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In this work, we present a simple method to improve the thermoelectric performance of the RF sputtered bismuth telluride films by raising the power of deposition. The as-deposited samples synthesized under different powers were investigated and compared. It shows that the films prepared under relatively higher power conditions exhibit much higher electrical conductivity to result in a greater power factor accompanied with a minor drop in the Seebeck coefficients. A relationship is established between the improvement in thermoelectric performance and the decrease in crystallinity, which might also reduce the thermal conductivity. A maximum power factor of 5.65 &times, 10&minus, 4 W&middot, m&minus, 1&middot, K&minus, 2 at 470 K is obtained for the sample deposited under 50 W with its Seebeck coefficient being &minus, 105 &mu, V/K. The temperature-dependent behaviors of the samples are also looked into and discussed. This work might offer an in-situ and cost-effective approach to improve the performance of thermoelectric materials.

A typical 6-layered metal-dielectric film structure of SiO2 (57.3 nm)/Cr (2.9 nm)/SiO2 (72.9 nm)/Cr (6.6 nm)/SiO2 (57.6 nm)/Cu (>100.0 nm) was designed and fabricated by magnetron sputtering. It showed a high solar absorption of about 95.8% in the wavelength range of 250–2000 nm, a low thermal emittance of about 0.104 at 600 K and good thermal stability at 673 K after annealing for 12 h in vacuum condition. The angle-dependent reflectance spectra indicated that the proposed 6-layered film structure has a great angular tolerance even when the incident angle increases to 50°. All of the excellent spectral properties and good thermal stability demonstrate the 6- layered planar film structure will be suitable for practical applications of solar-thermal conversion.

In this work, a tunable broadband near-infrared light absorber was designed and fabricated with a simple and lithography free approach by introducing an ultrathin phase-change material Ge 2 Sb 2 Te 5 (GST) layer into the metal–dielectric multilayered film structure with the structure parameters as that: SiO 2 (72.7 nm)/Ge 2 Sb 2 Te 5 (6.0 nm)/SiO 2 (70.2 nm)/Cu (>100.0 nm). The film structure exhibits a modulation depth of ∼ 72.6% and an extinction ratio of ∼ 8.8 dB at the wavelength of 1410 nm. The high light absorption (95%) of the proposed film structure at the wavelength of 450 nm in both of the amorphous and crystalline phase of GST, indicates that the intensity of the reflectance in the infrared region can be rapidly tuned by the blue laser pulses. The proposed planar layered film structure with layer thickness as the only controllable parameter and large reflectivity tuning range shows the potential for practical applications in near-infrared light modulation and absorption.

Light transmission at the Au/air interface was measured for wedge-shaped Au film samples. Light refraction continuously changing its sign from positive to negative at the Au/air interface in the spectrum range of 470–700 nm was observed with a zero refraction occurred at about 525 nm. The results indicate that the effective refraction index n e of samples are not correlated with wedge angles, implying that n e can be considered an intrinsic characteristic of the metal material. The positive and negative refractions observed in the experiment can be attributed to the dispersive feature of the dielectric function of Au with qualitative explanation according to the mechanisms of electron transition and the boundary conditions restricted at the interface.

Optical spectrometers play an important role in modern scientific research. In this work, we present a two-channel spectrometer with a pixel resolution of better than 0.1 nm/pixel in the wavelength range of 200 to 950 nm and an acquisition speed of approximately 25 spectra per second. The spectrometer reaches a high k factor which characterizes the spectral performance of the spectrometer as k = (working wavelength region)/(pixel resolution) = 7500. Instead of using mechanical moving parts in traditional designs, the spectrometer consists of 8 integrated sub-gratings for diffracting and imaging two sets of 4-folded spectra on the upper and lower parts, respectively, of the focal plane of a two-dimensional backside-illuminated complementary metal-oxide-semiconductor (BSI-CMOS) array detector, which shows a high peak quantum efficiency of approximately 90% at 400 nm. In addition to the advantage of being cost-effective, the compact design of the spectrometer makes it advantageous for applications in which it is desirable to use the same two-dimensional array detector to simultaneously measure multiple spectra under precisely the same working conditions to reduce environmental effects. The performance of the finished spectrometer is tested and confirmed with an Hg-Ar lamp.

In this work, 4-layered SiO2/Bi2Te3/SiO2/Cu film structures were designed and fabricated and the optical properties investigated in the wavelength region of 250–1200 nm for their promising applications for direct solar-thermal-electric conversion. A typical 4-layered film sample with the structure SiO2 (66.6 nm)/Bi2Te3 (7.0 nm)/SiO2 (67.0 nm)/Cu (>100.0 nm) was deposited on a Si or K9-glass substrate by magnetron sputtering. The experimental results agree well with the simulated ones showing an average optical absorption of 96.5%, except in the shorter wavelength region, 250–500 nm, which demonstrates the superior absorption property of the 4-layered film due to the randomly rough surface of the Cu layer resulting from the higher deposition power. The high reflectance of the film structure in the long wavelength region of 2–20 μm will result in a low thermal emittance, 0.064 at 600 K. The simpler 4-layered structure with the thermoelectric Bi2Te3 used as the absorption layer may provide a straightforward way to obtain solar-thermal-electric conversion more efficiently through future study.

To improve the optical absorptance of a solar selective absorber over a wide wavelength range, an eight-layered metal-dielectric film structure was designed by the transfer matrix method and fabricated with the magnetron sputtering method. The experimental results showed that the multilayered film structure yields a high solar absorptance of 98.3% with excellent spectral selectivity over a wide angular range in the solar radiation region of 250–2000 nm, a total hemispherical emittance of 0.12 at 400 K, and nearly unchanged reflectance after heat treatment at 673 K for 48 h in vacuum, indicating the high efficiency of the photo-to-thermal conversion achieved for the sample to have the potential being practically applied in many fields.

A solar selective absorber with a multilayered SiO2 (87.0 nm)/Cr (8.3 nm)/SiO2 (96.3 nm) film structure was designed and fabricated by magnetron sputtering on a surface-roughened copper (Cu) substrate. The proposed structure can enhance solar absorption by combining both the typical solar absorption designs of the textured surface and metal–dielectric multilayer film structure. The measured solar absorptance is about 94%, which yields an enhancement of about 2% accompanied by a slightly higher thermal emittance than that observed for the surface-smoothed structure. The increasing thermal emittance of the surface-roughened film structure is expected to markedly cancel the advantage of absorptance enhancement as the temperature increases to 600 K, implying that the proposed film structure functions more efficiently at low or intermediate temperatures (

In this work, optical constants of direct current (DC) and radio frequency (RF) co-sputtered Ti-SiO2 nanocomposite thin films were investigated and tuned by controlling the deposition power of Ti in the SiO2 host matrix. X-ray photoelectron spectroscopy (XPS) results confirmed that the metallic Ti was completely oxidized into different titanium oxide states while the Si4+ state was reduced to the Si2+ or Si0 state by observing the Ti 2p, O 1s and Si 2p line shapes changing under different deposition conditions. The optical constants of the composites were characterized with a spectroscopic ellipsometer (SE) and reduced by using the modified harmonic oscillator approximation (HOA) model. The results show that the metal-dielectric nanocomposite will have an advantage over natural materials because its optical properties of n and k can be properly tuned by adjusting the concentration of Ti in the Ti-SiO2 nanocomposites, thus satisfying the requirements of photonic device design and applications in broad spectral regions.