Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs wit...Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications.Here,we demonstrate the epitaxial growth of 1T'-MoTe_(2) on Au(111)and graphitized silicon carbide(Gr/SiC)by molecular beam epitaxy(MBE).We investigate the morphology of the grown1T'-MoTe_(2) at the atomic level by scanning tunnelling microscopy(STM)and reveal the corresponding microscopic growth mechanism.It is found that the unique ordered Te structures preferentially deposited on Au(111)regulate the growth of monolayer single crystal 1T'-MoTe_(2),while the Mo clusters were preferentially deposited on the Gr/SiC substrate,which impedes the ordered growth of monolayer MoTe_(2).We confirm that the size of single crystal 1T'-MoTe_(2) grown on Au(111)is nearly two orders of magnitude larger than that on Gr/SiC.By scanning tunnelling spectroscopy(STS),we observe that the STS spectrum of the monolayer 1T'-MoTe_(2) nano-island at the edge is different from that at the interior,which exhibits enhanced conductivity.展开更多
This paper describes the design of a ventilation system to be paired with a carbon capture system. The ventilation system utilizes the geometry of the George C. Wallace tunnel, located in the City of Mobile, Alabama, ...This paper describes the design of a ventilation system to be paired with a carbon capture system. The ventilation system utilizes the geometry of the George C. Wallace tunnel, located in the City of Mobile, Alabama, USA to capture and redirect emissions to a direct air capture (DAC) device to sequester 25% of the total CO2 mass generated from inside the tunnel. The total CO2 mass rate for the westbound traffic between the week-day hours of 7 a.m. and 6 p.m. has been estimated between 2,300 to 3,000 lbs./hr. By sequestering these emissions, the overall surrounding air quality was shown to be improved to a level that mirrors that from the pre-US industrial era of 270 ppm.展开更多
Due to the pristine interface of the 2D/3D face-tunneling heterostructure with an ultra-sharp doping profile, the 2D/3D tunneling field-effect transistor(TFET) is considered as one of the most promising low-power devi...Due to the pristine interface of the 2D/3D face-tunneling heterostructure with an ultra-sharp doping profile, the 2D/3D tunneling field-effect transistor(TFET) is considered as one of the most promising low-power devices that can simultaneously obtain low off-state current(IOFF), high on-state current(ION) and steep subthreshold swing(SS). As a key element for the 2D/3D TFET, the intensive exploration of the tunnel diode based on the 2D/3D heterostructure is in urgent need.The transfer technique composed of the exfoliation and the release process is currently the most common approach to fabricating the 2D/3D heterostructures. However, the well-established transfer technique of the 2D materials is still unavailable.Only a small part of the irregular films can usually be obtained by mechanical exfoliation, while the choice of the chemical exfoliation may lead to the contamination of the 2D material films by the ions in the chemical etchants. Moreover, the deformation of the 2D material in the transfer process due to its soft nature also leads to the nonuniformity of the transferred film,which is one of the main reasons for the presence of the wrinkles and the stacks in the transferred film. Thus, the large-scale fabrication of the high-quality 2D/3D tunnel diodes is limited. In this article, a comprehensive transfer technique that can mend up the shortages mentioned above with the aid of the water and the thermal release tape(TRT) is proposed. Based on the method we proposed, the MoS_(2)/Si tunnel diode is experimentally demonstrated and the transferred monolayer MoS_(2) film with the relatively high crystal quality is confirmed by atomic force microscopy(AFM), scanning electron microscopy(SEM), and Raman characterizations. Besides, the prominent negative differential resistance(NDR) effect is observed at room temperature, which verifies the relatively high quality of the MoS_(2)/Si heterojunction. The bilayer MoS_(2)/Si tunnel diode is also experimentally fabricated by repeating the transfer process we proposed, followed by the specific analysis of the electrical characteristics. This study shows the advantages of the transfer technique we proposed and indicates the great application foreground of the fabricated 2D/3D heterostructure for ultralow-power tunneling devices.展开更多
