Targeted positioning of quantum dots inside 3D silicon photonic crystals observed by synchrotron X-ray fluorescence tomography

It is a major challenge in nanotechnology to precisely position active nanoparticles, like quantum dots, inside a three-dimensional (3D) nanostructure in order to realize novel functions. This is notably relevant to tune and control spontaneous emission and lasing of embedded quantum emitters [1] , [2]. Here, we study 3D photonic band gap crystals made from silicon that are infiltrated with PbS nanocrystal quantum dots that emit in the near infrared including telecom. Our crystals have the inverse woodpile structure and exhibit a broad full 3D band gap. Such crystals strongly inhibit emission of semiconductor quantum dots [3]. The material distribution in the crystals is defined by two perpendicular arrays of pores ( Fig. 1(A) ), running in the Z and X-directions. The crystal are made by CMOS-compatible means by deep reactive ion-etching through tailored masks. The PbS nanocrystals are covalently bonded to polymer brush layers that are grafted to the Si-air interfaces inside the 3D nanostructure using surface-initiated atom transfer radical polymerization (SI-ATRP) [4].