The performance degradation of micro light-emitting diodes(micro-LEDs)is closely associated with the deterioration of sidewall passivation layers under prolonged electrical bias.We investigate reliability improvements...The performance degradation of micro light-emitting diodes(micro-LEDs)is closely associated with the deterioration of sidewall passivation layers under prolonged electrical bias.We investigate reliability improvements in 20μm×20μm InGaN/GaN blue micro-LEDs by suppressing the formation of an unstable interfacial layer during sidewall passivation.SiO_(2)is deposited on the etched mesa sidewalls using either Sputtering or plasma-enhanced chemical vapor deposition(PECVD).Comparative analysis reveals that PECVD-passivated devices experience more severe performance degradation,primarily due to the increased leakage current.After 100 h of accelerated aging,external quantum efficiency decreases by 44%in PECVD-passivated samples,whereas Sputter-passivated devices exhibit only an11%reduction.This discrepancy is attributed to the formation of a thicker and chemically unstable gallium oxynitride(Ga-O_(X)-N_(1-X))interfacial layer at the SiO_(2)∕GaN-based interface,which facilitates the generation of sidewall defects.Suppressing the formation of this interlayer enhances the crystallinity and structural stability of the passivation layer,thereby mitigating the activation of point defects.Notably,Sputter deposition is more effective in minimizing the formation of Ga-O-N interlayer.These findings emphasize the critical role of achieving low-defect-density sidewall passivation to improve the reliability of micro-LEDs for next-generation high-resolution display applications.展开更多
The roles of different point defects in persistent luminescence of SrAl2O4：Eu,Dy phosphors were investigated. The research results showed that Dyer plays an important role in the persistent luminescence of SrA1EO4：E...The roles of different point defects in persistent luminescence of SrAl2O4：Eu,Dy phosphors were investigated. The research results showed that Dyer plays an important role in the persistent luminescence of SrA1EO4：Eu, Dy phosphors. It can serve as the electron trap of suitable depth for persistent luminescence. V~ does not serve as the electron trap of suitable depth, but its existence can increase the depth of electron traps. There is interaction between the Dy^3＋（ DySr ） and the Eu^2＋（Eu^x Sr ）, and only if the distance between the Dy^3＋（DySr） and the Eu^2＋ （Eu^x Sr） is close enough, the Dyer can work as an effective electron trap. The point defect of V＂ Sr can be hole trap, but the change of its density in crystal matrix does not arouse the obvious change of persistent luminescence.展开更多
The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at sur...The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at surface atomic layers （SAL） relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.展开更多
Despite the long history of research that has focused on the role of defects on device performance, the studies have not always been fruitful. A major reason is because these defect studies have typically been conduct...Despite the long history of research that has focused on the role of defects on device performance, the studies have not always been fruitful. A major reason is because these defect studies have typically been conducted in a parallel mode wherein the semiconductor wafer was divided into multiple pieces for separate optical and structural characterization, as well as device fabrication and evaluation. The major limitation of this approach was that either the defect being investigated by structural characterization techniques was not the same defect that was affecting the device performance or else the defect was not characterized under normal device operating conditions. In this review, we describe a more comprehensive approach to defect study, namely a series mode, using an array of spatially-resolved optical, electrical, and structural characterization techniques, all at the individual defect level but applied sequentially on a fabricated device. This novel sequential approach enables definitive answers to key questions, such as:(ⅰ) how do individual defects affect device performance?(ⅱ) how does the impact depend on the device operation conditions?(ⅲ) how does the impact vary from one defect to another? Implementation of this different approach is illustrated by the study of individual threading dislocation defects in GaAs solar cells. Additionally,we briefly describe a 3-D Raman thermometry method that can also be used for investigating the roles of defects in high power devices and device failure mechanisms.展开更多
Based on density function theory （DFT） and the local density approximation （LDA）, the formation energy and transition levels of native point defects in LaBr3 were calculated under Br-rich conditions. From the calc...Based on density function theory （DFT） and the local density approximation （LDA）, the formation energy and transition levels of native point defects in LaBr3 were calculated under Br-rich conditions. From the calculated results, the following conclusions have been obtained： ① The dominant defect type is the triply positive lanthanum interstitial under p-type conditions. ② The triply negative lanthanum vacancy plays the most important role in n-type LaBr3.③ Neutral and singly positive bromine antisites are more stable in the middle of the band gap. ④ The singly positive （negative） bromine antisite can be a potential com- pensation source in n-type （p-type） LaBr3. ⑤ All the transition levels in LaBr3 belong to deep levels. The optimized geometric structures of bromine interstitials and antisites show that there is no formation of Br-Br covalent bond.展开更多
The formation energies and the equilibrium concentration of vacancies, interstitial H, K, P, O and antisite structural defects with P and K in KH2PO4 （KDP） crystals are investigated by ab initio total-energy calcula...The formation energies and the equilibrium concentration of vacancies, interstitial H, K, P, O and antisite structural defects with P and K in KH2PO4 （KDP） crystals are investigated by ab initio total-energy calculations. The formation energy of interstitial H is calculated to be about 2.06 eV and we suggest that it may be the dominant defect in KDP crystal. The formation energy of an O vacancy （5.25 eV） is much higher than that of interstitial O （0.60 eV）. Optical absorption centres can be induced by defects of O vacancies, interstitial O and interstitial H. We suggest that these defects may be responsible for the lowering of the damage threshold of the KDP. A K vacancy defect may increase the ionic conductivity and therefore the laser-induced damage threshold decreases.展开更多
