- Email: [email protected]
Microstructure and optical absorption property of Au nanoparticles and Au, Ag bimetal nanoparticles separately dispersed Al2O3 composite films
Journal of Alloys and Compounds 691 (2017) 772e777
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Microstructure and optical absorption property of Au nanoparticles and Au, Ag bimetal nanoparticles separately dispersed Al2O3 composite films Cuihua Zhao a, Baishi Li a, Junli Du a, Jianhua Chen b, *, Yuqiong Li b, ** a b
College of Material Science and Engineering, Guangxi University, Nanning 530004, China Guangxi Colleges and University Key Laboratory of Minerals Engineering, Guangxi University, Nanning 530004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 July 2016 Received in revised form 27 August 2016 Accepted 31 August 2016 Available online 1 September 2016
Au nanoparticles and Au, Ag bimetal nanoparticles separately dispersed Al2O3 composite films were prepared by sol-gel method. The microstructure and optical property of the films were studied by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and ultravioletevisible (UV/vis) absorption spectra. Gold in Au/Al2O3, and gold and silver in AuAg/Al2O3 composite films exist in the state of metal Au and Ag, and they are basically spherical nanoparticles. The optical absorption peaks of Au nanoparticles due to the surface plasmon resonance (SPR) in Au/Al2O3 films were observed in the range of 530e550 nm, and their absorptions intensity with the increase of Au contents. There are two SPR peaks corresponding to Au and Ag nanoparticles, which were observed in the range of 530e550 nm, 400e420 nm, respectively. The intensities of two SPR peaks change with various molar ratios of Au and Ag nanoparticles. The SPR peaks of Au nanoparticles intensity, and those of Ag nanoparticles weaken with the increase of Au contents, and decrease of Ag contents. The SPR speaks of Au and Ag nanoparticles shift slightly to the longer wavelength with an increase of Au and Ag contents in AuAg/Al2O3 composite films. © 2016 Elsevier B.V. All rights reserved.
Keywords: Au/Al2O3 AuAg/Al2O3 Sol-gel Microstructure Optical property
1. Introduction Composite films consisting of noble metal nanoparticles are gaining extreme attention because of their potential applications in optical switching [1,2], optoelectronic devices [3], optical limiters [4], optical waveguides [5], and ultrafast optical communication systems [6], etc. The linear and nonlinear optical properties of metal nanoparticles dispersed oxide film have been largely studied in the recent years, however, new systems and new phenomena are emerging in an endless stream. The main reason is still their significant promise in a variety of applications. The optical property of these nanocomposite films depends not only on the size, shape and volume fraction of metal nanoparticles, but also on the refractive indexes of the dielectric substrates. Therefore, the choice of the appropriate light wavelength, the host materials for the metallic nanoparticles as well as their nature and concentration are crucial
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Chen), [email protected] (Y. Li). http://dx.doi.org/10.1016/j.jallcom.2016.08.332 0925-8388/© 2016 Elsevier B.V. All rights reserved.
for dedicated application, such as light modulators, optical amplifiers and sensors. In the past decades, much attention has been paid to the changes of volume fraction of metal nanoparticles, and the composite of nanoparticles embedded in various matrices (TiO2, ZnO, BaTiO3, SiO2 and so on) for single metal dispersed composite films [7e12]. Although the intensity and frequency of SPR speak can be adjusted by changing the size, shape, content of nanoparticles and the types of the matrix, it is not always easy to control over particle size and shape, and require very specific and demanding reaction conditions. In recent years, bimetallic nanoparticles dispersed systems have been produced, mainly including two types of integration patterns: metal alloys [13e18] and core-shell NPs [19,20]. The bimetallic nanoparticles show unique structural, electronic, optical and catalytic properties than single metal samples, and can be used in different fields. For example, Bankura et al. prepared the silver-gold alloy nanoparticles by reduction of the correspondent metal precursors aqueous dextran solution for antimicrobial applications [15]. Li et al. fabricated Au-Ag alloy modified ZnO nanocomposite films by sol-gel method for photocatalytic application [16].
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
It is very difficult to prepare Au-Ag bimetal separately dispersed composite films because of nearly identical bulk lattice constants of Au and Ag [21]. As a result, the study on Au-Ag bimetal nanoparticles separately dispersed system is very rare. Our research group prepared Ag-Au bimetal dispersed separate SiO2 composite films [21]. To obtain the Ag-Au bimetal nanoparticles, the chemical solution approach combining with a sol-gel spin-coating process was used. First of all, Au/SiO2 and Ag/SiO2 precursor solutions with required molar ratio were prepared respectively. Then the Ag-Au bimetal dispersed separate films were obtained by the spincoating Aux/(SiO2)0.5x and Agy/(SiO2)0.5y films one after another on a SiO2 glass substrate. The composite films possess two SPR peaks. The unique optical properties widen the application field for composite films containing noble metal nanoparticles. In this paper, Au nanoparticles and Au, Ag bimetal nanoparticles separately dispersed Al2O3 composite films were prepared using sol-gel method. Matrix Al2O3 was chosen for its thermal stability up to high temperature, large band-offset and similar band gap to SiO2. And our research demonstrated that the Ag/Al2O3 nano-composite thin films have strong optical absorption property [7]. Therefore, we deduce that Au nanoparticles and Au, Ag bimetal nanoparticles dispersed Al2O3 composite films should have good nonlinear optical properties, and different matrix (Al2O3) may lead to different optical characteristics with Au-Ag bimetal dispersed SiO2 composite films. In addition, the preparing process of this study is more simple than that of (Ag, Au)/SiO2 thin films [21]. Only a precursor solution (AuAg/Al2O3) was prepared in the preparing process of AuAg/Al2O3 thin film. Ag and Au bimetal dispersed separate nanoparticles were obtained by controlling the preparing techniques, including the aging time of the sol, the pyrolyzing temperature and time, annealing temperature and time. And the microstructure and optical property of thin films were studied with a special emphasis on the influences of different molar ratio of Au and Ag nanoparticles. 2. Experiment procedures 2.1. Preparation of Au/Al2O3 and AuAg/Al2O3 precursor solution Aluminum trisecbutoxide ((C4H9O)3Al) and chloroauric (HAuCl4$4H2O) were used as raw materials. Isopropyl alcohol (CH(CH3)2OH), acetoacetate (C6H10O3) and distilled water were used as solvents. The molar ratio of (C4H9O)3Al, CH(CH3)2OH, C6H10O3, and H2O is 1:20:1:4. ((C4H9O)3Al) and (CH(CH3)2OH) were mixed, and stirred magnetically for 0.5 h at room temperature. A certain amount of C6H10O3 was added to the mixture, and stirred for 2 h again. Then the distilled water was added, and stirred for 1 h again. A transparent matrix solution was obtained. HAuCl4.4H2O was added into the matrix solution with molar ratio of Au/(Au þ Al2O3) ¼ 2, 5, 8 and 10 mol% followed by stirring for 1.5 h. Then the transparent precursor Au/Al2O3 solutions were obtained. When preparing the AuAg/Al2O3 precursor solution, AgNO3 was first added into the matrix solution followed by stirring for 2 h, then HAuCl4.4H2O was added into the mixture. The molar ratio of Au, Ag and Al2O3 matches with AuxAg0.4x(Al2O3)0.6 with x ¼ 0.02, 0.06 and 0.10. After further stirring for 2 h, the transparent precursor AuAg/Al2O3 precursor solutions were obtained.
