Morphological manipulation of the nonlinear optical response of ZnO thin films grown by thermal evaporation

Abstract

ZnO thin films with different micro-/nano-structured morphologies have been fabricated using thermal evaporation technique. The micro-/nano-structures ranged from dense grains to nanorods and nanowires. The fabricated films were characterized using x-ray diffraction and field emission scanning electron microscopy (FE-SEM) techniques for determining their crystalline behavior and evaluating their morphology, respectively. Photoluminescence (PL) studies revealed two emission peaks in these films, one in the UV region due to exciton emission and the other in the visible spectral region due to Zn or Oxygen vacancies/defects. The effect of these different micro-/nano-structures on the third-order nonlinear optical (NLO) response has been scrutinized using the Zscan technique with femtosecond (fs), MHz and picosecond (ps), kHz pulses at a wavelength of 800 nm. Various NLO coefficients such as two-photon absorption (β), nonlinear refractive index (n 2), Re [χ (3) ], Im [χ (3) ] and χ (3) were evaluated. The obtained χ (3) values were ∼10 −7 e.s.u. in the fs regime and ∼10 −10 e.s.u. in the ps regime. Optical limiting studies of these films were also performed and limiting thresholds were estimated to be 15-130 μJ cm −2 in the fs regime while in ps regime the corresponding values were 1-3 J cm −2. The NLO data clearly designates strong third-order nonlinearities in these ZnO thin films with possible applications in photonics.

The role of cobalt doping in tuning the band gap, surface morphology and third-order optical nonlinearities of ZnO nanostructures for NLO device applications

“…The result of our article are in excellent agreement with some previously reported NLO of ZnO materials; also, the magnitude of the third-order NLO susceptibilities is at least one order higher compared to that reported in ref. 57. In our current material, it was conrmed that the crystalline quality of the lms is the key factor for the large NLO properties.…”

The photoluminescence, field emission and femtosecond nonlinear absorption properties of Al-doped ZnO nanowires, nanobelts, and nanoplane-cone morphologies

“…The similar analysis process has been reported. [38][39][40][41][42][43] From the experimental results, the 2PA induced conduction band or defect state RSA (two-step 3PA) behavior of AZO nanostructures with different morphologies has been determined. With standard Z scan theory, we extract the effective nonlinear absorption coefficients with the sample approximation.…”

Hysteresis-free DC conduction in zinc oxide films with a conducting polymer counter electrode

“…No pronounced peak was found to have occurred in the visible range of the emission spectrum. This absence implies the formation of high crystal quality of ZnO films without the significant presence of oxygen vacancies [25]. The PL excitation spectrum is also recorded at the emission wavelength of 395 nm.…”