When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the prope...When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the properties of point defects like vacancies and interstitials is essential for the successful application of semiconductor materials. In the present study, first-principles calculations are carried out to explore the stability of point defects in GaAs/Al_(0.5)Ga_(0.5)As superlattice and their effects on electronic properties. The results show that the interstitial defects and Frenkel pair defects are relatively difficult to form, while the antisite defects are favorably created generally. Besides, the existence of point defects generally modifies the electronic structure of GaAs/Al_(0.5)Ga_(0.5)As superlattice significantly, and most of the defective SL structures possess metallic characteristics. Considering the stability of point defects and carrier mobility of defective states,we propose an effective strategy that AlAs, GaAs, and AlGaantisite defects are introduced to improve the hole or electron mobility of GaAs/Al_(0.5)Ga_(0.5)As superlattice. The obtained results will contribute to the understanding of the radiation damage effects of the GaAs/AlGaAs superlattice, and provide a guidance for designing highly stable and durable semiconductor superlattice-based electronics and optoelectronics for extreme environment applications.展开更多
Ferroelectric materials have enormous potential applications in advanced techniques. However, there are still many problems in its practical application. Dielectric and mechanical (internal friction) measurements are ...Ferroelectric materials have enormous potential applications in advanced techniques. However, there are still many problems in its practical application. Dielectric and mechanical (internal friction) measurements are very sensitive to phase transitions, relaxation process of point defects, domain walls and their mobility, which have severe effect on ferroelectric properties. These make them become very good means to investigate substantial information on structural features and to explore the fundamental principles in ferroelectric materials and their applications. In this paper, the dielectric and internal friction measurement were used to investigate the behaviors for point defects and phase transition in ferroelectric ceramics such as Bi_ 4-x La_ x Ti_ 3 O_ 12 , Bi_ 4 Ti_ 3-y Nb_ y O_ 12 , SrBi_ 2 Ti_ 2 O_ 9 , PbZr_ x Ti_ 1-x O_ 3 ,_ PMN-PT. They were used to clarify the mechanism for some ferroelectric behaviors.展开更多
Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO3 bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptor...Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO3 bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptors. The formation energies show that cation vacancies are energetically favorable in bulk LaAIO3 under O-rich conditions, while the AILa antisites are stable in reducing atmosphere. However, the same behavior does not appear in the case of LaAlO3 films. For LaO-terminated LaAlOa fihns, La or AI vacancies remain energetically favorable under O-rich and O-deficient conditions. For an AlO2-terminated surface, under O-rich condition the La interstitial atom is repelled from the outmost layer after optimization, which releases more stress leading to the decrease of total energy of the system. An AI interstitial atom has a smaller radius so that it can stay in distorted films and becomes more stable under O-deficient conditions, and the Al interstitial atoms can be another possible carrier source contribution to the conductivity of n-type interface under an ultrahigh vacuum. La and Al antisites have similar formation energy regardless of oxygen pressure. The results would be helpful to understand the defect structures of LaAlOa-related materials.展开更多
Point defect engineering endows catalysts with novel physical and chemical properties,elevating their electrocatalytic efficiency.The introduction of defects emerges as a promising strategy,effectively modifying the e...Point defect engineering endows catalysts with novel physical and chemical properties,elevating their electrocatalytic efficiency.The introduction of defects emerges as a promising strategy,effectively modifying the electronic structure of active sites.This optimization influences the adsorption energy of intermediates,thereby mitigating reaction energy barriers,altering paths,enhancing selectivity,and ultimately improving the catalytic efficiency of electrocatalysts.To elucidate the impact of defects on the electrocatalytic process,we comprehensively outline the roles of various point defects,their synthetic methodologies,and characterization techniques.Importantly,we consolidate insights into the relationship between point defects and catalytic activity for hydrogen/oxygen evolution and CO_(2)/O_(2)/N_(2) reduction reactions by integrating mechanisms from diverse reactions.This underscores the pivotal role of point defects in enhancing catalytic performance.At last,the principal challenges and prospects associated with point defects in current electrocatalysts are proposed,emphasizing their role in advancing the efficiency of electrochemical energy storage and conversion materials.展开更多
1.Introduction Nowadays,lithium-ion batteries(LIBs)have been extensively applied in portable electronic devices,electric vehicles,and energy storage.The increasing demands of energy density and cycle life encourage co...1.Introduction Nowadays,lithium-ion batteries(LIBs)have been extensively applied in portable electronic devices,electric vehicles,and energy storage.The increasing demands of energy density and cycle life encourage considerable research on the mechanisms of battery failure and the synthesis of new materials.Cathodes of LIBs,as the key component determining energy density and capacity,have been widely investigated.Considerable research has been conducted to reveal the degradation mechanisms of LIB cathodes,including bulk structure degradation in the form of phase transformations[1-4],point/extended defect formation[5],cracking[6,7],and cavitation[8-10],surface phase transformation into cationdensified phases[11-14],gassing[15],transition metal dissolution[16,17],and over-growth of the cathode-electrolyte interphases(CEIs)[18,19].展开更多