773
oven. The substrates were rotated at the rate of 200e300 rpm for 9 s and later at 2000e3000 rpm for 30 s for Au/Al2O3 thin film, 200 rpm for 40 s and later 3200 rpm for 1 min for AuAg/Al2O3 thin films. After one coating, the films were pyrolysized at about 200 C for 30 s for Au/Al2O3, 180 C for 1 min for AuAg/Al2O3 thin films to remove the solvent and a small amount of water. These sequences of coating and pyrolysis treatment were repeated 2 times for optical absorption samples and for 8 times for the X-ray diffraction (XRD) samples. The two-layer films are about 60 nm in thickness. The pyrolysized samples were annealed at 700 C for 30 min in air, and Au/Al2O3 thin films and AuAg/Al2O3 thin films were obtained. 2.3. Characterization Ag/Al2O3 and AuAg/Al2O3 nanocomposite films The crystalline phases of the films were characterized by XRD (Cu Ka radiation with a wavelength of l ¼ 0.15418 nm). The microstructures of the films were observed by TEM (JEM-100CG). The XPS spectra were measured using monochromatic Al Ka radiation (1486.6 eV) as the X-ray source (PHI-5300 ESCA). The absorption spectra of thin films were measured at room temperature in air by a UVevisible spectrophotometer (LAMBDA 950). 3. Results and discussion Fig. 1 shows the XRD patterns of Au0.1/(Al2O3)0.9 and Au0.1Ag0.3/ (Al2O3)0.6 composite films with the result of corresponding one of pure Al2O3 films for comparison. There is no any sharp diffraction peak for the pure Al2O3 film. There are four diffraction peaks at 38.08 , 44.30 , 64.65 and 77.68 for the Au0.1/(Al2O3)0.9 film, which correspond to (111), (200), (220) and (311) crystal planes of Au (PDF04-0784). The XRD curve of the Au0.1Ag0.3/(Al2O3)0.6 composite film is very similar with that of the Au0.1/(Al2O3)0.9 film except for the peak intensity. The diffraction peaks at 38.08 , 44.30 , 64.65 and 77.68 may correspond to (111), (200), (220) and (311) crystal planes of Au (PDF#04-0784) or Ag (PDF#04-0783) or Au-Ag alloy. Au and Ag possess the same face-centered-cubic (fcc) structure with almost the same bulk lattice parameter as described in our previous study [21]. Therefore, the chemical state of Au and Ag existence cannot be determined here. The intensities of XRD peaks for Au0.1Ag0.3/(Al2O3)0.6 are larger than that of Au0.1/(Al2O3)0.9 composite film, which may be due to different contents of Au or Ag.
2.2. Fabrication of Au/Al2O3 and AuAg/Al2O3 nanocomposite films The Au/Al2O3 and AuAg/Al2O3 nanocomposite films were obtained by spin-coating method. The aged Au/Al2O3 and AuAg/Al2O3 precursor solutions for 7e8 and 15e16 h respectively were dropped uniformly to the glass substrates which were ultrasonically cleaned in acetone, ethanol solution, deionized water and dried in a drying
Fig. 1. XRD patterns of pure Al2O3, Au/Al2O3 and and AuAg/Al2O3 composite films.
774
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
In Au0.1/(Al2O3)0.9 thin film, the content of Au is 10 mol%, while total content of Au and Ag is over 10 mol% for Au0.1Ag0.3/(Al2O3)0.6 thin films, no matter what chemical state Au and Ag are in. In all samples, no diffraction peaks of Al2O3 can be observed, indicating that Al2O3 in an amorphous state, which is in agreement with the result of Ag/Al2O3 thin films [7]. Fig. 2 shows the TEM micrograph of Au0.1/(Al2O3)0.9 (a), Au0.1Ag0.3/(Al2O3)0.6 (b) composite films and EDS spectra of the particle 1 (c) and particle 2 (d) in Au0.1Ag0.3/(Al2O3)0.6 film. It is seen that Au nanoparticles in Au0.1/(Al2O3)0.9 film and Au or Ag or alloy nanoparticles in Au0.1Ag0.3/(Al2O3)0.6 film are almost in a spherical structure. The diameters of the Au nanoparticles are mostly between 15 nm and 35 nm in Au0.1/(Al2O3)0.9 film, while the size distribution of Au or Ag or alloy particles are large in Au0.1Ag0.3/ (Al2O3)0.6 film. With very few exceptions, the particles diameters in Au0.1Ag0.3/(Al2O3)0.6 film is smaller than those of Au in Au0.1/ (Al2O3)0.9 film, which are mostly in the range of 3e30 nm. It seems that the particles in Au0.1Ag0.3/(Al2O3)0.6 film become small compared with Au0.1/(Al2O3)0.9 film. Our previous study indicated that the average diameter of Ag particles in Ag/Al2O3 nanocomposite films is in the range of 3e12 nm [7], which is much smaller than that of Au/Al2O3 film. As a result, we conclude that the relatively large particles could be Au, while relatively small ones could be Ag, which was confirmed by the EDS spectra of particle 1 (Fig. 2(c)) and particle 2 (Fig. 2 (d)) for the Au0.1Ag0.3/(Al2O3)0.6 film). There appeared Cu emission peak in the spectrum of particle 2, which may be due to the copper microgrid. In fact, we measured the EDS spectra of the particles of various sizes to determine the chemical state of gold and silver in Au0.1Ag0.3/(Al2O3)0.6 film. These EDS spectra reveal that gold and silver are really in metallic states instead of the Au-Ag alloy. In order to verify the chemical state of gold and silver, Au0.1/ (Al2O3)0.9 and Au0.1Ag0.3/(Al2O3)0.6 composite films were analyzed by XPS. Fig. 3 shows the XPS spectra of Au 4f, Al 2p and O 1s electrons for Au0.1/(Al2O3)0.9 film. The peaks corresponding to the Au 4f7/2 and 4f5/2 are located at 84.1eV and 87.8 eV, respectively, which are very close to those of standard Au crystal XPS (Au 4f7/2: 84.1 eV; Au 4f5/2: 87.7 eV) [22], suggesting that Au nanoparticles are in a metallic state in the Au0.1/(Al2O3)0.9 film. The peak corresponding to the Al 2p was observed at 74.1 eV, which is close to that of standard Al2O3 (Al 2p: 74.4 eV) [22], showing that the Al is in trivalence state. The peak at 531.4 eV corresponds to O 1s of Al2O3 [22]. These results show that the metal Au nanoparticles are dispersed in Al2O3 matrix for Au/Al2O3 composite film.
