Proceedings of the 2009 4th IEEE InternationalConference on Nano/Micro Engineered and Molecular Systems

January 5-8, 2009, Shenzhen, China

Calculation of phase transformation of vanadium oxide using MDsimulation and its validation by experimental values

Di Wangl#, Xiaodong Chen2

, Qun Zhangl, Yu Liul

, Jincheng Liu3, and Lijiang Hul *

1 Chemistry Department ofScience School, Harbin Institute ofTechnology, Harbin 150001, China

2School ofEconomic and management, Harbin Institute ofTechnology, Harbin 150001, China

3National Key Laboratory ofTunable Laser Technology, Harbin Institute ofTechnology, Harbin 150001, China

II. EXPERIMENTAL PART

III. RESULTS AND DISCUSSIONS

The refractive index (n) can be obtained based on thefollowing equation (2) and the calculation results:

(2)

(1)

When the absorption or refractive index in the higherwavelength range (10600 nm) is obtained using equations (1)and (2), the transmittance (T) in a wavelength range higherthan 6500 nm (10600 nm) can be calculated by using thefollowing expression:

B. Calculation Methodology

The models of vanadium oxide were generated with Chem­3D [12,13]. The simplified structures were optimized withMM2 of Chern-3D. The optimized three-dimensional structureand band structure were calculated by the program of theGaussNet 2000/Parallei (IA32-Linux- GnetRevP) for quantumchemical calculation at the website (Guizhou University). Theband energy was calculated at both Local DensityApproximation (LDA) and Density Function Theory (DFT)levels and with the GDIIS/GDPIS optimizer.

in the wavelength range of 10600 nm. The second aim of thiswork is to validate the phase transition characteristic of vanadiumoxide thin films using experimental values ofhysteresis properties.

A. Preparation ofFilms and Measurements

The preparations and measurements of the experimentalpart were referred to a report ofWang et al group [11].

A. Traditional Optical Equations

The relationship between the absorption (a) and wavelength(A) in the wavelength range of 1800 nm to 6500 nm isestablished based on equation (1) and the results of Gaussprogram calculation [14], expressed as following:

I. INTRODUCTION

Thermochromic vanadium oxide thin films undergo areversible semiconductor-to-metallic phase transition at atransition temperature from a low-temperature monoclinicphase to a high-temperature tetragonal phase [1]. This phasetransition is also accompanied by an important modification ofelectrical resistivity, optical transmittance and reflectance inthe infrared region [2-4]. These thin films are thus excellentmaterials for technological applications such as IR uncooledbolometer, holographic storage systems, fibre-optical switchingdevices, ultrafast switching, smart windows, smart radiatordevices for space craft and photonic crystal [5-8].

In general, vanadium may exist as yO, y 2+, y3+, y4+ and y5+,depending on the oxygen supplied during the film growthprocess. The hysteresis measurement of vanadium oxidematerials is essential to study the time- and temperature­dependent laser-induced phase transformations. The latestinvestigations proved that phase transformations of vanadiumoxide films and hysteresis property are strongly dependent ontemperatures and the size distribution of vanadium oxide grains[9,10].

Abstract - In the first part of this work, a combination of asoftware program (molecular dynamic simulation) andtraditional optical equations are employed to calculate the statedensity and band structures of vanadium oxide (including YO,V02, V20 3 and V20 S) in the wavelength range of 10600 nm toconfirm the presence of phase transformations of vanadium oxide.The calculations show that VO and V20 3 have transitedcompletely from a semiconductor phase to the metallic phase inthe temperature range of 278K to 353K, the transition of the V02

state occurred at a temperature of 341K and V20 S has nottransited in the same temperature range. In the second part ofthis work, the phase transition characteristic of vanadium oxidethin films was reported using experimental values of hysteresisproperties. The influence of the film components on the opticalproperties (transmittance) was studied.

Currently, optical properties of vanadium oxide can becalculated using the Gauss program only in the wavelengthrange of 1800 nm to 6500 nm. The first aim of this work isfocused on a combination of a software program (moleculardynamic simulation) and traditional optical equations tocalculate state density and band structures of vanadium oxide

Keywords - Vanadium oxide, Phase transformations,Transmittance, Quantum mechanical calculation, MD simulation

This project was funded by the Heilongjiang Key Sci. & Tech. Project(Zl00506-02) and the Harbin Key Sci. & Tech. Project (OC07A404), China.

*Contact author: for fabrication aspects ofthis project please contacthuiijiang@vip.sina.com.

