Incorporation of Au nanoparticles into thermoelectric mesoporous ZnO using a reverse triblock copolymer to enhance electrical conductivity

Accepted Manuscript Incorporation of Au nanoparticles into thermoelectric mesoporous ZnO using a reverse triblock copolymer to enhance electrical conductivity Min-Hee Hong, Wooje Han, Hyung-Ho Park PII:

S0254-0584(18)30247-5

DOI:

10.1016/j.matchemphys.2018.03.077

Reference:

MAC 20480

To appear in:

Materials Chemistry and Physics

Received Date: 6 February 2018 Revised Date:

20 March 2018

Accepted Date: 25 March 2018

Please cite this article as: M.-H. Hong, W. Han, H.-H. Park, Incorporation of Au nanoparticles into thermoelectric mesoporous ZnO using a reverse triblock copolymer to enhance electrical conductivity, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.03.077. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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ACCEPTED MANUSCRIPT

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Incorporation of Au nanoparticles into thermoelectric mesoporous ZnO using a reverse triblock copolymer to

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enhance electrical conductivity Min-Hee Hong, Wooje Han, Hyung-Ho Park*

Republic of Korea

Telephone: +82-2-2123-2853 Fax: +82-2-312-5375

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*Corresponding Author: Prof. Hyung-Ho Park

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Department of Materials Science and Engineering, Yonsei University, Seoul, 03722,

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Abstract

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E-mail: [email protected]

Since the thermoelectric properties are proportional to the electrical conductivity and inversely proportional to the thermal conductivity, independent control of thermal conductivity and electrical conductivity is essential. Therefore, in this study, mesoporous structure was applied to decrease thermal conductivity. And, Au NPs were incorporated to increase the electrical conductivity. Reverse triblock copolymer and cosolvent system were introduced for uniform dispersion of Au NPs. The collapse of the pore structure was minimized due to the uniform dispersion of Au NPs and the porosity increased by 10% from

ACCEPTED MANUSCRIPT 20% to 30% when compared with pristine ZnO thin films. A mesoporous ZnO composite thin film containing 1 at% Au NPs exhibited an electrical conductivity that was five times greater than that of a pristine mesoporous ZnO thin film. In addition, the power factor increased by

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about 3.5 times, from 9.53 ± 1.50 µW/mK2 to 32.72 ± 5.16 µW/mK2 at 503 K.

Keywords: thermoelectric; mesoporous ZnO thin film; Au nanoparticle; reverse triblock

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copolymer; co-solvent system

Introduction

The depletion of fossil fuels has generated great interest in alternative sources of energy [1-8], with much progress being made in the related technologies. Thermoelectric generation

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is a representative next-generation energy technology since it is non-polluting and enables the utilization of renewable energy. Here, “thermoelectric” refers to the direct conversion of

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waste heat into useful electricity. When a temperature gradient is produced in a thermoelectric material, an electric current is generated. The dimensionless figure of merit

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(ZT = S2σT/κ), which is a representative thermoelectric property, is based on the Seebeck coefficient (S), electrical conductivity (σ), thermal conductivity (κ), and temperature (T). To enhance the thermoelectric properties, much research has been undertaken with the goal of increasing both the Seebeck coefficient [9] and the electrical conductivity [10], as well as decreasing the thermal conductivity [11]. Herein, we examined the use of ZnO with a mesoporous structure, which limits its thermal conductivity by increasing the phonon scattering [12]. ZnO is a very useful n-type, wide band-gap, semiconductor material, which exhibits excellent electronic, optical, and photonic properties [13–15]. It was selected for use

ACCEPTED MANUSCRIPT as a thermoelectric material in the present study because of its high thermal stability and electrical conductivity. Furthermore, the mesoporous structure was produced by an evaporation-induced self-assembly (EISA) process [16, 17]. In the EISA process, a surfactant

