Two-dimensional(2D)precursor molecules-based surface treatment on three-dimensional(3D)lead halide perovskite(PVSK)has achieved huge successes,the in-depth understanding of the modification mechanism remains an urgent...Two-dimensional(2D)precursor molecules-based surface treatment on three-dimensional(3D)lead halide perovskite(PVSK)has achieved huge successes,the in-depth understanding of the modification mechanism remains an urgent need.Here the effect of alkyl-chain length on the reaction dynamics between alkylammonium salts(XI)and 3D PVSK matrix is studied,through examination of surface morphological and crystallographic properties of the 3D PVSK matrix.It is observed that the average crystallite size of 3D PVSK increases as XI is either spin-coated on 3D PVSK or penetrated through carbon-electrode(during the“in-situ healing”process).Secondary growth is observed for 3D PVSK,which is related to ion-exchanging reactions.Prolonging alkyl-chain length favors the secondary growth.Besides,the formation dynamics of 2D PVSK are studied.Adding alkyl-chain length increases the yields.The observations are thoroughly discussed with respect to the steric-hindrance effect held by alky-chains of XI molecule.The improved crystallization of 3D PVSK and increased yields of 2D PVSK help accelerate charge extraction and reduce recombination across the interface between PVSK and carbon-electrode(CE).Tuning alkyl-chain length of XI molecules,and the mass ratio between XI molecules and carbon black could mitigate the“in-situ healing”effect.Power conversion efficiency(PCE)of the carbonelectrode-based hole-conductor-free planar perovskite solar cells has been upgraded from 14% to 17%,and further upgraded to 20.4% by utilizing relatively thick CEs.Thanks to the hydrophobicity of long alkyl-chains owned by XI molecules,prolonged stability has been achieved on unsealed devices at the high-moisture environment(RH≈85%),meanwhile,shelf-stability up to 6400 h has been achieved.This study deepens the understanding of the 2D precursor-basing modification strategies.展开更多
The discovery of graphene,the first two-dimensional material with a thickness of an atomic layer,opened the prelude to the development of other atom-thin two-dimensional layered materials.They are considered to be one...The discovery of graphene,the first two-dimensional material with a thickness of an atomic layer,opened the prelude to the development of other atom-thin two-dimensional layered materials.They are considered to be one of the best candidates to extend Moore’s law.However,graphene is a zero-bandgap semimetal,which limits its application in logic circuits[1].展开更多
Flexible conductive films were fabricated from a low-temperature-cured, highly conductive composite of silver nanowires （as conducting filler） and polyvinyl alcohol （PVA, as binder）. Sheet resistance of 0.12 Ω/sq...Flexible conductive films were fabricated from a low-temperature-cured, highly conductive composite of silver nanowires （as conducting filler） and polyvinyl alcohol （PVA, as binder）. Sheet resistance of 0.12 Ω/sq, conductivity of 2.63 ×10^4 S/cm, and contact resistance of 1.0Ω/cm^2 were measured in the films, along with excellent resistance to scratch- ing and good flexibility, making them suitable electrical contact materials for flexible optoelectronic devices. Effects of curing temperature, curing duration, film thickness, and nanowire length on the film＇s electrical properties were studied. Due to the abundance of hydroxyl groups on its molecular chains, the addition of PVA improves the film＇s flexibility and resistance to scratching. Increased nanowire density and nanowire length benefit film conductance. Monte Carlo simulation was used to further explore the impact of these two parameters on the conductivity. It was observed that longer nanowires produce a higher length-ratio of conducting routes in the networks, giving better film conductivity.展开更多
