Enhanced Thermochromic Properties of Vanadium Dioxide (VO 2 )/Glass Heterostructure by Inserting a Zr-Based Thin Film Metallic Glasses (Cu 50 Zr 50 ) Buffer Layer

Featured Application: Smart windows and other transferable infrared devices. Abstract: Vanadium dioxide (VO 2 ) with reversible metal–insulator transition (MIT) is one of the most promising energy-efﬁcient materials. Especially for VO 2 -based smart windows, the visible transmittance and solar modulation ability are the most critical parameters. However, VO 2 thin ﬁlms that are directly deposited onto glass substrates are of poor crystallinity and MIT performance, limiting the practical applications of VO 2 /glass heterostructures. In this paper, a buffer layer of Cu 50 Zr 50 was introduced to build a novel Zr-based thin ﬁlm metallic glass (VO 2 /Cu 50 Zr 50 /glass) with multilayer structures for thermochromic applications. It is observed that the insertion of a Cu 50 Zr 50 buffer layer with appropriate thickness results in a clear enhancement of crystalline quality and MIT performance in the VO 2 /Cu 50 Zr 50 /glass thin ﬁlms, compared with the single-layer VO 2 /glass thin ﬁlms. Moreover, the VO 2 /Cu 50 Zr 50 /glass bi-layer ﬁlms exhibit better optical performance with enhanced solar modulation ability ( ∆ T sol = 14.3%) and a high visible transmittance ( T vis = 52.3%), which represents a good balance between ∆ T sol and T vis for smart window applications.


Introduction
In response to a large energy-consuming and environmentally deteriorating condition, developing energy-saving materials and sustainable energy has aroused wide attention. Vanadium dioxide (VO 2 ) thin film is a first-order phase-changed material with superfast reaction speed that is near the critical temperature, 340 K [1,2]. This phase transformation is called a metal-insulator transition (MIT), and involves significant changes in electrical and optical characteristics. Its phase switching behavior makes VO 2 a hopeful candidate for a variety of applications, such as smart windows [3], sensor devices [4], ultrafast switches [5], Mott field effect transistors [4,6], etc.
Various techniques have been developed to form VO 2 thin films, for instance, molecular beam epitaxy [7], pulsed laser deposition [8], magnetron sputtering [9], and chemical vapor deposition [10]. Over the past decades, high-quality VO 2 thin films with the single crystalline characteristics have been seeking because of the impact on MIT features. It is known that the characteristics of the chosen substrates play a major role in the thermochromic properties of VO 2 thin films [11,12]. A lot of single crystals have been employed to act as the growth substrates, such as titanium dioxide (TiO 2 ), silica (SiO 2 ), sapphire (Al 2 O 3 ), and magnesium fluoride (MgF 2 ). The employ of single crystals results in a high expense for the device preparations and therefore immensely limits practical manufacture based on VO 2 thin films. As an alternative approach, common glass substrates with very low cost and good optical transmittance are potentially promising for the production of smart windows and other transferable infrared devices. However, VO 2 thin films that are directly grown onto conventional glass substrates are generally of poor crystallinity. Hence, single-layer VO 2 /glass thin films have worse MIT and photoelectric properties [13,14]. In particular, the luminous transmittance and solar modulation ability are often especially bad in single-layer VO 2 /glass structures, which limits the practical manufacture of VO 2 -based smart windows. Thus, it is the need of the immediate to find a way to optimize the crystallinity and photoelectric properties in VO 2 /glass heterostructures.
One way to do this is to design and fabricate a multilayered structure. Multilayered VO 2 thin films have been completed on different substrates by use of "buffer layers" of materials, such as TiO 2 , SnO 2 , ZnO [15][16][17], conductive oxides (Aluminum-doped Zinc Oxied (AZO), Fluorine Tin Oxide (FTO), Indium Tin Oxide (ITO), etc.) [18][19][20], metals (Ag, Cu, etc.), thin films [21], etc. Recently, thin film metallic glasses (TFMGs) were introduced and showed better surface roughness [22] and good optical properties [23,24]. In particular, Zr-based TFMG have received much scientific research attention for potential applications, since their good mechanical, tribological and fatigue properties, and their corrosion resistance and excellent adhesion [25][26][27][28]. Recently, Zong found that the Zr-based thin film metallic glasses (Cu 50 Zr 50 ) have excellent near-infrared transmission (larger than 80%) [28]. Cu 50 Zr 50 , which can be prepared at room temperature, is a good candidate for template layers. The excellent near-infrared transmission and the appearance of the surface plasmon polaritons (SPPs) is anticipated to be favorable for the optical property of VO 2 thin films.