Fig. 4 shows the XPS spectra of Au 4f (a) and Ag 3d (b) electrons for Au0.1Ag0.3/(Al2O3)0.6 composite film. The peaks located at 84.0 eV and 87.6 eV belong to Au 4f7/2 and Au 4f5/2 of Au crystal [22]. The peaks at 368.1 eV and 374.1 eV correspond to Ag 3d5/2 and Ag 3d3/2, which is quite close to that of standard Ag crystal XPS (Ag 3d5/ 2: 368.3 eV; Ag 3d3/2: 374.3 eV) [22]. The XPS spectra of Al 2p and O 1s are very similar with those of Al 2p and O 1s in Au0.1(Al2O3)0.9 film (Fig. 3), which is not displayed here. The above results suggest that both gold and silver in Au0.1Ag0.3/(Al2O3)0.6 film exist in the state of metal Au and metal Ag, and are dispersed in Al2O3 matrix. Fig. 5 shows the optical absorption spectra of Au0.1/(Al2O3)0.9, Ag0.3/(Al2O3)0.7 and Au0.1Ag0.3/(Al2O3)0.6 composite films. For Au0.1/ (Al2O3)0.9 film, the SPR peak corresponding to Au nanoparticles appears at about 540 nm. According to our previous study for Ag/ Al2O3 films, the SPR peak of Ag nanoparticles for Ag0.3/(Al2O3)0.7 appears at about 410 nm [7], which is also shown in Fig. 5. There are two absorption peaks at about 530 nm and 409 nm for Au0.1Ag0.3/ (Al2O3)0.6 film, which shift to the side of short waves compared with the SPR peaks of Au nanoparticles in Au0.1/(Al2O3)0.9 and Ag nanopariticles in Ag0.3/(Al2O3)0.7 composite films. We speculate that the two peaks are related to the SPR of Au and Ag nanoparticles. The blue-shift may be due to the quantum size effect. The Au particles of Au0.1Ag0.3/(Al2O3)0.6 film are obviously much smaller than those of Au0.1/(Al2O3)0.9 with few exceptions (Fig. 2), which leads to a large blue-shift of Au SPR peak. It is impossible to form alloy Au-Ag nanoparticles, because alloy Au-Ag only have one SPR peak, which is located between the SPR peak position of monometal Au nanoparticles and monometal Ag nanoparticles dispersed systems [23]. These results show that two peaks in Au0.1Ag0.3/ (Al2O3)0.6 film correspond SPR peaks of Au and Ag nanoparticles, respectively, which further confirm the metal states of gold and silver in Au0.1Ag0.3/(Al2O3)0.6 composite film. Fig. 6 shows the optical absorption spectra of Au/Al2O3 films with different Au contents. All thin films exhibit an absorption peak in the range of 520e550 nm. The changing trend of optical absorption curves with the increase of Au content is similar with that of Ag/Al2O3 films with Ag concentration of 20e40 mol% [7]. In Ag/ Al2O3 films, the optical absorptions gradually increase with an increase of Ag content from 20 mol% to 40 mol%, which is because that the size of Ag particles increased with the increase of Ag content. The optical absorptions of Au/Al2O3 thin films are enhanced with increasing Au content from 2 mol% to 10 mol%, which may attribute to similar behavior. However, the optical absorption weakens due to the connection of highly dispersed Ag
Fig. 2. TEM micrograph of Au0.1/(Al2O3)0.9 (a), Au0.1Ag0.3/(Al2O3)0.6 (b) and EDS spectra of the particle 1 (c) and particle 2 (d) in Au0.1Ag0.3/(Al2O3)0.6 composite films.
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
775
Fig. 3. XPS spectra of Au0.1/(Al2O3)0.9 thin film: (a) Au 4f, (b) Al 2p, (c) O 1s.
Fig. 4. XPS spectra of Au0.1Ag0.3/(Al2O3)0.6 thin film: (a) Au 4f, (b) Ag 3d.
particles when Ag content is over 40 mol% in Ag/Al2O3 thin films [7]. In the present study, the optical absorption did not decrease with the increase of Au content, which may be due to that Au content is not enough to connect together (Maximum concentration of Au is only 10 mol%). In this paper, the optical absorptions of the Au/Al2O3 thin films with Au concentration above 10 mol% were not studied. The SPR peaks of Au/Al2O3 composite films show a red-shift trend, and sharpen with increasing the Au content, which are very similar with those of Ag/Al2O3 thin films. The red-shift may be due to the quantum size effect. The size of Au particles will increase with the increase of Au content. The narrowed peak may be due to the enhanced intrinsic free electron oscillation inside metal particles [7]. Fig. 7 shows the optical absorption spectra of (AuxAg0.4x(Al2O3)0.6 composite films with x ¼ 0.02, 0.06 and 0.10. It is seen that all thin films exhibit two absorption peaks at about 409 and 530 nm, which correspond to the SPR peaks of Au and Ag nanoparticles, respectively. The intensities of two peaks change with x values in AuxAg0.4x(Al2O3)0.6 thin films. When the values of
x increase from 0.02 to 0.1d that is, the content of Au increases from 2 mol% to 10 mol%, that of Ag decreases from 38 mol% to 30 mol% d the SPR peak of Au nanoparticles intensities, while that of Ag nanoparticles weakens. The changing trend of two SPR peaks with the contents of Au and Ag NPs is very similar with that of AuxAg0.2x/(SiO2)0.8 composite films [21]. In AuxAg0.2x/(SiO2)0.8 films, the intensity of Ag peak increases, while that of Au peak decreases with increasing x values from 0.02 to 0.1. However, the absorption wavelengths of two SPR peaks in AuxAg0.4x(Al2O3)0.6 composite films (409 nm, 430 nm) are different with those of AuxAg0.2x/(SiO2)0.8 films (410 nm, 540 nm), which can meet the requirements of different applications. In addition, the SPR peaks of Ag and Au particles shift slightly towards the longer wavelength side with the increase of Au and Ag content, respectively, which attribute to the quantum size effect.
4. Conclusions Au nanoparticles and Au, Ag bimetal nanoparticles dispersed Al2O3 composite films were prepared successfully by a sol-gel
776
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
Fig. 5. Optical absorption spectra of Au0.1/(Al2O3)0.9, Ag0.3/(Al2O3)0.7 and Au0.1Ag0.3/ (Al2O3)0.6 composite films.
Fig. 7. Optical absorption spectra of AuxAg0.4x(Al2O3)0.6 thin films with different x values.
Acknowledgements This research was supported by Guangxi Natural Science Foundation (No. 2014GXNSFAA118342), and National Undergraduate Training Program for Innovation and Entrepreneurship. References
Fig. 6. Optical absorption spectra of Au/Al2O3 thin films with different Au contents.
method. Gold in Au/Al2O3, and gold and siver in AuAg/Al2O3 composite films exist in the state metal Au and metal Ag, and are basically spherical. The diameters of Au particles in Au/Al2O3 are in the range of 15e35 nm, while those of Au and Ag particles are mostly in the range of 3e30 nm with very few exceptions. The SPR peaks of Au nanoparticles in Au/Al2O3 thin films intensity with the increase of Au contents. There are two SPR peaks corresponding to Au and Ag nanoparticles in AuxAg0.4x(Al2O3)0.6 films, which were observed at around 530 nm and 409 nm, respectively. The intensities of two SPR peaks depend on the molar ratios of Au and Ag nanoparticles. With increasing the Au content, and decreasing the Ag content, the SPR peaks of Au nanoparticles intensity, while those of Ag nanoparticles weaken. The SPR speaks of Au and Ag exhibit slightly red shift with an increase of Au and Ag contents due to the quantum size effect.