SiO2 nanoparticles were used to regulate the crystallizing process of lead halide perovskite films prepared by the sequential deposition method,which was used in the low-temperature-processed,carbon-electrode-basing,h...SiO2 nanoparticles were used to regulate the crystallizing process of lead halide perovskite films prepared by the sequential deposition method,which was used in the low-temperature-processed,carbon-electrode-basing,hole-conductor-free planar perovskite solar cells.It was observed that,after adding small amount of SiO2 precursor(1 vol%)into the lead iodide solution,performance parameters of open-circuit voltage,short-circuit current and fill factor were all upgraded,which helped to increase the power conversion efficiency(reverse scan)from 11.44(±1.83)%(optimized at 12.42%)to 14.01(±2.14)%(optimized at 15.28%,AM 1.5G,100 mW/cm^2).Transient photocurrent decay curve measurements showed that,after the incorporation of SiO2 nanoparticles,charge extraction was accelerated,while transient photovoltage decay and dark current curve tests both showed that recombination was retarded.The improvement is due to the improved crystallinity of the perovskite film.X-ray diffraction and scanning electron microscopy studies observed that,with incorporation of amorphous SiO2 nanoparticles,smaller crystallites were obtained in lead iodide films,while larger crystallites were achieved in the final perovskite film.This study implies that amorphous SiO2 nanoparticles could regulate the coarsening process of the perovskite film,which provides an effective method in obtaining high quality perovskite film.展开更多
In the past decades there have been many breakthroughs in low-dimensional materials,especially in two-dimensional(2D)atomically thin crystals like graphene.As structural analogues of graphene but with a sizeable band ...In the past decades there have been many breakthroughs in low-dimensional materials,especially in two-dimensional(2D)atomically thin crystals like graphene.As structural analogues of graphene but with a sizeable band gap,monolayers of atomically thin transition metal dichalcogenides(with formula of MX2,M=Mo,W;X=S,Se,Te,etc.)have emerged as the ideal 2D prototypes for exploring fundamentals in physics such as valleytronics due to the quantum confinement effects,and for engineering a wide range of nanoelectronic,optoelectronic,and photocatalytic applications.Transition metal trioxides as promising materials with low evaporation temperature,high work function,and inertness to air have been widely used in the fabrication and modification of MX2.In this review,we reported the fabrications of one-dimensional MoS2 wrapped MoO2 single crystals with varied crystal direction via atmospheric pressure chemical vapor deposition method and of 2D MoOx covered MoX2 by means of exposing MoX2 to ultraviolet ozone.The prototype devices show good performances.The approaches are common to other transition metal dichalcogenides and transition metal oxides.展开更多
Pure cobalt(Co)thin films were fabricated by direct current magnetron sputtering,and the effects of sputtering power and pres-sure on the microstructure and electromagnetic properties of the films were investigated.As...Pure cobalt(Co)thin films were fabricated by direct current magnetron sputtering,and the effects of sputtering power and pres-sure on the microstructure and electromagnetic properties of the films were investigated.As the sputtering power increases from 15 to 60 W,the Co thin films transition from an amorphous to a polycrystalline state,accompanied by an increase in the intercrystal pore width.Simultaneously,the resistivity decreases from 276 to 99μΩ·cm,coercivity increases from 162 to 293 Oe,and in-plane magnetic aniso-tropy disappears.As the sputtering pressure decreases from 1.6 to 0.2 Pa,grain size significantly increases,resistivity significantly de-creases,and the coercivity significantly increases(from 67 to 280 Oe),which can be attributed to the increase in defect width.Corres-pondingly,a quantitative model for the coercivity of Co thin films was formulated.The polycrystalline films sputtered under pressures of 0.2 and 0.4 Pa exhibit significant in-plane magnetic anisotropy,which is primarily attributable to increased microstress.展开更多
Hybrid organic–inorganic perovskite thin films have attracted much attention in optoelectronic and information fields because of their intriguing properties. Due to quantum confinement effects, ultrathin films in nm ...Hybrid organic–inorganic perovskite thin films have attracted much attention in optoelectronic and information fields because of their intriguing properties. Due to quantum confinement effects, ultrathin films in nm scale usually show special properties. Here, we report on the growth of methylammonium lead iodide(MAPbI_(3)) ultrathin films via co-deposition of PbI_2 and CH_3NH_3I(MAI) on chemical-vapor-deposition-grown monolayer MoS_(2) as well as the corresponding photoluminescence(PL) properties at different growing stages. Atomic