BACKGROUND Carpal tunnel syndrome(CTS)has been associated with gout and type 2 diabetes mellitus(T2DM).However,due to insufficient clinical understanding of goutrelated CTS and reliance on the diagnostic importance of...BACKGROUND Carpal tunnel syndrome(CTS)has been associated with gout and type 2 diabetes mellitus(T2DM).However,due to insufficient clinical understanding of goutrelated CTS and reliance on the diagnostic importance of elevated serum uric acid levels,such cases are prone to missed diagnosis,misdiagnosis,and delayed treatment.In addition,the effect of T2DM on gout-induced carpal tunnel syndrome has not been reported.CASE SUMMARY Herein,we present an unusual case of CTS and motor dysfunction caused by miliary tophaceous gout and T2DM.The patient presented to the hand and foot clinic with paresthesia of the fingers of both hands,especially at night.The patient was diagnosed with type 2 diabetes a month ago.Ultrasonography revealed bilateral transverse carpal ligament thickening with median nerve compression during hospitalization.The patient was successfully treated with carpal tunnel decompression and tendon release.The postoperative pathological examination revealed typical gout nodules.This case suggests that the presence of T2DM could accelerate tophi formation and worsen CTS symptoms,although no definitive proof in this regard has been described previously.CONCLUSION Tophi formation may most likely cause the co-occurrence of CTS and flexor dysfunction in gout and incipient diabetes patients.展开更多
Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly ...Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi2Sr2CaCu2O8＋δ （Bi2212） and YBa2Cu3O7-x （YBCO） along their c-axes on a scale shorter than the interlayer spacing. By tunneling into the （100） plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended fiat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a （110） surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.展开更多
The activation and dissociation of hydrogen molecules(H_(2))on the Cu(001)surface are studied theoretically.Using first-principles calculations,the activation barrier for the dissociation of H_(2) on Cu(001)is determi...The activation and dissociation of hydrogen molecules(H_(2))on the Cu(001)surface are studied theoretically.Using first-principles calculations,the activation barrier for the dissociation of H_(2) on Cu(001)is determined to be~0.59 eV in height.It is found that the electron transfer from the copper substrate to H_(2) plays a key role in the activation and breaking of the H–H bond,and the formation of the Cu–H bonds.Two stationary states are identified at around the critical height of bond breaking,corresponding to the molecular and the dissociative states,respectively.Using the transfer matrix method,we also investigate the role of quantum tunneling in the dissociation process along the minimum energy pathway(MEP),which is found to be significant at or below room temperature.At a given temperature,the tunneling contributions due to the translational and the vibrational motions of H_(2) are quantified for the dissociation process.Within a wide range of temperature,the effects of quantum tunneling on the effective barriers of dissociation and the rate constants are observed.The deduced energetic parameters associated with the thermal equilibrium and non-equilibrium(molecular beam)conditions are comparable to experimental data.In the low-temperature region,the crossover from classical to quantum regime is identified.展开更多
In this work,W/β-Ga_(2)O_(3)Schottky barrier diodes,prepared using a confined magnetic field-based sputtering method,were analyzed at different operation temperatures.Firstly,Schottky barrier height increased with in...In this work,W/β-Ga_(2)O_(3)Schottky barrier diodes,prepared using a confined magnetic field-based sputtering method,were analyzed at different operation temperatures.Firstly,Schottky barrier height increased with increasing temperature from 100 to 300 K and reached 1.03 eV at room temperature.The ideality factor decreased with increasing temperature and it was higher than 2 at 100 K.This apparent high value was related to the tunneling effect.Secondly,the series and on-resistances decreased with increasing operation temperature.Finally,the interfacial dislocation was extracted from the tunneling current.A high dislocation density was found,which indicates the domination of tunneling through dislocation in the transport mecha-nism.These findings are evidently helpful in designing better performance devices.展开更多