The existence and its movement rule of crystalline structure defect are closely related to the diffusion, solid phase reaction, sintering, phase transformation as well as the physical and chemical properties of materi...The existence and its movement rule of crystalline structure defect are closely related to the diffusion, solid phase reaction, sintering, phase transformation as well as the physical and chemical properties of materials. Point defect theory has been widely applied in material mineralization research, unfavorable transformation controlling, material modification, the research and development of new materials and so on. Point defect theory is one of the important theories for new material research and development. Herein we mainly discuss the application of point defect theory in some structural material researches.展开更多
In this study, we report the effect of Zn doping on the thermoelectric properties of CO1-xZnxSbS0.85Se0.15 solid solutions （x = 0, 0.02, 0.05, 0.08）. The results show the dimensionless figure of merit （zT） increas...In this study, we report the effect of Zn doping on the thermoelectric properties of CO1-xZnxSbS0.85Se0.15 solid solutions （x = 0, 0.02, 0.05, 0.08）. The results show the dimensionless figure of merit （zT） increases from 0.17 to 0.34 at 875 K for Co0.95Zn0.05SbS0.85Se0.15 sample, due to the noticeable decrease in the lattice thermal conductivity by introducing point defect, which is further confirmed by an analysis based on the Debye-Callaway- Klemens model. Meanwhile, the thermoelectric power factor is maintained at high temperatures. This work highlights the important role of point defect in improving the thermoelectric performance of CoSbS-based compounds.展开更多
The structural, elastic, and electronic properties of NiAI alloyed with rare earth element （REE） Ce have been investigated by using density functional theory （DFT）. It is found that Ce has a strong AI site prefere...The structural, elastic, and electronic properties of NiAI alloyed with rare earth element （REE） Ce have been investigated by using density functional theory （DFT）. It is found that Ce has a strong AI site preference and causes lattice distortion of NiAI. The calculation of elastic constants shows that Ce increased both the hardness and the ductility of NiAI, which could be explained by the formation of new ionic bonds between AI （and Ni） and Ce and the enhancement of covalent bonds in NisAl7Ce. Our results are in good agreement with the available experimental data and other theoretical results.展开更多
To date,the benchmark Bi_(2)Te_(3)-based alloys are still the only commercial material system used for ther-moelectric solid-state refrigeration.Nonetheless,the conspicuous performance imbalance between the p-type Bi_...To date,the benchmark Bi_(2)Te_(3)-based alloys are still the only commercial material system used for ther-moelectric solid-state refrigeration.Nonetheless,the conspicuous performance imbalance between the p-type Bi_(2-x)Sb_(x)Te_(3)and n-type Bi_(2)Te_(3-x)Se_(x) legs has become a major obstacle for the improvement of cooling devices to achieve higher efficiency.In our previous study,novel n-type Bi_(2-x)Sb_(x)Te_(3)alloy has been pro-posed via manipulating donor-like effect as an alternative to mainstream n-type Bi_(2)Te_(3-x)Se_(x).However,the narrow bandgap of Bi_(2-x)Sb_(x)Te_(3)provoked severe bipolar effect that constrained the further improvement of zT near room temperature.Herein,we have implemented band gap engineering in n-type Bi_(1.5)Sb_(0.5)Te_(3)by employing isovalent Se substitution to inhibit the undesired intrinsic excitation and achieve the dis-tinguished room-temperature zT.First,the preferential occupancy of Se at Te^(2)site appropriately enlarges the band gap,thereby concurrently improving the Seebeck coefficient and depressing the bipolar thermal conductivity.In addition,the Se alloying mildly suppresses the compensation mechanism and essentially preserves the already optimized carrier concentration,which maintains the peak zT near room tempera-ture.Moreover,the large strain field and mass fluctuation generated by Se alloying leads to the remark-able reduction of lattice thermal conductivity.Accordingly,the zT value of Bi_(1.5)Sb_(0.5)Te_(2.8)Se_(0.2)reaches 1.0 at 300 K and peaks 1.1 at 360 K,which surpasses that of most well-known room-temperature n-type thermoelectric materials.These results pave the way for n-type Bi_(2-x)Sb_(x)Te_(3)alloys to become a new and promising top candidate for large-scale solid-state cooling applications.展开更多
LiYGeO_(4):Eu^(3+)is a red persistent luminescent material with a duration of more than 21 h.Although its persistent luminescence phenomenon has been fully studied,its detailed mechanism is still the subject of debate...LiYGeO_(4):Eu^(3+)is a red persistent luminescent material with a duration of more than 21 h.Although its persistent luminescence phenomenon has been fully studied,its detailed mechanism is still the subject of debates.Herein,we performed first-principles study on the intrinsic point defects and the charge transfer processes in LiYGeO_(4):Eu^(3+)to reveal the mechanism of persistent luminescence.The results show that,under charge transfer excitation,the electron is promoted from the valence band(oxygen ion ligand)to the central Eu^(3+)ion to form Eu^(2+)ion in LiYGeO_(4):Eu^(3+),leaving a hole behind.The charge transfer excitation can relax quickly to the excited state of the Eu^(3+)ion,which produces the characteristic^(5)D_(0)→^(7)F_(J)(J=0-6)emission.The Li vacancies(V_(Li))and the antisite defects of Li replacing Y site(Li_(Y))and Y replacing Li site(YLi)are main defects,while O vacancies(V_(O))are less important in concentration due to high formation energy.VLi and Liy can serve as hole-type traps,with the trap depths suitable for trapping the holes produced by illumination.The delayed release holes can combine with the Eu^(2+)left behind by the illumination,leading to persistent luminescence.The VLi trap is shallower than Li_(Y),and the latter is responsible for the long duration of persistent luminescence.A schematic based on the calculation results is constructed to illustrate the mechanism of persistent luminescence.展开更多
