Z. M. Huang

Dielectric functions of ferroelectric Bi3.25La0.75Ti3O12 thin films on Si(100) substrates

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films were deposited directly on Si(100) substrates under annealing temperatures of 590 and 700 °C. The optical properties of the BLT films have been investigated using spectroscopic ellipsometry at room temperature in the 0.73–6 eV energy range. To model the dielectric functions of the BLT films, the double Tauc–Lorentz dispersion relation was successfully adopted. A four-layer model was used to fit the measured pseudodielectric function in order to deduce the complex dielectric functions. The results show that the annealing temperature mainly affects the dielectric functions of the BLT films beyond the fundamental band gap energy. The volume fraction of air present in the surface rough layer increases with increasing annealing temperature. The fundamental band gap was observed to shift slightly to a higher energy at a high annealing temperature. The difference of the optical properties due to the structure changes testifies the x-ray diffraction spectral results.

Optical properties of Mn1.56Co0.96Ni0.48O4 films studied by spectroscopic ellipsometry

Spectroscopic ellipsometry is used to determine the optical properties of the noncrystalline and crystalline Mn1.56Co0.96Ni0.48O4 (MCN) films prepared by chemical solution deposition method in the range of 250–1100 nm. A pronounced difference in the optical functions is found between 500 and 600 °C. Two distinctive peaks, attributed to the critical points of the MCN films, appear in the optical constant spectra for the films annealed at 600 °C while they are not obvious for the films annealed at 500 °C. The presented results are instructive, further understanding the physical properties of transition metal oxides in theory.

Optical and electrical properties of highly (100)-oriented PbZr1−xTixO3 thin films on the LaNiO3 buffer layer

In this paper, using wet chemical solution deposition processes, the (100)-highly oriented LaNiO3 buffer layers were grown on both silicon and platinized silicon wafers and, sequentially, the highly (100)-oriented PbZr1−xTixO3 thin films with various compositions were obtained on them. The misfit elastic strains were found to be critical factors to determine the orientation of PZT thin films, even though the used LaNiO3 buffer layer reduces the lattice mismatch between PZT films and silicon wafers. For the PZT thin films with x=0.5 and 0.6 on the LaNiO3/platinized silicon substrate, the infrared optical constant, ferroelectric, and dielectric properties were characterized and analyzed with relation to the film orientation and the film grain size. It was found that the finite grain size effect here played a key role in determining these optical and electrical properties. With nanoferroelectric thin films, it is the most useful way of controlling both grain size and crystallographic orientation to tune perf...

Optical properties of SrTiO3 thin films deposited by radio-frequency magnetron sputtering at various substrate temperatures

SrTiO3 thin films were deposited on vitreous silica substrates at various substrate temperatures (300–700°C) by rf magnetron sputtering technique. The transition from amorphous phase to polycrystalline phase for the films occurred at the substrate temperatures of 300–400°C. Their optical properties were investigated by transmittance measurements. The fitting method was used to calculate the refractive index and the film thickness from the transparent region of the transmittance spectra. The refractive index increased and the film thickness decreased with the substrate temperatures increasing. The dispersion of the refractive index was studied by considering a single electronic oscillator model. The band gaps of the films were estimated from Tauc’s law and showed a decreasing tendency to that of the bulk SrTiO3 with the substrate temperatures increasing. These results provide some useful references for the potential application of SrTiO3 films in integrated optics devices.

Ellipsometric characterization of LaNiO3−x films grown on Si (111) substrates: Effects of oxygen partial pressure

LaNiO3−x films have been grown on Si (111) substrates under different oxygen partial pressures using radio frequency magnetron sputtering. X-ray diffraction shows that these films are polycrystalline with a highly (100)-preferential orientation. The optical properties of the LaNiO3−x films have been systematically investigated by spectroscopic ellipsometry (SE) in the wavelength range of 400–1700 nm. For interpreting the SE experimental data, a parametrized Drude and double Lorentzian oscillator dispersion relation has been used to model the optical response of the LaNiO3−x films. The relations between the optical constants of the LaNiO3−x films and oxygen partial pressure have been characterized in detail. The resistivity can be calculated by the Drude term and these ellipsometric analysis results are nearly consistent with the electrical dc measurements. The resistivity (these values are about 5.5×103 μΩ cm) obtained by spectroscopic ellipsometry shows that these films would be good to use as bottom ele...