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forms micelles above the critical micelle concentration (CMC). The CMC can be attained during material processing through aging, vacuuming, annealing, and especially spin-coating in the case of film preparation. In the present study, the spin-coating process was adopted to

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prepare the mesoporous ZnO films. When the solvent is rapidly evaporated in the spincoating process, the concentration of the surfactant concentration exceeds the CMC, causing

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the EISA process to occur. These micelles become regularly arranged in the film due to intermicellar electrostatic repulsion. During calcination, the organic micelles decompose so that an ordered pore structure is obtained. This ordered pore structure dramatically decreases the thermal conductivity because the ordered pores act as scattering centers for phonons.

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However, the ordered structure also decreases the electrical conductivity because the ordered pores can also scatter electrons. In other words, electrical conductivity and thermal conductivity are proportional to one another. Although the decrease in thermal conductivity is

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greater than the decrease in electrical conductivity because of the longer mean free path of the phonons compared to the electrons, the diminished electrical conductivity remains a

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challenge that must be overcome to enable the application of the material to thermoelectrics [18]. Therefore, during the preparation of thermoelectric materials with mesoporous structures, increasing the electrical conductivity while maintaining the pore structure is a key issue affecting the enhancement of the thermoelectric properties. It was previously reported that the incorporation of Au nanoparticles (NPs) increases the electrical conductivity due to the surface plasmon effect [19]. Therefore, in the present study, Au NPs were incorporated into mesoporous ZnO to increase the electrical conductivity. In our previous work, an ordered mesoporous structure was found to be a better thermal insulator than a disordered structure

ACCEPTED MANUSCRIPT [20]. In the present study, mesoporous ZnO nanocomposite thin films incorporating Au NPs were synthesized using poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) triblock copolymers with a reverse micelle structure and an Au precursor

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with a hydrophilic ligand. When a micelle is formed, a PEO chain, which is hydrophilic, positions itself inside the micelle. Thus, Au NPs could be synthesized in the pores by taking advantage of the hydrophilic–hydrophilic attraction between the Au precursor and the tri-

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block copolymer. In PPO-PEO-PPO, the hydrophobic PPO blocks at both ends exhibit a significant hydrophobic effect, and these hydrophobic segments form a hard micellar

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structure [21].

To produce a reverse micelle structure, a co-solvent was used because the reverse triblock copolymer is hydrophobic. Since the hydrophilicity of a solvent is closely related to its dipole moment, a co-solvent system based on acetone exhibits less hydrophilicity than n-

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PrOH due to the smaller dipole moment of acetone; at room temperature, the dipole moments of n-propanol and acetone are 3.09 and 2.69, respectively [22]. Therefore, acetone was used to control the hydrophilicity of the solvent. Using the co-solvent system, the micelle structure

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could be synthesized well, thus improving the pore arrangement. Thus, the Au NPs could be uniformly distributed in the pores. In the present study, the effects of Au NP incorporation

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and co-solvent application on the pore structure, crystallinity, porosity, and thermoelectric properties were analyzed.

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Experimental procedure In this paper, mesoporous ZnO composite thin films with Au NPs were synthesized

through sol-gel and simple one-pot processes. In this experiment, SiO2 / Si substrate was

ACCEPTED MANUSCRIPT used, and acetone, ethanol, and DI water were cleaned after sonification for 15 min. npropanol / acetone, zinc acetate dehydrate [Zn(CH3COO)2⋅H2O] and monoethanolamine (MEA) were used as solvent, ZnO precursor and complex agent, respectively. HAuCl4 and

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pluronic 10R5 were used as Au precursor and surfactant. The ratio of zinc acetate dihydrate: MEA: pluronic 10R5 was set to 1:0.05:1:34.5 molar ratio. In the case of a single solvent (npropanol), zinc acetate dihydrate: n-propanol was added in a 1: 34.5 molar ratio and in the

