Keywords:carbon nanotubes, hexagonal boron nitride, photoluminescence
We study h-BN effects on PL excitation (PLE) spectra of CNTs by transferring CNTs on h-BN flakes. CNTs are first grown on a SiO2/Si substrate, and we prepare h-BN flakes on another SiO2/Si substrate by mechanical exfoliation. The CNTs are picked up by using a PDMS/anthracene stamp and transferred on the target h-BN flake by using the micromanipulator system. PDMS is peeled off and anthracene is sublimated at 110°C, leaving a clean surface for CNTs. It is noted that CNTs are transferred on the surrounding SiO2/Si substrate simultaneously due to the large area of the PDMS/anthracene stamp. An atomic force microscopy (AFM) phase image of CNTs on both h-BN and the SiO2/Si substrate is shown in Figure 1(a), and it is observed that many randomly oriented CNTs are firmly attached to both h-BN and the SiO2/Si substrate without showing any loose ends or segments.
Integrated PL images are taken in the same region as the AFM image and shown in Figure 1(b). Although CNTs are transferred on both the h-BN flake and the SiO2/Si substrate, only CNTs on h-BN show bright PL. Compared with conventional substrates, the h-BN substrate is atomically flat with no dangling bonds and low defects density, which might contribute to the considerable suppression of the substrate quenching effect. Moreover, the large redshifts in E11 and E22 of ~50 meV are observed, which is attributed to the dielectric screening effect.