[1] T. Hira, T. Homma, T. Uchiyama, K. Kuwamura, T. Saiki, Switching of localized surface plasmon resonance of gold nanoparticles on a GeSbTe film mediated by nanoscale phase change and modification of surface morphology, Appl. Phys. Lett. 103 (2013), 241101e;241101e4. [2] H. Inouye, K. Tanaka, I. Tanahashi, T. Hattori, H. Nakatsuka, Ultrafast optical switching in a silver nanoparticle system, Jpn. J. Appl. Phys. 39 (2000) 5132e5134. [3] H. Choi, S.J. Ko, Y. Choi, P. Joo, T. Kim, B.R. Lee, J.W. Jung, H.J. Choi, M. Cha, J.R. Jeong, I.W. Hwang, M.H. Song, B.S. Kim, J.Y. Kim, Versatile surface plasmon resonance of carbon-dot-supported silver nanoparticles in polymer optoelectronic devices, Nat. Photonics 7 (2013) 732e738. [4] P.B. Anand, C.S.S. Sandeep, K. Sridharan, T.N. Narayanan, S. Thomas, R. Philip, M.R. Anantharaman, An optical limiter based on silver-silica nanocomposites, Adv. Sci. 4 (2012) 33e38. [5] L.A. Ageev, V.K. Miloslavsky, E.D. Makovetsky, V.M. Volosenko, Periodic structures formed by Ag nanoparticles in AgCl-Ag film waveguides exposed to violet laser light, J. Appl. Spectrosc. 80 (2013) 389e394. [6] S. Bai, O. Li, H. Zhang, X.X. Chen, S. Luo, H. Gong, Y.Q. Yang, D. Zhao, M. Qiu, Large third-order nonlinear refractive index coefficient based on gold nanoparticles aggregate films, Appl. Phys. Lett. 107 (2015), 141111-1e;141111e5. [7] C.H. Zhao, J.L. Du, D.W. Huang, Y.Q. Li, J.H. Chen, W.Z. Li, Microstructure and strong optical absorption property of the Ag/Al2O3 nano-films, J. Alloy. Compd. 671 (2016) 419e423. [8] P.R. Ohodnicki Jr., C. Wang, S. Natesakhawat, J.P. Baltrus, T.D. Brown, In-situ and ex-situ characterization of TiO2 and Au nanoparticle incorporated TiO2 thin films for optical gas sensing at extreme temperatures, J. Appl. Phys. 111 (2011), 064320e;064320e11. [9] L. Giancaterini, C. Cantalini, M. Cittadini, M. Sturaro, M. Guglielmi, A. Martucci, A. Resmini, U. Anselmi-Tamburini, Au and Pt Nanoparticles effects on the optical and electrical gas sensing properties of Sol-Gel-Based ZnO thin film sensors, IEEE Sens. J. 15 (2015) 1068e1076. [10] N.M. Lyadov, A.I. Gumarow, R.N. Kashapov, A.I. Noskov, V.F. Valeev, V.I. Nuzhdin, V.V. Bazarov, R.I. Khaibullin, I.A. Faizrakhmanov, Structure and optical properties of ZnO with silver nanoparticles, Semiconductors 50 (2016) 43e49. [11] Y. Yang, M. Nogami, J. Shi, H. Chen, Y. Liu, S. Qian, Self-assembled semiconductor capped metal composite nanopariticles embedded in BaTiO3 thin films for nonlinear optical applications, J. Mater. Chem. 13 (2003) 3026e3032. [12] C.H. Zhao, B.P. Zhang, S.J. Wang, P.P. Shang, S. Li, L.P. Yan, Microstructure and optical absorption property of the Cu/SiO2 nano-films, Mater. Des. 32 (2011) 947e950. [13] Q. Cao, K.P. Yuan, Q.H. Liu, C.Y. Liang, X. Wang, Y.F. Cheng, Q.Q. Li, M. Wang, R. Che, Porous Au-Ag alloy particles inlaid AgCl membranes as versatile
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
[14] [15]
[16]
[17]
[18]
plasmonic catalytic interfaces with simultaneous in situ SERS monitoring, ACS Appl. Mater. Interfaces 7 (2015) 18491e18500. G. Suyal, Bimetallic colloids of silver and copper in thin films: sol-gel synthesis and characterization, Thin Solid films 426 (2003) 53e61. K. Bankura, D. Maity, M.M.R. Mollick, D. Mondal, B. Bhowmick, I. Roy, T. Midya, J. Sarkar, D. Rana, K. Acharya, D. Chattopadhyay, Antibacterial activity of AgAu alloy NPs and chemical sensor property of Au NPs synthesized by dextran, Carbohyd. Polym. 107 (2014) 151e157. Y. Li, B.P. Zhang, J.X. Zhao, Enhanced photocatalytic performance of Au-Ag alloy modified ZnO nanocomposite films, J. Alloy. Compd. 586 (2014) 663e668. N. Kumar, F. Alam, V. Dutta, Deposition of Ag and Au-Ag alloy nanoparticle films by spray pyrolysis technique with tuned plasmonic properties, J. Alloy. Compd. 585 (2014) 312e317. Y. Wu, G. Li, C. Cherqui, N.W. Bigelow, N. Thakkar, D.J. Masiello, J.P. Camden, P.D. Rack, Electron energy loss spectroscopy study of the full plasmonic
[19]
[20]
[21]
[22] [23]
777
spectrum of self-assembled Au-Ag alloy nanopariticles: unraveling size, composition, and substrate effects, ACS Photonics 3 (2016) 130e138. U. Sanyal, D.T. Davis, B.R. Jagirdar, Bimetallic core-shell nanocomposites using weak reducing agent and their transformation to alloy nanostructures, Dalton Trans. 42 (2013) 7147e7157. S. Sebastian, C.L. Linslal, C.P.G. Vallbhan, V.P.N. Nampoori, P. Radhakrishnan, M. Kailasnath, Formation of Au-Ag nanoalloy through Au core/Ag shell intermediate phase by laser ablation, Chem. Phys. Lett. 628 (2015) 25e29. Y. li, B.P. Zhang, C.H. Zhao, L. Zou, J.X. Zhao, Synthesis and optical absorption properties of Au-Ag nanoparticles bimetal dispersed SiO2 composite films, J. Mater. Res. 29 (2014) 221e229. J.F. Moulder, W.F. Stickle, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, PerkineElmer Corporation, America, 1992. P. Sangpour, O. Akhavan, A.Z. Moshfegh, The effect of Au/Ag ratios on surface composition and optical properties of co-sputtered alloy nanoparticles in AuAg:SiO2 thin films, J. Alloys Compd. 486 (2009) 22e28.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Microstructure and optical absorption property of Au nanoparticles and Au, Ag bimetal nanoparticles separately dispersed Al2O3 composite films Cuihua Zhao a, Baishi Li a, Junli Du a, Jianhua Chen b, *, Yuqiong Li b, ** a b
College of Material Science and Engineering, Guangxi University, Nanning 530004, China Guangxi Colleges and University Key Laboratory of Minerals Engineering, Guangxi University, Nanning 530004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 July 2016 Received in revised form 27 August 2016 Accepted 31 August 2016 Available online 1 September 2016
Au nanoparticles and Au, Ag bimetal nanoparticles separately dispersed Al2O3 composite films were prepared by sol-gel method. The microstructure and optical property of the films were studied by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and ultravioletevisible (UV/vis) absorption spectra. Gold in Au/Al2O3, and gold and silver in AuAg/Al2O3 composite films exist in the state of metal Au and Ag, and they are basically spherical nanoparticles. The optical absorption peaks of Au nanoparticles due to the surface plasmon resonance (SPR) in Au/Al2O3 films were observed in the range of 530e550 nm, and their absorptions intensity with the increase of Au contents. There are two SPR peaks corresponding to Au and Ag nanoparticles, which were observed in the range of 530e550 nm, 400e420 nm, respectively. The intensities of two SPR peaks change with various molar ratios of Au and Ag nanoparticles. The SPR peaks of Au nanoparticles intensity, and those of Ag nanoparticles weaken with the increase of Au contents, and decrease of Ag contents. The SPR speaks of Au and Ag nanoparticles shift slightly to the longer wavelength with an increase of Au and Ag contents in AuAg/Al2O3 composite films. © 2016 Elsevier B.V. All rights reserved.
