Thin films of tungsten （W）-doped thermochromic vanadium dioxide （VO2） were deposited onto soda-lime glass and fused silica by radio frequency magnetron sputtering. The doped VO2 films were characterized by X-ray d...Thin films of tungsten （W）-doped thermochromic vanadium dioxide （VO2） were deposited onto soda-lime glass and fused silica by radio frequency magnetron sputtering. The doped VO2 films were characterized by X-ray diffraction, optical transmittance measurement, and near field optical microscopy with Raman spectroscopy. X-ray diffraction patterns show that the （011） peak of W-doped thermochromic VO2 film shifts to a lower diffraction angle with the increase of W concentration. The optical measurements indicated that the transmittance change （AT） at wavelength of 2500 nm drops from 65% （AT at 35 ℃ and 80 ℃ for undoped VO2 film） to 38% （AT at 30 ℃ and 42 ℃ for the doped VO2 film）. At the same time, phase transition temperature drops from 65 ℃ to room temperature or lower with the increase of W concentration. Near field optical microscopy image shows that the surface of W-doped VO2 film is smooth. Raman results show that the main Raman modes of W-doped VO2 are centered at 614 cm 1, the same as that of undoped VO2, suggesting no Raman mode changes for lightly W-doped VO2 at room temperature, due to no phase transition appearing under this condition.展开更多
Vanadium dioxide thin films were fabricated through annealing vanadium oxide thin films deposited by dual ion beam sputtering. X-ray diffraction （XRD）, atom force microscopy （AFM）, and Fourier transform infrared s...Vanadium dioxide thin films were fabricated through annealing vanadium oxide thin films deposited by dual ion beam sputtering. X-ray diffraction （XRD）, atom force microscopy （AFM）, and Fourier transform infrared spectrum （FTIR） were employed to measure the crystalline structure, surface morphology, and infrared optical transmittance. The phase transition properties were characterized by transmittance. The results show that the annealed vanadium oxide thin film is composed of monoclinic VO2, with preferred orientation of （011）. The maximum of transmittance change is beyond 65% as the temperature increases from 20 to 80 C. The reversible changes in optical transmittance against temperature were observed. The change rate of transmittance at short wavelength is higher than that at long wavelength at the same temperature across semiconductor-metal phase transition. This phenomenon was discussed using diffraction effect.展开更多
As far as we known, with white powdery tungstic acid （WPTA） used as the dopant for the first time, tungsten-doped vanadium dioxide （VO2） nanopowders were synthesized through thermolysis at low temperature. The pro...As far as we known, with white powdery tungstic acid （WPTA） used as the dopant for the first time, tungsten-doped vanadium dioxide （VO2） nanopowders were synthesized through thermolysis at low temperature. The products were characterized by XRD, TEM and DSC. When WPTA was added into V205 （with W/V = 2 atom %）, the phase transition temperature （Tc） of VO2 decreased markedly from 67.15℃ to 26.46℃ after annealing at 500℃. Such a low Tc is beneficial to the application and development of smart windows materials.展开更多
This paper reports that the thermochromic vanadium dioxide films were deposited on various transparent substrates by radio frequency magnetron sputtering, and then aged under circumstance for years. Samples were chara...This paper reports that the thermochromic vanadium dioxide films were deposited on various transparent substrates by radio frequency magnetron sputtering, and then aged under circumstance for years. Samples were characterized with several different techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, and Raman, when they were fresh from sputter chamber and aged after years, respectively, in order to determine their structure and composition. It finds that a small amount of sodium occurred on the surface of vanadium dioxide films, which was probably due to sodium ion diffusion from soda-lime glass when sputtering was performed at high substrate temperature. It also finds that aging for years significantly affected the nonstoichiometry of vanadium dioxide films, thus inducing much change in Raman modes.展开更多
