Engineering of Large Third-Order Nonlinearities in Atomic Layer Deposition Grown Nitrogen-Enriched TiO2

The third-order nonlinear optical properties of nitrogen enriched TiO2 films deposited by atomic layer deposition (ALD) at a temperature between 100-300 degrees C on quartz substrates were studied using thermally managed Z-scan technique. TiO2 oxide films prepared by physical vapor deposition (PVD) at room temperature were used as control samples. The as-grown ALD films deposited at 150-300 degrees C exhibited values for the nonlinear index of refraction, n(2), between 0.6 x 10(-11) and 1 x 10(-9) cm(2)/W, which is 4-6 orders larger than previously reported. Annealing the films for 3 h at 450 degrees C in air reduced the nonlinearities below the detection limit of the experimental setup. Similarly, as-grown 100 degrees C ALD and PVD films did not produce a discernible Z-scan trace. Composition analysis performed by X-ray photoelectrons spectroscopy (XPS) reveals the presence of Ti-O-N metallic bonds in the films that showed high nonlinear optical response. The presence of the metallic bonding gives the films deposited on Si(100) a golden color. These results demonstrate the possibility of a new class of thin-film nonlinear materials in which their properties can be tailored by controlling the film composition.