Keywords: Au/Al2O3 AuAg/Al2O3 Sol-gel Microstructure Optical property
1. Introduction Composite films consisting of noble metal nanoparticles are gaining extreme attention because of their potential applications in optical switching [1,2], optoelectronic devices [3], optical limiters [4], optical waveguides [5], and ultrafast optical communication systems [6], etc. The linear and nonlinear optical properties of metal nanoparticles dispersed oxide film have been largely studied in the recent years, however, new systems and new phenomena are emerging in an endless stream. The main reason is still their significant promise in a variety of applications. The optical property of these nanocomposite films depends not only on the size, shape and volume fraction of metal nanoparticles, but also on the refractive indexes of the dielectric substrates. Therefore, the choice of the appropriate light wavelength, the host materials for the metallic nanoparticles as well as their nature and concentration are crucial
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Chen), [email protected] (Y. Li). http://dx.doi.org/10.1016/j.jallcom.2016.08.332 0925-8388/© 2016 Elsevier B.V. All rights reserved.
for dedicated application, such as light modulators, optical amplifiers and sensors. In the past decades, much attention has been paid to the changes of volume fraction of metal nanoparticles, and the composite of nanoparticles embedded in various matrices (TiO2, ZnO, BaTiO3, SiO2 and so on) for single metal dispersed composite films [7e12]. Although the intensity and frequency of SPR speak can be adjusted by changing the size, shape, content of nanoparticles and the types of the matrix, it is not always easy to control over particle size and shape, and require very specific and demanding reaction conditions. In recent years, bimetallic nanoparticles dispersed systems have been produced, mainly including two types of integration patterns: metal alloys [13e18] and core-shell NPs [19,20]. The bimetallic nanoparticles show unique structural, electronic, optical and catalytic properties than single metal samples, and can be used in different fields. For example, Bankura et al. prepared the silver-gold alloy nanoparticles by reduction of the correspondent metal precursors aqueous dextran solution for antimicrobial applications [15]. Li et al. fabricated Au-Ag alloy modified ZnO nanocomposite films by sol-gel method for photocatalytic application [16].
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
It is very difficult to prepare Au-Ag bimetal separately dispersed composite films because of nearly identical bulk lattice constants of Au and Ag [21]. As a result, the study on Au-Ag bimetal nanoparticles separately dispersed system is very rare. Our research group prepared Ag-Au bimetal dispersed separate SiO2 composite films [21]. To obtain the Ag-Au bimetal nanoparticles, the chemical solution approach combining with a sol-gel spin-coating process was used. First of all, Au/SiO2 and Ag/SiO2 precursor solutions with required molar ratio were prepared respectively. Then the Ag-Au bimetal dispersed separate films were obtained by the spincoating Aux/(SiO2)0.5x and Agy/(SiO2)0.5y films one after another on a SiO2 glass substrate. The composite films possess two SPR peaks. The unique optical properties widen the application field for composite films containing noble metal nanoparticles. In this paper, Au nanoparticles and Au, Ag bimetal nanoparticles separately dispersed Al2O3 composite films were prepared using sol-gel method. Matrix Al2O3 was chosen for its thermal stability up to high temperature, large band-offset and similar band gap to SiO2. And our research demonstrated that the Ag/Al2O3 nano-composite thin films have strong optical absorption property [7]. Therefore, we deduce that Au nanoparticles and Au, Ag bimetal nanoparticles dispersed Al2O3 composite films should have good nonlinear optical properties, and different matrix (Al2O3) may lead to different optical characteristics with Au-Ag bimetal dispersed SiO2 composite films. In addition, the preparing process of this study is more simple than that of (Ag, Au)/SiO2 thin films [21]. Only a precursor solution (AuAg/Al2O3) was prepared in the preparing process of AuAg/Al2O3 thin film. Ag and Au bimetal dispersed separate nanoparticles were obtained by controlling the preparing techniques, including the aging time of the sol, the pyrolyzing temperature and time, annealing temperature and time. And the microstructure and optical property of thin films were studied with a special emphasis on the influences of different molar ratio of Au and Ag nanoparticles. 2. Experiment procedures 2.1. Preparation of Au/Al2O3 and AuAg/Al2O3 precursor solution Aluminum trisecbutoxide ((C4H9O)3Al) and chloroauric (HAuCl4$4H2O) were used as raw materials. Isopropyl alcohol (CH(CH3)2OH), acetoacetate (C6H10O3) and distilled water were used as solvents. The molar ratio of (C4H9O)3Al, CH(CH3)2OH, C6H10O3, and H2O is 1:20:1:4. ((C4H9O)3Al) and (CH(CH3)2OH) were mixed, and stirred magnetically for 0.5 h at room temperature. A certain amount of C6H10O3 was added to the mixture, and stirred for 2 h again. Then the distilled water was added, and stirred for 1 h again. A transparent matrix solution was obtained. HAuCl4.4H2O was added into the matrix solution with molar ratio of Au/(Au þ Al2O3) ¼ 2, 5, 8 and 10 mol% followed by stirring for 1.5 h. Then the transparent precursor Au/Al2O3 solutions were obtained. When preparing the AuAg/Al2O3 precursor solution, AgNO3 was first added into the matrix solution followed by stirring for 2 h, then HAuCl4.4H2O was added into the mixture. The molar ratio of Au, Ag and Al2O3 matches with AuxAg0.4x(Al2O3)0.6 with x ¼ 0.02, 0.06 and 0.10. After further stirring for 2 h, the transparent precursor AuAg/Al2O3 precursor solutions were obtained.
