Dipartimento di Ingegneria dell'Informazione , Università di Pisa , via G. Caruso 16 , 56122 Pisa , Italy.
Istituto di Elettronica e di Ingegneria dell'Informazione e delle Telecomunicazioni , Consiglio Nazionale delle Ricerche , via G. Caruso 16 , 56122 Pisa , Italy.
ACS Sens. 2018 Mar 23;3(3):595-605. doi: 10.1021/acssensors.7b00650. Epub 2018 Jan 23.
Herein, we provide the first experimental evidence on the use of electrical double layer (EDL)-induced accumulation of charged ions (using both Na and K ions in water as the model) onto a negatively charged nanostructured surface (e.g., thermally growth SiO)-Ion Surface Accumulation, ISA-as a means of improving performance of nanostructured porous silicon (PSi) interferometers for optical refractometric applications. Nanostructured PSi interferometers are very promising optical platforms for refractive index sensing due to PSi huge specific surface (hundreds of m per gram) and low preparation cost (less than $0.01 per 8 in. silicon wafer), though they have shown poor resolution ( R) and detection limit (DL) (on the order of 10-10 RIU) compared to other plasmonic and photonic platforms ( R and DL on the order of 10-10 RIU). This can be ascribed to both low sensitivity and high noise floor of PSi interferometers when bulk refractive index variation of the solution infiltrating the nanopores either approaches or is below 10 RIU. Electrical double layer-induced ion surface accumulation (EDL-ISA) on oxidized PSi interferometers allows the interferometer output signal (spectral interferogram) to be impressively amplified at bulk refractive index variation below 10 RIU, increasing, in turn, sensitivity up to 2 orders of magnitude and allowing reliable measurement of refractive index variations to be carried out with both DL and R of 10 RIU. This represents a 250-fold-improvement (at least) with respect to the state-of-the-art literature on PSi refractometers and pushes PSi interferometer performance to that of state-of-the-art ultrasensitive photonics/plasmonics refractive index platforms.
在此，我们提供了第一个实验证据，证明了利用双层电介质（EDL）诱导带电荷离子的积累（以水作为模型，使用 Na 和 K 离子）到带负电荷的纳米结构表面（例如，热生长的 SiO2）上，即离子表面积累（ISA），作为提高纳米结构多孔硅（PSi）干涉仪在光学折射应用中的性能的一种手段。纳米结构 PSi 干涉仪由于 PSi 巨大的比表面积（每克数百平方米）和低廉的制备成本（每 8 英寸硅片不到 0.01 美元），是用于折射率传感的非常有前途的光学平台，尽管与其他等离子体和光子平台相比，它们显示出较差的分辨率（R）和检测限（DL）（约为 10-10 RIU）。这可以归因于当渗透纳米孔的溶液的体折射率变化接近或低于 10 RIU 时，PSi 干涉仪的灵敏度低和噪声基底高。在氧化 PSi 干涉仪上进行的双层电介质诱导离子表面积累（EDL-ISA），允许在体折射率变化低于 10 RIU 的情况下，干涉仪输出信号（光谱干涉图）得到显著放大，从而将灵敏度提高 2 个数量级，并允许可靠地测量折射率变化，其 DL 和 R 均为 10 RIU。这代表了与 PSi 折射计的现有技术文献相比至少提高了 250 倍，并将 PSi 干涉仪的性能提高到了最先进的超灵敏光子/等离子体折射率平台的水平。
