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Sintering Metal Nanoparticle Films University of Pennsylvania ScholarlyCommons Departmental Papers (MSE) Department of Materials Science & Engineering January 2008 Sintering Metal Nanoparticle Films Howard Wang State University of New York Liwei Huang State University of New York Zhiyong Xu State University of New York Congkang Xu State University of New York Russell J. Composto University of Pennsylvania, [email protected] See next page for additional authors Follow this and additional works at: https://repository.upenn.edu/mse_papers Recommended Citation Wang, H., Huang, L., Xu, Z., Xu, C., Composto, R. J., & Yang, Z. (2008). Sintering Metal Nanoparticle Films. Retrieved from https://repository.upenn.edu/mse_papers/154 Copyright 2008 IEEE. Reprinted from Flexible Electronics and Displays Conference and Exhibition, 2008, pages 1-3. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Pennsylvania's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it. This paper is posted at ScholarlyCommons. https://repository.upenn.edu/mse_papers/154 For more information, please contact [email protected]. Sintering Metal Nanoparticle Films Abstract We have carried out several measurements in order to understand the process of metal nanoparticle (MNP) film sintering. Small angle neutron scattering has been used to reveal the average diameters of silver and gold nanoparticles (Ag-NPs and Au-NPs) used in this study to be 4.6 and 3.8 nm, respectively, with a size distribution of ca. 20%. Spun- cast Ag-NP and Au-NP films have been sintered at temperature ranges of 80-160ºC and 180-210º, respectively, for various times. The resulting film composition, morphology and electric resistance have been revealed. Upon sintering, the organic content in MNP films reduces to less than 10% while the overall film thickness educesr to about the half of the as-cast film thickness. The resistance of sintered Ag-NP films can arv y over more than 7 decades depending on the sintering temperature. The conductivity of Ag-NP films sintered at 150º is 2.4 times 10-8Ωm. The transport properties are affected by both the composition and morphology of sintered films. Keywords metal nanoparticles, ion beam analysis, printable electronics, silver nanoparticles, sintering Comments Copyright 2008 IEEE. Reprinted from Flexible Electronics and Displays Conference and Exhibition, 2008, pages 1-3. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Pennsylvania's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it. Author(s) Howard Wang, Liwei Huang, Zhiyong Xu, Congkang Xu, Russell J. Composto, and Zhihao Yang This conference paper is available at ScholarlyCommons: https://repository.upenn.edu/mse_papers/154 Sintering Metal Nanoparticle Films Howard Wang'*, Liwei Huang', Zhiyong Xul, Congkang Xul, Russell J. Composto2, Zhihao Yang3 'Department of Mechanical Engineering, Center for Advanced Microelectronics Manufacturing, Binghamton University, SUNY, Binghamton, NY 13902 2Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104 3NanoMas Technologies, Inc, Vestal, NY 13850 Email: Abstract applying a range of characterization methods including spectroscopic, thermal, microscopic and scattering techniques, We have carried out several measurements in order to we illustrate details of structures and behaviors of MNPs in understand the process of metal nanoparticle (MNP) film both solution suspensions and deposited films. We try to gain Small neutron has been used to sintering. angle scattering fundamental understandings of nanomaterials processing in reveal the average diameters of silver and gold nanoparticles device applications. The insights in the sintering mechanism (Ag-NPs and Au-NPs) used in this study to be 4.6 and 3.8 would offer guidance in materials design and processing nm, respectively, with a size distribution of ca. 20%. Spun- cast Ag-NP and Au-NP films have been sintered at 2. Materials temperature ranges of 80 - 160 °C and 180 - 210 °C, High-quality metal nanoparticles are obtained from respectively, for various times. The resulting film NanoMas Technologies, Inc, who has developed synthesis composition, morphology and electric resistance have been routines for large scale production of silver and gold MNP revealed. Upon sintering, the organic content in MNP films with ultra-small particle size (2 to 10 nm) and narrow reduces to less than 10% while the overall film thickness distribution. MNPs are stabilized with a thin layer of reduces to about the half of