force microscopy and scanning electron microscopy measurements reveal the MoS_(2) tuned growth of MAPbI_(3) in a Stranski–Krastanov mode. PL and Kelvin probe force microscopy results confirm that MAPbI_(3) /MoS_(2) heterostructures have a type-Ⅱ energy level alignment at the interface. Temperaturedependent PL measurements on layered MAPbI_(3) (at the initial stage) and on MAPbI_(3) crystals in averaged size of 500 nm(at the later stage) show rather different temperature dependence as well as the phase transitions from tetragonal to orthorhombic at 120 and 150 K, respectively. Our findings are useful in fabricating MAPbI_(3) /transition-metal dichalcogenide based innovative devices for wider optoelectronic applications.展开更多
Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically ...Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically investigated a convenient and effective method,ultraviolet ozone treatment,for p-type doping of MoTe2 field-effect transistors to enormously enhance the corresponding electrical performance.The resulted hole concentration and mobility are near 100 times enhanced to be〜1.0×10^13 cm^-2 and 101.4 cm^2/(V·s),respectively,and the conductivity is improved by 5 orders of magnitude.These values are comparable to the highest ones ever obtained via annealing doping or non-lithographic fabrication methods at room temperature.Compared with the pristine one,the photoresponsivity(522 mA/W)is enhanced approximately 100 times.Such excellent performances can be attributed to the sharply reduced Schottky barrier because of the surface charge transfer from MoTe2 to MoOx(x<3),as proved by photoemission spectroscopy.Additionally,the p-doped devices exhibit excellent stability in ambient air.Our findings show significant potential in future nanoelectronic and optoelectronic applications.展开更多
Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional(2D)materials are considered to have broad prospects in solving the energy dissipation p...Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional(2D)materials are considered to have broad prospects in solving the energy dissipation problem.Herein the thermal transport of a typical 2D ternary chalcogenide Ta_(2)NiS_(5) is investigated.For the first time we have observed strongly anisotropic in-plane thermal conductivity towards armchair and zigzag axes of suspended few-layer Ta_(2)NiS_(5) flakes through Raman thermometry.For 7-nm-thick Ta_(2)NiS_(5) flakes,theκz i g z a g is 4.76 W·m^(−1)·K^(−1) andκa r m c h a i r is 7.79 W·m^(−1)·K^(−1),with a large anisotropic ratio(κa r m c h a i r/κz i g z a g)of 1.64 mainly ascribed to different phonon mean-free-paths along armchair and zigzag axes.Moreover,the thickness dependence of thermal anisotropy is also discussed.As the flake thickness increases,theκa r m c h a i r/κz i g z a g reduces sharply from 1.64 to 1.07.This could be attributed to the diversity in phonon boundary scattering,which decreases faster in zigzag direction than in armchair direction.Such anisotropic property enables heat flow manipulation in Ta_(2)NiS_(5) based devices to improve thermal management and device performance.Our work helps reveal the anisotropy physics of ternary transition metal chalcogenides,along with significant guidance to develop energy-efficient next generation nanodevices.展开更多
Elementary excitations,such as in-plane anisotropic phonons and phonon polaritons(PhPs),inα-MoO_(3) play key roles in its outstanding physical properties like high carrier mobility and ultralow phonon thermal conduct...Elementary excitations,such as in-plane anisotropic phonons and phonon polaritons(PhPs),inα-MoO_(3) play key roles in its outstanding physical properties like high carrier mobility and ultralow phonon thermal conductivity().Understanding the excitation mechanisms like phonon–phonon interactions is the most fundamental step to further applications.Here,we report on the systematic Raman investigations on phonon anisotropy and anharmonicity of representative Mo–O stretching vibration phonon modes(SVPMs)in physical vapor deposition(PVD)-grownα-MoO_(3) flakes.Polarizations of SVPMs verify the phonon anisotropy.The abnormal temperature dependence of SVPMs reveals that giant quartic-phonon decay dominates the phonon anharmonicity inα-MoO_(3).An ultrashort phonon lifetime of~0.34 ps gives evidence of theoretically predicted ultralow inα-MoO_(3).Our findings give deep insight into the phonon–phonon interactions inα-MoO_(3) and provide an indicator for its extreme thermal device applications.展开更多
