An optical slot-antenna-coupled cavity (SAC) framework towards tunable free-space graphene photonic surfaces
An optical slot-antenna-coupled cavity (SAC) framework towards tunable free-space graphene photonic surfaces
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DOI：
10.1007/s12274-020-3184-z
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发表时间：
2020-11
期刊：
影响因子：
9.9
通讯作者：
Sidan Fu;Xiaoxin Wang;Haozhe Wang;Xiaoxue Gao;K. Broderick;J. Kong;Jifeng Liu
中科院分区：
文献类型：
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作者：
Sidan Fu;Xiaoxin Wang;Haozhe Wang;Xiaoxue Gao;K. Broderick;J. Kong;Jifeng Liu
单层石墨烯(SLG)的光学导电性可以通过电选通调节费米能级来显著和可逆地改变。然而，到目前为止，这一有趣的性质还很少应用于自由空间二维(2D)光子器件，因为SLG的表面入射绝对吸收限制在1%-2%。即使SLG在选通时是透明的，也不会观察到反射率或透射率的显著变化。为了在允许选通的器件结构中显著增强SLG的表面入射光吸收，我们在这里将SLG嵌入到光学缝隙-天线耦合腔(SAC)框架中，同时将SLG的吸收提高高达20倍，并潜在地实现了SLG的电子选通，作为迈向可调2D光子表面的一步。该框架将超高折射率半金属缝隙天线的近场增强与可见光和红外波段的宽带谐振相结合，比单独垂直腔体结构的效率高约3倍。这种结构的一个例子是由自组装的紧密堆积的锡纳米点组成，这些纳米点在SLG/SiO_2/Al堆栈上被~10 nm的纳米隙隔开，这使得在λ=600-1,900 nm处的SLG光吸收显著增加到10%-25%。增强的SLG吸收光谱也可以通过绝缘层厚度来控制。例如，嵌入在该框架中的具有150 nm厚的二氧化硅绝缘层的SLG显示出独特的红色，与白光照射下同一样品上没有SLG的周围区域形成鲜明对比。这开辟了一条通向栅极可调光谱反射器的潜在途径。总体而言，这项工作开创了一种新的方法来实现可调谐的2D光子表面。
The optical conductivity of single layer graphene (SLG) can be significantly and reversibly modified when the Fermi level is tuned by electrical gating. However, so far this interesting property has rarely been applied to free-space two-dimensional (2D) photonic devices because the surface-incident absolute absorption of SLG is limited to 1%–2%. No significant change in either reflectance or transmittance would be observed even if SLG is made transparent upon gating. To achieve significantly enhanced surface-incident optical absorption in SLG in a device structure that also allows gating, here we embed SLG in an optical slot-antenna-coupled cavity (SAC) framework, simultaneously enhancing SLG absorption by up to 20 times and potentially enabling electrical gating of SLG as a step towards tunable 2D photonic surfaces. This framework synergistically integrates near-field enhancement induced by ultrahigh refractive index semimetal slot-antenna with broadband resonances in visible and infrared regimes, ~ 3 times more effective than a vertical cavity structure alone. An example of this framework consists of self-assembled, close-packed Sn nanodots separated by ~ 10 nm nanogaps on a SLG/SiO2/Al stack, which dramatically increases SLG optical absorption to 10%-25% atλ= 600–1,900 nm. The enhanced SLG absorption spectrum can also be controlled by the insulator thickness. For example, SLG embedded in this framework with a 150 nm-thick SiO2insulating layer displays a distinctive red color in contrast to its surrounding regions without SLG on the same sample under white light illumination. This opens a potential path towards gate-tunable spectral reflectors. Overall, this work initiates a new approach towards tunable 2D photonic surfaces.