The point defect concentrations of L12-A13X（Sc, Zr, Er） were systematically investigated using the first- principle calculations with thermodynamics approach. The results show that the constitutional point defects o...The point defect concentrations of L12-A13X（Sc, Zr, Er） were systematically investigated using the first- principle calculations with thermodynamics approach. The results show that the constitutional point defects of off- stoichiometric L12-A13X（Sc, Zr, Er） prefer to occur in X sublattice, that is X anti-site in X-rich alloy and X vacancy in Al-rich alloy, respectively. And A1 anti-site also has a high density in Al-rich Llz-A13X（Sc, Er）. It is found that the point defect concentrations of stoichiometric L12-A/3X（Sc, Zr） follow in the sequence as： A1 vacancies （VA0 〉 X vacancies （Vx） 〉 X anti-sites （XA1） 〉 A1 anti- sites （Alx）. The point defect concentration of stoichio- metric A13Er is similar to that of L12-A13X（Sc, Zr）. The result suggests that the A1 vacancy （VA1） is a dominant point defect in L12-A13X（Sc, Zr, Er）. A simple parameter Hvx-HVA1 can be used for a rough estimation of the point defect concentrations in L12-A13X structure. Some rules of point defect concentrations for L12-A13X（Sc, Zr, Er） are also revealed.展开更多
Bismuth-telluride-based alloys are the best thermoelectric materials used in commercial solid-state refrigeration near room temperature.Nevertheless,for n-type polycrystalline alloys,their thermoelectric figure of mer...Bismuth-telluride-based alloys are the best thermoelectric materials used in commercial solid-state refrigeration near room temperature.Nevertheless,for n-type polycrystalline alloys,their thermoelectric figure of merit(zT) values at room temperature are often less than1.0,due to the high electron concentration originating from the donor-like effect induced by the mechanical deformation process.Herein,carrier concentration for better performance near room temperature was optimized through manipulating intrinsic point defects by sulfur alloying.Sulfur alloying significantly decreases antisite defects concentration and suppresses donor-like effect,resulting in optimized carrier concentration and reduced electronic thermal conductivity.The hot deformation process was also applied to improve carrier mobility due to the enhanced texture.As a result,a high zT value of 1 at 300 K and peak zT value of 1.1 at 350 K were obtained for the twice hot-deformed Bi_(2) Te_(2.7)Se_(0.21)S_(0.09) sample,which verifies sulfur alloying is an effective method to improve thermoelectric performance of n-type polycrystalline Bi2 Te3-based alloys near room temperature.展开更多
Doping- and alloying-induced point defects lead to mass and strain field fluctuations which can be used as effective strategies to decrease the lattice thermal conductivity and consequently boost the performance of th...Doping- and alloying-induced point defects lead to mass and strain field fluctuations which can be used as effective strategies to decrease the lattice thermal conductivity and consequently boost the performance of thermoelectric materials. Herein, we report the effects of Sm and S co-doping on thermoelectric transport properties of copper antimony selenides in the temperature range of 300 K 〈 T〈 650 K. Through the Callaway model, it demonstrates that Sm and S co-doping induces strong mass differences and strain field fluctuations in Cu3SbSe4. The results prove that doping with suitable elements can increase point defect scattering of heat-carrying phonons, leading to a lower thermal conductivity and a better ther- moelectric performance. The highest figure of merit （ZT） of - 0.55 at 648 K is obtained for the Sm and S co-doped sample with nominal composition of Cu2.995Sm0.005Sb- Se3.95S0.05, which is about 55% increase compared to the ZT of pristine Cu3SbSe4.展开更多
With improvements on high-pressure experimental techniques in multi-anvil apparatus and the development of new analytical tools, major progress has been made on diffusion in garnets in the past several decades. The da...With improvements on high-pressure experimental techniques in multi-anvil apparatus and the development of new analytical tools, major progress has been made on diffusion in garnets in the past several decades. The data obtained in the experimental determination of diffusion coefficients in garnets are of fundamental importance for diffusion modeling and timescales of geological and planetary processes. In this review, we have compiled experimental data on self-diffusion(Si, O, cations), trace element diffusion(Li, Y, Ga, Cr, Sr, REEs), and interdiffusion(Ca–Fe/Mg, Si–Al) in garnet in the light of new advances and recent applications. In addition, some empirical relationships among diffusion parameters(pre-exponential factor D_0,activation energy E, ionic radius) are also discussed. We hope that this review can provide a useful data digest and guide to future study of diffusion in garnet.展开更多
基金supported by the Samsung Research Funding&Incubation Center of Samsung Electronics under Project No.SRFC-MA2402-05supported by the KENTECH Center for Shared Research Facilities。
文摘The performance degradation of micro light-emitting diodes(micro-LEDs)is closely associated with the deterioration of sidewall passivation layers under prolonged electrical bias.We investigate reliability improvements in 20μm×20μm InGaN/GaN blue micro-LEDs by suppressing the formation of an unstable interfacial layer during sidewall passivation.SiO_(2)is deposited on the etched mesa sidewalls using either Sputtering or plasma-enhanced chemical vapor deposition(PECVD).Comparative analysis reveals that PECVD-passivated devices experience more severe performance degradation,primarily due to the increased leakage current.After 100 h of accelerated aging,external quantum efficiency decreases by 44%in PECVD-passivated samples,whereas Sputter-passivated devices exhibit only an11%reduction.This discrepancy is attributed to the formation of a thicker and chemically unstable gallium oxynitride(Ga-O_(X)-N_(1-X))interfacial layer at the SiO_(2)∕GaN-based interface,which facilitates the generation of sidewall defects.Suppressing the formation of this interlayer enhances the crystallinity and structural stability of the passivation layer,thereby mitigating the activation of point defects.Notably,Sputter deposition is more effective in minimizing the formation of Ga-O-N interlayer.These findings emphasize the critical role of achieving low-defect-density sidewall passivation to improve the reliability of micro-LEDs for next-generation high-resolution display applications.