Motivated by the above demands for the thermochromic application of VO 2 /glass thin films, in the present study we constructed a Zr-based thin film metallic glass (VO 2 /Cu 50 Zr 50 /glass) with a multilayer structure, consisting of Cu 50 Zr 50 TFMG as a buffer layer on amorphous glass substrates. The thickness dependence of the microstructure and optoelectronic properties of the VO 2 /Cu 50 Zr 50 /glass multilayers was investigated. The achievements may be more comprehensive to understand the role of Cu 50 Zr 50 buffer layers in the formation of high-crystalline VO 2 thin films on glass substrates, and thus pave a way towards heightening the photoelectrical properties of VO 2 thin film-based devices.

Method for Film Deposition
VO 2 /glass monolayer and VO 2 /Cu 50 Zr 50 /glass bilayer structures (different Cu 50 Zr 50 buffer layer thicknesses) were prepared by pulsed laser deposition (wavelength 248 nm). The targets are V (99.95% purity, 25 mm diameter, 3 mm thick) and Cu 50 Zr 50 alloy (99.99% purity, 40 mm diameter, 5 mm thick). Cleaned the amorphous glass substrates (BF33) with an ethanol/acetone solution, rinsed with distilled water, and finally blown with pure nitrogen. Prior to deposition, the base pressure was controlled at 1.0 × 10 −4 Pa and the target-substrate distance was 6 cm. During the deposition, the laser operated at repetition rate of 5 Hz and output pulse energy of 200 mJ for entire deposition, the target and substrate were rotated at a rate of 18 rpm. The deposition conditions for the VO 2 film and buffer layer were 500 • C with P O2 = 0.9 Pa for VO 2 film, room temperature without oxygen inlet for Cu 50 Zr 50 . The oxygen flow rate was 25 sccm for VO 2 . The film thickness was controlled by deposition time and corrected by step profiler (DektakXT, Bruker, Karlsruhe, Germany). The Cu 50 Zr 50 buffer layers had thicknesses of 40 nm, 80 nm, and 160 nm in the three multilayer VO 2 /Cu 50 Zr 50 /glass thin films. For comparison, the single-layer VO 2 thin films were grown directly on an amorphous glass substrate under the same conditions as the VO 2 /Cu 50 Zr 50 /glass thin films. The thickness of all the VO 2 thin films was 60 nm. The four thin films were marked as VO 2 (60 nm)/glass, VO 2 (60 nm)/Cu 50 Zr 50 (40 nm)/glass, VO 2 (60 nm)/Cu 50 Zr 50 (80 nm)/glass, and VO 2 (60 nm)/Cu 50 Zr 50 (160 nm)/glass.

Film Characterization
The crystallographic properties of the sample was characterized by X-ray diffraction (XRD) using a instrument modeled LabXRD-6000 (Shimadzu, Kyushu, Japan) (λ = 0.15406 nm). Using atomic force microscopy (AFM), the surface morphology of the samples was studied with a profilometer (Dektak 150, Bruker, Karlsruhe, Germany)). Images were additionally acquired by scanning electron microscopy (SEM) (Zeiss Supa 50VP, Jena Germany). The temperature-driven MIT properties were measured during the heating and cooling process within the temperature range 30-120 • C by the Hall Effect Measurement System (HMS-5300, Ecopia, Pyeongchang, South Korea). A double beam spectrophotometer (UV-3600, Shimadzu, Kyushu, Japan) with a spectral range of 200-2650 nm was used to record the transmittance spectra of the films. The temperature was controlled in situ by a heater. Figure 1 shows the XRD diffraction patterns of the VO 2 /glass film and VO 2 /Cu 50 Zr 50 /glass films. The generalized diffraction with the 2θ ranging from 15 • to 30 • indicates the glass properties of the substrates. For the thin films, the peaks that were located at 27.80 • are attributed to the VO 2 (011) peak (JCPDS No. 43-1051), which is the feature diffraction peak for M1-phase VO 2 thin films [29]. All of the VO 2 thin films are strongly oriented along the [011] direction, whether or not buffer layers were inserted on the glass substrate. The diffraction peak located at 31.47 • belongs to the ZrO 2 (111) peak (JCPDS No. 65-1024), implying the monoclinic symmetry characteristics of the ZrO 2 . The peak located at 42.42 • is assigned to the Cu 2 O (200) peak (JCPDS No. 77-0199). The appearance of ZrO 2 and Cu 2 O may be due to the incorporation of Zr and Cu ions with oxygen during the VO 2 thin film growth. In addition, as the thickness of the buffer layer increases, the intensity of VO 2 (011) peaks (in units of counts per second (cps)) initially increases and then decreases, indicating that the crystal quality of VO 2 thin films initially improves and then worsens. The characteristic peaks of the VO 2 phase disappear in the 160 nm-thick VO 2 /Cu 50 Zr 50 /glass thin films, which clearly indicates that thicker buffer layers make VO 2 amorphous.