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case of a co-solvent system, the weight ratio of n-propanol and acetone was 1: 1. In the case of the addition of Au NPs, HAuCl4 was added to the sol by calculating the atomic ratio of

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Au: Zn to 1: 100 since 1 at.% Au NPs additionally minimized the collapse of the pore structure [23]. First, the pluronic 10R5 is dissolved in the solvent and stirred for 1 h. Then, HAuCl4, zinc acetate dihydrate and MEA are added to make a sol. The synthesized sol is stirred for 24 h to make a stable solution. The as-synthesized sol is spin-coated on the cleaned

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SiO2 / Si substrate at 3000 rpm for 30 seconds. Then, pyrolyze the film on a hotplate for 10 min at 300°C for residual organic decomposition. Mesoporous ZnO composite thin films incorporating Au NPs were synthesized after annealing at 450°C for 4 h at a heating rate of

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1 °C/min. The crystallinity of the mesoporous ZnO thin films was analyzed using wide-angle X-ray diffraction (WAXRD). Then, using the full-width at half-maximum (FWHM) value

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and Scherrer equations, the grain/crystalline size was calculated [24]. The pore arrangement in the mesoporous ZnO thin films was analyzed using small-angle X-ray diffraction (SAXRD) in the 2θ range from 1° to 5° using Cu K radiation (1.5418 Å). Grazing-incidence smallangle X-ray scattering (GISAXS) was performed at the 3C beam line ( = 1.24 Å and ∆E/E = 2 × 10−4) of the Pohang Light Source (PLS) in Korea [25]. A vacuum of 10-2 torr was applied to the sample chamber to fix the sample to the beamline position, depletion of fossil and the sample to detector distance (SDD) was fixed at 2 m to analyze the alignment between 3 nm and 78 nm. The surface morphology was analyzed using field emission scanning electron

ACCEPTED MANUSCRIPT microscopy (FE-SEM, JEOL, JSM 7001F), while energy-dispersive X-ray (EDX) analysis was used to perform elemental mapping of the surface. The porosity of the mesoporous ZnO thin films was measured using an ellipsometer (Gatan L117C, 632.8-nm He-Ne lasers) and

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the Lorentz-Lorenz equation [26]. The Seebeck coefficients and electrical resistivity of the mesoporous ZnO thin films were measured by determining the Seebeck voltage and the

Results and discussion

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temperature difference from 383 K to 503 K at 30° intervals.

To investigate the crystallinity of the ZnO thin films incorporating Au NPs through the application of a co-solvent system, wide-angle XRD was performed, the results of which are shown in Fig. 1. XRD is a device for analyzing crystal structure. When the Bragg equation is satisfied, a peak occurs. The regular, repetitive, and periodic interplanar distance of the

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crystal can be calculated through the Bragg equation. All the ZnO thin films were found to exhibit a hexagonal wurtzite structure. The diffraction peaks at 2θ values of approximately 31.77°, 33.44°, 36.24°, 47.54°, and 56.64° were indexed to 100, 002, 101, 102, and 110,

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respectively [27]. The presence of Au NPs could be confirmed from the Au 111 diffraction

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peak at 38.2°. The size of the Au NPs, as calculated using the Scherrer equation with a full width at half maximum (FWHM) value of Au 111, was around 15.0 nm [24]. Despite the Au NP incorporation and the introduction of the co-solvent system, the crystallization of the ZnO was not affected. The grain sizes of ZnO, with and without the Au NPs, as calculated using the Scherrer equation, were 16.8 and 17.1 nm for n-PrOH, and 17.6 and 16.5 nm for the cosolvent system. From these results, we could confirm that Au NP incorporation and the introduction of a co-solvent system did not affect the hexagonal wurtzite structure or grain growth of mesoporous ZnO thin films.