基金This study is financially supported by the Jiangxi University of Finance and Economy (Project No. 0421205) Jiangxi Provincial Department of Education (Project No. (2007) 260)
文摘The roles of different point defects in persistent luminescence of SrAl2O4：Eu,Dy phosphors were investigated. The research results showed that Dyer plays an important role in the persistent luminescence of SrA1EO4：Eu, Dy phosphors. It can serve as the electron trap of suitable depth for persistent luminescence. V~ does not serve as the electron trap of suitable depth, but its existence can increase the depth of electron traps. There is interaction between the Dy^3＋（ DySr ） and the Eu^2＋（Eu^x Sr ）, and only if the distance between the Dy^3＋（DySr） and the Eu^2＋ （Eu^x Sr） is close enough, the Dyer can work as an effective electron trap. The point defect of V＂ Sr can be hole trap, but the change of its density in crystal matrix does not arouse the obvious change of persistent luminescence.
基金supported by National Basic Research Program of China (No.2007CB209803)the National Natural Science Foundation of China (No.51231002)the Applied Basic Research Program from Hebei Province
文摘The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at surface atomic layers （SAL） relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.
基金supported by ARO/Electronics (Grant No. W911NF-16-1-0263)the support of Bissell Distinguished Professorship at UNC-Charlotte。
文摘Despite the long history of research that has focused on the role of defects on device performance, the studies have not always been fruitful. A major reason is because these defect studies have typically been conducted in a parallel mode wherein the semiconductor wafer was divided into multiple pieces for separate optical and structural characterization, as well as device fabrication and evaluation. The major limitation of this approach was that either the defect being investigated by structural characterization techniques was not the same defect that was affecting the device performance or else the defect was not characterized under normal device operating conditions. In this review, we describe a more comprehensive approach to defect study, namely a series mode, using an array of spatially-resolved optical, electrical, and structural characterization techniques, all at the individual defect level but applied sequentially on a fabricated device. This novel sequential approach enables definitive answers to key questions, such as:(ⅰ) how do individual defects affect device performance?(ⅱ) how does the impact depend on the device operation conditions?(ⅲ) how does the impact vary from one defect to another? Implementation of this different approach is illustrated by the study of individual threading dislocation defects in GaAs solar cells. Additionally,we briefly describe a 3-D Raman thermometry method that can also be used for investigating the roles of defects in high power devices and device failure mechanisms.
基金Supported by the National Nature Science Foundation of China(11275142)
文摘Based on density function theory （DFT） and the local density approximation （LDA）, the formation energy and transition levels of native point defects in LaBr3 were calculated under Br-rich conditions. From the calculated results, the following conclusions have been obtained： ① The dominant defect type is the triply positive lanthanum interstitial under p-type conditions. ② The triply negative lanthanum vacancy plays the most important role in n-type LaBr3.③ Neutral and singly positive bromine antisites are more stable in the middle of the band gap. ④ The singly positive （negative） bromine antisite can be a potential com- pensation source in n-type （p-type） LaBr3. ⑤ All the transition levels in LaBr3 belong to deep levels. The optimized geometric structures of bromine interstitials and antisites show that there is no formation of Br-Br covalent bond.
基金Project supported by the Program for New Century Excellent Talents at the University of China (Grant No.NCET-08-0722)
文摘The formation energies and the equilibrium concentration of vacancies, interstitial H, K, P, O and antisite structural defects with P and K in KH2PO4 （KDP） crystals are investigated by ab initio total-energy calculations. The formation energy of interstitial H is calculated to be about 2.06 eV and we suggest that it may be the dominant defect in KDP crystal. The formation energy of an O vacancy （5.25 eV） is much higher than that of interstitial O （0.60 eV）. Optical absorption centres can be induced by defects of O vacancies, interstitial O and interstitial H. We suggest that these defects may be responsible for the lowering of the damage threshold of the KDP. A K vacancy defect may increase the ionic conductivity and therefore the laser-induced damage threshold decreases.