The interplay between topology and magnetism is vital for realizing exotic quantum phenomena,significant examples including quantum anomalous Hall effect,axion insulators,and high-order topological states.These states...The interplay between topology and magnetism is vital for realizing exotic quantum phenomena,significant examples including quantum anomalous Hall effect,axion insulators,and high-order topological states.These states host great potential for future applications in high-speed and low-consumption electronic devices.Despite being extensively investigated,practical platforms are still scarce.In this work,with molecular beam epitaxy(MBE),we provide the first experimental report on high-quality Bi(110)/CrTe_(2) magnetic heterostructure.By employing in-situ high-resolution scanning tunneling microscopy,we are able to examine the interaction between magnetism and topology.There is a potential edge state at an energy level above the Fermi level,but no edge states observed near the Fermi level The absence of high-order topological corner states near EF highlights the importance of lattice matching and interface engineering in designing high-order topological states.Our study provides key insights into the interplay between two-dimensional magnetic and topological materials and offers an important dimension for engineering magnetic topological states.展开更多
We investigate the transport properties of electron in a 1T'-MoS_(2)-based p–n junction.The anisotropic refraction of electron is found when the electron beam crosses the p–n junction,which brings the phenomenon...We investigate the transport properties of electron in a 1T'-MoS_(2)-based p–n junction.The anisotropic refraction of electron is found when the electron beam crosses the p–n junction,which brings the phenomenon of valley splitting without any external fields.Moreover,it is found that the valley-spin-dependent anomalous Klein tunneling,i.e.,the perfect transmission exists at a nonzero incident angle of valley-spin-dependent electron,happens when the vertical electric field is equal to the critical electric field.These two peculiar properties arise from the same reason that the tilted band structure makes the directions of wavevector and velocity different.Our work designs a special valley splitter without any external fields and finds a new type of Klein tunneling.展开更多
The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are f...The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl 2 O 4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5.10 eV for MgAl 2 O 4 and 4.81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point ( band), the coherent tunneling effect might be expected to appear in MgAl 2 O 4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2.9 J m 2 ) and MgAl 2 O 4 (2.27 J m 2 ) on the {100} orientation, and the smaller lattice mismatch between MgAl 2 O 4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl 2 O 4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.展开更多
Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surroundi...Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study.The support capacity of 2^(nd) Generation-Negative Poisson’s Ratio(2G-NPR)bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel.The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault,as a result,the rock mass on the upper part of the fault slips as a whole.Furthermore,small-scale deformation and loss of blocks are observed around the tunnel;however,the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability.Due to the blocking effect of fault,the stress of the surrounding rock on the upper and lower parts of the fault is significantly different,and the stress at the left shoulder of the tunnel is greater than that at the right shoulder.The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock.The present numerical scheme is in good agreement with the model test results,and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel.In comparison to unsupported and ordinary PR(Poisson’s Ratio)bolt support,2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel.The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.展开更多
Interface emission from heterojunction is a shortcoming for electroluminescent devices.A buffer layer introduced in the heterojunctional interfaces is a potential solution for the challenge.However,the dynamics for ca...Interface emission from heterojunction is a shortcoming for electroluminescent devices.A buffer layer introduced in the heterojunctional interfaces is a potential solution for the challenge.However,the dynamics for carrier tunneling to control the interface emission is still a mystery.Herein,the low-refractive HfO_(2)with a proper energy band configuration is em-ployed as the buffer layer in achieving ZnO-microwire/HfO_(2)/GaN heterojunctional light-emitting diodes(LEDs).The optic-ally pumped lasing threshold and lifetime of the ZnO microwire are reduced with the introduced HfO_(2)layer.As a result,the interface emission is of blue-shift from visible wavelengths to 394 nm whereas the ultraviolet(UV)emission is en-hanced.To regulate the interface recombination between electrons in the conduction band of ZnO and holes in the valence band of GaN,the tunneling electrons with higher conduction band are employed to produce a higher tunneling current through regulation of thin HfO_(2)film causing blue shift and interface emission enhancement.Our results provide a method to control the tunneling electrons in heterojunction for high-performance LEDs.展开更多
