Large-scale high aspect ratio Al-doped ZnO nanopillars arrays as anisotropic metamaterials

Abstract

High aspect ratio free-standing Al-doped ZnO (AZO) nanopillars and nanotubes were fabricated using a combination of advanced reactive ion etching and atomic layer deposition (ALD) techniques. Prior to the pillar and tube fabrication, AZO layers were grown on flat silicon and glass substrates with different Al concentrations at 150-250 °C. For each temperature and Al concentration the ALD growth behavior, crystalline structure, physical, electrical and optical properties were investigated. It was found that AZO films deposited at 250 °C exhibit the most pronounced plasmonic behavior with the highest plasma frequency. During pillar fabrication, AZO conformally passivates the silicon template, which is characteristic of typical ALD growth conditions. The last step of fabrication is heavily dependent on the selective chemistry of the SF 6 plasma. It was shown that silicon between AZO structures can be selectively removed with no observable influence on the ALD deposited coatings. The prepared free-standing AZO structures were characterized using Fourier transform infrared spectroscopy (FTIR). The restoration of the effective permittivities of the structures reveals that their anisotropy significantly deviates from the effective medium approximation (EMA) prognoses. It suggests that the permittivity of the AZO in tightly confined nanopillars is very different from that of flat AZO films.

Confined Growth of ZIF‐8 Nanocrystals with Tunable Structural Colors

“…The pulse times of both precursors were 0.1 s, the purge time for water was 0.5 s, while the purge time for DEZ was set to be 20 s to remove any reaction byproducts and unreacted precursors. Since a low deposition temperature can give better structural and optical qualities of ZnO thin film, the reaction temperature was set to be 200 °C, under which the deposition rate was suggested to be 0.15 nm per cycle …”

Highly Ordered 3D Silicon Micro‐Mesh Structures Integrated with Nanowire Arrays: A Multifunctional Platform for Photodegradation, Photocurrent Generation, and Materials Conversion

“…After plasma ashing, the remaining photoresist layer and the FC layer on the silicon structures were removed, thus a clean highly ordered 3D silicon micro‐mesh substrate was prepared for the subsequent ALD process, during which a ZnO layer with 50 nm thickness was deposited conformally as shown in Figure a(5). The ALD deposited ZnO thin film is polycrystalline with a major orientation of (002), and it will serve as the seed layer for the ZnO NWs growth via a hydrothermal reaction (Figure a(6)) ,. Since ALD process is conformal, ZnO NWs would grow following the 3D silicon substrate, also on the bottom part of the suspended silicon structures.…”

Electrochemical Coprecipitation of Zinc and Aluminum in Aqueous Electrolytes for ZnO and AZO Coverage Deposition

“…Two additional series of probes have been prepared from the initial electrolytes. In the first series electrolytes have been diluted 6ˑ10 6 times, while in the second series the dilution has been done 3.6•10 7 , in order to reach the concentration of ions (Al and Zn) in the range 0-10 mcg/l.…”

“…AZO thin films can be prepared by various techniques such as sol-gel synthesis [1][2][3], atomic layer deposition [4][5][6], chemical pyrolysis [7], chemical vapor deposition (CVD) [8], magnetron sputtering [9,10], and pulsed laser deposition [11]. Most of these methods require a controlled environment, which makes the processing complicated and expensive.…”