基金Project supported by the NSAF Joint Foundation of China (Grant No. U1930120)the Key Natural Science Foundation of Gansu Province, China (Grant No. 20JR5RA211)the National Natural Science Foundation of China (Grant No. 11774044)。
文摘When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the properties of point defects like vacancies and interstitials is essential for the successful application of semiconductor materials. In the present study, first-principles calculations are carried out to explore the stability of point defects in GaAs/Al_(0.5)Ga_(0.5)As superlattice and their effects on electronic properties. The results show that the interstitial defects and Frenkel pair defects are relatively difficult to form, while the antisite defects are favorably created generally. Besides, the existence of point defects generally modifies the electronic structure of GaAs/Al_(0.5)Ga_(0.5)As superlattice significantly, and most of the defective SL structures possess metallic characteristics. Considering the stability of point defects and carrier mobility of defective states,we propose an effective strategy that AlAs, GaAs, and AlGaantisite defects are introduced to improve the hole or electron mobility of GaAs/Al_(0.5)Ga_(0.5)As superlattice. The obtained results will contribute to the understanding of the radiation damage effects of the GaAs/AlGaAs superlattice, and provide a guidance for designing highly stable and durable semiconductor superlattice-based electronics and optoelectronics for extreme environment applications.
文摘Ferroelectric materials have enormous potential applications in advanced techniques. However, there are still many problems in its practical application. Dielectric and mechanical (internal friction) measurements are very sensitive to phase transitions, relaxation process of point defects, domain walls and their mobility, which have severe effect on ferroelectric properties. These make them become very good means to investigate substantial information on structural features and to explore the fundamental principles in ferroelectric materials and their applications. In this paper, the dielectric and internal friction measurement were used to investigate the behaviors for point defects and phase transition in ferroelectric ceramics such as Bi_ 4-x La_ x Ti_ 3 O_ 12 , Bi_ 4 Ti_ 3-y Nb_ y O_ 12 , SrBi_ 2 Ti_ 2 O_ 9 , PbZr_ x Ti_ 1-x O_ 3 ,_ PMN-PT. They were used to clarify the mechanism for some ferroelectric behaviors.
基金Supported by the Hebei Provincial Young Top-Notch Talent Support Program under Grant No BJRC2016the Innovative Funding Project of Graduates of Hebei University under Grant No hbu2018ss62the Midwest Universities Comprehensive Strength Promotion Project
文摘Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO3 bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptors. The formation energies show that cation vacancies are energetically favorable in bulk LaAIO3 under O-rich conditions, while the AILa antisites are stable in reducing atmosphere. However, the same behavior does not appear in the case of LaAlO3 films. For LaO-terminated LaAlOa fihns, La or AI vacancies remain energetically favorable under O-rich and O-deficient conditions. For an AlO2-terminated surface, under O-rich condition the La interstitial atom is repelled from the outmost layer after optimization, which releases more stress leading to the decrease of total energy of the system. An AI interstitial atom has a smaller radius so that it can stay in distorted films and becomes more stable under O-deficient conditions, and the Al interstitial atoms can be another possible carrier source contribution to the conductivity of n-type interface under an ultrahigh vacuum. La and Al antisites have similar formation energy regardless of oxygen pressure. The results would be helpful to understand the defect structures of LaAlOa-related materials.
基金supported by the National Natural Science Foundation of China(U21A20281)the Special Fund for Young Teachers from Zhengzhou University(JC23557030,JC23257011)+1 种基金the Key Research Projects of Higher Education Institutions of Henan Province(24A530009)the Project of Zhongyuan Critical Metals Laboratory(GJJSGFYQ202336).
文摘Point defect engineering endows catalysts with novel physical and chemical properties,elevating their electrocatalytic efficiency.The introduction of defects emerges as a promising strategy,effectively modifying the electronic structure of active sites.This optimization influences the adsorption energy of intermediates,thereby mitigating reaction energy barriers,altering paths,enhancing selectivity,and ultimately improving the catalytic efficiency of electrocatalysts.To elucidate the impact of defects on the electrocatalytic process,we comprehensively outline the roles of various point defects,their synthetic methodologies,and characterization techniques.Importantly,we consolidate insights into the relationship between point defects and catalytic activity for hydrogen/oxygen evolution and CO_(2)/O_(2)/N_(2) reduction reactions by integrating mechanisms from diverse reactions.This underscores the pivotal role of point defects in enhancing catalytic performance.At last,the principal challenges and prospects associated with point defects in current electrocatalysts are proposed,emphasizing their role in advancing the efficiency of electrochemical energy storage and conversion materials.
基金supported by the National Natural Science Foundat ion of China(52388201 and 51525102)。
文摘1.Introduction Nowadays,lithium-ion batteries(LIBs)have been extensively applied in portable electronic devices,electric vehicles,and energy storage.The increasing demands of energy density and cycle life encourage considerable research on the mechanisms of battery failure and the synthesis of new materials.Cathodes of LIBs,as the key component determining energy density and capacity,have been widely investigated.Considerable research has been conducted to reveal the degradation mechanisms of LIB cathodes,including bulk structure degradation in the form of phase transformations[1-4],point/extended defect formation[5],cracking[6,7],and cavitation[8-10],surface phase transformation into cationdensified phases[11-14],gassing[15],transition metal dissolution[16,17],and over-growth of the cathode-electrolyte interphases(CEIs)[18,19].