The terahertz technology has attracted considerable attention because of its potential applications in various fields.However,the research of functional devices,including polarization converters,remains a major demand...The terahertz technology has attracted considerable attention because of its potential applications in various fields.However,the research of functional devices,including polarization converters,remains a major demand for practical applications.In this work,a reflective dual-functional terahertz metadevice is presented,which combines two different polarization conversions through using a switchable metasurface.Different functions can be achieved because of the insulator-to-metal transition of vanadium dioxide(VO_(2)).At room temperature,the metadevice can be regarded as a linear-to-linear polarization convertor containing a gold circular split-ring resonator(CSRR),first polyimide(PI)spacer,continuous VO_(2) film,second PI spacer,and gold substrate.The converter possesses a polarization conversion ratio higher than 0.9 and a bandwidth ratio of 81%in a range from 0.912 THz to 2.146 THz.When the temperature is above the insulator-to-metal transition temperature(approximately 68℃)and VO_(2) becomes a metal,the metasurface transforms into a wideband linear-to-circular polarization converter composed of the gold CSRR,first PI layer,and continuous VO_(2) film.The ellipticity is close to-1,while the axis ratio is lower than 3 dB in a range of 1.07 THz-1.67 THz.The metadevice also achieves a large angle tolerance and large manufacturing tolerance.展开更多
We proposed a vanadium dioxide(VO2)-integrated multi-functional metamaterial structure that consists of three metallic grating layers and two VO2 films separated by SiO2 dielectric spacers.The proposed structure can b...We proposed a vanadium dioxide(VO2)-integrated multi-functional metamaterial structure that consists of three metallic grating layers and two VO2 films separated by SiO2 dielectric spacers.The proposed structure can be flexibly switched among three states by adjusting temperature,incident direction,and polarization.In state 1,the incident wave is strongly transmitted and perfectly converted to its orthogonal polarization state.In state 2,the incident wave is perfectly absorbed.In state 3,incident wave is totally reflected back.The working frequency of the multi-functional metamaterial can be arbitrarily tuned within a broad pass band.We believe that our findings are beneficial in designing temperature-controlled metadevices.展开更多
We present a design of terahertz modulator based on metamaterial absorber structure withvanadium dioxide （VO2）, which can be controlled by optical-pumping or temperature variation. With the state change of VO2 from ...We present a design of terahertz modulator based on metamaterial absorber structure withvanadium dioxide （VO2）, which can be controlled by optical-pumping or temperature variation. With the state change of VO2 from an insulator to a metal, the absorption has an abrupt increase from zero to 88.5%. In particular, the VO2 layer here is used to not only provide the modulating character, but also replace the metal ground plane to join the resonance operating as a metamaterial absorber. This work demonstrates a feasibility of VO2 in metamaterial perfect absorber, and exhibits potential applications in controllable terahertz devices.展开更多
A tunable perfect absorber composed of hexagonal-arranged aluminum nano-disk array embedded in the vanadium dioxide(VO_2) film is proposed. The aim is to achieve the tunability of resonance absorption peak in the visi...A tunable perfect absorber composed of hexagonal-arranged aluminum nano-disk array embedded in the vanadium dioxide(VO_2) film is proposed. The aim is to achieve the tunability of resonance absorption peak in the visible and near-infrared regimes. Numerical results reveal that the absorption peak achieves a large tunability of 76.6% while VO_2 undergoes a structural transition from insulator phase to metallic phase. By optimizing the structural parameters, an average absorption of 95% is achieved from 1242 to 1815 nm at the metallic phase state. In addition, the near unity absorption can be fulfilled in a wide range of incident angle(0°–60°) and under all polarization conditions. The method and results presented here would be beneficial for the design of active optoelectronic devices.展开更多