With the packing density growing continuously in integrated electronic devices,sufficient heat dissipation becomes a serious challenge.Recently,dielectric materials with high thermal conductivity have brought insight ...With the packing density growing continuously in integrated electronic devices,sufficient heat dissipation becomes a serious challenge.Recently,dielectric materials with high thermal conductivity have brought insight into effective dissipation of waste heat in electronic devices to prevent them from overheating and guarantee the performance stability.Layered CrOCl,an antiferromagnetic insulator with low-symmetry crystal structure and atomic level flatness,might be a promising solution to the thermal challenge.Herein,we have systematically studied the thermal transport of suspended few-layer CrOCl flakes by microRaman thermometry.The CrOCl flakes exhibit high thermal conductivities along zigzag direction,from~392±33 to~1,017±46 W·m^(−1)·K^(−1) with flake thickness from 2 to 50 nm.Besides,pronounced thickness-dependent thermal conductivity ratio(/from~2.8±0.24 to~4.3±0.25)has been observed in the CrOCl flakes,attributed to the discrepancy of phonon dispersion and phonon surface scattering.As a demonstration to the heat sink application of layered CrOCl,we then investigate the energy dissipation in graphene devices on CrOCl,SiO_(2) and hexagonal boron nitride(h-BN)substrates,respectively.The graphene device temperature rise on CrOCl is only 15.4%of that on SiO_(2) and 30%on h-BN upon the same electric power density,indicating the efficient heat dissipation of graphene device on CrOCl.Our study provides new insights into two-dimentional(2D)dielectric material with high thermal conductivity and strong anisotropy for the application of thermal management in electronic devices.展开更多
Improving thermal transport between substrate and transistors has become a vital solution to the thermal challenge in nanoelectronics.Recently 2D WTe_(2) has sparked extensive interest because of heavy atomic mass and...Improving thermal transport between substrate and transistors has become a vital solution to the thermal challenge in nanoelectronics.Recently 2D WTe_(2) has sparked extensive interest because of heavy atomic mass and low Debye temperature.Here,the thermal transport of supported WTe_(2) was studied via Raman thermometry with electrical heating.The supported 30 nm WTe2 encased with 70 nm Al_(2)O_(3) delivered 4.8 W·m^(-1)·K^(-1)in-plane thermal conductivity along zigzag direction at room temperature,which was almost 1.6 times larger than that along armchair direction(3.0 W·m^(-1)·K^(-1)).Interestingly,the superior and inferior directions for thermal transport are just opposite of those for electrical transport.Hence,a heat manipulation model in WTe_(2) FET device was proposed.Within the designed configuration,waste heat in WTe_(2) would be mostly dissipated to metal contacts located along zigzag,relieving the local temperature discrepancy in the channel effectively and preventing degradation or breakdown.Our study provides new insight into thermal transport of anisotropic 2D materials,which might inspire energy-efficient nanodevices in the future.展开更多
基金financial support of the National Natural Science Foundation of China(NSFC,No.62374185)the Key Scientific Research Project of Education Department of Hunan Province(No.22A0005)the financial support from the Fundamental Research Funds for the Central South University(No.2024ZZTS0478)。
文摘Two-dimensional(2D)precursor molecules-based surface treatment on three-dimensional(3D)lead halide perovskite(PVSK)has achieved huge successes,the in-depth understanding of the modification mechanism remains an urgent need.Here the effect of alkyl-chain length on the reaction dynamics between alkylammonium salts(XI)and 3D PVSK matrix is studied,through examination of surface morphological and crystallographic properties of the 3D PVSK matrix.It is observed that the average crystallite size of 3D PVSK increases as XI is either spin-coated on 3D PVSK or penetrated through carbon-electrode(during the“in-situ healing”process).Secondary growth is observed for 3D PVSK,which is related to ion-exchanging reactions.Prolonging alkyl-chain length favors the secondary growth.Besides,the formation dynamics of 2D PVSK are studied.Adding alkyl-chain length increases the yields.The observations are thoroughly discussed with respect