VO2 thin films based active and passive thermochromic devices for energy management applications

Ba, C.; Bah, Souleymane Toubou; D’Auteuil, Marc; Fortin, Vincent; Ashrit, P. V.; Vallée, Réal

doi:10.1016/j.cap.2014.09.005

Cited by 26 publications

(15 citation statements)

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“…The use of polymer templates and surfactants has also been shown to change the surface microstructure and thus the thermochromic efficiency [176,184]. In some cases VO 2 films that consisted of nanoparticles have been found to result in wider hysteresis widths (10-20 • C), although they tended to have lower critical transition temperatures (~40 • C) [150], it has been suggested that the hysteresis width is inversely proportional to the average crystallite and grain sizes of the materials [185,186] however, this is not found to be the case in all studies [163].…”

Section: Improving Thermochromic Efficiencymentioning

confidence: 99%

Thin Films for Advanced Glazing Applications

et al. 2016

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Functional thin films provide many opportunities for advanced glazing systems. This can be achieved by adding additional functionalities such as self-cleaning or power generation, or alternately by providing energy demand reduction through the management or modulation of solar heat gain or blackbody radiation using spectrally selective films or chromogenic materials. Self-cleaning materials have been generating increasing interest for the past two decades. They may be based on hydrophobic or hydrophilic systems and are often inspired by nature, for example hydrophobic systems based on mimicking the lotus leaf. These materials help to maintain the aesthetic properties of the building, help to maintain a comfortable working environment and in the case of photocatalytic materials, may provide external pollutant remediation. Power generation through window coatings is a relatively new idea and is based around the use of semi-transparent solar cells as windows. In this fashion, energy can be generated whilst also absorbing some solar heat. There is also the possibility, in the case of dye sensitized solar cells, to tune the coloration of the window that provides unheralded external aesthetic possibilities. Materials and coatings for energy demand reduction is highly desirable in an increasingly energy intensive world. We discuss new developments with low emissivity coatings as the need to replace scarce indium becomes more apparent. We go on to discuss thermochromic systems based on vanadium dioxide films. Such systems are dynamic in nature and present a more sophisticated and potentially more beneficial approach to reducing energy demand than static systems such as low emissivity and solar control coatings. The ability to be able to tune some of the material parameters in order to optimize the film performance for a given climate provides exciting opportunities for future technologies. In this article, we review recent progress and challenges in these areas and provide a perspective for future trends and developments.

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Section: Improving Thermochromic Efficiencymentioning

confidence: 99%

Thin Films for Advanced Glazing Applications

et al. 2016

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“…The metal‐to‐insulator transition (MIT) temperature ( T C ~ 334 K), the reverse direction transition of the IMT, can be founded by cooling of the sample from above T C . Generally, there is hysteresis gap between T H and T C . VO 2 bulk crystals show sharp and clear transitions in the resistance measurement with narrowed the hysteresis gap, as small as ~5 K .…”

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confidence: 98%

“…The T H of VO 2 film related with the thickness of the film—thinner film has higher T H , but still below T H of bulk. The increased aspect (length/width) ratio of the composed nanocrystals from 0.3 to 1.25 results the T H increases 18 K . But, the transition temperatures of each VO 2 film keep at the nearly same points during repeated thermal cycles …”

mentioning

confidence: 99%

“…The optical properties and other various physical properties of VO 2 are abruptly changed near the IMT . The change of physical properties of VO 2 could be initiated not only by temperature, but also by electric field, electromagnetic wave, physical stress, and so on . These transition properties of VO 2 make the material as a good candidate of several practical applications—switches, field effect transistors, sensors, and thermochromic smart window …”

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Metal‐to‐Insulator Transition of Hydrothermally Prepared VO₂ Crystal During Repeated Thermal Cycles

Lee

Kim

2015

Bulletin Korean Chem Soc

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One of the most well-known transition phenomena in solids is insulator-metal transition (IMT) of VO 2 , 1 which is related to the first-order transition between insulating monoclinic (M-VO 2 -low temperature phase) and metallic rutile (R-VO 2 -high temperature phase) VO 2 phase around 340 K. The electrical conductivity of VO 2 is suddenly changed by several orders of magnitude at the transition.1 The optical properties and other various physical properties of VO 2 are abruptly changed near the IMT. Even though the IMT of VO 2 was investigated for last several decades, the origin of the transition is still unclear. 10-14Strongly correlated electron theory (Mott-Hubbard) and electron-lattice interaction theory (Peierls) are equally accepted as explanation model for the transition.10 Especially, the transition of VO 2 accompanied with the structural transformation makes hard to unveil the origin of the transition.The IMT temperature (T H~3 40 K) can be founded by heating of the sample from below T H . The metal-to-insulator transition (MIT) temperature (T C~3 34 K), the reverse direction transition of the IMT, can be founded by cooling of the sample from above T C . Generally, there is hysteresis gap between T H and T C . 8,11,12 VO 2 bulk crystals show sharp and clear transitions in the resistance measurement with narrowed the hysteresis gap, as small as~5 K. 1,11,12,15,16 However, a thin film VO 2 , which consists of submicro-sized crystals of VO 2 , shows unclear and continuous transition at the both transitions. The T H of VO 2 film related with the thickness of the film-thinner film has higher T H , but still below T H of bulk. The increased aspect (length/width) ratio of the composed nanocrystals from 0.3 to 1.25 results the T H increases 18 K. 8,17 But, the transition temperatures of each VO 2 film keep at the nearly same points during repeated thermal cycles. 17There have been several reports for the preparation and characterization of VO 2 crystals, 11,12,14-16 thin film, 17 nanowire, 18 and so on. 19,20 In general, the observation of clear MIT and IMT of VO 2 in the resistance measurement was reported in the well-grown single crystalline samples. [11][12][13][14][15][16]18 And the most of hydrothermally prepared crystalline samples 9,19,20 and thin films showed unclear transition in the resistivity measurement as mentioned. 8,17 However, recently we reported that the hydrothermally prepared high quality VO 2 crystals, which have clear MIT and IMT in the electrical conductivity measurement. 21 In this investigation, the origin of the shift of the transition temperature, sharpness, and clearness of the first-order transition of hydrothermally prepared VO 2 crystals, were discussed.Figure 1(a) shows the XRD patterns of the product of the hydrothermal reaction, which prepared under various reaction temperatures (436, 463, 483, and 503 K). Even though there were reports 9,22 that claimed similar processes 9,22 produce VO 2 , all the patterns of the samples could be indexed as VO 2 ÁH 2 O (JCPDS No. 50-1797). Th...