Vanadium dioxide （VO2） is a phase transition material which undergoes a reversible metal-insulator transition （MIT） when triggered by thermal, photo, electrical, and even stress. The huge conduction change of VO2 ...Vanadium dioxide （VO2） is a phase transition material which undergoes a reversible metal-insulator transition （MIT） when triggered by thermal, photo, electrical, and even stress. The huge conduction change of VO2 renders it a promising material for terahertz （THz） manipulation. In this paper, some interesting works concerning the growth and characteristics of the VO2 film are selectively reviewed. A switching of THz radiation by photo-driven VO2 film is demonstrated. Experiments indicate an ultrafast optical switching to THz transmission within 8 picoseconds, and a switching ratio reaches to over 80%during a wide frequency range from 0.3 THz to 2.5 THz.展开更多
Vanadium dioxide(VO_(2))is a strongly correlated material,and it has become known due to its sharp metal-insulator transition(MIT)near room temperature.Understanding the thermal properties and their change across MIT ...Vanadium dioxide(VO_(2))is a strongly correlated material,and it has become known due to its sharp metal-insulator transition(MIT)near room temperature.Understanding the thermal properties and their change across MIT of VO_(2)thin film is important for the applications of this material in various devices.Here,the changes in thermal conductivity of epitaxial and polycrystalline VO_(2)thin film across MIT are probed by the time-domain thermoreflectance(TDTR)method.The measurements are performed in a direct way devoid of deposition of any metal thermoreflectance layer on the VO_(2)film to attenuate the impact from extra thermal interfaces.It is demonstrated that the method is feasible for the VO_(2)films with thickness values larger than 100 nm and beyond the phase transition region.The observed reasonable thermal conductivity change rates across MIT of VO_(2)thin films with different crystal qualities are found to be correlated with the electrical conductivity change rate,which is different from the reported behavior of single crystal VO_(2)nanowires.The recovery of the relationship between thermal conductivity and electrical conductivity in VO_(2)film may be attributed to the increasing elastic electron scattering weight,caused by the defects in the film.This work demonstrates the possibility and limitation of investigating the thermal properties of VO_(2)thin films by the TDTR method without depositing any metal thermoreflectance layer.展开更多
Vanadium dioxide(VO 2)thin films are used for protection from high-energy laser hits due to their semiconductor-to-metal phase transition experienced during heating at temperature of approximately 68 ℃,which followed...Vanadium dioxide(VO 2)thin films are used for protection from high-energy laser hits due to their semiconductor-to-metal phase transition experienced during heating at temperature of approximately 68 ℃,which followed by a abrupt change of optical behavior, namely from transparent semiconductor state below 68 ℃ to highly reflective metallic state beyond 68 ℃.The preparation and properties of the films are described as well as the primary principle of the device for protection from high energy laser hits. An ion-beam-sputtering system is used to deposit VO 2 thin films.The technique is reactive ion beam sputtering of vanadium at temperature of 200 ℃ on Si, Ge and Si 3N 4 substrates in a well controlled atmosphere of argon with a partial pressure of O 2, followed by a post annealing at 400-550 ℃ with argon gas.The optical transmittance changes from 60% to 4% are obtained within the temperature range from 50 ℃ to 70 ℃. X-ray diffraction (XRD) shows that the films are of single-phase VO 2.展开更多
By using LDA＋U approach based on the density functional theory, the structural stability of I41/amd VO2 is investigated. According to the phonon dispersion and stability criteria, the I41/amd is suggested to be anoth...By using LDA＋U approach based on the density functional theory, the structural stability of I41/amd VO2 is investigated. According to the phonon dispersion and stability criteria, the I41/amd is suggested to be another possible and stable structure for the VO2. Lattice parameters of the I41/amd VO2 are determined by geometry optimization. The energy band structure shows that the I41/amd VO2 should be a metal. Furthermore, the upper valence band has dominant 2p-orbital characters, but the lower conduction band shows distinctive 3d-orbital characters. Obvious hybridization between the O-2p and V-3d orbitals is observed.展开更多