to the steric-hindrance effect held by alky-chains of XI molecule.The improved crystallization of 3D PVSK and increased yields of 2D PVSK help accelerate charge extraction and reduce recombination across the interface between PVSK and carbon-electrode(CE).Tuning alkyl-chain length of XI molecules,and the mass ratio between XI molecules and carbon black could mitigate the“in-situ healing”effect.Power conversion efficiency(PCE)of the carbonelectrode-based hole-conductor-free planar perovskite solar cells has been upgraded from 14% to 17%,and further upgraded to 20.4% by utilizing relatively thick CEs.Thanks to the hydrophobicity of long alkyl-chains owned by XI molecules,prolonged stability has been achieved on unsealed devices at the high-moisture environment(RH≈85%),meanwhile,shelf-stability up to 6400 h has been achieved.This study deepens the understanding of the 2D precursor-basing modification strategies.
文摘The discovery of graphene,the first two-dimensional material with a thickness of an atomic layer,opened the prelude to the development of other atom-thin two-dimensional layered materials.They are considered to be one of the best candidates to extend Moore’s law.However,graphene is a zero-bandgap semimetal,which limits its application in logic circuits[1].
基金Project supported by the National Natural Science Foundation of China(Grant No.61306080)the Natural Science Foundation of Hunan Province,China(Grant No.2015JJ3143)the Scientific and Technological Project of Hunan Provincial Development and Reform Commission,China
文摘Flexible conductive films were fabricated from a low-temperature-cured, highly conductive composite of silver nanowires （as conducting filler） and polyvinyl alcohol （PVA, as binder）. Sheet resistance of 0.12 Ω/sq, conductivity of 2.63 ×10^4 S/cm, and contact resistance of 1.0Ω/cm^2 were measured in the films, along with excellent resistance to scratch- ing and good flexibility, making them suitable electrical contact materials for flexible optoelectronic devices. Effects of curing temperature, curing duration, film thickness, and nanowire length on the film＇s electrical properties were studied. Due to the abundance of hydroxyl groups on its molecular chains, the addition of PVA improves the film＇s flexibility and resistance to scratching. Increased nanowire density and nanowire length benefit film conductance. Monte Carlo simulation was used to further explore the impact of these two parameters on the conductivity. It was observed that longer nanowires produce a higher length-ratio of conducting routes in the networks, giving better film conductivity.
基金Project supported by the Fundamental Research Funds for the Central South University,China(Grant No.2019zzts426)the National Natural Science Foundation of China(Grant Nos.61172047,61774170,and 51673218)+1 种基金the Scientific and Technological Project of Hunan Provincial Development and Reform Commission,China,the National Science Foundation,USA(Grant Nos.CBET-1437656 and DMR-1903962)the Innovation-Driven Project of Central South University(Grant No.2020CX006)。
文摘SiO2 nanoparticles were used to regulate the crystallizing process of lead halide perovskite films prepared by the sequential deposition method,which was used in the low-temperature-processed,carbon-electrode-basing,hole-conductor-free planar perovskite solar cells.It was observed that,after adding small amount of SiO2 precursor(1 vol%)into the lead iodide solution,performance parameters of open-circuit voltage,short-circuit current and fill factor were all upgraded,which helped to increase the power conversion efficiency(reverse scan)from 11.44(±1.83)%(optimized at 12.42%)to 14.01(±2.14)%(optimized at 15.28%,AM 1.5G,100 mW/cm^2).Transient photocurrent decay curve measurements showed that,after the incorporation of SiO2 nanoparticles,charge extraction was accelerated,while transient photovoltage decay and dark current curve tests both showed that recombination was retarded.The improvement is due to the improved crystallinity of the perovskite film.X-ray diffraction and scanning electron microscopy studies observed that,with incorporation of amorphous SiO2 nanoparticles,smaller crystallites were obtained in lead iodide films,while larger crystallites were achieved in the final perovskite film.This study implies that amorphous SiO2 nanoparticles could regulate the coarsening process of the perovskite film,which provides an effective method in obtaining high quality perovskite film.
