The point-contact high-purity germanium detector(HPGe)has the advantages of low background,low energy threshold,and high energy resolution and can be applied in the detection of rare-event physics.However,the performa...The point-contact high-purity germanium detector(HPGe)has the advantages of low background,low energy threshold,and high energy resolution and can be applied in the detection of rare-event physics.However,the performance of HPGe must be further improved to achieve superior energy resolution,low noise,and long-term reliability.In this study,we combine computational simulations and experimental comparisons to deeply understand the passivation mechanism of Ge.The surface passivation effect is calculated and inferred from the band structure and density of interface states,and further con-firmed by the minority carrier lifetime.The first-principles method based on the density functional theory was adopted to systematically study the lattice structure,band structure,and density of state(DOS)of four different systems:Ge–H,Ge–Ge-NH 2,Ge-OH,and Ge-SiO_(x).The electronic char-acteristics of the Ge(100)unit cell with different passi-vation groups and Si/O atomic ratios were compared.This shows that H,N,and O atoms can effectively reduce the surface DOS of the Ge atoms.The passivation effect of the SiO_(x) group varied with increasing O atoms and Si/O atomic ratios.Experimentally,SiO and SiO_(2) passivation films were fabricated by electron beam evaporation on a Ge substrate,and the valence state of Si and resistivity was measured to characterize the film.The minority carrier lifetime of Ge-SiO_(2) is 21.3 ls,which is approximately quadruple that of Ge-SiO.The passivation effect and mechanism are discussed in terms of hopping conduction and surface defect density.This study builds a relationship between the passivation effect and different termination groups,and provides technical support for the potential passivation layer,which can be applied in Ge detectors with ultralow energy thresholds and especially in HPGe for rare-event physics detection experiments in future.展开更多
MXenes are a novel family of two-dimensional(2D)materials that are fast gaining popularity due to their versatile characteristics.The surfaces of these materials are often functionalized by negatively charged terminal...MXenes are a novel family of two-dimensional(2D)materials that are fast gaining popularity due to their versatile characteristics.The surfaces of these materials are often functionalized by negatively charged terminal groups,such as=O,OH,and F during their synthesis,and it has been hypothesized that regulating the surface terminators enables to control the material characteristics.However,there is still a large gap between computational and experimental investigations regarding comprehending the surface functional groups.Surfaces with mixed terminations are consistently synthesized in experiments,although pure terminated surfaces are predicted by computational research.Here we summarized the nature of chemical bonding in transition metal carbide materials(MXenes)by1H and19F nuclear magnetic resonance(NMR),Raman,X-ray absorption near edge structure(XANES),extended X-ray absorption fine structure(EXAFS),ultraviolet photoelectron spectroscopy(UPS),X-ray photoelectron spectroscopy(XPS)/scanning transmission electron microscopy(STEM),and thermogravimetric analysis-mass spectrometry(TGA-MS)characterizations.Previous literature reveals that=O,–OH,–F,and–Cl are typical MXene surface terminators.However,recent comparative investigations on the valence band intensity distribution in MXenes reveal that the–OH cannot be considered an intrinsic termination species in MXenes.The surface terminals(=O,–OH,–F,and–Cl)of several MXenes,particularly V2CTxand Ti3C2Tx,will be identified and quantified here.We have also discussed different etching approaches for the synthesis of MXene,the dependence of MXene conductivity on MXene terminating groups,and the emission of various gaseous products that evolved during its chemical transformations.This paper provides significance,especially in the field of energy conversion and storage materials,where the intercalation process is crucial.展开更多
