Department of Electrical and Computer Engineering, Micro and Nanotechnology Lab, University of Illinois Urbana-Champaign , 208 N. Wright St., Urbana, Illinois 61801, United States.
Nano Lett. 2013 Sep 11;13(9):4569-74. doi: 10.1021/nl402766t. Epub 2013 Sep 3.
Infrared absorption spectroscopy of vibro-rotational molecular resonances provides a powerful method for investigation of a wide range of molecules and molecular compounds. However, the wavelength of light required to excite these resonances is often orders of magnitude larger than the absorption cross sections of the molecules under investigation. This mismatch makes infrared detection and identification of nanoscale volumes of material challenging. Here we demonstrate a new type of infrared plasmonic antenna for long-wavelength nanoscale enhanced sensing. The plasmonic materials utilized are epitaxially grown semiconductor engineered metals, which results in high-quality, low-loss infrared plasmonic metals with tunable optical properties. Nanoantennas are fabricated using nanosphere lithography, allowing for cost-effective and large-area fabrication of nanoscale structures. Antenna arrays are optically characterized as a function of both the antenna geometry and the optical properties of the plasmonic semiconductor metals. Thin, weakly absorbing polymer layers are deposited upon the antenna arrays, and we are able to observe very weak molecular absorption signatures when these signatures are in spectral proximity to the antenna resonance. Experimental results are supported with finite element modeling with strong agreement.
振动旋转分子共振的红外吸收光谱为广泛的分子和分子化合物的研究提供了一种强大的方法。然而，激发这些共振所需的光的波长通常比所研究的分子的吸收截面大几个数量级。这种不匹配使得对纳米级体积的材料进行红外检测和识别具有挑战性。在这里，我们展示了一种用于长波长纳米级增强传感的新型红外等离子体天线。所利用的等离子体材料是外延生长的半导体工程金属，这导致了具有可调光学性质的高质量、低损耗红外等离子体金属。纳米天线是使用纳米球光刻法制造的，这允许进行具有成本效益的、大面积的纳米结构制造。作为天线几何形状和等离子体半导体金属光学性质的函数，对天线阵列进行了光学特性研究。在天线阵列上沉积了薄的、弱吸收聚合物层，当这些特征与天线共振光谱接近时，我们能够观察到非常微弱的分子吸收特征。实验结果得到了有限元建模的有力支持，吻合得很好。