Temperature dependent optical properties of Mn doped (Pb,Sr)TiO3 ferroelectric films in absorption region: Electron–phonon interaction

The 2 mol % Mn doped Pb0.5Sr0.5TiO3 films were fabricated on sapphire substrates by chemical solution deposition. The complex dielectric functions and optical parameters of the films determined by transmittance spectroscopy in a broad temperature range of 80–500 K were investigated. Apparent thermally-driven band-gap energy shrinkage, line-width of interband electron transition broadening and the Urbach band tail behaviors were observed. The results can be mainly correlated with the renormalization of electronic band structure and band-gap energy due to the electron–phonon interaction, which is well established in terms of the Bose–Einstein model.

Optical characterization of ferroelectric Bi3.25La0.75Ti3O12 thin films

Abstract.Amorphous and crystalline Bi3.25La0.75Ti3O12 (BLT) thin films on vitreous silica and sapphire substrates are prepared from chemical solutions. Their optical properties are investigated by transmittance measurements at energies from 1.1 to 5.0 eV. A four-phase model consisting of air, surface rough layer, BLT, and substrate is used to simulate the measured transmittance spectra. The inverse synthesis method with a double Tauc-Lorentz (DTL) dispersion function is used to calculate the optical constants and film thicknesses. The dispersion of the refractive index in the transparent region agrees with Sellmeier’s dispersion relation. The absorption edges of the BLT films are different in the amorphous and crystalline cases.

Optical properties of 92%Pb(Mg1∕3Nb2∕3)O3–8%PbTiO3 thin films prepared by chemical solution deposition

92%Pb(Mg1∕3Nb2∕3)O3–8%PbTiO3 (PMNT) thin films have been prepared on Pt∕Ti∕SiO2∕Si substrate with a LaNiO3 buffer layer and on sapphire substrate by a chemical solution deposition method. X-ray diffraction analysis shows that the PMNT thin films on Pt∕Ti∕SiO2∕Si substrate are polycrystalline with (110)-preferential orientation. The optical properties of PMNT thin film in 2.5–12.5μm and 200–1100nm ranges have been investigated using infrared spectroscopic ellipsometry and ultravisible transmission spectra, respectively. The optical constants and thickness of the thin films have been obtained by fitting the measured ellipsometric parameter (Δ and Ψ) data and transmission spectrum with classical infrared and Tauc-Lorentz models. The optical band gap energy of the PMNT thin films on sapphire substrate is derived to be about 4.02eV.

Spectroscopic-ellipsometry characterization of the interface layer of PbZr0.40Ti0.60O3/LaNiO3/Pt multilayer thin films

The PbZr0.40Ti0.60O3/LaNiO3 multilayer thin films with different LaNiO3 film thickness were deposited on Pt/Ti/SiO2/Si substrates by a modified sol-gel technique. The optical properties of the PbZr0.40Ti0.60O3 thin films, LaNiO3 thin films, and the interface layers between them have been investigated using spectroscopic ellipsometry in the wavelength region of 400–1700 nm. For fitting the ellipsometric data to interpret the optical constants of the multilayer films, the unknown dielectric function of the PbZr0.40Ti0.60O3 films, LaNiO3 films, and the interface layers were constructed using a single-Lorentz oscillator. It is noted that the shapes of the optical constants are different for the three different layers because the fitted values of the model parameters are markedly different. It is found that the PbZr0.40Ti0.60O3 films are entirely transparent (namely the extinction coefficient κ=0) in the 400–1700 nm wavelength region. Moreover, the optical constants of the interface layer and the LaNiO3 films ...

Study on the fabrication and performance of Mn1.56Co0.96Ni0.48O4 film optically immersed infrared detector

Abstract Mn1.56Co0.96Ni0.48O4 (MCN) thin films with cubic spinel phase were prepared by chemical solution deposition. The variable temperature electrical properties showed that the temperature coefficient of resistance reached − 4% K− 1 at 295 K. The immersed and non-immersed infrared (IR) detectors based on MCN films were fabricated and characterised. The experiment results indicated that the performance of immersed detector was better than the non-immersed one. It exhibited a responsivity of 4.4 × 103 V W− 1, detectivity of approximately 5 × 108 cm Hz1/2 W− 1, and thermal time constant of 18 ms at 295 K and 10 Hz. These results provide a possible avenue to develop a high-performance uncooled IR bolometer based on the thermistor materials.