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“…VO 2 thin film samples were prepared by depositing films of metallic vanadium using ion-assisted dual AC magnetron deposition method. 17 The metallic film was oxidized to vanadium dioxide using thermal oxidation in a controlled atmosphere 18 to a thickness of 98 nm. A substrate of Zerodur (Schott Glass) was chosen for the experiment to minimize lensing effects due to thermal bumps at the surface (Zerodur's thermal expansion coefficient is $10 À8 K À1 ).…”

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Nanometer-thick flat lens with adjustable focus

Son

Vallée

et al. 2014

Applied Physics Letters

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We report laser beam focusing by a flat, homogeneous film with a thickness of less than 100 nm. The effect relies on refractive index changes occurring in vanadium dioxide as it undergoes a phase transition from insulator to metal. Phase front curvature is achieved by means of temperature gradients, and adjustable focal lengths from infinity to 30 cm are attained. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4903887] Thin flat lenses have found applications in areas such as integrated optics and satellite optical instruments, where lightweight and small-volume optical components are desired, as well as x-ray optics, where standard lens materials are ineffective. While the traditional approach to creating thin lenses is based on the Fresnel zone plate design, there has been a resurgence of activity exploiting effects of nanoplasmonics and metamaterials. For example, a quasiperiodic arrangement of sub-wavelength holes on a thin gold film was found to focus light to sub-wavelength spatial resolution. 1-3 Similarly, light focusing by ultrathin lenses was demonstrated by exploiting the properties of nano-antennas etched on a surface, 4,5 thus forming a type of optically functionalized metasurface. 6,7 In this paper, we report yet an alternative method for focusing light with a thin layer of material. There are three key differences that distinguish this work from previous studies:(1) it exploits a different mechanism, namely, the large refractive index change occurring during a phase transition from insulator-to-metal, (2) the focusing capability is dynamic, and can be adjusted in real time, and (3) the material used is uniform and does not require prior physical patterning. In the latter aspect, it is analogous to gradient-index (GRIN) and other such thin lenses, [8][9][10][11][12] with the exception that its index of refraction is not spatially profiled beforehand.When light interacts with a layer of vanadium dioxide (VO 2 ), it acquires a phase shift which depends on the state of the material. In the temperature range where VO 2 undergoes a transition from insulator to metal (roughly 50-80 C), the optical phase shift is approximately linear with temperature, as was shown in a previous study. 13 Figure 1 illustrates the concept. Figure 2 presents ellipsometry measurements showing the change in refractive index as VO 2 undergoes a phase transition. Given the complex refractive indices, Fresnel reflection coefficients at the air/VO 2 and VO 2 /substrate interfaces introduce phase shifts of 0.51 rad and 0.75 rad, respectively, during the phase transition of the material. Meanwhile, the round-trip propagation phase in the layer varies by À1.0 rad. From this we conclude that both propagation and reflection phases are responsible for the observed phase shift.From Figure 1(b), we see that between a temperature T A (the onset of the phase transition) and a temperature T B (the end of the phase transition), the optical phase shift from VO 2 changes by some amount D/. As a result, by mean of a temperature gradien...

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VO2 thin films based active and passive thermochromic devices for energy management applications

Cited by 26 publications

References 21 publications

Thin Films for Advanced Glazing Applications

Thin Films for Advanced Glazing Applications

Metal‐to‐Insulator Transition of Hydrothermally Prepared VO₂ Crystal During Repeated Thermal Cycles

Nanometer-thick flat lens with adjustable focus

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VO2 thin films based active and passive thermochromic devices for energy management applications

Cited by 26 publications

References 21 publications

Thin Films for Advanced Glazing Applications

Thin Films for Advanced Glazing Applications

Metal‐to‐Insulator Transition of Hydrothermally Prepared VO2 Crystal During Repeated Thermal Cycles

Nanometer-thick flat lens with adjustable focus

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Metal‐to‐Insulator Transition of Hydrothermally Prepared VO₂ Crystal During Repeated Thermal Cycles