ACCEPTED MANUSCRIPT The presence of Au NPs was also confirmed by transmission electron microscopy (TEM) observation and EDX analysis, as shown in Fig. 2. The Au NPs, about 15 nm in size, were incorporated into the mesoporous ZnO structure. The size of the Au NP in this TEM image

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was in good agreement with the results obtained by XRD (Fig. 1). To confirm the distribution of the Au NPs in the mesoporous ZnO matrix, EDX data and an Au element distribution map were obtained by SEM, as shown in Fig. 3. The presence of

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the Au NPs in the ZnO was confirmed from the Au M X-ray signal (around 2.12 keV) in the EDX map and the wide but relatively intense distribution of the Au signal in the element

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distribution map.

The changes in the pore structure followed by Au NP incorporation and the use of the cosolvent system were analyzed by SAXRD. The results are shown in Fig. 4. The appearance of diffraction peaks in the SAXRD results indicates that an ordered structure was formed in the

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thin films. As shown in Fig. 4, the mesoporous ZnO thin films have broad diffraction peaks with relatively low peak intensities, relative to those of conventional mesoporous SiO2 and TiO2 [28]. This is because, given the high reactivity of the Zn ion precursor, the three-

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dimensional micelle structure is difficult to form. Therefore, it is more difficult to form the Zn–O bonds of the ZnO lattice through hydrolysis and condensation reactions than it is for

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the Si–O and Ti–O bonds of SiO2 and TiO2 lattices, respectively [29, 30]. Therefore, in this paper, by introducing a reverse triblock copolymer and a cosolvent system, it is possible to synthesize regular micelle form. Generally, triblock copolymers have both hydrophilic and hydrophobic properties, so the micelle structure varies greatly depending on the type of solvent. [31]. Therefore, when the reverse triblock copolymer is used, the PEO chain is located inside the micelle. Hence, the reverse triblock copolymer (PPO-PEO-PPO) exhibits more predominant amphiphilic properties with predominant hydrophobicity than the micelle-structured (PEO-PPO-PEO) surfactant [32]. Therefore, in

ACCEPTED MANUSCRIPT order to induce regular micelle formation of the reverse triblock copolymer with hydrophobic properties, the dipole moment was controlled by introducing acetone-added cosolvent system. These reverse triblock copolymers help to attract Au NPs into the pores because hydrophilic

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PEO chains are formed inside the micelle. Therefore, in this work, the co-solvent system was applied, the overall SAXRD peak intensity increased significantly.

Consequently, Au NPs could form inside the micelle since the Au precursor has a

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hydrophilic ligand [33]. Therefore, with the application of the co-solvent system, Au NPs were uniformly incorporated into the pore structure. As shown in Fig. 4(b), the SAXRD peak

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intensity decreases slightly with the incorporation of the Au NPs. Since Au NPs were uniformly distributed as they are impregnated into the pores, the SAXRD peak intensity is not reduced because the regular structure is not significantly destroyed by the addition of Au NPs.

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To enable the more accurate analysis of the effect of Au NP incorporation on the pore structure of mesoporous ZnO, a GISAXS analysis carried out and the results of which are shown in Fig. 5. Normally, the GISAXS wing pattern corresponds to a thin film with an

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ordered structure [25]. GISAXS is a device that analyzes scattering by electrons contained in atoms that make up a material when irradiated with highly focused synchrotron radiation.

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Since the wavelength of the X-ray is smaller than the distance between the atoms, the scattered X-rays at different atoms can be analyzed through GISAXS. In this paper, pore structure is analyzed using GISAXS wing pattern. In the case of mesoporous ZnO prepared using the co-solvent system, however, the GISAXS wing pattern originates from the ordered pore structure. Interestingly, although the GISAXS wing pattern collapsed as a result of the Au NP incorporation, the pore arrangement was maintained because the Au NPs were uniformly distributed in the pores through the hydrophilic–hydrophilic interaction. The SAXRD and GISAXS results shown in Figs. 4 and 5 indicate that an ordered pore structure

ACCEPTED MANUSCRIPT was well synthesized when using the co-solvent system. When Au NPs were incorporated into the ZnO pore structure, the GISAXS wing pattern intensity decreased due to the size of the Au NPs (15 nm). Therefore, the micelle structure partially collapsed. This collapse of the

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pore arrangement could be confirmed quantitatively by the result shown in Fig. S1. The integrated intensity of the SAXRD peak, which shows the degree of pore arrangement, decreased to about 4% (from 3987 to 3829) as a result of the addition of the Au NPs,

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indicating that the pore alignment was affected.