FA-Cs mixed-cation perovskite has been reported as a promising candidate for obtaining highly efficient and stable photovoltaic devices.Phenylethylamine iodide(PEAI)post-treatment is a widely used and effective method...FA-Cs mixed-cation perovskite has been reported as a promising candidate for obtaining highly efficient and stable photovoltaic devices.Phenylethylamine iodide(PEAI)post-treatment is a widely used and effective method for surface passivation of FA-Cs perovskite layer in devices.However,it is still controversial whether the PEAI post-treatment would form two-dimensional(2D)perovskite PEA_(2)PbI_(4) capping layer or just result in PEA+terminated surface.Here in this work,the function of PEAI post-treatment on FA-Cs mixed-cation perovskite FA_(1-x)Cs_(x)PbI_(3)(x=0.1–0.9)with varied Cs contents is elucidated.With increased Cs content,the FA-Cs perovskite shows higher resistance to the cation exchange between FA+and PEA+.This Cs-content-dependent cation exchange results in the different PEAI reaction preferences with FA-Cs mixed-cation perovskites.Furthermore,higher Cs content with stronger resistance to cation exchange reaction leads to a wider processing window for post-treatment and defect passivation,which is beneficial for the fabrication of large-scale photovoltaic devices.展开更多
Bottom-up approach to constructing low-dimensional nanostructures on surfaces with terminal alkynes has drawn great interest because of its potential applications in fabricating advanced functional nanomaterials. The ...Bottom-up approach to constructing low-dimensional nanostructures on surfaces with terminal alkynes has drawn great interest because of its potential applications in fabricating advanced functional nanomaterials. The diversity of the achieved products manifests rich chemistry of terminal alkynes and hence careful linking strategies and proper controlling methodologies are required for selective preparations of high-quality target nanoarchitectures. This review summarizes various on-surface linking strategies for terminal alkynes, including non-bonding interactions as well as organometallic and covalent bonds, and presents examples to show effective control of surface assemblies and reactions of terminal alkynes by variations of the precursor structures, substrates and activation modes. Systematic studies of the on-surface linkage of terminal alkynes may help efficient and predictable preparations of surface nanomaterials and further understanding of surface chemistry.展开更多
MXenes are a group of recently discovered 2D materials and have attracted extensive attention since their first report in 2011;they have shown excellent prospects for energy storage applications owing to their unique ...MXenes are a group of recently discovered 2D materials and have attracted extensive attention since their first report in 2011;they have shown excellent prospects for energy storage applications owing to their unique layered microstructure and tunable electrical properties.One major feature of MXenes is their tailorable surface terminations(e.g.,-F,-O,-OH).Numerous studies have indicated that the composition of the surface terminations can significantly impact the electrochemical properties of MXenes.Nonetheless,the underlying mechanisms are still poorly understood,mainly because of the difficulties in quantitative analysis and characterization.This review summarizes the latest research progress on MXene terminations.First,a systematic introduction to the approaches for preparing MXenes is presented,which generally dominates the surface terminations.Then,theoretical and experimental efforts regarding the surface terminations are discussed,and the influence of surface terminations on the electronic and electrochemical properties of MXenes are generalized.Finally,we present the significance and research prospects of MXene terminations.We expect this review to encourage research on MXenes and provide guidance for usingthese materials for batteries and supercapacitors.展开更多
