Extracting Thin-film Optical Parameters from Spectrophotometric Data by Evolutionary Optimization

Extracting optical parameters from spectrophotometric measurements is a challenging task. In a photometric setup, an unknown thin-film is subjected to an incident light beam for a range of admissible wavelengths, which outputs reflectance and transmittance spectra. The current work attempts to solve an inverse problem of extracting thin-film thickness and complex refractive index from reflectance and transmittance spectra for an incident angle of light. The film thickness is a scalar quantity, and the complex refractive index is composed of real and imaginary parts as functions of wavelengths. We leverage evolutionary optimization techniques to solve the underlying inverse problem, which determines the desired parameters associated with two optical dispersion models: ensemble of Tauc-Lorentz (TL) and ensemble of Gaussian oscillators, such that the generated spectra accurately fit the input data. The optimal parameters involved in the adopted models are determined using efficient evolutionary algorithms (EAs). Numerical results validate the effectiveness of the proposed approach in estimating the optical parameters of interest.

Effect of deposition temperature on the properties of F and Ti co-doped zinc oxide films

ZnO + 1.5 wt.% TiO2 powder is calcined at [Formula: see text] and sintered at [Formula: see text] to prepare the Ti-doped ZnO ceramic target, and RF sputtering is used to deposit F and Ti co-doped ZnO (FTZO) films by introducing Ar + CF4 mixing gas (CF4 flow rate is 0.2%) into the deposition chamber. The deposition temperature is changed from room temperature to [Formula: see text], and the thicknesses of all deposited FTZO films are controlled at about 320 nm. After FTZO films are deposited, X-ray diffraction pattern is used to analyze their crystalline properties, field-effect scanning electron microscope is used to observe their surface morphologies and confirm their thicknesses. n&k analyzer is used to measure the transmittance spectra in the wavelength range of 300–1100 nm and we find that the absorption edge of FTZO films is shifted to lower wavelength as the deposition temperature increases. The optical energy band gap of FTZO films is calculated using the transmittance spectra and the electrical properties of FTZO films are measured using a Hall equipment. Finally, secondary-ion mass spectrometry is used to analyze the C, O, F, Si and Ti elements with different deposition temperatures for confirming the existence and distribution of [Formula: see text] ions and non-existence of C element.

Growth of Ga2O3 Nanowires by a Vapor Transport Method and their Optical Transmittance Spectra

Gallium oxide (Ga2O3) nanowires were grown on fused quartz and Si substrates by a vapor transport method of heating gallium metal at 750−1100 °C in a tube of the horizontal furnace. The obtained white colored product has shown to be the Ga2O3 nanowires with average diameters ranging from 30 to 80 nm. The optical transmittance spectra indicated that the bandgap energy of Ga2O3 nanowire increases as the diameter of nanowire decreases.