The effects of the co-solvent and the incorporation of Au NPs into mesoporous ZnO thin

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films were also confirmed by porosity measurements. In this study, ellipsometry was used to measure the refractive index of the thin film, and the calculated porosity of the thin film was calculated using the Lorentz-Lorenz equation. Within the visible light range, each material has an inherent refractive index, and if there are pores in the material, the refractive index

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decreased. The Lorentz-Lorenz equation can be used to calculate the porosity change due to the refractive index difference between the material and the structure. The overall porosity changes in the mesoporous ZnO nanocomposite thin films were calculated using the Lorentz-

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Lorenz equation [26].

1−

=

−1 +2 −1 +2

Here, Fp is the pore volume fraction, nf is the refractive index of the films, and ns is the refractive index of the structure. The refractive index of the films, nf, was obtained using ellipsometry. To determine the refractive index of the structure (ns), the refractive index of ZnO was assumed to be 2.1 [34] and that of Au was assumed to be 0.2 [35]. Thus, an ns value

ACCEPTED MANUSCRIPT of 2.081 was obtained for ZnO with a 1 at% Au NP content (2.1 x 99% + 0.2 x 1%). As shown in Table 1, the mesoporous ZnO nanocomposite thin films prepared using the cosolvent system exhibited higher porosities (29.54%) than those prepared using the n-PrOH

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single-solvent system (24.23%), due to the enhanced pore arrangement. Moreover, when Au NPs were incorporated into the mesoporous ZnO thin films, the porosity decreased slightly; this result was in good agreement with the SAXRD and GISAXS results. In particular, the

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decrease in the porosity of a mesoporous ZnO film prepared using the co-solvent system (around 3%) was twice of that of a mesoporous ZnO film prepared using the n-PrOH single-

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solvent system (around 1.5%). This result further confirms the better distribution of Au NPs in the pores when the co-solvent system is used.

The changes in the thermoelectric properties of mesoporous ZnO nanocomposite thin films incorporating Au NPs were measured. The results, shown in Fig. 6, indicate that the

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electrical conductivity increased with the incorporation of the Au NPs, as a result of the uniform distribution of the Au NPs and the decrease in the porosity. The Seebeck coefficient has a negative value because ZnO is an n-type semiconductor and the coefficient exhibits an

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inverse relationship to the electrical conductivity. As shown in Fig. 6, the electrical conductivity of the ZnO films increased by more than five times, from 3.5 to 20.4 /Ωcm at

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503 K, as a result of the use of the co-solvent system and the incorporation of the Au NPs. The incorporation of Au NPs into the ZnO structure caused the electrical conductivity to increase as a result of the surface plasmon effect [19]. With the incorporation of the Au NPs into the ZnO structure, electrons could be transferred from the Au surface to the ZnO. Therefore, electrons accumulated at the interface and, given the ease with which the electrons could be transferred, the electrical conductivity increased. However, the Seebeck coefficient decreased by 23.6%, from -165 to -126 µV/K at 503 K. Therefore, it can be concluded that the thermoelectric properties of ZnO were enhanced because the increase in the electrical

ACCEPTED MANUSCRIPT conductivity greatly outweighs the decrease in the Seebeck coefficient. At 503 K, the power factor had increased by 3.5 times, from 9.53 ± 1.50 µW/mK2 to 32.72 ± 5.16 µW/mK2, due to the use of the co-solvent system and the Au NPs. Overall, it was confirmed that the

incorporation of distribution-controlled metal NPs.

