Elsevier

Optik

Volume 220, October 2020, 165186
Optik

Structure-changed third-order optical nonlinearity in CaCu3Ti4O12 thin films grown on MgO(111) substrates

https://doi.org/10.1016/j.ijleo.2020.165186Get rights and content

Abstract

CaCu3Ti4O12 (CCTO) thin films of preference (220) orientation are deposited on MgO(111) substrates using pulsed laser deposition method. The third-order optical nonlinearity of CCTO films was investigated using Z-scan technique at a wavelength of 532 nm with 25 ps duration pulses. The self-focusing behavior in CCTO films was observed, which is different from the traditional CCTO films grown on LaAlO3 (0001), MgO(100), and fused silica substrates of self-defocusing behavior. The third-order nonlinear refraction coefficient is determined of a value 0.76 cm2/GW, along with the fifth-order nonlinear refractive index -0.2 cm4/GW2, the nonlinear absorption coefficient -1.87 × 10−7 m/W and saturable absorption intensity 1.72 GW/cm2. The structure-changed nonlinear refraction and fast response at picosecond time-domain extend the potential applications of CaCu3Ti4O12 thin films for nonlinear photonics devices.

Introduction

Thin films of excellent third-order optical nonlinearity are essential for integrated all-optical processing devices, such as switching, computing, storage and communication [1]. Comparing with bulk materials, the linear and nonlinear optical properties of thin films can be flexibly modulated by introducing atom composition deviation, interface effects, and orientation of crystallization during the fabrication [[2], [3], [4], [5], [6], [7], [8]]. Especially, the integrated photonic devices may be fabricated on different substrates, which lead to different growth orientation of films due to lattice mismatch. Over the past few years, the third-order optical nonlinearity in films grown on various substrates of different crystallization states, e.g. amorphous [3,9], polycrystalline [10,11], preferred orientation [12,13], nanocrystalline doped in matrices [5,14], were intensively studied. Fruitful results were obtained. However, few reports are on the comparison of the optical nonlinearity in the same materials of different crystallization states [8,13]. Considering the application of nonlinear films, the detailed study on the effect of film structures on the optical nonlinearity has practical significance for the integrated photonic devices.

Calcium copper titanate (CaCu3Ti4O12, CCTO) film with perovskite-like structure of high dielectric permittivity for microelectronics [15,16], photochemistry [[17], [18], [19]] and large third-order optical nonlinearity has drawn much attentions [8,12]. The nonlinear refraction in CCTO originates from the d-orbital between transition metal and oxygen, i.e. Ti-O and Cu-O, and determined by the bond length quadratically [12]. The bond length between transition metal and oxygen can be modulated by lattice mismatch between the film and substrate, and thus to change the nonlinear refraction. In our previous studies, we have reported the optical nonlinearity in the films deposited on different substrates, e.g. LaAlO3 (0001), MgO (002) and fused silica (SiO2) substrates, of different preferred growth orientation [8,12]. The negative nonlinear refractive index γ2 of different values ∼10−14  m2/W was obtained in those films. The two-photon absorption in the films grown on MgO(002) substrates while the saturable absorption in the films on LaAlO3 (0001) and fused silica substrates were observed. The results indicate that the optical nonlinearity is indeed affected by the structure of film. In this paper, we further deposited CCTO films on MgO(111) substrates, and the CCTO films of (220) orientation are obtained. The self-focusing behavior in CCTO films of positive nonlinear refraction was first observed, which is different from the films grown on aforementioned substrates of self-defocusing behavior. The nonlinear refraction coefficient, along with the nonlinear saturable absorption intensity is determined.

Section snippets

Experimental method

The CCTO films were grown on single crystal double-polished (111) MgO substrates by pulsed laser deposition technique. The processes are almost the same as we reported [8,12]. Briefly, a XeCl excimer laser beam (308 nm, 27 ns, 4 Hz) was focused onto a CCTO target with a typical energy about 2 J/cm2. The films were deposited under 30 Pa of O2 at 800 °C, followed by annealing for 30 min at the deposition temperature in 1 atm oxygen. The thickness of films was controlled by deposition time, and

Results and discussion

The crystallization of a CCTO film on an MgO (111) substrate is shown in Fig. 1. The diffraction angles at 34.26° and 72.18° correspond to Miller indices (220) and (440) of CCTO, respectively, indicating that the CCTO film has a (220)-preferred orientation. The lattice parameters can be calculated using Bragg’s law nλ=2dhkl sinθ with n an integer, λ the wavelength of X-ray, θ the incident angle of X-ray to the surface of sample, and dhkl the inter-planar spacing with indice (hkl). The lattice

Conclusions

In summary, we investigated the optical nonlinearity of the CCTO thin films of (220)-orientation grown on MgO(111) using Z scan technique at a wavelength of 532 nm with the pulse duration of 25 ps. The nonlinear saturable absorption coefficient, saturable intensity and modulation depth was determined, and suitable for high-power mode-lock laser. The large positive third-order nonlinear refraction of value 0.76 cm2/GW and negative fifth-order nonlinear refraction of value -0.2 cm4/GW2 were

Funding

We acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 11404195) and China Postdoctoral Science Foundation (Grant No. 2015M582127).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (39)

  • C.H. Cheng et al.

    Strong optical nonlinearity of the nonstoichiometric silicon carbide

    J. Mater. Chem. C Mater. Opt. Electron. Devices

    (2015)
  • C. Torres-Torres et al.

    Thermo-optic effect and optical nonlinearity in nc-Si embedded in a silicon-nitride film

    Opt. Express

    (2008)
  • T. Ning et al.

    Effect of structure on nonlinear optical properties in CaCu3Ti4O12 films

    J. Appl. Phys.

    (2015)
  • B. Ding et al.

    Third-order optical nonlinearity in silicon nitride films prepared using magnetron sputtering and application for optical bistability

    J. App. Phys.

    (2019)
  • B. Gu et al.

    Giant optical nonlinearity of a Bi2Nd2Ti3O12 ferroelectric thin film

    Appl. Phys. Lett.

    (2004)
  • H. Shin et al.

    Large nonlinear optical response of polycrystalline Bi3.25La0.75Ti3O12 ferroelectric thin films on quartz substrates

    Opt. Lett.

    (2007)
  • T. Ning et al.

    Large optical nonlinearity in CaCu3Ti4O12 thin films

    Appl. Phys. A

    (2009)
  • H.S. Kushwaha et al.

    Efficient Solar Energy Conversion Using CaCu3Ti4O12 Photoanode for Photocatalysis and Photoelectrocatalysis

    Sci. Rep.

    (2016)
  • M. Ahmadipour et al.

    Effect of thickness on humidity sensing properties of RF magnetron sputtered CaCu3Ti4O12 thin films on alumina substrate

    IEEE Sens. J.

    (2017)
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