773
oven. The substrates were rotated at the rate of 200e300 rpm for 9 s and later at 2000e3000 rpm for 30 s for Au/Al2O3 thin film, 200 rpm for 40 s and later 3200 rpm for 1 min for AuAg/Al2O3 thin films. After one coating, the films were pyrolysized at about 200 C for 30 s for Au/Al2O3, 180 C for 1 min for AuAg/Al2O3 thin films to remove the solvent and a small amount of water. These sequences of coating and pyrolysis treatment were repeated 2 times for optical absorption samples and for 8 times for the X-ray diffraction (XRD) samples. The two-layer films are about 60 nm in thickness. The pyrolysized samples were annealed at 700 C for 30 min in air, and Au/Al2O3 thin films and AuAg/Al2O3 thin films were obtained. 2.3. Characterization Ag/Al2O3 and AuAg/Al2O3 nanocomposite films The crystalline phases of the films were characterized by XRD (Cu Ka radiation with a wavelength of l ¼ 0.15418 nm). The microstructures of the films were observed by TEM (JEM-100CG). The XPS spectra were measured using monochromatic Al Ka radiation (1486.6 eV) as the X-ray source (PHI-5300 ESCA). The absorption spectra of thin films were measured at room temperature in air by a UVevisible spectrophotometer (LAMBDA 950). 3. Results and discussion Fig. 1 shows the XRD patterns of Au0.1/(Al2O3)0.9 and Au0.1Ag0.3/ (Al2O3)0.6 composite films with the result of corresponding one of pure Al2O3 films for comparison. There is no any sharp diffraction peak for the pure Al2O3 film. There are four diffraction peaks at 38.08 , 44.30 , 64.65 and 77.68 for the Au0.1/(Al2O3)0.9 film, which correspond to (111), (200), (220) and (311) crystal planes of Au (PDF04-0784). The XRD curve of the Au0.1Ag0.3/(Al2O3)0.6 composite film is very similar with that of the Au0.1/(Al2O3)0.9 film except for the peak intensity. The diffraction peaks at 38.08 , 44.30 , 64.65 and 77.68 may correspond to (111), (200), (220) and (311) crystal planes of Au (PDF#04-0784) or Ag (PDF#04-0783) or Au-Ag alloy. Au and Ag possess the same face-centered-cubic (fcc) structure with almost the same bulk lattice parameter as described in our previous study [21]. Therefore, the chemical state of Au and Ag existence cannot be determined here. The intensities of XRD peaks for Au0.1Ag0.3/(Al2O3)0.6 are larger than that of Au0.1/(Al2O3)0.9 composite film, which may be due to different contents of Au or Ag.
2.2. Fabrication of Au/Al2O3 and AuAg/Al2O3 nanocomposite films The Au/Al2O3 and AuAg/Al2O3 nanocomposite films were obtained by spin-coating method. The aged Au/Al2O3 and AuAg/Al2O3 precursor solutions for 7e8 and 15e16 h respectively were dropped uniformly to the glass substrates which were ultrasonically cleaned in acetone, ethanol solution, deionized water and dried in a drying
Fig. 1. XRD patterns of pure Al2O3, Au/Al2O3 and and AuAg/Al2O3 composite films.
774
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
In Au0.1/(Al2O3)0.9 thin film, the content of Au is 10 mol%, while total content of Au and Ag is over 10 mol% for Au0.1Ag0.3/(Al2O3)0.6 thin films, no matter what chemical state Au and Ag are in. In all samples, no diffraction peaks of Al2O3 can be observed, indicating that Al2O3 in an amorphous state, which is in agreement with the result of Ag/Al2O3 thin films [7]. Fig. 2 shows the TEM micrograph of Au0.1/(Al2O3)0.9 (a), Au0.1Ag0.3/(Al2O3)0.6 (b) composite films and EDS spectra of the particle 1 (c) and particle 2 (d) in Au0.1Ag0.3/(Al2O3)0.6 film. It is seen that Au nanoparticles in Au0.1/(Al2O3)0.9 film and Au or Ag or alloy nanoparticles in Au0.1Ag0.3/(Al2O3)0.6 film are almost in a spherical structure. The diameters of the Au nanoparticles are mostly between 15 nm and 35 nm in Au0.1/(Al2O3)0.9 film, while the size distribution of Au or Ag or alloy particles are large in Au0.1Ag0.3/ (Al2O3)0.6 film. With very few exceptions, the particles diameters in Au0.1Ag0.3/(Al2O3)0.6 film is smaller than those of Au in Au0.1/ (Al2O3)0.9 film, which are mostly in the range of 3e30 nm. It seems that the particles in Au0.1Ag0.3/(Al2O3)0.6 film become small compared with Au0.1/(Al2O3)0.9 film. Our previous study indicated that the average diameter of Ag particles in Ag/Al2O3 nanocomposite films is in the range of 3e12 nm [7], which is much smaller than that of Au/Al2O3 film. As a result, we conclude that the relatively large particles could be Au, while relatively small ones could be Ag, which was confirmed by the EDS spectra of particle 1 (Fig. 2(c)) and particle 2 (Fig. 2 (d)) for the Au0.1Ag0.3/(Al2O3)0.6 film). There appeared Cu emission peak in the spectrum of particle 2, which may be due to the copper microgrid. In fact, we measured the EDS spectra of the particles of various sizes to determine the chemical state of gold and silver in Au0.1Ag0.3/(Al2O3)0.6 film. These EDS spectra reveal that gold and silver are really in metallic states instead of the Au-Ag alloy. In order to verify the chemical state of gold and silver, Au0.1/ (Al2O3)0.9 and Au0.1Ag0.3/(Al2O3)0.6 composite films were analyzed by XPS. Fig. 3 shows the XPS spectra of Au 4f, Al 2p and O 1s electrons for Au0.1/(Al2O3)0.9 film. The peaks corresponding to the Au 4f7/2 and 4f5/2 are located at 84.1eV and 87.8 eV, respectively, which are very close to those of standard Au crystal XPS (Au 4f7/2: 84.1 eV; Au 4f5/2: 87.7 eV) [22], suggesting that Au nanoparticles are in a metallic state in the Au0.1/(Al2O3)0.9 film. The peak corresponding to the Al 2p was observed at 74.1 eV, which is close to that of standard Al2O3 (Al 2p: 74.4 eV) [22], showing that the Al is in trivalence state. The peak at 531.4 eV corresponds to O 1s of Al2O3 [22]. These results show that the metal Au nanoparticles are dispersed in Al2O3 matrix for Au/Al2O3 composite film.