All-inorganic α-CsPbBr_(x)I_(3-x)perovskites featuring nano-sized crystallites show great potential for pure-red light-emitting diode(LED)applications.Currently,the CsPbBr_(x)I_(3-x)LEDs based on nano-sized α-CsPbBr...All-inorganic α-CsPbBr_(x)I_(3-x)perovskites featuring nano-sized crystallites show great potential for pure-red light-emitting diode(LED)applications.Currently,the CsPbBr_(x)I_(3-x)LEDs based on nano-sized α-CsPbBr_(x)I_(3-x)crystallites have been fabricated mainly via the classical colloidal route including a tedious procedure of nanocrystal synthesis,purification,ligand or anion exchange,film casting,etc.With the usually adopted conventional LED device structure,only high turn-on voltages(>2.7)have been achieved for CsPbBrxl3-x LEDs.Moreover,this mix-halide system may suffer from severe spectra-shift under bias.In this report,CsPbBr_(x)I_(3-x)thin films featuring nano-sized crystallites are prepared by incorporating multiple ammonium ligands in a one-step spin-coating route.The multiple ammonium ligands constrain the growth of CsPbBr_(x)I_(3-x)nanograins.Such CsPbBr_(x)I_(3-x)thin films benefit from quantum confinement.The corresponding CsPbBr_(x)I_(3-x)LEDs,adopting a conventional LED structure of indium-doped tin oxide(ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)/CsPbBr_(x)I_(3-x)/[6,6]-phenyl C61 butyric acid methyl ester(PCBM)/bathocuproine(BCP)/AI,emit pure-red color at Commission Internationale de I'eclairage(CIE)coordinates of(0.709,0.290),(0.711,0.289),etc.,which represent the highest color-purity for reported pure-red perovskite LEDs and meet the Rec.2020 requirement at CIE(0.708,0.292)very well.The CsPbBr_(x)I_(3-x)LED shows a low turn-on voltage of 1.6 V,maximum external quantum efficiency of 8.94%,high luminance of 2,859 cd·m^(-2),and good color stability under bias.展开更多
This paper addresses the attitude tracking control problem of a rigid spacecraft in the presence of the modeling uncertainty,external disturbance,and saturated control input by designing two robust att计ude tracking c...This paper addresses the attitude tracking control problem of a rigid spacecraft in the presence of the modeling uncertainty,external disturbance,and saturated control input by designing two robust att计ude tracking controllers.The basic controller is formulated using an integral sliding mode surface which is continuous and provides an asymptotic convergence rate for the closed-loop system.In this case,only the external disturbance with the prior information is considered.Then,to provide a finite time convergence rate and further improve the robustness of the control system under the unknown system uncertainty containing both the modeling uncertainty and external disturbance,a novel integral terminal sliding mode surface(ITSMS)is designed and associated w计h the continuous adaptive control method.Besides,a command filter is utilized to deal with the immeasurability problem within the proposed ITSMS and an auxiliary system to counteract the input saturation problem.Digital simulations are presented to verify the effectiveness of the proposed controllers.展开更多
基金supported by the National Natural Science Foundation of China Youth Fund(No.12005017)。
文摘The point-contact high-purity germanium detector(HPGe)has the advantages of low background,low energy threshold,and high energy resolution and can be applied in the detection of rare-event physics.However,the performance of HPGe must be further improved to achieve superior energy resolution,low noise,and long-term reliability.In this study,we combine computational simulations and experimental comparisons to deeply understand the passivation mechanism of Ge.The surface passivation effect is calculated and inferred from the band structure and density of interface states,and further con-firmed by the minority carrier lifetime.The first-principles method based on the density functional theory was adopted to systematically study the lattice structure,band structure,and density of state(DOS)of four different systems:Ge–H,Ge–Ge-NH 2,Ge-OH,and Ge-SiO_(x).The electronic char-acteristics of the Ge(100)unit cell with different passi-vation groups and Si/O atomic ratios were compared.This shows that H,N,and O atoms can effectively reduce the surface DOS of the Ge atoms.The passivation effect of the SiO_(x) group varied with increasing O atoms and Si/O atomic ratios.Experimentally,SiO and SiO_(2) passivation films were fabricated by electron beam evaporation on a Ge substrate,and the valence state of Si and resistivity was measured to characterize the film.The minority carrier lifetime of Ge-SiO_(2) is 21.3 ls,which is approximately quadruple that of Ge-SiO.The passivation effect and mechanism are discussed in terms of hopping conduction and surface defect density.This study builds a relationship between the passivation effect and different termination groups,and provides technical support for the potential passivation layer,which can be applied in Ge detectors with ultralow energy thresholds and especially in HPGe for rare-event physics detection experiments in future.