Microstructural Properties
Cu50Zr50 thickness   Figure 2 shows the AFM micrographs of the surfaces of the VO 2 /glass film and VO 2 /Cu 50 Zr 50 /glass films. The surfaces of the VO 2 /Cu 50 Zr 50 /glass films are smoother and more uniform than the VO 2 /glass film. The measured roughnesses of the VO 2 /Cu 50 Zr 50 /glass films without a buffer layer, and with buffer layers with thicknesses of 40 nm, 80 nm, and 160 nm, are 2.86 nm, 1.32 nm, 1.51 nm, and 2.12 nm, respectively, indicating that the surface morphology of VO 2 films that are grown on glass substrates can be optimized effectively by embedding a Cu 50 Zr 50 buffer layer. What calls for special attention is a suitable thickness needs that the Cu 50 Zr 50 buffer layer need to select, since excess thickness of Cu 50 Zr 50 layers will generate rougher films.  To further show the effects of the buffer layer thickness on the microstructures, the SEM images of the surface morphology of the VO2/Cu50Zr50/glass thin films with different buffer layer thicknesses are shown in Figure 3. The surfaces of all the films are found to be continuous and dense. The bright white segments that are visible on the surface of films are identified as amorphous metal V particles, according to the elemental analysis illustrated in the small red circles of Figure 3c,d by Energy-dispersive X-ray spectroscopy (EDS). After embedding an alloy buffer layer, the number of the amorphous metal V particles increases clearly, resulting in poor crystallinity of the VO2 thin films on the thick buffer layer. To further show the effects of the buffer layer thickness on the microstructures, the SEM images of the surface morphology of the VO 2 /Cu 50 Zr 50 /glass thin films with different buffer layer thicknesses are shown in Figure 3. The surfaces of all the films are found to be continuous and dense. The bright white segments that are visible on the surface of films are identified as amorphous metal V particles, according to the elemental analysis illustrated in the small red circles of Figure 3c,d by Energy-dispersive X-ray spectroscopy (EDS). After embedding an alloy buffer layer, the number of the amorphous metal V particles increases clearly, resulting in poor crystallinity of the VO 2 thin films on the thick buffer layer.
By combining the above analysis, the following can be conjectured. When the buffer layer thickness is relatively thin (~40 nm), the incorporation of Zr atoms with O atoms during deposition forms monoclinic ZrO 2. The ZrO 2 interfacial layer serves as a template to improve the crystallinity of the upper VO 2 thin films. This result is highly consistent with the case of the VO 2 /Y-doped ZrO 2 /Si thin films [30], where the Y-doped ZrO 2 served as the buffer layer. As the buffer layer thickness increases to 80 nm, the high roughness and impure phase of Cu 2 O deteriorates the crystal quality of the VO 2 thin films. When the buffer layer thickness increases to 160 nm, much more oxygen is consumed and too many amorphous metal V particles are present on the film surface, which reduces the crystalline quality of the VO 2 (M) thin film.