Fig. 4 shows the XPS spectra of Au 4f (a) and Ag 3d (b) electrons for Au0.1Ag0.3/(Al2O3)0.6 composite film. The peaks located at 84.0 eV and 87.6 eV belong to Au 4f7/2 and Au 4f5/2 of Au crystal [22]. The peaks at 368.1 eV and 374.1 eV correspond to Ag 3d5/2 and Ag 3d3/2, which is quite close to that of standard Ag crystal XPS (Ag 3d5/ 2: 368.3 eV; Ag 3d3/2: 374.3 eV) [22]. The XPS spectra of Al 2p and O 1s are very similar with those of Al 2p and O 1s in Au0.1(Al2O3)0.9 film (Fig. 3), which is not displayed here. The above results suggest that both gold and silver in Au0.1Ag0.3/(Al2O3)0.6 film exist in the state of metal Au and metal Ag, and are dispersed in Al2O3 matrix. Fig. 5 shows the optical absorption spectra of Au0.1/(Al2O3)0.9, Ag0.3/(Al2O3)0.7 and Au0.1Ag0.3/(Al2O3)0.6 composite films. For Au0.1/ (Al2O3)0.9 film, the SPR peak corresponding to Au nanoparticles appears at about 540 nm. According to our previous study for Ag/ Al2O3 films, the SPR peak of Ag nanoparticles for Ag0.3/(Al2O3)0.7 appears at about 410 nm [7], which is also shown in Fig. 5. There are two absorption peaks at about 530 nm and 409 nm for Au0.1Ag0.3/ (Al2O3)0.6 film, which shift to the side of short waves compared with the SPR peaks of Au nanoparticles in Au0.1/(Al2O3)0.9 and Ag nanopariticles in Ag0.3/(Al2O3)0.7 composite films. We speculate that the two peaks are related to the SPR of Au and Ag nanoparticles. The blue-shift may be due to the quantum size effect. The Au particles of Au0.1Ag0.3/(Al2O3)0.6 film are obviously much smaller than those of Au0.1/(Al2O3)0.9 with few exceptions (Fig. 2), which leads to a large blue-shift of Au SPR peak. It is impossible to form alloy Au-Ag nanoparticles, because alloy Au-Ag only have one SPR peak, which is located between the SPR peak position of monometal Au nanoparticles and monometal Ag nanoparticles dispersed systems [23]. These results show that two peaks in Au0.1Ag0.3/ (Al2O3)0.6 film correspond SPR peaks of Au and Ag nanoparticles, respectively, which further confirm the metal states of gold and silver in Au0.1Ag0.3/(Al2O3)0.6 composite film. Fig. 6 shows the optical absorption spectra of Au/Al2O3 films with different Au contents. All thin films exhibit an absorption peak in the range of 520e550 nm. The changing trend of optical absorption curves with the increase of Au content is similar with that of Ag/Al2O3 films with Ag concentration of 20e40 mol% [7]. In Ag/ Al2O3 films, the optical absorptions gradually increase with an increase of Ag content from 20 mol% to 40 mol%, which is because that the size of Ag particles increased with the increase of Ag content. The optical absorptions of Au/Al2O3 thin films are enhanced with increasing Au content from 2 mol% to 10 mol%, which may attribute to similar behavior. However, the optical absorption weakens due to the connection of highly dispersed Ag
Fig. 2. TEM micrograph of Au0.1/(Al2O3)0.9 (a), Au0.1Ag0.3/(Al2O3)0.6 (b) and EDS spectra of the particle 1 (c) and particle 2 (d) in Au0.1Ag0.3/(Al2O3)0.6 composite films.
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
775
Fig. 3. XPS spectra of Au0.1/(Al2O3)0.9 thin film: (a) Au 4f, (b) Al 2p, (c) O 1s.
Fig. 4. XPS spectra of Au0.1Ag0.3/(Al2O3)0.6 thin film: (a) Au 4f, (b) Ag 3d.
particles when Ag content is over 40 mol% in Ag/Al2O3 thin films [7]. In the present study, the optical absorption did not decrease with the increase of Au content, which may be due to that Au content is not enough to connect together (Maximum concentration of Au is only 10 mol%). In this paper, the optical absorptions of the Au/Al2O3 thin films with Au concentration above 10 mol% were not studied. The SPR peaks of Au/Al2O3 composite films show a red-shift trend, and sharpen with increasing the Au content, which are very similar with those of Ag/Al2O3 thin films. The red-shift may be due to the quantum size effect. The size of Au particles will increase with the increase of Au content. The narrowed peak may be due to the enhanced intrinsic free electron oscillation inside metal particles [7]. Fig. 7 shows the optical absorption spectra of (AuxAg0.4x(Al2O3)0.6 composite films with x ¼ 0.02, 0.06 and 0.10. It is seen that all thin films exhibit two absorption peaks at about 409 and 530 nm, which correspond to the SPR peaks of Au and Ag nanoparticles, respectively. The intensities of two peaks change with x values in AuxAg0.4x(Al2O3)0.6 thin films. When the values of
x increase from 0.02 to 0.1d that is, the content of Au increases from 2 mol% to 10 mol%, that of Ag decreases from 38 mol% to 30 mol% d the SPR peak of Au nanoparticles intensities, while that of Ag nanoparticles weakens. The changing trend of two SPR peaks with the contents of Au and Ag NPs is very similar with that of AuxAg0.2x/(SiO2)0.8 composite films [21]. In AuxAg0.2x/(SiO2)0.8 films, the intensity of Ag peak increases, while that of Au peak decreases with increasing x values from 0.02 to 0.1. However, the absorption wavelengths of two SPR peaks in AuxAg0.4x(Al2O3)0.6 composite films (409 nm, 430 nm) are different with those of AuxAg0.2x/(SiO2)0.8 films (410 nm, 540 nm), which can meet the requirements of different applications. In addition, the SPR peaks of Ag and Au particles shift slightly towards the longer wavelength side with the increase of Au and Ag content, respectively, which attribute to the quantum size effect.
4. Conclusions Au nanoparticles and Au, Ag bimetal nanoparticles dispersed Al2O3 composite films were prepared successfully by a sol-gel
776
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
Fig. 5. Optical absorption spectra of Au0.1/(Al2O3)0.9, Ag0.3/(Al2O3)0.7 and Au0.1Ag0.3/ (Al2O3)0.6 composite films.
Fig. 7. Optical absorption spectra of AuxAg0.4x(Al2O3)0.6 thin films with different x values.
Acknowledgements This research was supported by Guangxi Natural Science Foundation (No. 2014GXNSFAA118342), and National Undergraduate Training Program for Innovation and Entrepreneurship. References
Fig. 6. Optical absorption spectra of Au/Al2O3 thin films with different Au contents.
method. Gold in Au/Al2O3, and gold and siver in AuAg/Al2O3 composite films exist in the state metal Au and metal Ag, and are basically spherical. The diameters of Au particles in Au/Al2O3 are in the range of 15e35 nm, while those of Au and Ag particles are mostly in the range of 3e30 nm with very few exceptions. The SPR peaks of Au nanoparticles in Au/Al2O3 thin films intensity with the increase of Au contents. There are two SPR peaks corresponding to Au and Ag nanoparticles in AuxAg0.4x(Al2O3)0.6 films, which were observed at around 530 nm and 409 nm, respectively. The intensities of two SPR peaks depend on the molar ratios of Au and Ag nanoparticles. With increasing the Au content, and decreasing the Ag content, the SPR peaks of Au nanoparticles intensity, while those of Ag nanoparticles weaken. The SPR speaks of Au and Ag exhibit slightly red shift with an increase of Au and Ag contents due to the quantum size effect.