the as-cast film thickness. The surfactant molecules, which also render MNPs soluble in non- resistance of sintered Ag-NP films can vary over more than 7 polar organic solvents such as cyclohexane or toluene. UV- decades depending on the sintering temperature. The conductivity of Ag-NP films sintered at 1500C is 2.4 x 10-8 Qm. The transport properties are affected by both the composition and morphology of sintered films. Keywords Keywords, Metal nanoparticles, silver nanoparticles, sintering, printable electronics, ion beam analysis 1. Introduction Fig. 1. (a) SEM micrograph of ca. 5 nm silver nanoparticles, Printable electronics manufactured using roll-to-roll and (b) TEM micrograph of ca. 4 nm gold nanoparticles. processes will offer the unique opportunities for mass production of large format and inexpensive flexible 1..0 electronics [1]. A popular choice of the printable conductor o SANS Data precursor is metal nanoparticles (MNPs), which could be .5 Core-Shell Model Fitting printed to substrates from solutions and sintered to conductive 0..5- films at low temperatures because of the size effect [2]. Particularly, silver nanoparticles (Ag-NPs) are considered by .E many the most important precursor candidate for printed 0 0..0 X conductors for the good balance of cost and performance [3]. On the other hand, gold-nanoparticles (Au-NPs) are desirable C) -0..5 because Au has better chemical stability and high work Results: ± function. There have been extensive R&D efforts in Core radius: 23 1 A Core radius 5.5A methods for mass of -1. c: developing production high quality Ag- .0 Shell 6 ± 1 A and Au-NPs and exploring their applications in fabricating thickness: flexible devices [e.g., 3-6]. However, the understanding of -2.0 -1.5 -1.0 -0.5 the sintering process from precursor MNP to conductive Log (Q) [A] metallic film is rather limited. In this paper, we report Fig. 2. Small angle neutron scattering of silver nanoparticles in measurements in order to gain better understanding and better deuterated toluene reveals an ensemble-averaged Ag core control of the MNP application to conductive film formation. diameter of 4.6 nm with 20% dispersion, which is consistent with This study is possible because high-quality and large electron microscopy observation. The thickness of the organic quantities of uniform MNPs particles become available. By shell is found be ca. 0.6 nm in solutions. 978-1-4244-2054-4/08/$25.00 2008 IEEE Energy (MeV) Energyr (MeV) visible absorption spectroscopy shows narrow absorption 0.5 l.o 1.5 2.0 lo 1.0 1.2 60 peaks centered at ca. 420 and 510 nm for Ag- and Au-NPs in 190 °C - (b) 50- (a) dilute cyclohexane solutions, respectively. X-ray diffraction detector indicates that both MNPs have the same crystalline structures N40 H 180 OC_ A ca as the bulk metals. The size and uniformity of particles are 190 °C 180 °C examined using electron microscopy and small angle neutron ' 20 D scattering (SANS). Figure 1 shows a SEM micrograph of ca. As-cast 10 Si S 5 nm Ag-NPs (a), and a TEM micrograph of ca. 4 nm Au-NPs Au S (b). SANS measurement of Ag-NP in toluene is shown in 50 100 150 200 250 300 350 400 100 150 200 250 Channel Channel Fig. 2, in which the SANS data (open circles) are fitted with a Fig. 3. (a) RBS spectra of Au-NP films showing increasing Au core-shell model to give the average Ag-NP characteristics. density upon sintering. (b) A blow-up view of the Si and S front The ensemble-averaged Ag-NP core diameter is found to be showing diminishing S signals with sintering. 4.6 +0.2 nm with a standard deviation dispersion of 1.1 rnm, or + 20%, which is consistent with electron microscopy 3.2. FRES observation. The thickness of the organic shell is found be The loss of hydrocarbon coating molecules upon sintering ca. 0.6 nm in solutions and 0.3 nm in the dried state. We is also evident from the FRES measurements. Figure 4a emphasize the importance of characterizing bulk properties shows hydrogen peaks of FRES spectra of as-cast and for achieving better performances in device applications. sintered Ag- and Au-NP films. Figure 4a shows FRES spectra of Ag-NP films after various times at 80 °C. The H- 3. Experiment signal decreases with sintering time, indicating that sintering at a temperature as low as 80 °C for a time as short as a few Films of Ag-NPs and Au-NPs were spun-cast from minutes is sufficient to drive majority of hydrocarbon away cyclohexane solutions with 10% and 500 MNP solid mass, from the film.
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