Fig. 1: Characterization of 2,6-bis(4-hexylphenyl)anthracene (C6DPA) monolayer molecule crystals (MMCs) and bimolecular layer p–n heterojunctions.
From: Sub-5 nm single crystalline organic p–n heterojunctions
a Molecular arrangement of C6DPA MMCs with thickness of around 2.7 nm. Blue represents carbon atom and gray represents hydrogen atom. b–f Characterizations of C6DPA MMCs: b cross-polarized optical micrograph; c atomic force microscopy (AFM) image; d high-resolution AFM (HR-AFM) image (insert: corresponding 2D Fourier transfer pattern); e, f optical and fluorescent images of large area MMCs, respectively (the dotted line areas refer to poly(methyl methacrylate) (PMMA) and the others C6DPA MMCs). g Molecular arrangement schematic of bimolecular layer p–n heterojunctions consisting of 2,2′-(2,8-bis(3-hexylundecyl)-1,3,7,9-tetraoxo-1,2,3,7,8,9-hexahydro-[1,3]dithiolo[4′,5′:5,6]benzo[1,2,3,4-lmn][1,3]dithiolo[4,5-f][3,8]phenanthroline-5,11-diylidene)dimalononitrile (NDI) MMC (top, around 1.8 nm thick) and C6DPA MMC (bottom, around 2.8 nm thick). Red represents oxygen atom, yellow represents sulfur atom, purple represents nitrogen atom. h–n Characterizations of NDI-C6DPA MMCs based p–n heterojunctions: h optical image; i fluorescent image at the excitation wavelength of 365 nm (the dark and green regions refer to NDI and C6DPA, respectively); j fluorescent image at the excitation wavelength of 530 nm (the red and dark regions refer to NDI and C6DPA, respectively, the exposure time is elongated for better contrast to show the clear p–n interface); k AFM image; l cross-sectional transmission electron microscope (TEM) image; m, n HR-AFM of C6DPA MMCs (b: 0.48 nm, c: 0.48 nm, θ: 102.1°) and NDI MMCs (b: 0.45 nm, c: 0.46 nm, θ: 99.1°), respectively. The insert images are corresponding 2D Fourier transfer patterns.