In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube spec...In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube specimens coated and uncoated with SiO_(2) aerogel-cement mortar(SiO_(2)-ACM)were heated to simulate tunnel fire for 0.5,1,1.5,2,2.5,3 and 4 h,respectively.The residual compressive strength was tested after the specimens were cooled to room temperature by natural cooling and water cooling.The results show that,the damages of specimens become more serious as fire time goes on,but the residual strength of specimens coated with SiO_(2)-ACM is always higher than that of uncoated with SiO_(2)-ACM.In addition,the residual strength of specimens cooled by water cooling is lower than that of natural cooling.However,for the specimens coated with SiO_(2)-ACM,the adverse effects of water cooling are lessened.With the increase of fire time,the protective effect of SiO_(2)-ACM is still gradually improved.Finally,a formula was established to predict the residual 150 mm cube compressive strength of specimens protected by SiO_(2)-ACM after a simulated tunnel fire.展开更多
A new two-dimensional atomic crystal, monolayer cuprous telluride（Cu2Te） has been fabricated on a grapheneSi C（0001） substrate by molecular beam epitaxy（MBE）. The low-energy electron diffraction（LEED） characte...A new two-dimensional atomic crystal, monolayer cuprous telluride（Cu2Te） has been fabricated on a grapheneSi C（0001） substrate by molecular beam epitaxy（MBE）. The low-energy electron diffraction（LEED） characterization shows that the monolayer Cu2Te forms ■ superstructure with respect to the graphene substrate. The atomic structure of the monolayer Cu2Te is investigated through a combination of scanning tunneling microscopy（STM） experiments and density functional theory（DFT） calculations. The stoichiometry of the Cu2Te sample is verified by x-ray photoelectron spectroscopy（XPS） measurement. The angle-resolved photoemission spectroscopy（ARPES） data present the electronic band structure of the sample, which is in good agreement with the calculated results. Furthermore, air-exposure experiments reveal the chemical stability of the monolayer Cu2Te. The fabrication of this new 2D material with a particular structure may bring new physical properties for future applications.展开更多
基金Project supported by the National Key R&D Program of China (Grant No.2022YFA1204302)the National Natural Science Foundation of China (Grant Nos.52022029,52221001,92263107,U23A20570,62090035,U19A2090,and 12174098)+1 种基金the Hunan Provincial Natural Science Foundation of China (Grant Nos.2022JJ30142 and 2019XK2001)in part supported by the State Key Laboratory of Powder Metallurgy,Central South University。
文摘Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications.Here,we demonstrate the epitaxial growth of 1T'-MoTe_(2) on Au(111)and graphitized silicon carbide(Gr/SiC)by molecular beam epitaxy(MBE).We investigate the morphology of the grown1T'-MoTe_(2) at the atomic level by scanning tunnelling microscopy(STM)and reveal the corresponding microscopic growth mechanism.It is found that the unique ordered Te structures preferentially deposited on Au(111)regulate the growth of monolayer single crystal 1T'-MoTe_(2),while the Mo clusters were preferentially deposited on the Gr/SiC substrate,which impedes the ordered growth of monolayer MoTe_(2).We confirm that the size of single crystal 1T'-MoTe_(2) grown on Au(111)is nearly two orders of magnitude larger than that on Gr/SiC.By scanning tunnelling spectroscopy(STS),we observe that the STS spectrum of the monolayer 1T'-MoTe_(2) nano-island at the edge is different from that at the interior,which exhibits enhanced conductivity.
文摘This paper describes the design of a ventilation system to be paired with a carbon capture system. The ventilation system utilizes the geometry of the George C. Wallace tunnel, located in the City of Mobile, Alabama, USA to capture and redirect emissions to a direct air capture (DAC) device to sequester 25% of the total CO2 mass generated from inside the tunnel. The total CO2 mass rate for the westbound traffic between the week-day hours of 7 a.m. and 6 p.m. has been estimated between 2,300 to 3,000 lbs./hr. By sequestering these emissions, the overall surrounding air quality was shown to be improved to a level that mirrors that from the pre-US industrial era of 270 ppm.