#Contact author: for microrobotic aspects ofthis project please contactdiwangl030@126.com.

978-1-4244-4630-8/09/$25.00 ©2009 IEEE 593

T = (l-R)2 +4Rsin2

lf1 (3)exp(a d) +R2 exp(-ad) - 2R cos 2(lp + lfI)

where d is the thickness (125 run) of vanadium oxide thinfilms. R, qJ and VI can be obtained by the following equations[15, 16]:

TABLE 2THE TRANSMITTANCE (%) OF VANADIUM OXIDES (10600 NM)

Temp VO V02 V20 3 V20 S(K)

278 10.10 66.44 22.78 97.09

298 6.12 63.32 21.78 97.11

313 3.07 61.78 20.95 97.02

341 1.90 8.94 18.63 96.80

353 1.79 5.39 16.83 96.69

TABLE 3THE REFRACTIVE INDEX OF VANADIUM OXIDES (10600 NM)

Temp VO V02 V20 3 V20 S(K)

278 9.33 3.54 7.05 2.39

298 10.66 3.54 7.17 2.38

313 13.40 3.79 7.30 2.40

341 15.44 9.18 7.48 2.44

353 15.54 10.53 7.61 2.45

> 14(])............c

0 12$-.I+oJC,,)(])

10......-I

e(/) 8(])

+oJco+oJ 6U)

t+-t0 4»

+oJ.r-t 2(/)

c(])

0 0-10 -8 -6 -4 -2 0 2 4

Energy (eV)

Figure 2. States density OfV20 3 in the temperature range of278K to 353K.

(4)

(5)

(6)

2/indqJ=--

A

R = (n _1)2 + (aA/4/i)2

(n+l)2 + (aA/4/i)2

aA/21llfI =arctan------:.---

n2+ (aA/41l)2-1

% 14

§ -278K+oJ 12 -298kC)

~ 10 -313K~ -341KCIJ

(]) 8~+oJ 6C/)

4-l0 4>.

.;:: 2CIJl:~ 0

-12 -10 -8 -6 -4 -2 0 2 4

B. Calculation ofState Density and Optical Properties

Fig.l and 2 show the state density of VO and V203 in thetemperature range of 278K to 353K. In the figures, both theVO and V20 3 forbidden bands at about -0.7 eV vanishcompletely, indicating the semiconductor-to-metallic phasetransition at a temperature range of278K to 353K. From Table1 and 2, both the absorption and transmittance values of VO,calculating in the wavelength range of 10600 run, are from775.92 (at 278K) to 7035.65 (at 353K) and from 9.33% (at278K) to 15.54% (at 353K), respectively, and the absorptionvalues of V20 3 are from 1452.15 (at 278K) to 2800.07 (at353K), indicating that the VO and V20 3 states have transitedcompletely to the metallic phase in this temperature range.

FnerlZv(eV)

Figure 3. States density ofV02 in the temperature range of278K to 353K.

Figure 1. States density ofVO in the temperature range of278K to 353K.

TABLE 1THE ABSORPTION OF VANADIUM OXIDES (l 0600 NM)

Temp VO V02 V20 3 V20 S(K)

278 775.92 2109.73 1452.15 0.16

298 2994.07 2573.25 1393.16 0.23

313 1126.00 2265.32 1269.33 0.22

341 4587.57 4607.84 2015.60 0.29

353 7035.65 7091.76 2800.07 0.72

> 14(J)

............c0 12$-l

+oJU

~ 10e

CIJ 8(J)

+oJcd

+oJ 6C/:J

~

0 4>.

+oJ'.-l 2CIJc(J)

Q 0-10 -8 -6 -4 -2

Energy(eV)o 2 4

594

Figure 5. Spectral transmittance of films containing 64.11 % V02, 14.77%V20 3, 5.55% VO and 15.57% V20 S• (10600 nm) [11]

Temperature JOC

Fig. 3 shows the state density of V02in the temperaturerange of 278K to 353K. The V02forbidden band at about -0.7eV still exists in the temperature range of 278K to 341K, butthe band narrows at a higher temperature until it almostdisappears at temperatures above 341K. From Table 1, 2 and 3,the absorption, transmittance and refractive index of V02,calculating in the wavelength range of 10600 nm, at thetemperature from 278K to 353K, are from 2109.73 to 7091.76,from 66.44% to 5.39%, and from 3.54 to 10.53, respectively,showing the obviously larger differences, especially at thetemperature from 313K to 341K or higher. Table 4 lists theratio of the optical parameter of the vanadium oxides between313K and 341K. The transmittance ofV02 at 341K is 8 timesas big as the transmittance at 341K. The above informationshows that the transition of the V02 state from a low­temperature semiconductor phase to a high-temperaturemetallic phase has taken place at a temperature of 341K.