基金supported by the National Natural Science Foundation of China(21703147 and U1401248)the support of China Scholarship Council(2018SLJ022487)。
文摘MXenes are a novel family of two-dimensional(2D)materials that are fast gaining popularity due to their versatile characteristics.The surfaces of these materials are often functionalized by negatively charged terminal groups,such as=O,OH,and F during their synthesis,and it has been hypothesized that regulating the surface terminators enables to control the material characteristics.However,there is still a large gap between computational and experimental investigations regarding comprehending the surface functional groups.Surfaces with mixed terminations are consistently synthesized in experiments,although pure terminated surfaces are predicted by computational research.Here we summarized the nature of chemical bonding in transition metal carbide materials(MXenes)by1H and19F nuclear magnetic resonance(NMR),Raman,X-ray absorption near edge structure(XANES),extended X-ray absorption fine structure(EXAFS),ultraviolet photoelectron spectroscopy(UPS),X-ray photoelectron spectroscopy(XPS)/scanning transmission electron microscopy(STEM),and thermogravimetric analysis-mass spectrometry(TGA-MS)characterizations.Previous literature reveals that=O,–OH,–F,and–Cl are typical MXene surface terminators.However,recent comparative investigations on the valence band intensity distribution in MXenes reveal that the–OH cannot be considered an intrinsic termination species in MXenes.The surface terminals(=O,–OH,–F,and–Cl)of several MXenes,particularly V2CTxand Ti3C2Tx,will be identified and quantified here.We have also discussed different etching approaches for the synthesis of MXene,the dependence of MXene conductivity on MXene terminating groups,and the emission of various gaseous products that evolved during its chemical transformations.This paper provides significance,especially in the field of energy conversion and storage materials,where the intercalation process is crucial.
基金supported by the National Key Research and Development Program of China(2017YFE0127100)the National Natural Science Foundation of China(NSFC,Grant 22025505)+1 种基金the Program of Shanghai Academic Technology Research Leader(Grant 20XD1422200)the Key Laboratory of Resource Chemistry,Ministry of Education(KLRC_ME2003)。
文摘FA-Cs mixed-cation perovskite has been reported as a promising candidate for obtaining highly efficient and stable photovoltaic devices.Phenylethylamine iodide(PEAI)post-treatment is a widely used and effective method for surface passivation of FA-Cs perovskite layer in devices.However,it is still controversial whether the PEAI post-treatment would form two-dimensional(2D)perovskite PEA_(2)PbI_(4) capping layer or just result in PEA+terminated surface.Here in this work,the function of PEAI post-treatment on FA-Cs mixed-cation perovskite FA_(1-x)Cs_(x)PbI_(3)(x=0.1–0.9)with varied Cs contents is elucidated.With increased Cs content,the FA-Cs perovskite shows higher resistance to the cation exchange between FA+and PEA+.This Cs-content-dependent cation exchange results in the different PEAI reaction preferences with FA-Cs mixed-cation perovskites.Furthermore,higher Cs content with stronger resistance to cation exchange reaction leads to a wider processing window for post-treatment and defect passivation,which is beneficial for the fabrication of large-scale photovoltaic devices.
基金jointly supported by National Natural Science Foundation of China (NSFC) (Nos. 91527303, 21333001)
文摘Bottom-up approach to constructing low-dimensional nanostructures on surfaces with terminal alkynes has drawn great interest because of its potential applications in fabricating advanced functional nanomaterials. The diversity of the achieved products manifests rich chemistry of terminal alkynes and hence careful linking strategies and proper controlling methodologies are required for selective preparations of high-quality target nanoarchitectures. This review summarizes various on-surface linking strategies for terminal alkynes, including non-bonding interactions as well as organometallic and covalent bonds, and presents examples to show effective control of surface assemblies and reactions of terminal alkynes by variations of the precursor structures, substrates and activation modes. Systematic studies of the on-surface linkage of terminal alkynes may help efficient and predictable preparations of surface nanomaterials and further understanding of surface chemistry.