基金Project supported by the National Natural Science Foundation of China (Grant No.61851405)。
文摘Due to the pristine interface of the 2D/3D face-tunneling heterostructure with an ultra-sharp doping profile, the 2D/3D tunneling field-effect transistor(TFET) is considered as one of the most promising low-power devices that can simultaneously obtain low off-state current(IOFF), high on-state current(ION) and steep subthreshold swing(SS). As a key element for the 2D/3D TFET, the intensive exploration of the tunnel diode based on the 2D/3D heterostructure is in urgent need.The transfer technique composed of the exfoliation and the release process is currently the most common approach to fabricating the 2D/3D heterostructures. However, the well-established transfer technique of the 2D materials is still unavailable.Only a small part of the irregular films can usually be obtained by mechanical exfoliation, while the choice of the chemical exfoliation may lead to the contamination of the 2D material films by the ions in the chemical etchants. Moreover, the deformation of the 2D material in the transfer process due to its soft nature also leads to the nonuniformity of the transferred film,which is one of the main reasons for the presence of the wrinkles and the stacks in the transferred film. Thus, the large-scale fabrication of the high-quality 2D/3D tunnel diodes is limited. In this article, a comprehensive transfer technique that can mend up the shortages mentioned above with the aid of the water and the thermal release tape(TRT) is proposed. Based on the method we proposed, the MoS_(2)/Si tunnel diode is experimentally demonstrated and the transferred monolayer MoS_(2) film with the relatively high crystal quality is confirmed by atomic force microscopy(AFM), scanning electron microscopy(SEM), and Raman characterizations. Besides, the prominent negative differential resistance(NDR) effect is observed at room temperature, which verifies the relatively high quality of the MoS_(2)/Si heterojunction. The bilayer MoS_(2)/Si tunnel diode is also experimentally fabricated by repeating the transfer process we proposed, followed by the specific analysis of the electrical characteristics. This study shows the advantages of the transfer technique we proposed and indicates the great application foreground of the fabricated 2D/3D heterostructure for ultralow-power tunneling devices.
基金Supported by Science and Technology Bureau of Jining,No.2021YXNS115.
文摘BACKGROUND Carpal tunnel syndrome(CTS)has been associated with gout and type 2 diabetes mellitus(T2DM).However,due to insufficient clinical understanding of goutrelated CTS and reliance on the diagnostic importance of elevated serum uric acid levels,such cases are prone to missed diagnosis,misdiagnosis,and delayed treatment.In addition,the effect of T2DM on gout-induced carpal tunnel syndrome has not been reported.CASE SUMMARY Herein,we present an unusual case of CTS and motor dysfunction caused by miliary tophaceous gout and T2DM.The patient presented to the hand and foot clinic with paresthesia of the fingers of both hands,especially at night.The patient was diagnosed with type 2 diabetes a month ago.Ultrasonography revealed bilateral transverse carpal ligament thickening with median nerve compression during hospitalization.The patient was successfully treated with carpal tunnel decompression and tendon release.The postoperative pathological examination revealed typical gout nodules.This case suggests that the presence of T2DM could accelerate tophi formation and worsen CTS symptoms,although no definitive proof in this regard has been described previously.CONCLUSION Tophi formation may most likely cause the co-occurrence of CTS and flexor dysfunction in gout and incipient diabetes patients.
基金Supported by the National Natural Science Foundation of Chinathe National Key Research and Development Program of China under Grant No 2016YFA0300203
文摘Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi2Sr2CaCu2O8＋δ （Bi2212） and YBa2Cu3O7-x （YBCO） along their c-axes on a scale shorter than the interlayer spacing. By tunneling into the （100） plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended fiat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a （110） surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11474285 and 12074382)。
文摘The activation and dissociation of hydrogen molecules(H_(2))on the Cu(001)surface are studied theoretically.Using first-principles calculations,the activation barrier for the dissociation of H_(2) on Cu(001)is determined to be~0.59 eV in height.It is found that the electron transfer from the copper substrate to H_(2) plays a key role in the activation and breaking of the H–H bond,and the formation of the Cu–H bonds.Two stationary states are identified at around the critical height of bond breaking,corresponding to the molecular and the dissociative states,respectively.Using the transfer matrix method,we also investigate the role of quantum tunneling in the dissociation process along the minimum energy pathway(MEP),which is found to be significant at or below room temperature.At a given temperature,the tunneling contributions due to the translational and the vibrational motions of H_(2) are quantified for the dissociation process.Within a wide range of temperature,the effects of quantum tunneling on the effective barriers of dissociation and the rate constants are observed.The deduced energetic parameters associated with the thermal equilibrium and non-equilibrium(molecular beam)conditions are comparable to experimental data.In the low-temperature region,the crossover from classical to quantum regime is identified.