基金supported by the Chinese Universities Scientific Fund (Grant No. 2013QJ007)the Science Fund of China Agricultural University (Grant No. 2007037)the Major Project Foundation of Science and Technology Innovation in Advanced Education (Grant No. 21010112)
文摘Thin films of tungsten （W）-doped thermochromic vanadium dioxide （VO2） were deposited onto soda-lime glass and fused silica by radio frequency magnetron sputtering. The doped VO2 films were characterized by X-ray diffraction, optical transmittance measurement, and near field optical microscopy with Raman spectroscopy. X-ray diffraction patterns show that the （011） peak of W-doped thermochromic VO2 film shifts to a lower diffraction angle with the increase of W concentration. The optical measurements indicated that the transmittance change （AT） at wavelength of 2500 nm drops from 65% （AT at 35 ℃ and 80 ℃ for undoped VO2 film） to 38% （AT at 30 ℃ and 42 ℃ for the doped VO2 film）. At the same time, phase transition temperature drops from 65 ℃ to room temperature or lower with the increase of W concentration. Near field optical microscopy image shows that the surface of W-doped VO2 film is smooth. Raman results show that the main Raman modes of W-doped VO2 are centered at 614 cm 1, the same as that of undoped VO2, suggesting no Raman mode changes for lightly W-doped VO2 at room temperature, due to no phase transition appearing under this condition.
基金supported by the National High-Tech Research and Development Program of China(No.2008AA031401)the National Natural Science Foundation of China (No.60771019)+2 种基金the Natural Science Foundation of Tianjin, China (No.08JCZD-JC17500)the StateKey Lab on Integrated Optoelectronics (No.2010KFB001)The Research Fund for the Doctoral Program of Higher Education of China (No.20100032120029)
文摘Vanadium dioxide thin films were fabricated through annealing vanadium oxide thin films deposited by dual ion beam sputtering. X-ray diffraction （XRD）, atom force microscopy （AFM）, and Fourier transform infrared spectrum （FTIR） were employed to measure the crystalline structure, surface morphology, and infrared optical transmittance. The phase transition properties were characterized by transmittance. The results show that the annealed vanadium oxide thin film is composed of monoclinic VO2, with preferred orientation of （011）. The maximum of transmittance change is beyond 65% as the temperature increases from 20 to 80 C. The reversible changes in optical transmittance against temperature were observed. The change rate of transmittance at short wavelength is higher than that at long wavelength at the same temperature across semiconductor-metal phase transition. This phenomenon was discussed using diffraction effect.
文摘As far as we known, with white powdery tungstic acid （WPTA） used as the dopant for the first time, tungsten-doped vanadium dioxide （VO2） nanopowders were synthesized through thermolysis at low temperature. The products were characterized by XRD, TEM and DSC. When WPTA was added into V205 （with W/V = 2 atom %）, the phase transition temperature （Tc） of VO2 decreased markedly from 67.15℃ to 26.46℃ after annealing at 500℃. Such a low Tc is beneficial to the application and development of smart windows materials.
基金supported by the National Natural Science Foundation of China (Grant No 60776039)China Agricultural University Foundation (Grant No 2007037)
文摘This paper reports that the thermochromic vanadium dioxide films were deposited on various transparent substrates by radio frequency magnetron sputtering, and then aged under circumstance for years. Samples were characterized with several different techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, and Raman, when they were fresh from sputter chamber and aged after years, respectively, in order to determine their structure and composition. It finds that a small amount of sodium occurred on the surface of vanadium dioxide films, which was probably due to sodium ion diffusion from soda-lime glass when sputtering was performed at high substrate temperature. It also finds that aging for years significantly affected the nonstoichiometry of vanadium dioxide films, thus inducing much change in Raman modes.