By combining the above analysis, the following can be conjectured. When the buffer layer thickness is relatively thin (~40 nm), the incorporation of Zr atoms with O atoms during deposition forms monoclinic ZrO2. The ZrO2 interfacial layer serves as a template to improve the crystallinity of the upper VO2 thin films. This result is highly consistent with the case of the VO2/Y-doped ZrO2/Si thin films [30], where the Y-doped ZrO2 served as the buffer layer. As the buffer layer thickness increases to 80 nm, the high roughness and impure phase of Cu2O deteriorates the crystal quality of the VO2 thin films. When the buffer layer thickness increases to 160 nm, much more oxygen is consumed and too many amorphous metal V particles are present on the film surface, which reduces the crystalline quality of the VO2(M) thin film.  Figure 4 shows the square resistance variation with temperature in the heating and cooling cycles of the VO2 thin films with various thicknesses of Cu50Zr50 inserting buffer layers. In Figure 4a, the VO2/glass thin films show a resistance-temperature curve with a wide transformation hysteresis. In the cases of the 40-and 80-nm-thick buffer layers, the VO2 thin films both exhibit sharper decreases in sheet resistance with increasing temperature, as illustrated in Figure 4b,c, strongly implying the occurrence of an MIT. However, no MIT occurs when the buffer layer thickness attains to 160 nm. This result can be attributed to poor crystallization in the VO2/Cu50Zr50/glass thin films, which is good corresponding to the XRD analysis.   Figure 4 shows the square resistance variation with temperature in the heating and cooling cycles of the VO 2 thin films with various thicknesses of Cu 50 Zr 50 inserting buffer layers. In Figure 4a, the VO 2 /glass thin films show a resistance-temperature curve with a wide transformation hysteresis. In the cases of the 40-and 80-nm-thick buffer layers, the VO 2 thin films both exhibit sharper decreases in sheet resistance with increasing temperature, as illustrated in Figure 4b,c, strongly implying the occurrence of an MIT. However, no MIT occurs when the buffer layer thickness attains to 160 nm. This result can be attributed to poor crystallization in the VO 2 /Cu 50 Zr 50 /glass thin films, which is good corresponding to the XRD analysis.

Electrical Properties
To better comparing, the observed electrical properties of VO 2 films with various buffer layer thicknesses are summarized in Table 1. The transition temperature (T c ) is defined as the center of the derivative curve of the heating curve in the insets of Figure 3. Here, we defined the amplitude of MIT (∆R) as the relative resistance change ratio between room temperature and a temperature of 100 • C. The hysteresis width (∆H) is the difference between the T c values that were measured during the heating and cooling cycles. From Table 1, the single-layer VO 2 thin films have higher T c than the buffered VO 2 thin films. After introducing the buffer layer (40 nm and 80 nm in thickness), the T c values of VO 2 thin films are similar to that of the bulk VO 2 single crystal (68 • C), which is generally due to the release of stress [31]. The ∆R values of the VO 2 /glass thin films are slightly larger than those of the 40-and 80-nm-thick VO 2 /Cu 50 Zr 50 /glass thin films. This could be due to the larger crystal size in the non-buffered VO 2 thin films [32]. The samples with smaller or larger ∆H values can be applied in different fields and the ∆H value is closely connected with the quality of crystallization and crystallite dimension in the VO 2 thin films [33][34][35]. From Table 1, it can be seen that the ∆H values of the buffered VO 2 thin films are much smaller than the non-buffered one. The buffer layer serves as a good template for VO 2 thin film growth and it thus results in a better crystallinity in the 40-and 80-nm-thick VO 2 /Cu 50 Zr 50 /glass thin films. These conclusions point out that the electrical characteristic of VO 2 films can be significantly enhanced by inserting Cu 50 Zr 50 buffer layer of appropriate thickness. buffered VO2 thin films. After introducing the buffer layer (40 nm and 80 nm in thickness), the Tc values of VO2 thin films are similar to that of the bulk VO2 single crystal (68 °C), which is generally due to the release of stress [31]. The ΔR values of the VO2/glass thin films are slightly larger than those of the 40-and 80-nm-thick VO2/Cu50Zr50/glass thin films. This could be due to the larger crystal size in the non-buffered VO2 thin films [32]. The samples with smaller or larger ΔH values can be applied in different fields and the ΔH value is closely connected with the quality of crystallization and crystallite dimension in the VO2 thin films [33][34][35]. From Table 1, it can be seen that the ΔH values of the buffered VO2 thin films are much smaller than the non-buffered one. The buffer layer serves as a good template for VO2 thin film growth and it thus results in a better crystallinity in the 40-and 80-nm-thick VO2/Cu50Zr50/glass thin films. These conclusions point out that the electrical characteristic of VO2 films can be significantly enhanced by inserting Cu50Zr50 buffer layer of appropriate thickness.