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1A2C1013693)the Technology Innovation Program (20016102, Development of 1.2k V Gallium oxide power semiconductor devices technology and RS2022-00144027, Development of 1.2k V-class low-loss gallium oxide transistor) by the Ministry of Trade, Industry, and Energy (MOTIE, Korea)
文摘In this work,W/β-Ga_(2)O_(3)Schottky barrier diodes,prepared using a confined magnetic field-based sputtering method,were analyzed at different operation temperatures.Firstly,Schottky barrier height increased with increasing temperature from 100 to 300 K and reached 1.03 eV at room temperature.The ideality factor decreased with increasing temperature and it was higher than 2 at 100 K.This apparent high value was related to the tunneling effect.Secondly,the series and on-resistances decreased with increasing operation temperature.Finally,the interfacial dislocation was extracted from the tunneling current.A high dislocation density was found,which indicates the domination of tunneling through dislocation in the transport mecha-nism.These findings are evidently helpful in designing better performance devices.
文摘The interplay between topology and magnetism is vital for realizing exotic quantum phenomena,significant examples including quantum anomalous Hall effect,axion insulators,and high-order topological states.These states host great potential for future applications in high-speed and low-consumption electronic devices.Despite being extensively investigated,practical platforms are still scarce.In this work,with molecular beam epitaxy(MBE),we provide the first experimental report on high-quality Bi(110)/CrTe_(2) magnetic heterostructure.By employing in-situ high-resolution scanning tunneling microscopy,we are able to examine the interaction between magnetism and topology.There is a potential edge state at an energy level above the Fermi level,but no edge states observed near the Fermi level The absence of high-order topological corner states near EF highlights the importance of lattice matching and interface engineering in designing high-order topological states.Our study provides key insights into the interplay between two-dimensional magnetic and topological materials and offers an important dimension for engineering magnetic topological states.
基金the National Natural Science Foundation of China(Grant Nos.12104232,11805103,and 11804167)the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20190137 and BK20180739)+1 种基金the Innovation Research Project of Jiangsu Province(Grant No.CZ0070619002)NJUPT-SF(Grant No.NY218128)。
文摘We investigate the transport properties of electron in a 1T'-MoS_(2)-based p–n junction.The anisotropic refraction of electron is found when the electron beam crosses the p–n junction,which brings the phenomenon of valley splitting without any external fields.Moreover,it is found that the valley-spin-dependent anomalous Klein tunneling,i.e.,the perfect transmission exists at a nonzero incident angle of valley-spin-dependent electron,happens when the vertical electric field is equal to the critical electric field.These two peculiar properties arise from the same reason that the tilted band structure makes the directions of wavevector and velocity different.Our work designs a special valley splitter without any external fields and finds a new type of Klein tunneling.
基金supported by the National Natural Science Foundation of China (Nos. 50831002, 50971025, 11174031,51071022)Program for Changjiang Scholars and Innovative Research Team in University, Beijing Nova Program (No.2011031)+1 种基金Beijing Natural Science Foundation (No.2102032)the National Basic Research Program of China(No. 2012CB932702)
文摘The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl 2 O 4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5.10 eV for MgAl 2 O 4 and 4.81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point ( band), the coherent tunneling effect might be expected to appear in MgAl 2 O 4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2.9 J m 2 ) and MgAl 2 O 4 (2.27 J m 2 ) on the {100} orientation, and the smaller lattice mismatch between MgAl 2 O 4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl 2 O 4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.