基金This work was supported by the "863" program (No. 2003AA322020)
文摘The existence and its movement rule of crystalline structure defect are closely related to the diffusion, solid phase reaction, sintering, phase transformation as well as the physical and chemical properties of materials. Point defect theory has been widely applied in material mineralization research, unfavorable transformation controlling, material modification, the research and development of new materials and so on. Point defect theory is one of the important theories for new material research and development. Herein we mainly discuss the application of point defect theory in some structural material researches.
基金financially supported by the National Natural Science Foundation of China (Nos. 11344010. 11404044 and 51472036)the Fundamental Research Funds for the Central Universities (No. 106112016CDJZR308808)
文摘In this study, we report the effect of Zn doping on the thermoelectric properties of CO1-xZnxSbS0.85Se0.15 solid solutions （x = 0, 0.02, 0.05, 0.08）. The results show the dimensionless figure of merit （zT） increases from 0.17 to 0.34 at 875 K for Co0.95Zn0.05SbS0.85Se0.15 sample, due to the noticeable decrease in the lattice thermal conductivity by introducing point defect, which is further confirmed by an analysis based on the Debye-Callaway- Klemens model. Meanwhile, the thermoelectric power factor is maintained at high temperatures. This work highlights the important role of point defect in improving the thermoelectric performance of CoSbS-based compounds.
基金supported by the National Natural Science Foundation of China under grant No.50871035
文摘The structural, elastic, and electronic properties of NiAI alloyed with rare earth element （REE） Ce have been investigated by using density functional theory （DFT）. It is found that Ce has a strong AI site preference and causes lattice distortion of NiAI. The calculation of elastic constants shows that Ce increased both the hardness and the ductility of NiAI, which could be explained by the formation of new ionic bonds between AI （and Ni） and Ce and the enhancement of covalent bonds in NisAl7Ce. Our results are in good agreement with the available experimental data and other theoretical results.
基金The work is supported by the National Natural Science Foundation of China(No.52071218)Shenzhen Science and Technology Innovation Commission(Nos.20200731215211001,20200814110413001)Guangdong Basic and Applied Basic Research Foundation(No.2022A1515012492).The authors also appreciate the Instrumental Analysis Center of Shenzhen University.
文摘To date,the benchmark Bi_(2)Te_(3)-based alloys are still the only commercial material system used for ther-moelectric solid-state refrigeration.Nonetheless,the conspicuous performance imbalance between the p-type Bi_(2-x)Sb_(x)Te_(3)and n-type Bi_(2)Te_(3-x)Se_(x) legs has become a major obstacle for the improvement of cooling devices to achieve higher efficiency.In our previous study,novel n-type Bi_(2-x)Sb_(x)Te_(3)alloy has been pro-posed via manipulating donor-like effect as an alternative to mainstream n-type Bi_(2)Te_(3-x)Se_(x).However,the narrow bandgap of Bi_(2-x)Sb_(x)Te_(3)provoked severe bipolar effect that constrained the further improvement of zT near room temperature.Herein,we have implemented band gap engineering in n-type Bi_(1.5)Sb_(0.5)Te_(3)by employing isovalent Se substitution to inhibit the undesired intrinsic excitation and achieve the dis-tinguished room-temperature zT.First,the preferential occupancy of Se at Te^(2)site appropriately enlarges the band gap,thereby concurrently improving the Seebeck coefficient and depressing the bipolar thermal conductivity.In addition,the Se alloying mildly suppresses the compensation mechanism and essentially preserves the already optimized carrier concentration,which maintains the peak zT near room tempera-ture.Moreover,the large strain field and mass fluctuation generated by Se alloying leads to the remark-able reduction of lattice thermal conductivity.Accordingly,the zT value of Bi_(1.5)Sb_(0.5)Te_(2.8)Se_(0.2)reaches 1.0 at 300 K and peaks 1.1 at 360 K,which surpasses that of most well-known room-temperature n-type thermoelectric materials.These results pave the way for n-type Bi_(2-x)Sb_(x)Te_(3)alloys to become a new and promising top candidate for large-scale solid-state cooling applications.
基金the Natural Science Foundation of Xinjiang Uygur Autonomous Region(2022DO1A98)the National Natural Science Foundation of China(11974338,11974022,21805082)China-Poland Intergovernmental Science and Technology Cooperation Program(202015/10)。
文摘LiYGeO_(4):Eu^(3+)is a red persistent luminescent material with a duration of more than 21 h.Although its persistent luminescence phenomenon has been fully studied,its detailed mechanism is still the subject of debates.Herein,we performed first-principles study on the intrinsic point defects and the charge transfer processes in LiYGeO_(4):Eu^(3+)to reveal the mechanism of persistent luminescence.The results show that,under charge transfer excitation,the electron is promoted from the valence band(oxygen ion ligand)to the central Eu^(3+)ion to form Eu^(2+)ion in LiYGeO_(4):Eu^(3+),leaving a hole behind.The charge transfer excitation can relax quickly to the excited state of the Eu^(3+)ion,which produces the characteristic^(5)D_(0)→^(7)F_(J)(J=0-6)emission.The Li vacancies(V_(Li))and the antisite defects of Li replacing Y site(Li_(Y))and Y replacing Li site(YLi)are main defects,while O vacancies(V_(O))are less important in concentration due to high formation energy.VLi and Liy can serve as hole-type traps,with the trap depths suitable for trapping the holes produced by illumination.The delayed release holes can combine with the Eu^(2+)left behind by the illumination,leading to persistent luminescence.The VLi trap is shallower than Li_(Y),and the latter is responsible for the long duration of persistent luminescence.A schematic based on the calculation results is constructed to illustrate the mechanism of persistent luminescence.