Conclusion

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thermoelectric properties of mesoporous oxide materials could be enhanced through the

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In the present study, mesoporous ZnO nanocomposite thin films incorporating Au NPs were successfully synthesized using a reverse triblock copolymer and a co-solvent system. The Au NPs were incorporated into the pores through controlled formation using the PPO-PEO-PPO triblock copolymer surfactant to enhance the electrical conductivity of mesoporous ZnO films as a result of their surface plasmon effect. Acetone was used as a co-solvent for n-PrOH to

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facilitate the formation of the mesoporous structure by increasing the hydrophobicity of the solvent. XRD, SAXRD, and GISAXS analyses revealed that an enhanced mesoporous structure was obtained with the co-solvent system, and that the incorporation of Au NPs did

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not affect the crystallization of the skeleton-structured ZnO or the ordering of the pores in the

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mesoporous ZnO film. Moreover, as a result of using the co-solvent system and reverse triblock copolymer, the porosity increased from 24.23 to 29.54%. Further, with the incorporation of the Au NPs into the mesoporous ZnO thin films, the electrical conductivity increased by more than five times, while the Seebeck coefficient decreased by 23.6%. Our findings indicate that incorporating metal NPs into mesoporous thin films could enable their application as thermoelectric materials due to their enhanced porosity and electrical conductivity, with a minimal reduction in the Seebeck coefficient.

ACCEPTED MANUSCRIPT Supporting Information For supporting Information, see Supplementary Materials in the online publication of this

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article.

Acknowledgements

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This work was supported by 'Korea-Africa Joint Research Program' grant funded by the Korea government (Ministry of Science, Technology & ICT) in 2017K1A3A1A09085891.

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This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(NRF2015R1D1A1A02062229). Experiments at PLS were supported in part by MEST and

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POSTECH.

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ACCEPTED MANUSCRIPT Figure captions Fig. 1 Wide angle XRD patterns of mesoporous ZnO nanocomposite thin films prepared using n-PrOH single-solvent system and n-PrOH/acetone co-solvent system: (a) without and

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(b) with Au NPs. Fig. 2. TEM image of Au NPs incorporated mesoporous ZnO composite thin films.

ZnO thin films prepared using the co-solvent system.

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Fig. 3 EDX spectra and Zn, O, and Au element maps of Au NP-incorporated mesoporous

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Fig. 4 Small angle XRD patterns of mesoporous ZnO nanocomposite thin films prepared using n-PrOH single-solvent system and n-PrOH/acetone co-solvent system: (a) without and (b) with Au NPs.

Fig. 5 GISAXS patterns of mesoporous ZnO nanocomposite thin films prepared using n-

Au NPs.

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PrOH single-solvent system and n-PrOH/acetone co-solvent system: (a) without and (b) with

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Fig. 6 (a) electrical conductivity and (b) Seebeck coefficient of mesoporous ZnO nanocomposite thin films prepared using n-PrOH single-solvent system and n-PrOH/acetone

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co-solvent system with or without Au NPs.

ACCEPTED MANUSCRIPT Table 1. Refractive index of structure (ns), refractive index of thin films (nf), and calculated porosity of mesoporous ZnO thin films prepared using n-PrOH single solvent system and n-PrOH/acetone co-

Refractive index

Refractive index

Calculated porosity

of structure (ns)

of thin films (nf)

of thin films (%)

2.1

1.739±0.003

2.1

1.673±0.003

2.081

1.747±0.003

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solvent system

2.081

1.698±0.003

26.74±0.24

n-PrOH + Acetone (without Au) n-PrOH(with Au) n-PrOH + Acetone

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(with Au)

24.23±0.25 29.54±0.25 22.83±0.23

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n-PrOH(without Au)

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n-PrOH

25

30

35

40

45

2q (deg.)