80.0

70.0

';:R 60.0~

(1) 50.0

~ 40.0

'i 30.0

~ 20.0

10.0

0.0 .0 10

Cooling

20 30 40 50 60 70

TABLE 4THE RATIO OF OPTICAL PARAMETERSOF VANADIUM OXIDES (10600 NM)

313-341 (K) VO V02 V 20 3 V 20 S

Absorption 4.1 2.0 1.6 1.3

Refractive Index 1.2 2.4 1.0 1.0

Transmittance 1.6 6.9 1.1 1.0

However, the V20 5 forbidden band at about 0.7 eV is stillvisible in the temperature range of 278K to 353K as shown inFig. 4. The absorption, transmittance and refractive index ofV20 5 in the temperature range are not likely changed (seeTable 1-4). This information shows that the transition of theV205 state from a semiconductor phase to a metallic phase hasnot taken place in the temperature range.

> 20(])

18'-......c:0 16~

+oJC,)

14(])......-I

~ 12f/)(]) 10+oJco

+oJ 8U)

~ 60

>. 4.~f/) 2c:(])

Cl 0-8 -6 -4 -2 0 2 4 6

Energy (eV)

Figure 4. States density ofV20 S in the temperature range of278K to 353K.

c. Validation of the Phase Ttransition Characteristic[ll]

Under static heating condition and relatively low intensityof laser radiation, the change in the film transmittance in thetemperature range shows a wider hysteresis profile for thefilms contained more V02 (64.11%), heating from 5°C(transmittence: 70.8%) to 69°C(transmittence: 11.3%), in Fig.5, and narrow hysteresis profile for the films contained smaller

60.0

50.0

~..........40.0(1)

()

=(1)

t 30.0·sCf.)

§ 20.0~

~

10.0

0.0

0 10 20 30 40 50 60 70

Temperature JOC

Figure 6. Spectral transmittance of films containing 39.04 % V02, 28.35%V20 3, 16.52% VO and 18.10% V20 S• (10600 nm) [11]

70.0

60.0

';::R 50.0~

·1

40.0

30.0

~ 20.0Cooling

10.0

0.0

0 10 20 30 40 50 60 70 80

Temperature JOC

Figure 7. Spectral transmittance of films containing 12.82% V02, 41.92%V20 3, 36.72% VO and 6.53% V20 S• (10600 nm) [11]

V02(39.04% and 12.82% respectively) contents as representedin Fig. 6 and 7. The former corresponds to more homogeneousstructure and crystalline properties of V02 grains as comparedto bulk single VO2 crystals [17]. The latter corresponds toamorphous nature with relatively a small among of V02grains

595

and dispersion in the volume. The profiles indicated thatvanadium oxides exhibit reversible semiconductor-to-metallicphase transition at a transition temperature from a low­temperature monoclinic phase to a high-temperature tetragonalphase [18].

IV. CONCLUSIONS

The calculation results show that the va, V02 and V20 3

states have transited completely from a semiconductor phaseto the metallic phase in the temperature range of 278K to353K, however, the transition of the V20 S state has not takenplace in this temperature range. The transition of the V02 statefrom a low-temperature semiconductor phase to a high­temperature metallic phase occurred at a temperature of341K.

The validation of the phase transition properties of thevanadium oxides using experimental data (hysteresis profiles)provides a compliance with the calculation results of moleculardynamic simulation.

ACKNOWLEDGMENT

We acknowledge the Department of Science andTechnology of the Government of Heilongjiang Province andHarbin City, China, for the supporting this work (ZJG0506­02).

We also acknowledge advice and experimental parts fromProfessor Wang and Dr. Tian of National Key Laboratory ofTunable Laser Technology, Harbin Institute ofTechnology.

REFERENCES

[1] M. Soltan, M. Chaker, E. Haddad and R. Kruzelesky, "lx2 opticalswitch devices based on semiconductor-to-metallic phase smarttransition characteristics of V02 coatings" Meas.Sci.Technol., Vol. 17(2006), 1052-1056.

[2] A.L. Pergament, E.L. Kazakova and G.B. Stefanovich, "Optical andelectrical properties of vanadium pentoxide xerogel films: Modificationin electric field and the role of iontran sport" J. Phys. D: Appl. Phys.,Vol. 35 (2002), pp. 2187-2197.

