Kondo transport properties through a Kondo-type quantum dot （QD） with a side-coupled triple-QD structure are systematically investigated by using the non-equilibrium Green＇s function method. We firstly derive the f...Kondo transport properties through a Kondo-type quantum dot （QD） with a side-coupled triple-QD structure are systematically investigated by using the non-equilibrium Green＇s function method. We firstly derive the formulae of the current, the linear conductance, the transmission coefficient, and the local density of states. Then we carry out the analytical and numerical studies and some universal conductance properties are obtained. It is shown that the number of the conductance valleys is intrinsically determined by the side-coupled QDs and at most equal to the number of the QDs included in the side-coupled structure in the asymmetric limit. In the process of forming the conductance valleys, the side-coupled QD system plays the dominant role while the couplings between the Kondo-type QD and the side-coupled structure play the subsidiary and indispensable roles. To testify the validity of the universal conductance properties, another different kinds of side-coupled triple-QD structures are considered. It should be emphasized that these universal properties axe applicable in understanding this kind of systems with arbitrary many-QD side structures.展开更多
Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implanta...Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implantation at energies of 0.5-5 keV, at a dose of 1×1015 As+ /cm 2 and spike annealing. Experimentally the damaged layer of the as-implanted wafer and the recrystallization and activation of the post-annealed wafer were evaluated by SE in the spectral range from 0.27 to 20 m. The PCR amplitude decreased monotonically with the increasing implantation energy. The experimental results also showed that the PCR amplitudes of post-annealed USJ wafers were greatly enhanced, compared to the non-implanted and non-annealed substrate wafer. The PL measurements showed the enhanced PCR signals were attributed to the band-edge emissions of silicon. For explaining the PL enhancement, the electronic transport properties of USJ wafers were extracted via multi-wavelength PCR experiment and fitting. The fitted results showed the decreasing surface recombination velocity and the decreasing diffusion coefficient of the implanted layer contributed to the PCR signal enhancement with the decreasing implantation energy. SE, PCR and PL were proven to be non-destructive metrology tools for characterizing ultra-shallow junctions.展开更多
The ongoing discoveries and studies of novel topological quantum materials have become an emergent and important field of condensed matter physics. Recently, Hfres ignited renewed interest as a candidate of a novel to...The ongoing discoveries and studies of novel topological quantum materials have become an emergent and important field of condensed matter physics. Recently, Hfres ignited renewed interest as a candidate of a novel topological material. The single-layer Hffes is predicted to be a tWOldimensional large band gap topological insulator and can be stacked into a bulk that may host a temperatureldriven topological phase transition. Historically, Hfres attracted considerable interest for its anomalous transport properties characterized by a peculiar resistivity peak accompanied by a sign reversal carrier type. The origin of the transport anomaly remains under a hot debate. Here we report the first high-resolution laserlbased anglelresolved photoemission measurements on the temperature-dependent electronic structure in Hffes. Our results indicated that a temperature-induced Lifshitz transition occurs in Hffes, which provides a natural understanding on the origin of the transport anomaly in Hffe~. In addition, our observa- tions suggest that Hffes is a weak topological insulator that is located at the phase boundary between weak and strong topological insulators at very low temperature.展开更多
Perovskite quantum-dot-based light-emitting diodes(QLEDs)are highly promising for future solid-state lightings and high-definition displays due to their excellent color purity.However,their device performance is easil...Perovskite quantum-dot-based light-emitting diodes(QLEDs)are highly promising for future solid-state lightings and high-definition displays due to their excellent color purity.However,their device performance is easily affected by charge accumulation induced luminescence quenching due to imbalanced charge injection in the devices.Here we report green perovskite QLEDs with simultaneously improved efficiency and operational lifetime through balancing the charge injection with the employment of a bilayered electron transport structure.The charge-balanced QLEDs exhibit a color-saturated green emission with a full-width at half-maximum(FWHM)of 18 nm and a peak at 520 nm,a low turn-on voltage of2.0 V and a champion external quantum efficiency(EQE)of 21.63%,representing one of the most efficient perovskite QLEDs so far.In addition,the devices with modulated charge balance demonstrate a nearly 20-fold improvement in the operational lifetime compared to the control device.Our results demonstrate the great potential of further improving the device performance of perovskite QLEDs toward practical applications in lightings and displays via rational device engineering.展开更多
We investigate an electron transport bilayer fabricated at 〈110℃ to form all low-temperature processed, thermally stable, efficient perovskite solar cells with negligible hysteresis. The components of the bilayer cr...We investigate an electron transport bilayer fabricated at 〈110℃ to form all low-temperature processed, thermally stable, efficient perovskite solar cells with negligible hysteresis. The components of the bilayer create a symbiosis that results in improved devices compared with either of the components being used in isolation. A sol-gel derived ZnO layer facilitates improved energy level alignment and enhanced charge carrier extraction and a [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） layer to reduce hysteresis and enhance perovskite thermal stability. The creation of a bilayer structure allows materials that are inherently unsuitable to be in contact with the perovskite active layer to be used in efficient devices through simple surface modification strategies.展开更多
基金Supported by the National Nature Science Foundation of China under Grant Nos.10604005 and 10974015 the Program for New Century Excellent Talents in University under Grant No.NCET-08-0044
文摘Kondo transport properties through a Kondo-type quantum dot （QD） with a side-coupled triple-QD structure are systematically investigated by using the non-equilibrium Green＇s function method. We firstly derive the formulae of the current, the linear conductance, the transmission coefficient, and the local density of states. Then we carry out the analytical and numerical studies and some universal conductance properties are obtained. It is shown that the number of the conductance valleys is intrinsically determined by the side-coupled QDs and at most equal to the number of the QDs included in the side-coupled structure in the asymmetric limit. In the process of forming the conductance valleys, the side-coupled QD system plays the dominant role while the couplings between the Kondo-type QD and the side-coupled structure play the subsidiary and indispensable roles. To testify the validity of the universal conductance properties, another different kinds of side-coupled triple-QD structures are considered. It should be emphasized that these universal properties axe applicable in understanding this kind of systems with arbitrary many-QD side structures.
