Hafnium oxide (HfO₂) thin films have been made by atomic vapor deposition (AVD) onto Si substrates under different growth temperature and oxygen flow. The effect of different growth conditions on the structure and optical characteristics of deposited HfO₂ film has been studied using X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD) and variable angle spectroscopic ellipsometry (VASE). The XPS measurements and analyses revealed the insufficient chemical reaction at the lower oxygen flow rate and the film quality improved at higher oxygen flow rate. Via GIXRD, it was found that the HfO₂ films on Si were amorphous in nature, as deposited at lower deposition temperature, while being polycrystalline at higher deposition temperature. The structural phase changes from interface to surface were demonstrated. The values of optical constants and bandgaps and their variations with the growth conditions were determined accurately from VASE and XPS. All analyses indicate that appropriate substrate temperature and oxygen flow are essential to achieve high quality of the AVD-grown HfO₂ films.

Optical properties and defect characterization of Ta-doped β-Ga ₂ O ₃ single crystals grown by the optical floating zone method.

Systematic investigations are performed to understand the temperature-dependent optical properties of graphene on Si and SiO₂/Si substrates by using a variable angle spectroscopic ellipsometry. The optical constants of graphene have revealed changes with the substrate and temperature. While the optical refractive index (n) of monolayer graphene on Si exhibited clear anomalous dispersions in the visible and near-infrared region (400–1200 nm), the modification is moderate for graphene on SiO₂/Si substrate. Two graphene sheets have shown a pronounced absorption in the ultraviolet region with peak position related to the Van Hove singularity in the density of states. By increasing the temperature from 300 K to 500 K, for monolayer graphene on Si, the n value is gradually increased while k decreased. However, the optical constants [n, k] of monolayer graphene on SiO₂/Si exhibited unpredictable wave variations. In the wavelength range of 400–1200 nm, an experiential formula of a like-Sellmeier equation is found well suited for describing the dispersions of graphene on Si and SiO₂/Si substrates.

In-rich InGaN nanoscale thin films grown on (0001) sapphire (Al2O3) using migration enhanced plasma-assisted metal-organic chemical vapor deposition (MEPA-MOCVD) method are characterized by high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy (RSS), as well as variable angle spectroscopic ellipsometry (VASE). Theoretical calculations were performed to acquire the optical constants and vibrational properties of the films. The indium composition x (In) values determined by HR-XRD and from the surface area calculated by XPS are in good agreement with each other. The valence band maxima of InxGa1−xN films (x = 0.65-0.80) were observed to shift to lower binding energy with the increase of indium concentration. The RSS results confirmed the one-phonon behavior for the A1(LO) and E2(high) modes with x (In) - independent of phonon frequencies of the substrate. The simulated refractive index n was found to increase with In composition, the band gap (Eg) shifted, however, towards the lower energy side. For a given In composition and by increasing the measurement temperature from 30℃ to 600℃, the variations of optical constants (n and Eg) showed similar trends as in samples with increasing In composition.

A series of ultrathin InSb films grown on GaAs by low‐pressure metalorganic chemical vapor deposition with different V/III ratios were investigated thoroughly using spectroscopic ellipsometry (SE), X‐ray diffraction, and synchrotron radiation X‐ray absorption spectroscopy. The results predicted that InSb films on GaAs grown under too high or too low V/III ratios are with poor quality, while those grown with proper V/III ratios of 4.20–4.78 possess the high crystalline quality. The temperature‐dependent SE (20–300°C) and simulation showed smooth variations of SE spectra, optical constants (n, k, e₁, and ε₂), and critical energy points (E₁, E₁ + Δ₁, , E₂, and ) for InSb film when temperature increased from 20°C to 250°C, while at 300°C, large changes appeared. Our study revealed the oxidation of about two atomic layers and the formation of an indium‐oxide (InO) layer of ∼5.4 nm. This indicates the high temperature limitation for the use of InSb/GaAs materials, up to 250°C.

Because a traditional optical fiber light guiding system includes a tracking device, it also inevitably has a complex structure, high construction and maintenance costs, short life span and low reliability. Although several types have been developed for decades, there are no successful products on the market. The biggest cause of the problem is that all traditional optical fiber light guiding systems must have a tracking device. This paper studies a solar fiber optic guide system without a tracking device, hoping to solve this problem. A fixed fiber light guide system using concave outlet concentrators as its receiving unit is proposed. The structure and working principle of the concave outlet concentrator, the receiving unit and the light guide system are introduced. With optical simulation software and the actual sunlight experimental method, this paper first discusses the conceptual design of the concentrator, then studies the transmission efficiency curve of the receiving unit with different angles of incident light, and finally tests the output illuminance of the whole system in actual sunlight. Field test results show that when the average sunshine intensity is about 800 W/m², the system has an output of nearly 300 lux at 0.4 m in front of the outlet end of the fiber bundle with only $3.11\times {10}^{-2} {\mathrm{m}}^2$ receiving area. This illumination has been able to meet people’s daily lighting requirements. The results of computer simulation and actual sunlight experiments show that this fixed optical fiber light guide system with non-tracing structure is feasible. The absence of a tracking structure means that all moving parts of the system are completely discarded. This greatly improves the working reliability and operation life of the light guide system, and greatly reduces the maintenance and operating costs.