[3] I. S. Jacobs and C. P. Bean, "Fine particles, thin films and exchangeanisotropy," in Magnetism, vol. III, G. T. Rado and H. Suhl, Eds. NewYork: Academic, 1963, pp. 271-350.

[4] K. Y. Tsai, Fong-Hsu Wu, Han-Ping D. Shieh, Tsung-Shune Chin,"Optical switching properties of V02 films driven by using WDM­aligned lasers" Materi. Chem. Phys., Vol. 96 (2006), pp. 331-336.

[5] L. J. Burcham,G. Deo, X. Gao, and I.E. Wachs, "Insitu IR, Raman, andUV-VisDR Sspectroscopy of supported vanadium oxide catalysts duringmethanol oxidation" Top. Catal., Vol. 11/12 (2000), pp. 85-100.

[6] H. Wang, X. Vi, and Y. Li, "Fabrication of V02 films with lowtransition temperature for optical switching applications" Opt. Comm.,256 (2005), pp. 305-309.

[7] O.P. Vinogradova, A.A. Ostrosablina, and A.1. Sidorov, "Nonlinear­optical properties of thick composite media with vanadium dioxidenanoparticles. II. Self-focusing of mid-IR radiation" J. Opt. Tech., Vol.73 (2006), pp. 83-86.

[8] S.A. Pollack, D.B. Chang, F.A. Chudnovky, and LA. Khakhaev,"Passive Q switching and mode-locking of Er:glass lasers usingV02mirrors" J. Appl. Phys., Vol. 78 (1995), pp. 3592-3599.

[9] GJ. Petrovand, and V.V. Yakovlev, "Raman microscopy analysis ofphase transformation mechanisms invanadiumdioxide" J. Elec. Mater.,Vol. 33 (2004), pp. 1023-1025.

[10] S. Chen, H. Ma, X. Vi, T. Xiong, H. Wang, and C. Ke, "Smart V02 thinfilm for protection of sensitive infrared detectors from strong laserradiation," Sensorsand Actuators A, Vol. 115 (2004), pp. 28-31.

[11] X.S. Tian, J.C. Liu, and Q. Wang, "Component effects on the vanadiumoxide thin films phase transition character phenomenon observed,"Laser Phys., Vol. 18 (2008), pp. 1207-1211.

[12] X. Zhang, L. Hu, Y. Huang, D. Sun, and Y. Sun, "Three-dimensionalconfigurations of organic/inorganic hybrid nanostructural blocks: Aquantum mechanical investigation for ladderlike structure ofvinylsilsesquioxane," Sci. Chin. Ser. B Chem., Vol. 47(2004), pp. 388­395.

[13] X. Zhang, L. Hu, D. Sun, and W. Zhao, "Three-dimensionalconfigurations of organic/inorganic hybrid nanostructureal blocks: Aquantum chemical investigation for cage structure of (y­glycidoxypropyl)-sisesquioxane," J. Mol. Struc., Vol. 872 (2008) pp.197-204.

[14] S. Beke, S. Giorgio, L. Krosi, L. Nanai, and W. Marine, "Structural andoptical properties of pulsed laser deposited V20S thin films," Thin SolidFilms, Vol. 516 ( 2008), pp. 4659-4664.

[15] S.A. Pollack, D.B. Chang, F.A. Chudnovky, and LA. Khakhaev,"Passive Q switching and mode-locking of Er: glass lasers using V02mirrors," J. Appl. Phys., Vol. 78 (1995), pp. 3592-3599.

[16] G.B. Altshuler, N.R. Belashenkov, A.A. Solovnin, LA. Khakhaev, andE.A. Chudnovskii, International Laser Optics Conference, S1. PetersburgRussia, 21-25 June 1993, Paper Summary, Part I, pp. 245.

[17] H. Liu, S. Lysenko, A. Rua, V. Vikhnin, G. Zhang, O. Vasquez, and F.E.Fernandez, "Laser excitation and excited state dynamics in vanadiumdioxidethinlm," J. Luminescence, Vol. 119-120 (2006), pp. 404-411.

[18] M. Soltan, M. Chaker, E. Haddad and R. Kruzelesky, "lx2 opticalswitch devices based on semiconductor-to-metallic phase smarttransition characteristics of V02coatings," Meas.Sci.Technol., Vol. 17(2006), pp. 1052-1056.

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