Department of Chemical Engineering, Stanford University , Stanford, California 94305, United States.
Nano Lett. 2013 Jul 10;13(7):3352-7. doi: 10.1021/nl401641v. Epub 2013 Jul 1.
Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity, where benefits in conversion efficiency and economy can be obtained. On a fundamental level, it is of great interest to explore whether the ultimate limits in light absorption per unit volume can be achieved by capitalizing on the advances in metamaterial science and nanosynthesis. Here, we combine block copolymer lithography and atomic layer deposition to tune the effective optical properties of a plasmonic array at the atomic scale. Critical coupling to the resulting nanocomposite layer is accomplished through guidance by a simple analytical model and measurements by spectroscopic ellipsometry. Thereby, a maximized absorption of light exceeding 99% is accomplished, of which up to about 93% occurs in a volume-equivalent thickness of gold of only 1.6 nm. This corresponds to a record effective absorption coefficient of 1.7 × 10(7) cm(-1) in the visible region, far exceeding those of solid metals, graphene, dye monolayers, and thin film solar cell materials. It is more than a factor of 2 higher than that previously obtained using a critically coupled dye J-aggregate, with a peak width exceeding the latter by 1 order of magnitude. These results thereby substantially push the limits for light harvesting in ultrathin, nanoengineered systems.
用尽可能少的材料实现对可见光的完全吸收，这对于许多应用来说都是非常理想的，包括太阳能转化为燃料和电能，这样可以提高转化效率和经济效益。从根本上讲，探索通过利用超材料科学和纳米合成技术是否可以实现单位体积内光吸收的极限，这是非常有趣的。在这里，我们结合嵌段共聚物光刻和原子层沉积，在原子尺度上调整等离子体阵列的有效光学性质。通过简单的分析模型指导和光谱椭圆偏振测量，实现了与所得纳米复合材料层的临界耦合。从而实现了超过 99%的最大光吸收，其中高达约 93%的光吸收发生在仅 1.6nm 厚的金体积等效层中。这对应于在可见光区域中创纪录的有效吸收系数 1.7×10(7)cm(-1)，远远超过固体金属、石墨烯、染料单层和薄膜太阳能电池材料的吸收系数。这比使用临界耦合染料 J-聚集体获得的吸收系数高 2 倍以上，其峰值宽度比后者宽 1 个数量级。这些结果大大推动了在超薄、纳米工程系统中进行光收集的极限。
