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Takano K, Asai M, Kato K, Komiyama H, Yamaguchi A, Iyoda T, Tadokoro Y, Nakajima M, Bakunov MI. Terahertz emission from gold nanorods irradiated by ultrashort laser pulses of different wavelengths. Sci Rep 2019; 9:3280. [PMID: 30824828 PMCID: PMC6397179 DOI: 10.1038/s41598-019-39604-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Accepted: 01/28/2019] [Indexed: 11/09/2022] Open
Abstract
Electron photoemission and ponderomotive acceleration by surface enhanced optical fields is considered as a plausible mechanism of terahertz radiation from metallic nanostructures under ultrafast laser excitation. To verify this mechanism, we studied experimentally terahertz emission from an array of gold nanorods illuminated by intense (~10-100 GW/cm2) femtosecond pulses of different central wavelengths (600, 720, 800, and 1500 nm). We found for the first time that the order of the dependence of the terahertz fluence on the laser intensity is, unexpectedly, almost the same (~4.5-4.8) for 720, 800, and 1500 nm and somewhat higher (~6.6) for 600 nm. The results are explained by tunneling currents driven by plasmonically enhanced laser field. In particular, the pump-intensity dependence of the terahertz fluence is more consistent with terahertz emission from the sub-cycle bursts of the tunneling current rather than with the ponderomotive mechanism.
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Affiliation(s)
- Keisuke Takano
- Center for Energy and Environmental Science, Shinshu University, 4-17-1 Wakasato, Nagano, 380-8553, Japan.
- Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871, Japan.
| | - Motoki Asai
- Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Kosaku Kato
- Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Hideaki Komiyama
- JST-ERATO Iyoda Supra-Integrated Material Project, Tokyo Institute of Technology, 4259 Nagatsuda-Cho, Midori-Ku, Yokohama, Kanagawa, 226-8503, Japan
| | - Akihisa Yamaguchi
- JST-ERATO Iyoda Supra-Integrated Material Project, Tokyo Institute of Technology, 4259 Nagatsuda-Cho, Midori-Ku, Yokohama, Kanagawa, 226-8503, Japan
| | - Tomokazu Iyoda
- JST-ERATO Iyoda Supra-Integrated Material Project, Tokyo Institute of Technology, 4259 Nagatsuda-Cho, Midori-Ku, Yokohama, Kanagawa, 226-8503, Japan
| | - Yuzuru Tadokoro
- Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Makoto Nakajima
- Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Michael I Bakunov
- University of Nizhny Novgorod, 23 Gagarin Avenue, Nizhny Novgorod, 603950, Russia.
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Seed-Mediated Electroless Deposition of Gold Nanoparticles for Highly Uniform and Efficient SERS Enhancement. NANOMATERIALS 2019; 9:nano9020185. [PMID: 30717277 PMCID: PMC6409782 DOI: 10.3390/nano9020185] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/13/2019] [Revised: 01/29/2019] [Accepted: 01/29/2019] [Indexed: 12/13/2022]
Abstract
A seed-mediated electroless deposition (SMED) approach for fabrication of large-area and uniform gold nanoparticle films as efficient and reproducible as surface-enhanced Raman scattering (SERS) substrates was presented. This approach involved a seeding pretreatment procedure and a subsequent growth step. The former referred to activation of polylysine-coated glass slides in gold seed solution, and the latter required a careful control of the reactant concentration and reaction time. With the aid of gold seeds and appropriate reaction conditions, a large-area and uniform nanofilm with evenly distributed gold nanoparticles (Au NPs) was formed on the surface of the substrates after adding a mixed solution containing ascorbic acid and trisodium citrate. The morphology of the Au nanofilm was examined by scanning electron microscopy. The size evolution of Au NPs on the surface of the substrates was analyzed in detail. The nanofilm substrate was prepared by reaction conditions of the seeded activation process: 10 mL ascorbic acid and trisodium citrate mixture and 30 min of soaking time, which exhibited an excellent uniformity and reproducibility of SERS enhancement with relative standard deviation (RSD) values of less than 8% (particularly, a RSD value of 3% can be reached for the optimized measurement). Compared to the common electroless deposition, the seed-mediated electroless deposition possessed inherent advantages in controllability, reproducibility, and economic benefit.
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