基金Project supported by the National Natural Science Foundation of China(Grant No.11874427)the National Science Foundation DMR-1903962the Fundamental Research Funds for the Central Universities of Central South University(Grant No.2019zzts429).
文摘In the past decades there have been many breakthroughs in low-dimensional materials,especially in two-dimensional(2D)atomically thin crystals like graphene.As structural analogues of graphene but with a sizeable band gap,monolayers of atomically thin transition metal dichalcogenides(with formula of MX2,M=Mo,W;X=S,Se,Te,etc.)have emerged as the ideal 2D prototypes for exploring fundamentals in physics such as valleytronics due to the quantum confinement effects,and for engineering a wide range of nanoelectronic,optoelectronic,and photocatalytic applications.Transition metal trioxides as promising materials with low evaporation temperature,high work function,and inertness to air have been widely used in the fabrication and modification of MX2.In this review,we reported the fabrications of one-dimensional MoS2 wrapped MoO2 single crystals with varied crystal direction via atmospheric pressure chemical vapor deposition method and of 2D MoOx covered MoX2 by means of exposing MoX2 to ultraviolet ozone.The prototype devices show good performances.The approaches are common to other transition metal dichalcogenides and transition metal oxides.
基金the financial support from the National Key Research and Development Program of China(No.2017YFB0305500)the State Key Laboratory of Powder Metallurgy,Central South University,Changsha,China.
文摘Pure cobalt(Co)thin films were fabricated by direct current magnetron sputtering,and the effects of sputtering power and pres-sure on the microstructure and electromagnetic properties of the films were investigated.As the sputtering power increases from 15 to 60 W,the Co thin films transition from an amorphous to a polycrystalline state,accompanied by an increase in the intercrystal pore width.Simultaneously,the resistivity decreases from 276 to 99μΩ·cm,coercivity increases from 162 to 293 Oe,and in-plane magnetic aniso-tropy disappears.As the sputtering pressure decreases from 1.6 to 0.2 Pa,grain size significantly increases,resistivity significantly de-creases,and the coercivity significantly increases(from 67 to 280 Oe),which can be attributed to the increase in defect width.Corres-pondingly,a quantitative model for the coercivity of Co thin films was formulated.The polycrystalline films sputtered under pressures of 0.2 and 0.4 Pa exhibit significant in-plane magnetic anisotropy,which is primarily attributable to increased microstress.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11874427 and 11804395)the Fundamental Research Funds for the Central Universities of Central South University (Grant No.2020zzts377)。
文摘Hybrid organic–inorganic perovskite thin films have attracted much attention in optoelectronic and information fields because of their intriguing properties. Due to quantum confinement effects, ultrathin films in nm scale usually show special properties. Here, we report on the growth of methylammonium lead iodide(MAPbI_(3)) ultrathin films via co-deposition of PbI_2 and CH_3NH_3I(MAI) on chemical-vapor-deposition-grown monolayer MoS_(2) as well as the corresponding photoluminescence(PL) properties at different growing stages. Atomic force microscopy and scanning electron microscopy measurements reveal the MoS_(2) tuned growth of MAPbI_(3) in a Stranski–Krastanov mode. PL and Kelvin probe force microscopy results confirm that MAPbI_(3) /MoS_(2) heterostructures have a type-Ⅱ energy level alignment at the interface. Temperaturedependent PL measurements on layered MAPbI_(3) (at the initial stage) and on MAPbI_(3) crystals in averaged size of 500 nm(at the later stage) show rather different temperature dependence as well as the phase transitions from tetragonal to orthorhombic at 120 and 150 K, respectively. Our findings are useful in fabricating MAPbI_(3) /transition-metal dichalcogenide based innovative devices for wider optoelectronic applications.