基金the National Natural Science Foundation of China(Grant No.62001444)the Natural Science Foundation of Zhejiang Province,China(Grant No.LQ20F010009)+1 种基金the Basic Public Welfare Research Project of Zhejiang Province,China(Grant No.LGF19F010003)the State Key Laboratory of Crystal Materials,Shandong University,China(Grant No.KF1909)。
文摘The terahertz technology has attracted considerable attention because of its potential applications in various fields.However,the research of functional devices,including polarization converters,remains a major demand for practical applications.In this work,a reflective dual-functional terahertz metadevice is presented,which combines two different polarization conversions through using a switchable metasurface.Different functions can be achieved because of the insulator-to-metal transition of vanadium dioxide(VO_(2)).At room temperature,the metadevice can be regarded as a linear-to-linear polarization convertor containing a gold circular split-ring resonator(CSRR),first polyimide(PI)spacer,continuous VO_(2) film,second PI spacer,and gold substrate.The converter possesses a polarization conversion ratio higher than 0.9 and a bandwidth ratio of 81%in a range from 0.912 THz to 2.146 THz.When the temperature is above the insulator-to-metal transition temperature(approximately 68℃)and VO_(2) becomes a metal,the metasurface transforms into a wideband linear-to-circular polarization converter composed of the gold CSRR,first PI layer,and continuous VO_(2) film.The ellipticity is close to-1,while the axis ratio is lower than 3 dB in a range of 1.07 THz-1.67 THz.The metadevice also achieves a large angle tolerance and large manufacturing tolerance.
基金Project supported by the Scientific and Technological Developing Scheme of Jilin Province,China(Grant No.20180101281JC)the"135"Research Project of Education Bureau of Jilin Province,China(Grant No.JJKH20190579KJ)the"111"Project of China(Grant No.D17017).
文摘We proposed a vanadium dioxide(VO2)-integrated multi-functional metamaterial structure that consists of three metallic grating layers and two VO2 films separated by SiO2 dielectric spacers.The proposed structure can be flexibly switched among three states by adjusting temperature,incident direction,and polarization.In state 1,the incident wave is strongly transmitted and perfectly converted to its orthogonal polarization state.In state 2,the incident wave is perfectly absorbed.In state 3,incident wave is totally reflected back.The working frequency of the multi-functional metamaterial can be arbitrarily tuned within a broad pass band.We believe that our findings are beneficial in designing temperature-controlled metadevices.
基金supported by the National Basic Research Program of China under Grant No.2014CB339800the National High Technology Research and Development Program of China under Grant No.2011AA010205+1 种基金the National Natural Science Foundation of China under Grant No.61171027the Tianjin Science and Technology Plan Project under Grant No.13RCGFGX01127
文摘We present a design of terahertz modulator based on metamaterial absorber structure withvanadium dioxide （VO2）, which can be controlled by optical-pumping or temperature variation. With the state change of VO2 from an insulator to a metal, the absorption has an abrupt increase from zero to 88.5%. In particular, the VO2 layer here is used to not only provide the modulating character, but also replace the metal ground plane to join the resonance operating as a metamaterial absorber. This work demonstrates a feasibility of VO2 in metamaterial perfect absorber, and exhibits potential applications in controllable terahertz devices.
基金Supported by the National Natural Science Foundation of China under Grant No 41675154the Six Major Talent Peak Expert of Jiangsu Province under Grant Nos 2015-XXRJ-014 and R2016L01+1 种基金the Jiangsu 333 High-Level Talent Cultivation Program under Grant No BRA2016425the Research Innovation Program for College Graduates of Jiangsu Province under Grant No KYCX18_1022
文摘A tunable perfect absorber composed of hexagonal-arranged aluminum nano-disk array embedded in the vanadium dioxide(VO_2) film is proposed. The aim is to achieve the tunability of resonance absorption peak in the visible and near-infrared regimes. Numerical results reveal that the absorption peak achieves a large tunability of 76.6% while VO_2 undergoes a structural transition from insulator phase to metallic phase. By optimizing the structural parameters, an average absorption of 95% is achieved from 1242 to 1815 nm at the metallic phase state. In addition, the near unity absorption can be fulfilled in a wide range of incident angle(0°–60°) and under all polarization conditions. The method and results presented here would be beneficial for the design of active optoelectronic devices.
