Gold nanoshells (GNSs), formed by a silica core surrounded by a gold shell, present a shift on their surface plasmon resonance (SPR) to the near-infrared (NIR) part of the electromagnetic spectrum when synthesized with specific dimensions. This chapter presents a simple method to prepare the nanoshells, a step-by-step characterization, as well as their absorbance spectrum. For the synthesis, silica spheres, with approximately 190 ± 5 nm in diameter, were prepared using the Stöber method and then functionalized with 3-aminopropyltriethoxysilane (APTES). The gold nanoparticles (GNPs), with a diameter of 7 ± 3 nm, were produced by the reduction of chloroauric acid. Then, the silica was seeded with the GNPs to later grow a gold shell with the help of Au(OH) 4¯ ions and formaldehyde. UV-Vis spectroscopy results showed an increase of absorbance starting at 520 nm. It reached its maximum around 600 nm and kept absorbing all through 1200 nm. Transmission electron microscope (TEM) and scanning electron microscope (SEM) images suggest that the absorption peak movement coincided with the completion of the shell. Furthermore, when the sample was irradiated with an 820 nm wavelength/3.1 mW laser, its temperatures increased by 6.3°C in 2 min, showing its absorbance in the NIR.
Absorbent materials are being developed to replace semiconductor materials such as p-type silicon, GaAs, CdTe, and quaternary compounds such as CIGS (copper indium gallium selenide). Cu2O is a potential candidate because it is non-toxic, inexpensive, an abundant compound in the Earth’s crust, and has good optical properties, such as a high absorption coefficient. In this work, Cu2O was obtained simply by reducing Benedict’s solution with glucose in an alkaline medium (pH 10.2 ± 0.2) at 65°C. The samples were synthesized by varying glucose content from 1 g to 7 g. The results showed a phase proportion variation between 95.56% and 99.50% of the Cu2O phase. It was found that the changes in crystallite size, microstrains, particle size, and morphology are due to reaction times, which were influenced by the use of different glucose amounts. The use of a higher glucose amount in the synthesis favors a faster reaction, forming smaller crystallites with more microstrains. Lower glucose amount leads to a slower reaction giving the crystallites more time to grow, which relaxes the microstrains. When increasing glucose content, the obtained morphologies changed from cubes, irregular cubes, prismatic spheres, cauliflower-like, to spherical shapes. The XPS spectra confirmed only the presence of chemical species such as Cu(I) and Cu(II), and chemical defects, such as oxygen vacancies (Vo), were detected in the samples. All samples presented a broad absorption range from 200 nm to 570 nm indistinctly of the morphology. The band gap showed an insignificant change from 2.04 eV to 2.09 eV when glucose was increased from 1 g to 7 g. The in-situ phase transformation study was analyzed from 25°C to 700°C. The results indicated a phase transition from Cu2O to Cu and CuO when the temperature was above 280°C.
In this work, thin films with a ZnO:Al/Ag/ZnO:Al multilayer structure were deposited by radio frequency (RF) and pulsed DC sources in a magnetron sputtering system on glass substrates at 50 °C with different deposition times of the Ag layer. The results showed that the thin films' properties improved with increasing the deposition time of the silver metallic interlayer and with thermal treatment at 300 °C for one hour. The highest average transmittance in the visible range was 89 %. The best values of resistivity and conductivity were 10-4 Ω·cm and 103 Ω-1cm-1, respectively. Finally, the XRD patterns showed that with an increase in the Ag layer's deposition time, the plane's peak (111) belonging to the Ag plane was observed.
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