基金We acknowledge the financial support from the National Natural Science Foundation of China(Nos.11874427,11874423).Dr.H an H uang acknowledges support from the Innovation-Driven project of Central South University(No.2017CX018)and from the Natural Science Foundation of H unan province(No.2016JJ1021).Mr.Xiaoming Zheng acknowledges the support from the Fundamental Research Funds for the Central Universities of Central South University(No.2017zzts066).
文摘Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier,which is crucial for the realization of high-performance logic components.Here,we systematically investigated a convenient and effective method,ultraviolet ozone treatment,for p-type doping of MoTe2 field-effect transistors to enormously enhance the corresponding electrical performance.The resulted hole concentration and mobility are near 100 times enhanced to be〜1.0×10^13 cm^-2 and 101.4 cm^2/(V·s),respectively,and the conductivity is improved by 5 orders of magnitude.These values are comparable to the highest ones ever obtained via annealing doping or non-lithographic fabrication methods at room temperature.Compared with the pristine one,the photoresponsivity(522 mA/W)is enhanced approximately 100 times.Such excellent performances can be attributed to the sharply reduced Schottky barrier because of the surface charge transfer from MoTe2 to MoOx(x<3),as proved by photoemission spectroscopy.Additionally,the p-doped devices exhibit excellent stability in ambient air.Our findings show significant potential in future nanoelectronic and optoelectronic applications.
基金supported by the National Natural Science Foundation of China(NSFC,Nos.11874423 and 11404399)the National Defense Science and Technology Innovation Zone,and the Scientific Researches Foundation of National University of Defense Technology(Nos.ZK20-16 and ZZKY-YX-08-06).
文摘Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional(2D)materials are considered to have broad prospects in solving the energy dissipation problem.Herein the thermal transport of a typical 2D ternary chalcogenide Ta_(2)NiS_(5) is investigated.For the first time we have observed strongly anisotropic in-plane thermal conductivity towards armchair and zigzag axes of suspended few-layer Ta_(2)NiS_(5) flakes through Raman thermometry.For 7-nm-thick Ta_(2)NiS_(5) flakes,theκz i g z a g is 4.76 W·m^(−1)·K^(−1) andκa r m c h a i r is 7.79 W·m^(−1)·K^(−1),with a large anisotropic ratio(κa r m c h a i r/κz i g z a g)of 1.64 mainly ascribed to different phonon mean-free-paths along armchair and zigzag axes.Moreover,the thickness dependence of thermal anisotropy is also discussed.As the flake thickness increases,theκa r m c h a i r/κz i g z a g reduces sharply from 1.64 to 1.07.This could be attributed to the diversity in phonon boundary scattering,which decreases faster in zigzag direction than in armchair direction.Such anisotropic property enables heat flow manipulation in Ta_(2)NiS_(5) based devices to improve thermal management and device performance.Our work helps reveal the anisotropy physics of ternary transition metal chalcogenides,along with significant guidance to develop energy-efficient next generation nanodevices.
基金We acknowledge the financial support from the National Natural Science Foundation of China(NSFC,No.11874427).