50

55

60

(002)

(101)

(100)

mesoporous ZnO with Au NPs n-PrOH + acetone (110)

(102)

Au (111)

(110)

(102)

n-PrOH + acetone

Intensity (arb. units)

(101)

(b)

mesoporous ZnO without Au NPs

(002)

Intensity (arb. units)

(100)

(a)

n-PrOH 25

30

35

40

45

2q (deg.)

50

55

60

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Au NPs

Cu (grid)

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Zn

ZnO Au-ZnO

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Intensity (arb. units)

Au M

Si K

Zn L

OK

0.0

0.5

1.0

1.5

2.0

2.5

3.0

500 nm

3.5

4.0

Energy (keV)

O

Au

500 nm

500 nm

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(a)

(b)

n-PrOH + acetone

n-PrOH

1

2

3

2q (deg.)

4

mesoporous ZnO with Au NPs

Intensity (arb. units)

Intensity (arb. units)

mesoporous ZnO without Au NPs

5

n-PrOH + acetone

n-PrOH

1

2

3

2q (deg.)

4

5

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n-PrOH

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(a)

n-PrOH + acetone

without Au NPs

(b)

n-PrOH

n-PrOH + acetone with Au NPs

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Conductivity(/Wcm)

102

n-PrOH n-PrOH+acetone n-PrOH (Au NPs) n-PrOH+acetone (Au NPs)

1

10

100

390

420

450

480

Temperature (K)

510

Seebeck Coefficient(mV/K)

(b)

(a)

-30

n-PrOH n-PrOH+acetone n-PrOH (Au NPs) n-PrOH+acetone (Au NPs)

-60 -90 -120 -150 -180 -210

390

420

450

480

Temperature (K)

510

ACCEPTED MANUSCRIPT Highlights

Au incorporated mesoporous ZnO thin films were synthesized with Pluronic 10R5.

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Pluronic 10R5 surfactant led to a uniform distribution of Au nanoparticles. Co-solvent system played an important role to synthesize mesoporous structure.

Applying co-solvent system and Au nanoparticles improved thermoelectric

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properties.

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Incorporation of Au nanoparticles into thermoelectric mesoporous ZnO using a reverse triblock copolymer to

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enhance electrical conductivity

Min-Hee Hong, Wooje Han, Hyung-Ho Park*

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Department of Materials Science and Engineering, Yonsei University, Seoul, 03722,

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Republic of Korea

*Corresponding Author: Prof. Hyung-Ho Park

Telephone: +82-2-2123-2853, Fax: +82-2-312-5375

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E-mail: [email protected]

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Figure S1 shows SAXRD integrated intensity value of mesoporous ZnO nanocomposite thin films prepared using single/cosolvent and Au NPs incorporation. As shown at Fig. S1, when co-solvent system was applied, integrated intensity increased when comparing with single solvent used system (n-PrOH).

This intensity increase

was followed by pore arrangement. As the reverse triblock copolymer was used, it is more likely to synthesize regular micellar structures in the cosolvent system. The

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interpore distance was calculated as 5 nm for the single solvent system and 6 nm for the cosolvent system when calculating the interpore distance to the inflection point of the

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integrated intensity.

Figure S2 shows GISAXS 2d intensity distribution of mesoporous ZnO

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nanocomposite thin films prepared using n-PrOH single-solvent system and

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n-PrOH/acetone co-solvent system.

As shown at Fig. S2, the cosolvent system improves the pore arrangement. Also, interpore distance could be calculated from GISAXS 2d graph, which is calculated as 15

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nm along with in-plane direction.

Figure S1. Integrated intensity value of mesoporous ZnO nanocomposite thin films prepared using n-PrOH single-solvent system and n-PrOH/acetone co-solvent system.

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Figure S2. GISAXS 2d intensity distribution of mesoporous ZnO nanocomposite thin films prepared using n-PrOH single-solvent system and n-PrOH/acetone co-solvent

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system.