Optical Properties
The optical parameters of VO 2 /glass and VO 2 /Cu 50 Zr 50 /glass thin films is measured with in situ varying temperature. Figure 5 depicts the thermochromic transmittance curves of VO 2 /glass and VO 2 /Cu 50 Zr 50 /glass films in response to preset temperatures (from room temperature to 100 • C). Objectively speaking, the transmittance of all the samples in the visible region is almost constant. However, the transmittance of VO 2 (60 nm)/glass, VO 2 (60 nm)/Cu 50 Zr 50 (40 nm)/glass, and VO 2 (60 nm)/Cu 50 Zr 50 (80 nm)/glass decreases clearly with the temperature increases in the infrared region, as shown in Figure 5a-c, while in the VO 2 (60 nm)/Cu 50 Zr 50 (160 nm)/glass thin films the transmittance changes relatively little (Figure 5d).

Optical Properties
The optical parameters of VO2/glass and VO2/Cu50Zr50/glass thin films is measured with in situ varying temperature. Figure 5 depicts the thermochromic transmittance curves of VO2/glass and VO2/Cu50Zr50/glass films in response to preset temperatures (from room temperature to 100 °C). Objectively speaking, the transmittance of all the samples in the visible region is almost constant. However, the transmittance of VO2(60 nm)/glass, VO2(60 nm)/Cu50Zr50(40 nm)/glass, and VO2(60 nm)/Cu50Zr50(80 nm)/glass decreases clearly with the temperature increases in the infrared region, as shown in Figure 5a-c, while in the VO2(60 nm)/Cu50Zr50(160 nm)/glass thin films the transmittance changes relatively little (Figure 5d). The optical modulation properties of the VO2 thin film are investigated to evaluate its potential in smart windows. In order to realize the applications of VO2 in smart windows, technological challenges need to be addressed, including improving the maximum visible transmittance (Tvis), maintaining high solar modulating efficiency (ΔTsol), and undergoing more than 10,000 cycles without any degradation [36]. The Tvis, ΔTsol, and near-infrared (NIR) switching efficiency (ΔT2500nm) of all the samples were obtained by the calculation of the transmittance spectra and are displayed in Figure 6. The solar transmittance (Tsol, 300-2500 nm) and the ΔTsol values are derived from the following formulas: where T(λ) is defined as the transmittance at wavelength λ and φsol is the solar irradiance spectrum for air mass 1.5 (corresponding to the sun standing 37° above the horizon) [37]. As shown in Figure  6, the Tvis, ΔTsol, and ΔT2500nm values of the monolayer VO2 film are 44.6%, 7.2% and 42.7%, respectively. Therefore, the good thermochromic properties with enhanced luminous transmittance The optical modulation properties of the VO 2 thin film are investigated to evaluate its potential in smart windows. In order to realize the applications of VO 2 in smart windows, technological challenges need to be addressed, including improving the maximum visible transmittance (T vis ), maintaining high solar modulating efficiency (∆T sol ), and undergoing more than 10,000 cycles without any degradation [36]. The T vis , ∆T sol , and near-infrared (NIR) switching efficiency (∆T 2500nm ) of all the samples were obtained by the calculation of the transmittance spectra and are displayed in Figure 6. The solar transmittance (T sol , 300-2500 nm) and the ∆T sol values are derived from the following formulas: where T(λ) is defined as the transmittance at wavelength λ and ϕ sol is the solar irradiance spectrum for air mass 1.5 (corresponding to the sun standing 37 • above the horizon) [37]. As shown in Figure 6, the T vis , ∆T sol , and ∆T 2500nm values of the monolayer VO 2 film are 44.6%, 7.2% and 42.7%, respectively. Therefore, the good thermochromic properties with enhanced luminous transmittance is obtained by introducing Cu 50 Zr 50 as buffer layer, possibly because Cu 50 Zr 50 can act as an anti-reflection layer (AR) for VO 2 films. When compared with the VO 2 (60 nm)/glass, the samples of VO 2 (60 nm)/Cu 50 Zr 50 (40 nm)/glass and VO 2 (60 nm)/Cu 50 Zr 50 (80 nm)/glass have higher ∆T sol and ∆ T 2500nm values. According to [28], Cu 50 Zr 50 possesses a metallic property in the infrared region. For the sandwich structure VO 2 /Cu 50 Zr 50 /glass, p-polarized SPPs are supported on the metallic film interfaces in the corresponding range. The appearance of the SPPs probably effectively modulates the optical properties. This mechanism will be further studied in the future [38,39]. When increasing the Cu 50 Zr 50 buffer layer thickness to 160 nm, the ∆T sol and ∆T 2500nm values clearly decreased. The main reason for this is the effect of crystallization quality, which corresponds to the above XRD data analysis. Favorable thermochromic properties are achieved in the sample of VO 2 (60 nm)/Cu 50 Zr 50 (40 nm)/glass. The sample of VO 2 (60 nm)/Cu 50 Zr 50 (40 nm)/glass shows better optical thermochromic performance, and the ∆T sol value is as high as~14.3% with the T vis value up to 52.3% and the ∆T 2500nm value up to 60.2%, which represents a good balance between ∆T sol and T vis for smart window applications. These results can be compared with previous experimental results, such as those for periodic and aperiodic porous VO 2 (M1) films that were prepared through complex chemical and physical processes in multiple layers of TiO 2 (or SiO 2 )/VO 2 /substrate films [40][41][42] and VO 2 -based composite thin films [43,44]. All in all, optimizing optical properties of VO 2 films had indeed been enhanced by the introduction of Cu 50 Zr 50 buffer layer. is obtained by introducing Cu50Zr50 as buffer layer, possibly because Cu50Zr50 can act as an anti-reflection layer (AR) for VO2 films. When compared with the VO2(60 nm)/glass, the samples of VO2(60 nm)/Cu50Zr50(40 nm)/glass and VO2(60 nm)/Cu50Zr50(80 nm)/glass have higher ΔTsol and Δ-T2500nm values. According to [28], Cu50Zr50 possesses a metallic property in the infrared region. For the sandwich structure VO2/Cu50Zr50/glass, p-polarized SPPs are supported on the metallic film interfaces in the corresponding range. The appearance of the SPPs probably effectively modulates the optical properties. This mechanism will be further studied in the future [38,39]. When increasing the Cu50Zr50 buffer layer thickness to 160 nm, the ΔTsol and ΔT2500nm values clearly decreased. The main reason for this is the effect of crystallization quality, which corresponds to the above XRD data analysis. Favorable thermochromic properties are achieved in the sample of VO2(60 nm)/Cu50Zr50(40 nm)/glass. The sample of VO2(60 nm)/Cu50Zr50(40 nm)/glass shows better optical thermochromic performance, and the ΔTsol value is as high as ~14.3% with the Tvis value up to 52.3% and the ΔT2500nm value up to 60.2%, which represents a good balance between ΔTsol and Tvis for smart window applications. These results can be compared with previous experimental results, such as those for periodic and aperiodic porous VO2(M1) films that were prepared through complex chemical and physical processes in multiple layers of TiO2(or SiO2)/VO2/substrate films [40][41][42] and VO2-based composite thin films [43,44]. All in all, optimizing optical properties of VO2 films had indeed been enhanced by the introduction of Cu50Zr50 buffer layer.

Conclusions
To conclude, VO2 thin films with monoclinic crystal phase are here successfully grown on glass substrates by PLD (Plused Laser Deposition) techniques. Cu50Zr50 buffer layers of various thicknesses were introduced to modulate the MIT and optical properties. It is observed that a pronounced smaller ΔH across the MIT is achieved in the optimized VO2 (60 nm)/Cu50Zr50(40 nm)/glass film. The ΔTsol value is as high as ~14.3%, with the Tvis value up to 52.3%. A ΔT2500nm value of up to 60.2% is achieved in the VO2 (60 nm)/Cu50Zr50(40 nm)/glass film. The present study suggests that the introduction of a Cu50Zr50 buffer layer of appropriate thickness on a glass substrate is beneficial to the improvement of crystalline quality and thermochronic properties of VO2 thin films, which makes VO2 a candidate material for use in photoelectronic devices and smart windows.

Conclusions
To conclude, VO 2 thin films with monoclinic crystal phase are here successfully grown on glass substrates by PLD (Plused Laser Deposition) techniques. Cu 50 Zr 50 buffer layers of various thicknesses were introduced to modulate the MIT and optical properties. It is observed that a pronounced smaller ∆H across the MIT is achieved in the optimized VO 2 (60 nm)/Cu 50 Zr 50 (40 nm)/glass film. The ∆T sol value is as high as~14.3%, with the T vis value up to 52.3%. A ∆T 2500nm value of up to 60.2% is achieved in the VO 2 (60 nm)/Cu 50 Zr 50 (40 nm)/glass film. The present study suggests that the introduction of a Cu 50 Zr 50 buffer layer of appropriate thickness on a glass substrate is beneficial to the improvement of crystalline quality and thermochronic properties of VO 2 thin films, which makes VO 2 a candidate material for use in photoelectronic devices and smart windows.