Figure 4: Sub-wavelength χ⁽²⁾ grating fabrication.

(a) Schematic showing the grating-shadowed oblique-angle deposition approach used to periodically pattern the distribution of donor–acceptor interface in a DAS multilayer. Samples consist of a sinusoidal photoresist grating on glass, with uniformly deposited CBP spacer and rubrene donor layers, and obliquely deposited C₆₀ acceptor layers. The nominal thickness of each layer is 5 nm and complete samples contain five DAS periods. (b,c) Cross-sectional scanning electron micrographs show the bare photoresist grating template (b) together with the result after coating with three DAS periods (c). The scale bar is 200 nm in both b and c. The individual layers in c are purposely grown with an exaggerated thickness of 25 nm for image clarity to enable the periodic accumulation of C₆₀ on the right-hand grating facets to be discerned.