基金financially supported by the National Natural Science Foundation of China(Nos.51401093 and 51341010)the Natural Science Foundation of Jiangsu Province (No.BK20130233)
文摘The point defect concentrations of L12-A13X（Sc, Zr, Er） were systematically investigated using the first- principle calculations with thermodynamics approach. The results show that the constitutional point defects of off- stoichiometric L12-A13X（Sc, Zr, Er） prefer to occur in X sublattice, that is X anti-site in X-rich alloy and X vacancy in Al-rich alloy, respectively. And A1 anti-site also has a high density in Al-rich Llz-A13X（Sc, Er）. It is found that the point defect concentrations of stoichiometric L12-A/3X（Sc, Zr） follow in the sequence as： A1 vacancies （VA0 〉 X vacancies （Vx） 〉 X anti-sites （XA1） 〉 A1 anti- sites （Alx）. The point defect concentration of stoichio- metric A13Er is similar to that of L12-A13X（Sc, Zr）. The result suggests that the A1 vacancy （VA1） is a dominant point defect in L12-A13X（Sc, Zr, Er）. A simple parameter Hvx-HVA1 can be used for a rough estimation of the point defect concentrations in L12-A13X structure. Some rules of point defect concentrations for L12-A13X（Sc, Zr, Er） are also revealed.
基金financially supported by the National Key Research and Development Program of China(No.2019YFA0704902)the National Natural Science Foundation of China(Nos.51871199 and 61534001)。
文摘Bismuth-telluride-based alloys are the best thermoelectric materials used in commercial solid-state refrigeration near room temperature.Nevertheless,for n-type polycrystalline alloys,their thermoelectric figure of merit(zT) values at room temperature are often less than1.0,due to the high electron concentration originating from the donor-like effect induced by the mechanical deformation process.Herein,carrier concentration for better performance near room temperature was optimized through manipulating intrinsic point defects by sulfur alloying.Sulfur alloying significantly decreases antisite defects concentration and suppresses donor-like effect,resulting in optimized carrier concentration and reduced electronic thermal conductivity.The hot deformation process was also applied to improve carrier mobility due to the enhanced texture.As a result,a high zT value of 1 at 300 K and peak zT value of 1.1 at 350 K were obtained for the twice hot-deformed Bi_(2) Te_(2.7)Se_(0.21)S_(0.09) sample,which verifies sulfur alloying is an effective method to improve thermoelectric performance of n-type polycrystalline Bi2 Te3-based alloys near room temperature.
基金financially supported by the German Research Foundation within the DFG Priority Program SPP 1386 (No.WE 2803/2-2)Federal Ministry for Economics Affairs and Energy (BMWI)(No. Nr 19U15006F)
文摘Doping- and alloying-induced point defects lead to mass and strain field fluctuations which can be used as effective strategies to decrease the lattice thermal conductivity and consequently boost the performance of thermoelectric materials. Herein, we report the effects of Sm and S co-doping on thermoelectric transport properties of copper antimony selenides in the temperature range of 300 K 〈 T〈 650 K. Through the Callaway model, it demonstrates that Sm and S co-doping induces strong mass differences and strain field fluctuations in Cu3SbSe4. The results prove that doping with suitable elements can increase point defect scattering of heat-carrying phonons, leading to a lower thermal conductivity and a better ther- moelectric performance. The highest figure of merit （ZT） of - 0.55 at 648 K is obtained for the Sm and S co-doped sample with nominal composition of Cu2.995Sm0.005Sb- Se3.95S0.05, which is about 55% increase compared to the ZT of pristine Cu3SbSe4.
基金supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB 18010401)the 1000Plan Program for Young Talents and Hundred Talent Program of CASNSF of China (41303048)
文摘With improvements on high-pressure experimental techniques in multi-anvil apparatus and the development of new analytical tools, major progress has been made on diffusion in garnets in the past several decades. The data obtained in the experimental determination of diffusion coefficients in garnets are of fundamental importance for diffusion modeling and timescales of geological and planetary processes. In this review, we have compiled experimental data on self-diffusion(Si, O, cations), trace element diffusion(Li, Y, Ga, Cr, Sr, REEs), and interdiffusion(Ca–Fe/Mg, Si–Al) in garnet in the light of new advances and recent applications. In addition, some empirical relationships among diffusion parameters(pre-exponential factor D_0,activation energy E, ionic radius) are also discussed. We hope that this review can provide a useful data digest and guide to future study of diffusion in garnet.