[1] T. Hira, T. Homma, T. Uchiyama, K. Kuwamura, T. Saiki, Switching of localized surface plasmon resonance of gold nanoparticles on a GeSbTe film mediated by nanoscale phase change and modification of surface morphology, Appl. Phys. Lett. 103 (2013), 241101e;241101e4. [2] H. Inouye, K. Tanaka, I. Tanahashi, T. Hattori, H. Nakatsuka, Ultrafast optical switching in a silver nanoparticle system, Jpn. J. Appl. Phys. 39 (2000) 5132e5134. [3] H. Choi, S.J. Ko, Y. Choi, P. Joo, T. Kim, B.R. Lee, J.W. Jung, H.J. Choi, M. Cha, J.R. Jeong, I.W. Hwang, M.H. Song, B.S. Kim, J.Y. Kim, Versatile surface plasmon resonance of carbon-dot-supported silver nanoparticles in polymer optoelectronic devices, Nat. Photonics 7 (2013) 732e738. [4] P.B. Anand, C.S.S. Sandeep, K. Sridharan, T.N. Narayanan, S. Thomas, R. Philip, M.R. Anantharaman, An optical limiter based on silver-silica nanocomposites, Adv. Sci. 4 (2012) 33e38. [5] L.A. Ageev, V.K. Miloslavsky, E.D. Makovetsky, V.M. Volosenko, Periodic structures formed by Ag nanoparticles in AgCl-Ag film waveguides exposed to violet laser light, J. Appl. Spectrosc. 80 (2013) 389e394. [6] S. Bai, O. Li, H. Zhang, X.X. Chen, S. Luo, H. Gong, Y.Q. Yang, D. Zhao, M. Qiu, Large third-order nonlinear refractive index coefficient based on gold nanoparticles aggregate films, Appl. Phys. Lett. 107 (2015), 141111-1e;141111e5. [7] C.H. Zhao, J.L. Du, D.W. Huang, Y.Q. Li, J.H. Chen, W.Z. Li, Microstructure and strong optical absorption property of the Ag/Al2O3 nano-films, J. Alloy. Compd. 671 (2016) 419e423. [8] P.R. Ohodnicki Jr., C. Wang, S. Natesakhawat, J.P. Baltrus, T.D. Brown, In-situ and ex-situ characterization of TiO2 and Au nanoparticle incorporated TiO2 thin films for optical gas sensing at extreme temperatures, J. Appl. Phys. 111 (2011), 064320e;064320e11. [9] L. Giancaterini, C. Cantalini, M. Cittadini, M. Sturaro, M. Guglielmi, A. Martucci, A. Resmini, U. Anselmi-Tamburini, Au and Pt Nanoparticles effects on the optical and electrical gas sensing properties of Sol-Gel-Based ZnO thin film sensors, IEEE Sens. J. 15 (2015) 1068e1076. [10] N.M. Lyadov, A.I. Gumarow, R.N. Kashapov, A.I. Noskov, V.F. Valeev, V.I. Nuzhdin, V.V. Bazarov, R.I. Khaibullin, I.A. Faizrakhmanov, Structure and optical properties of ZnO with silver nanoparticles, Semiconductors 50 (2016) 43e49. [11] Y. Yang, M. Nogami, J. Shi, H. Chen, Y. Liu, S. Qian, Self-assembled semiconductor capped metal composite nanopariticles embedded in BaTiO3 thin films for nonlinear optical applications, J. Mater. Chem. 13 (2003) 3026e3032. [12] C.H. Zhao, B.P. Zhang, S.J. Wang, P.P. Shang, S. Li, L.P. Yan, Microstructure and optical absorption property of the Cu/SiO2 nano-films, Mater. Des. 32 (2011) 947e950. [13] Q. Cao, K.P. Yuan, Q.H. Liu, C.Y. Liang, X. Wang, Y.F. Cheng, Q.Q. Li, M. Wang, R. Che, Porous Au-Ag alloy particles inlaid AgCl membranes as versatile
C. Zhao et al. / Journal of Alloys and Compounds 691 (2017) 772e777
[14] [15]
[16]
[17]
[18]
plasmonic catalytic interfaces with simultaneous in situ SERS monitoring, ACS Appl. Mater. Interfaces 7 (2015) 18491e18500. G. Suyal, Bimetallic colloids of silver and copper in thin films: sol-gel synthesis and characterization, Thin Solid films 426 (2003) 53e61. K. Bankura, D. Maity, M.M.R. Mollick, D. Mondal, B. Bhowmick, I. Roy, T. Midya, J. Sarkar, D. Rana, K. Acharya, D. Chattopadhyay, Antibacterial activity of AgAu alloy NPs and chemical sensor property of Au NPs synthesized by dextran, Carbohyd. Polym. 107 (2014) 151e157. Y. Li, B.P. Zhang, J.X. Zhao, Enhanced photocatalytic performance of Au-Ag alloy modified ZnO nanocomposite films, J. Alloy. Compd. 586 (2014) 663e668. N. Kumar, F. Alam, V. Dutta, Deposition of Ag and Au-Ag alloy nanoparticle films by spray pyrolysis technique with tuned plasmonic properties, J. Alloy. Compd. 585 (2014) 312e317. Y. Wu, G. Li, C. Cherqui, N.W. Bigelow, N. Thakkar, D.J. Masiello, J.P. Camden, P.D. Rack, Electron energy loss spectroscopy study of the full plasmonic
[19]
[20]
[21]
[22] [23]
777
spectrum of self-assembled Au-Ag alloy nanopariticles: unraveling size, composition, and substrate effects, ACS Photonics 3 (2016) 130e138. U. Sanyal, D.T. Davis, B.R. Jagirdar, Bimetallic core-shell nanocomposites using weak reducing agent and their transformation to alloy nanostructures, Dalton Trans. 42 (2013) 7147e7157. S. Sebastian, C.L. Linslal, C.P.G. Vallbhan, V.P.N. Nampoori, P. Radhakrishnan, M. Kailasnath, Formation of Au-Ag nanoalloy through Au core/Ag shell intermediate phase by laser ablation, Chem. Phys. Lett. 628 (2015) 25e29. Y. li, B.P. Zhang, C.H. Zhao, L. Zou, J.X. Zhao, Synthesis and optical absorption properties of Au-Ag nanoparticles bimetal dispersed SiO2 composite films, J. Mater. Res. 29 (2014) 221e229. J.F. Moulder, W.F. Stickle, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, PerkineElmer Corporation, America, 1992. P. Sangpour, O. Akhavan, A.Z. Moshfegh, The effect of Au/Ag ratios on surface composition and optical properties of co-sputtered alloy nanoparticles in AuAg:SiO2 thin films, J. Alloys Compd. 486 (2009) 22e28.