11) cm^(-2) eV^(-1).The processing of germanium oxynitrogen passivation films is expected to be used in direct dark matter detection of the HPGe detector surface passivation technology to reduce the detector leakage currents.展开更多
Nitrogenation of SmFelolVIo2 powders was performed in a self-made furnace under a high-purity N2 atmo- sphere up to 40 MPa at 500 ℃. Upon nitrogenation at atmospheric pressure, the lattice parameters a and c increase...Nitrogenation of SmFelolVIo2 powders was performed in a self-made furnace under a high-purity N2 atmo- sphere up to 40 MPa at 500 ℃. Upon nitrogenation at atmospheric pressure, the lattice parameters a and c increase by 0.5% and 2.7%, respectively, whereas the Curie temperature Tc increases from 519 to 633 K. With further increasing the nitrogenation pressure to 20 and 40 MPa, the 1：12 main phase starts to decompose and a large amount of Mo and a-Fe precipitates. This leads to variation of Mo concentration in the 1：12 phase and causes a sharp decrease in Tc and in the coercivity. The relative complex permittivity and permeability of paraffin-SmFeloMO2 composites show multi-resonant behavior. After nitrogenation, the magnetic loss of the powders decreases, which may originate from the influence of eddy currents due to the increase in the particle size.展开更多
Nitrogenation of La0.5Pr0.5Fe11.4Si1.6 with a particle size of 100-150 μm was performed in a high-purity N2 atmosphere of 40 MPa. La0.5Pr0.5Fe11.4Si1.6N0.3 nitrogenated at 480 ℃ exhibits an increase in the Curie tem...Nitrogenation of La0.5Pr0.5Fe11.4Si1.6 with a particle size of 100-150 μm was performed in a high-purity N2 atmosphere of 40 MPa. La0.5Pr0.5Fe11.4Si1.6N0.3 nitrogenated at 480 ℃ exhibits an increase in the Curie temperature Tc from 187 to 195 K. Moreover, for a field change from 0 to 1.5 T, the maximum hysteresis loss at Tc is remarkably reduced from 53 to 3 J kg^-1 and a large magnetic-entropy change ASm of over 10 J kg^-1 K^-1 is maintained. For a La0.5Pr0.5- Fe11.4Si1.6N1.2 sample, nitrogenated at 550 ℃, the XRD pattern clearly exhibits two 1：13 phases and, accordingly, the thermal magnetic curves exhibit two transitions, at 210 and at 295 K. The two transitions lead, for a field change of 5 T, to a ASm larger than 2 J kg^-1 K^-1 over a large temperature range from 200 to 310 K with a maximum value of 5.3 J kg^-1 K^-1 at 225 K. Upon further increase in the nitrogenation temperature to 650 ℃, the amount of the nitrogen- poor phase strongly decreases and a large amount of α-Fe precipitates, resulting in a large reduction in the MCE.展开更多
基金supported by the National Natural Science Foundation of China(No.12005017).
文摘High-purity germanium(HPGe)detectors,which are used for direct dark matter detection,have the advantages of a low threshold and excellent energy resolution.The surface passivation of HPGe has become crucial for achieving an extremely low energy threshold.In this study,first-principles simulations,passivation film preparation,and metal oxide semiconductor(MOS)capacitor characterization were combined to study surface passivation.Theoretical calculations of the energy band structure of the -H,-OH,and -NH_(2) passivation groups on the surface of Ge were performed,and the interface state density and potential with five different passivation groups with N/O atomic ratios were accurately analyzed to obtain a stable surface state.Based on the theoretical calculation results,the surface passivation layers of the Ge_(2)ON_(2) film were prepared via magnetron sputtering in accordance with the optimum atomic ratio structure.The microstructure,C-V,and I-V electrical properties of the layers,and the passivation effect of the Al/Ge_(2)ON_(2)/Ge MOS were characterized to test the interface state density.The mean interface state density obtained by the Terman method was 8.4×10^(11) cm^(-2) eV^(-1).The processing of germanium oxynitrogen passivation films is expected to be used in direct dark matter detection of the HPGe detector surface passivation technology to reduce the detector leakage currents.
基金financially supported by the National Natural Science Foundation of China (No. 51261001)Liaoning Provincial Natural Science Foundation (No. 2013020105)Shenyang Science and Technology Foundation (No. F13-316-139)
文摘Nitrogenation of SmFelolVIo2 powders was performed in a self-made furnace under a high-purity N2 atmo- sphere up to 40 MPa at 500 ℃. Upon nitrogenation at atmospheric pressure, the lattice parameters a and c increase by 0.5% and 2.7%, respectively, whereas the Curie temperature Tc increases from 519 to 633 K. With further increasing the nitrogenation pressure to 20 and 40 MPa, the 1：12 main phase starts to decompose and a large amount of Mo and a-Fe precipitates. This leads to variation of Mo concentration in the 1：12 phase and causes a sharp decrease in Tc and in the coercivity. The relative complex permittivity and permeability of paraffin-SmFeloMO2 composites show multi-resonant behavior. After nitrogenation, the magnetic loss of the powders decreases, which may originate from the influence of eddy currents due to the increase in the particle size.
基金financially supported by the Liaoning Provincial Natural Science Foundation(No.2013020105)the Shenyang Science and Technology Foundation(No.F13-3161-39)
文摘Nitrogenation of La0.5Pr0.5Fe11.4Si1.6 with a particle size of 100-150 μm was performed in a high-purity N2 atmosphere of 40 MPa. La0.5Pr0.5Fe11.4Si1.6N0.3 nitrogenated at 480 ℃ exhibits an increase in the Curie temperature Tc from 187 to 195 K. Moreover, for a field change from 0 to 1.5 T, the maximum hysteresis loss at Tc is remarkably reduced from 53 to 3 J kg^-1 and a large magnetic-entropy change ASm of over 10 J kg^-1 K^-1 is maintained. For a La0.5Pr0.5- Fe11.4Si1.6N1.2 sample, nitrogenated at 550 ℃, the XRD pattern clearly exhibits two 1：13 phases and, accordingly, the thermal magnetic curves exhibit two transitions, at 210 and at 295 K. The two transitions lead, for a field change of 5 T, to a ASm larger than 2 J kg^-1 K^-1 over a large temperature range from 200 to 310 K with a maximum value of 5.3 J kg^-1 K^-1 at 225 K. Upon further increase in the nitrogenation temperature to 650 ℃, the amount of the nitrogen- poor phase strongly decreases and a large amount of α-Fe precipitates, resulting in a large reduction in the MCE.