文摘Elementary excitations,such as in-plane anisotropic phonons and phonon polaritons(PhPs),inα-MoO_(3) play key roles in its outstanding physical properties like high carrier mobility and ultralow phonon thermal conductivity().Understanding the excitation mechanisms like phonon–phonon interactions is the most fundamental step to further applications.Here,we report on the systematic Raman investigations on phonon anisotropy and anharmonicity of representative Mo–O stretching vibration phonon modes(SVPMs)in physical vapor deposition(PVD)-grownα-MoO_(3) flakes.Polarizations of SVPMs verify the phonon anisotropy.The abnormal temperature dependence of SVPMs reveals that giant quartic-phonon decay dominates the phonon anharmonicity inα-MoO_(3).An ultrashort phonon lifetime of~0.34 ps gives evidence of theoretically predicted ultralow inα-MoO_(3).Our findings give deep insight into the phonon–phonon interactions inα-MoO_(3) and provide an indicator for its extreme thermal device applications.
基金supported by the National Natural Science Foundation of China(No.11874423).
文摘With the packing density growing continuously in integrated electronic devices,sufficient heat dissipation becomes a serious challenge.Recently,dielectric materials with high thermal conductivity have brought insight into effective dissipation of waste heat in electronic devices to prevent them from overheating and guarantee the performance stability.Layered CrOCl,an antiferromagnetic insulator with low-symmetry crystal structure and atomic level flatness,might be a promising solution to the thermal challenge.Herein,we have systematically studied the thermal transport of suspended few-layer CrOCl flakes by microRaman thermometry.The CrOCl flakes exhibit high thermal conductivities along zigzag direction,from~392±33 to~1,017±46 W·m^(−1)·K^(−1) with flake thickness from 2 to 50 nm.Besides,pronounced thickness-dependent thermal conductivity ratio(/from~2.8±0.24 to~4.3±0.25)has been observed in the CrOCl flakes,attributed to the discrepancy of phonon dispersion and phonon surface scattering.As a demonstration to the heat sink application of layered CrOCl,we then investigate the energy dissipation in graphene devices on CrOCl,SiO_(2) and hexagonal boron nitride(h-BN)substrates,respectively.The graphene device temperature rise on CrOCl is only 15.4%of that on SiO_(2) and 30%on h-BN upon the same electric power density,indicating the efficient heat dissipation of graphene device on CrOCl.Our study provides new insights into two-dimentional(2D)dielectric material with high thermal conductivity and strong anisotropy for the application of thermal management in electronic devices.
基金supported by the National Natural Science Foundation of China(Nos.61801498,11404399,11874423,and 51701237)the National Defense Science and Technology Innovation Zone,the Scientific Researches Foundation of National University of Defense Technology(Nos.ZK18-01-03,ZK18-03-36,ZK20-16,and ZZKY-YX-08-06)+1 种基金the China Postdoctoral Science Foundation(CPSF)(No.2019M663569)the Youth Talent Lifting Project(No.17-JCJQ-QT-004).
文摘Improving thermal transport between substrate and transistors has become a vital solution to the thermal challenge in nanoelectronics.Recently 2D WTe_(2) has sparked extensive interest because of heavy atomic mass and low Debye temperature.Here,the thermal transport of supported WTe_(2) was studied via Raman thermometry with electrical heating.The supported 30 nm WTe2 encased with 70 nm Al_(2)O_(3) delivered 4.8 W·m^(-1)·K^(-1)in-plane thermal conductivity along zigzag direction at room temperature,which was almost 1.6 times larger than that along armchair direction(3.0 W·m^(-1)·K^(-1)).Interestingly,the superior and inferior directions for thermal transport are just opposite of those for electrical transport.Hence,a heat manipulation model in WTe_(2) FET device was proposed.Within the designed configuration,waste heat in WTe_(2) would be mostly dissipated to metal contacts located along zigzag,relieving the local temperature discrepancy in the channel effectively and preventing degradation or breakdown.Our study provides new insight into thermal transport of anisotropic 2D materials,which might inspire energy-efficient nanodevices in the future.