基金supported by the National Natural Science Foundation of China under Grant No.61131005Keygrant Project of Chinese Ministry of Education under Grant No.313013+1 种基金New Century Excellent Talent Foundation under Grant No.NCET-11-0068Sichuan Youth S.&T.Foundation under Grant No.2011JQ0001
文摘Vanadium dioxide （VO2） is a phase transition material which undergoes a reversible metal-insulator transition （MIT） when triggered by thermal, photo, electrical, and even stress. The huge conduction change of VO2 renders it a promising material for terahertz （THz） manipulation. In this paper, some interesting works concerning the growth and characteristics of the VO2 film are selectively reviewed. A switching of THz radiation by photo-driven VO2 film is demonstrated. Experiments indicate an ultrafast optical switching to THz transmission within 8 picoseconds, and a switching ratio reaches to over 80%during a wide frequency range from 0.3 THz to 2.5 THz.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61825102,51872038,and 52021001)the“111”Project,China(Grant No.B18011).
文摘Vanadium dioxide(VO_(2))is a strongly correlated material,and it has become known due to its sharp metal-insulator transition(MIT)near room temperature.Understanding the thermal properties and their change across MIT of VO_(2)thin film is important for the applications of this material in various devices.Here,the changes in thermal conductivity of epitaxial and polycrystalline VO_(2)thin film across MIT are probed by the time-domain thermoreflectance(TDTR)method.The measurements are performed in a direct way devoid of deposition of any metal thermoreflectance layer on the VO_(2)film to attenuate the impact from extra thermal interfaces.It is demonstrated that the method is feasible for the VO_(2)films with thickness values larger than 100 nm and beyond the phase transition region.The observed reasonable thermal conductivity change rates across MIT of VO_(2)thin films with different crystal qualities are found to be correlated with the electrical conductivity change rate,which is different from the reported behavior of single crystal VO_(2)nanowires.The recovery of the relationship between thermal conductivity and electrical conductivity in VO_(2)film may be attributed to the increasing elastic electron scattering weight,caused by the defects in the film.This work demonstrates the possibility and limitation of investigating the thermal properties of VO_(2)thin films by the TDTR method without depositing any metal thermoreflectance layer.
文摘Vanadium dioxide(VO 2)thin films are used for protection from high-energy laser hits due to their semiconductor-to-metal phase transition experienced during heating at temperature of approximately 68 ℃,which followed by a abrupt change of optical behavior, namely from transparent semiconductor state below 68 ℃ to highly reflective metallic state beyond 68 ℃.The preparation and properties of the films are described as well as the primary principle of the device for protection from high energy laser hits. An ion-beam-sputtering system is used to deposit VO 2 thin films.The technique is reactive ion beam sputtering of vanadium at temperature of 200 ℃ on Si, Ge and Si 3N 4 substrates in a well controlled atmosphere of argon with a partial pressure of O 2, followed by a post annealing at 400-550 ℃ with argon gas.The optical transmittance changes from 60% to 4% are obtained within the temperature range from 50 ℃ to 70 ℃. X-ray diffraction (XRD) shows that the films are of single-phase VO 2.
基金supported by the Science and Technology Plans of Tianjin(No.15PTSYJC00250)
文摘By using LDA＋U approach based on the density functional theory, the structural stability of I41/amd VO2 is investigated. According to the phonon dispersion and stability criteria, the I41/amd is suggested to be another possible and stable structure for the VO2. Lattice parameters of the I41/amd VO2 are determined by geometry optimization. The energy band structure shows that the I41/amd VO2 should be a metal. Furthermore, the upper valence band has dominant 2p-orbital characters, but the lower conduction band shows distinctive 3d-orbital characters. Obvious hybridization between the O-2p and V-3d orbitals is observed.