基金funded by the National Natural Science Foundation of China(Nos.51731004 and 51902051)Natural Science Foundation of Jiangsu Province(No.BK20200386)。
文摘MXenes are a group of recently discovered 2D materials and have attracted extensive attention since their first report in 2011;they have shown excellent prospects for energy storage applications owing to their unique layered microstructure and tunable electrical properties.One major feature of MXenes is their tailorable surface terminations(e.g.,-F,-O,-OH).Numerous studies have indicated that the composition of the surface terminations can significantly impact the electrochemical properties of MXenes.Nonetheless,the underlying mechanisms are still poorly understood,mainly because of the difficulties in quantitative analysis and characterization.This review summarizes the latest research progress on MXene terminations.First,a systematic introduction to the approaches for preparing MXenes is presented,which generally dominates the surface terminations.Then,theoretical and experimental efforts regarding the surface terminations are discussed,and the influence of surface terminations on the electronic and electrochemical properties of MXenes are generalized.Finally,we present the significance and research prospects of MXene terminations.We expect this review to encourage research on MXenes and provide guidance for usingthese materials for batteries and supercapacitors.
基金the Energy Materials and Surface Sciences Unit of the Okinawa Institute of Science and Technology Graduate University(OIST),the OIST Proof of Concept(POC)Program,the OIST R&D Cluster Research Program,and the Japan Society for the Promotion of Science(JSPS)Grants-in-Aid for Scientific Research[KAKENHI](No.JP18K05266).
文摘All-inorganic α-CsPbBr_(x)I_(3-x)perovskites featuring nano-sized crystallites show great potential for pure-red light-emitting diode(LED)applications.Currently,the CsPbBr_(x)I_(3-x)LEDs based on nano-sized α-CsPbBr_(x)I_(3-x)crystallites have been fabricated mainly via the classical colloidal route including a tedious procedure of nanocrystal synthesis,purification,ligand or anion exchange,film casting,etc.With the usually adopted conventional LED device structure,only high turn-on voltages(>2.7)have been achieved for CsPbBrxl3-x LEDs.Moreover,this mix-halide system may suffer from severe spectra-shift under bias.In this report,CsPbBr_(x)I_(3-x)thin films featuring nano-sized crystallites are prepared by incorporating multiple ammonium ligands in a one-step spin-coating route.The multiple ammonium ligands constrain the growth of CsPbBr_(x)I_(3-x)nanograins.Such CsPbBr_(x)I_(3-x)thin films benefit from quantum confinement.The corresponding CsPbBr_(x)I_(3-x)LEDs,adopting a conventional LED structure of indium-doped tin oxide(ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)/CsPbBr_(x)I_(3-x)/[6,6]-phenyl C61 butyric acid methyl ester(PCBM)/bathocuproine(BCP)/AI,emit pure-red color at Commission Internationale de I'eclairage(CIE)coordinates of(0.709,0.290),(0.711,0.289),etc.,which represent the highest color-purity for reported pure-red perovskite LEDs and meet the Rec.2020 requirement at CIE(0.708,0.292)very well.The CsPbBr_(x)I_(3-x)LED shows a low turn-on voltage of 1.6 V,maximum external quantum efficiency of 8.94%,high luminance of 2,859 cd·m^(-2),and good color stability under bias.
基金supported by the National Natural Science Foundation of China under Grant No.61174037
文摘This paper addresses the attitude tracking control problem of a rigid spacecraft in the presence of the modeling uncertainty,external disturbance,and saturated control input by designing two robust att计ude tracking controllers.The basic controller is formulated using an integral sliding mode surface which is continuous and provides an asymptotic convergence rate for the closed-loop system.In this case,only the external disturbance with the prior information is considered.Then,to provide a finite time convergence rate and further improve the robustness of the control system under the unknown system uncertainty containing both the modeling uncertainty and external disturbance,a novel integral terminal sliding mode surface(ITSMS)is designed and associated w计h the continuous adaptive control method.Besides,a command filter is utilized to deal with the immeasurability problem within the proposed ITSMS and an auxiliary system to counteract the input saturation problem.Digital simulations are presented to verify the effectiveness of the proposed controllers.