基金supported by the National Natural Science Foundation of China(NSFC)(41941018)the Program of China Scholarship Council(202106430031)。
文摘Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study.The support capacity of 2^(nd) Generation-Negative Poisson’s Ratio(2G-NPR)bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel.The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault,as a result,the rock mass on the upper part of the fault slips as a whole.Furthermore,small-scale deformation and loss of blocks are observed around the tunnel;however,the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability.Due to the blocking effect of fault,the stress of the surrounding rock on the upper and lower parts of the fault is significantly different,and the stress at the left shoulder of the tunnel is greater than that at the right shoulder.The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock.The present numerical scheme is in good agreement with the model test results,and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel.In comparison to unsupported and ordinary PR(Poisson’s Ratio)bolt support,2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel.The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.
基金Ths work was supported by NSFC(11734005.62075041,61821002)Na tional Key Research and Development Program of China(2018YFA0209101,2017YFA0700500).
文摘Interface emission from heterojunction is a shortcoming for electroluminescent devices.A buffer layer introduced in the heterojunctional interfaces is a potential solution for the challenge.However,the dynamics for carrier tunneling to control the interface emission is still a mystery.Herein,the low-refractive HfO_(2)with a proper energy band configuration is em-ployed as the buffer layer in achieving ZnO-microwire/HfO_(2)/GaN heterojunctional light-emitting diodes(LEDs).The optic-ally pumped lasing threshold and lifetime of the ZnO microwire are reduced with the introduced HfO_(2)layer.As a result,the interface emission is of blue-shift from visible wavelengths to 394 nm whereas the ultraviolet(UV)emission is en-hanced.To regulate the interface recombination between electrons in the conduction band of ZnO and holes in the valence band of GaN,the tunneling electrons with higher conduction band are employed to produce a higher tunneling current through regulation of thin HfO_(2)film causing blue shift and interface emission enhancement.Our results provide a method to control the tunneling electrons in heterojunction for high-performance LEDs.
基金Funded by the National Natural Science Foundation of China(No.51678081)Natural Science Foundation of the Jiangsu Higher Education Institution of China(No.18KJB560001)。
文摘In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube specimens coated and uncoated with SiO_(2) aerogel-cement mortar(SiO_(2)-ACM)were heated to simulate tunnel fire for 0.5,1,1.5,2,2.5,3 and 4 h,respectively.The residual compressive strength was tested after the specimens were cooled to room temperature by natural cooling and water cooling.The results show that,the damages of specimens become more serious as fire time goes on,but the residual strength of specimens coated with SiO_(2)-ACM is always higher than that of uncoated with SiO_(2)-ACM.In addition,the residual strength of specimens cooled by water cooling is lower than that of natural cooling.However,for the specimens coated with SiO_(2)-ACM,the adverse effects of water cooling are lessened.With the increase of fire time,the protective effect of SiO_(2)-ACM is still gradually improved.Finally,a formula was established to predict the residual 150 mm cube compressive strength of specimens protected by SiO_(2)-ACM after a simulated tunnel fire.
基金Project supported by the National Key Research&Development Program of China(Grant Nos.2016YFA0202300 and 2018YF A0305800)the National Natural Science Foundation of China(Grant Nos.61888102,11604373,61622116,and 51872284)+2 种基金the CAS Pioneer Hundred Talents Program,China,the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB30000000 and XDB28000000)Beijing Nova Program,China(Grant No.Z181100006218023)the University of Chinese Academy of Sciences
文摘A new two-dimensional atomic crystal, monolayer cuprous telluride（Cu2Te） has been fabricated on a grapheneSi C（0001） substrate by molecular beam epitaxy（MBE）. The low-energy electron diffraction（LEED） characterization shows that the monolayer Cu2Te forms ■ superstructure with respect to the graphene substrate. The atomic structure of the monolayer Cu2Te is investigated through a combination of scanning tunneling microscopy（STM） experiments and density functional theory（DFT） calculations. The stoichiometry of the Cu2Te sample is verified by x-ray photoelectron spectroscopy（XPS） measurement. The angle-resolved photoemission spectroscopy（ARPES） data present the electronic band structure of the sample, which is in good agreement with the calculated results. Furthermore, air-exposure experiments reveal the chemical stability of the monolayer Cu2Te. The fabrication of this new 2D material with a particular structure may bring new physical properties for future applications.
