Modulation of the Visible Absorption and Reflection Profiles of ITO Nanocrystal Thin Films by Plasmon Excitation
Modulation of the Visible Absorption and Reflection Profiles of ITO Nanocrystal Thin Films by Plasmon Excitation
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DOI：
10.1021/acsphotonics.9b01825
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发表时间：
2020-05-20
期刊：
影响因子：
7
通讯作者：
Roberts, Sean T.
中科院分区：
文献类型：
--
作者：
Blemker, Michelle A.;Gibbs, Stephen L.;Roberts, Sean T.
重掺杂金属氧化物纳米晶(NCs)具有可调谐的红外局域表面等离子体共振(LSPR)，使其在光热治疗、智能电致变色窗口、光催化和光学门控等领域具有广阔的应用前景。然而，对这些材料的光响应的研究在很大程度上局限于短波红外(SWIR)光谱区域，在那里它们的LSPR响应峰值。很少有人研究LSPR激发如何调制这些材料在UV/可见光区域的带隙附近的光学性质。在这里，我们展示了掺锡In2O_3(ITO)纳米晶薄膜在LSPR激发下的光吸收和反射率的变化。ITO纳米碳管的SWIR辐照大大加热了它们的自由电荷载流子，改变了纳米碳管薄膜的介电响应。这导致了薄膜反射率和吸收率的超快增加，随着热电荷载流子与NC晶格的热化，薄膜的反射率和吸收率在光激发后松弛在1ps以内。根据Drude模型和Fermi-Dirac统计量建立了一个能解释自由电荷载流子行为的模型，我们再现了这一行为，并预测通过充分的SWIR辐照，ITO纳米薄膜的反射率可以达到约6%的变化。我们还将我们的模型应用于其他常见的等离子体材料，强调了等离子体金属氧化物纳米薄膜可以在整个可见光区域获得大的、光谱平坦的反射率变化。我们的结果表明，这些材料具有用作太赫兹光学门的潜力，并进一步加深了我们对其等离子体行为的基本理解。
Heavily doped metal oxide nanocrystals (NCs) possess tunable infrared localized surface plasmon resonances (LSPRs) that give them utility for several potential applications, including photothermal therapy, smart electrochromic windows, photocatalysis, and optical gating. However, studies of the photoresponse of these materials have largely been limited to the short-wave infrared (SWIR) spectral region, where their LSPR response peaks. Little has been done to study how LSPR excitation modulates the optical properties of these materials around their band gap in the UV/visible region. Here we demonstrate changes in the optical absorption and reflectivity of Sn-doped In2O3 (ITO) nanocrystal thin films following LSPR excitation. SWIR irradiation of ITO NCs substantially heats their free charge carriers, altering the NC films dielectric response. This gives rise to an ultrafast increase in film reflectivity and absorptivity that relaxes within 1 ps following photoexcitation as hot charge carriers thermalize with the NC lattice. Using a model that accounts for free charge carrier behavior according to the Drude model as well as Fermi-Dirac statistics, we reproduce this behavior and predict that reflectivity changes of similar to 6% can be achieved via sufficient SWIR irradiation of ITO NC films. We also apply our model to other common plasmonic materials, highlighting that plasmonic metal oxide NC films can be used to obtain large, spectrally flat reflectivity changes throughout the visible region. Our results suggest these materials hold potential for use as terahertz optical gates and further our fundamental understanding of their plasmonic behavior.