Sub-nanometer Thin Oxide Film Sensing with Localized Surface Phonon Polaritons
Sub-nanometer Thin Oxide Film Sensing with Localized Surface Phonon Polaritons
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DOI：
10.1021/acsphotonics.7b01482
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发表时间：
2018-07-01
期刊：
影响因子：
7
通讯作者：
Caldwell, Joshua D.
中科院分区：
文献类型：
--
作者：
Berte, Rodrigo;Gubbin, Christopher R.;Caldwell, Joshua D.
基于表面极化激元共振的化学传感方法源于它们的强近场和对局部折射率变化的敏感性。极性介电晶体（例如，SiC，hBN）支持从中红外到太赫兹范围的表面声子极化激元（SPhP），其模式体积和品质因子超过了等离子体对应物获得的最佳情况，使其成为共振表面增强红外光谱的强有力候选者。我们报告的行为的SPhP共振的SiC纳米柱后，将通过原子层沉积获得的亚纳米和纳米涂层的Al 2 O3和ZrO 2。沉积亚纳米Al 2 O3薄膜时，观察到SPhP共振的同时异常红移和蓝移，其移动方向由相对于Al 2 O3的普通纵向光学声子的模式位置决定。这些并发的位移，这是由于耦合到Berreman模式的Al 2 O3层，坚持较厚的膜，并正确预测采用测量的Al 2 O3介电常数的数值计算。ZrO 2的沉积，其声子共振是从SPhP失谐，也导致异常的横向和纵向SPhP共振蓝移约900厘米（-1）的薄膜高达类似的1.5纳米，逆转到较厚的层的正则红移。这些异常的位移没有再现数值使用测得的ZrO 2介电常数，并建议存在一个本地化的表面状态，当建模为一个简单的洛伦兹振荡器，提供半定量的协议与实验结果。此外，较厚的ZrO 2层的预测位移，因此可以提供一个工具，用于实时监控的ZrO 2膜的生长。
Chemical sensing methods based on surface polaritonic resonances stem from their intense near fields and resultant sensitivity to changes in local refractive index. Polar dielectric crystals (e.g., SiC, hBN) support surface phonon polaritons (SPhPs) from the mid-infrared to terahertz range with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts, making them strong candidates for resonant surface-enhanced infrared spectroscopy. We report on the behavior of SPhP resonances of SiC nanopillars following the incorporation of sub-nano and nanometric coatings of Al2O3 and ZrO2 obtained by atomic layer deposition. Concurrent anomalous red- and blue-shifts of SPhP resonances were observed upon deposition of sub-nanometric Al2O3 films, with shift direction dictated by the mode position relative to the ordinary longitudinal optic phonon of Al2O3. These concurrent shifts, which are attributed to coupling to the Berreman mode of the Al2O3 layer, persist for thicker films and are correctly predicted by numerical calculations employing the measured Al2O3 permittivity. Deposition of ZrO2, whose phonon resonances are detuned from the SPhPs, also led to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900 cm(-1) for films up to similar to 1.5 nm, reversing to the canonical red-shift for thicker layers. These anomalous shifts were not reproduced numerically using the measured ZrO2 permittivity and suggest the existence of a localized surface state, which when modeled as a simple Lorentz oscillator, provides semiquantitative agreement with experimental results. In addition, predicted shifts for thicker ZrO2 layers may thus provide a tool for real-time monitoring of ultrathin film growth.