基金supported by the National Natural Science Foundation of China(Grant Nos. 61076090 and 60676058)
文摘Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implantation at energies of 0.5-5 keV, at a dose of 1×1015 As+ /cm 2 and spike annealing. Experimentally the damaged layer of the as-implanted wafer and the recrystallization and activation of the post-annealed wafer were evaluated by SE in the spectral range from 0.27 to 20 m. The PCR amplitude decreased monotonically with the increasing implantation energy. The experimental results also showed that the PCR amplitudes of post-annealed USJ wafers were greatly enhanced, compared to the non-implanted and non-annealed substrate wafer. The PL measurements showed the enhanced PCR signals were attributed to the band-edge emissions of silicon. For explaining the PL enhancement, the electronic transport properties of USJ wafers were extracted via multi-wavelength PCR experiment and fitting. The fitted results showed the decreasing surface recombination velocity and the decreasing diffusion coefficient of the implanted layer contributed to the PCR signal enhancement with the decreasing implantation energy. SE, PCR and PL were proven to be non-destructive metrology tools for characterizing ultra-shallow junctions.
基金supported by the National Key Research and Development Program of China (2016YFA0300600)the National Natural Science Foundation of China(11574367)+1 种基金the National Basic Research Program of China (2013CB921700,2013CB921904 and 2015CB921300)the Strategic Priority Research Program(B) of the Chinese Academy of Sciences(XDB07020300)
文摘The ongoing discoveries and studies of novel topological quantum materials have become an emergent and important field of condensed matter physics. Recently, Hfres ignited renewed interest as a candidate of a novel topological material. The single-layer Hffes is predicted to be a tWOldimensional large band gap topological insulator and can be stacked into a bulk that may host a temperatureldriven topological phase transition. Historically, Hfres attracted considerable interest for its anomalous transport properties characterized by a peculiar resistivity peak accompanied by a sign reversal carrier type. The origin of the transport anomaly remains under a hot debate. Here we report the first high-resolution laserlbased anglelresolved photoemission measurements on the temperature-dependent electronic structure in Hffes. Our results indicated that a temperature-induced Lifshitz transition occurs in Hffes, which provides a natural understanding on the origin of the transport anomaly in Hffe~. In addition, our observa- tions suggest that Hffes is a weak topological insulator that is located at the phase boundary between weak and strong topological insulators at very low temperature.
基金supported by the National Natural Science Foundation of China (51922049, 61604074)the National Key Research and Development Program of China (2016YFB0401701)+2 种基金the Natural Science Foundation of Jiangsu Province (BK20180020)the Fundamental Research Funds for the Central Universities (30920032102)PAPD of Jiangsu Higher Education Institutions
文摘Perovskite quantum-dot-based light-emitting diodes(QLEDs)are highly promising for future solid-state lightings and high-definition displays due to their excellent color purity.However,their device performance is easily affected by charge accumulation induced luminescence quenching due to imbalanced charge injection in the devices.Here we report green perovskite QLEDs with simultaneously improved efficiency and operational lifetime through balancing the charge injection with the employment of a bilayered electron transport structure.The charge-balanced QLEDs exhibit a color-saturated green emission with a full-width at half-maximum(FWHM)of 18 nm and a peak at 520 nm,a low turn-on voltage of2.0 V and a champion external quantum efficiency(EQE)of 21.63%,representing one of the most efficient perovskite QLEDs so far.In addition,the devices with modulated charge balance demonstrate a nearly 20-fold improvement in the operational lifetime compared to the control device.Our results demonstrate the great potential of further improving the device performance of perovskite QLEDs toward practical applications in lightings and displays via rational device engineering.
基金the China Scholarship Council for financial support for PhD studiessupport through the EPSRC Centre for Doctoral Training in Plastic Electronics(EP/L016702/1)
文摘We investigate an electron transport bilayer fabricated at 〈110℃ to form all low-temperature processed, thermally stable, efficient perovskite solar cells with negligible hysteresis. The components of the bilayer create a symbiosis that results in improved devices compared with either of the components being used in isolation. A sol-gel derived ZnO layer facilitates improved energy level alignment and enhanced charge carrier extraction and a [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） layer to reduce hysteresis and enhance perovskite thermal stability. The creation of a bilayer structure allows materials that are inherently unsuitable to be in contact with the perovskite active layer to be used in efficient devices through simple surface modification strategies.
