Figure 5: The controlled joining of organic single-crystal wires.

(a) Dark-field fluorescent micrograph of an array of 90° joined organic wires formed on square-structured micropillars with a pillar length of 40 μm. Dark-field fluorescent micrographs of single (c) square, (f) pentagonal, (h) hexagonal and (j) circular BPEA wires, demonstrating that organic, 1D structures can be grown at precise internal angles of 90° (square), 108° (pentagon), 120° (hexagon) and nearly 180° (circle, technically a super-polygon). (b) Simulated electric field intensity distribution (surface: electric field norm (V m⁻¹), λ=488 nm, n=1.80) in the 90° joined BPEA wires. The electric field intensity in each bent section indicates that the energy of the electric field can be well confined in the structure as exciton polariton resonators. (d) Schematic illustration of optical waveguiding along square-patterned organic wires. A laser beam was focused on the wires to investigate the optical propagation. (e,g,i,k) PL images of waveguiding wire patterns under laser excitation. A 488-nm continuous-wave argon-ion laser was focused to a beam spot size of 1 μm to excite the aligned organic single-crystal wires at an excitation power of <2 W cm⁻². The light could waveguide through small radii of curvature, for example, internal angles of 90°, 108°, 120° and nearly 180°. A luminescence spot appeared at each joint of the wire patterns, indicating some optical loss in these regions. This effect was particularly strong in the circular wire pattern. Scale bars, a 20 μm, c,e 10 μm, f–k 10 μm.