Simultaneous superhydrophobic and visible range antireflective properties are demonstrated in hydrothermally grown ZnO nanorods (NRs) on chemically textured Si surfaces. A drastic transformation of Si micro-pyramids from hydrophobic to superhydrophobic is observed by securing the formation of polycrystalline ZnO NRs at surfaces, showing an increment of apparent contact angle from ∼102° to ∼157° and further explained in the light of a decrease in solid fractional surface area, according to the Cassie-Baxter model. Moreover, wurtzite phase of ZnO NRs is confirmed by the X-ray diffraction and Raman analysis. Such hierarchical structures further exhibit a large visible range antireflection (∼5\%), and correlated it to the variation in aspect ratio of Si pyramids in conjunction with the formation of graded refractive index. The combined superhydrophobic and large antireflection phenomena in the present dual-scale structures is believed to be useful for Si-based photovoltaic applications. © 2019 IOP Publishing Ltd.

Aloke Kanjilal

Physics

(SoNS) School of Natural Sciences

Sharma D.

Bhowmick S.

Das A.

Saini C.P.

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Shiv Nadar University

Materials Research Express

Oxygen vacancy (OV) controlled hydrophobicity of self-assembled TiO2 nanorods (NRs) on chemically etched Si pyramids is investigated by irradiating with 50 keV Ar+-ions at room temperature. Apparent contact angle (CA) is found to increase from 122° to 141° up to a fluence of 1 × 1015 ions/cm2, followed by a gradual reduction to 130° at 1 × 1017 ions/cm2. However, the drop in apparent CA is found to be associated with the decrease in fractional surface area via transformation of NRs to an amorphous layer above 1 × 1015 ions/cm2, though it is still higher than that of as-grown one. Detailed X-ray photoelectron spectroscopy and electron paramagnetic resonance measurements suggest that the control of hydrophobic behavior is related to the suppression of surface free energy via migration of OVs into the voids in TiOx layers. © 2016 American Chemical Society.

Journal of Physical Chemistry C

Role of oxygen vacancy on the hydrophobic behavior of TiO2 nanorods on chemically etched Si pyramids

Post-deposition annealing mediated evolution of self-decorated Au nanoparticles (NPs) on chemically etched Si pyramids is presented. A distinct transformation of Si surfaces from hydrophilic to hydrophobic is initially found after chemical texturing, showing an increase in contact angle (CA) from 58°to 98°(±1°). Further improvement of hydrophobicity with CA up to ∼118°has been established after annealing a 10 nm thick Au-coated Si pyramids at 400°C that led to the formation of Au NPs on Si facets along with self-ordering at the pyramid edges. Detailed x-ray diffraction studies suggest the evolution of crystalline Au NPs on strained Si facets. Microstructural studies, however, indicate no mixing of Au and Si atoms at the Au/Si interfaces, instead of forming Au nanocrystals at 400°C. The improved hydrophobicity of Si pyramids, even with Au NPs can be explained in the light of a decrease in solid fractional surface area according to Wenzel's model. Moreover, a sharp drop in specular reflectance from Si pyramids in the range of 300-800 nm, especially in the ultraviolet region up to ∼0.4\% is recorded in the presence of Au NPs by ultraviolet-visible spectroscopy, reflecting the possible use in photovoltaic devices with improved antireflection property. © 2016 AIP Publishing LLC.

Journal of Applied Physics

Self-decorated Au nanoparticles on antireflective Si pyramids with improved hydrophobicity

Chemically textured Si with improved absorption in the complete range of solar spectrum is investigated by ultraviolet/visible/near-infrared (UV/Vis/NIR) spectroscopy, showing an average specular reflectance of ∼0.4\% in the wavelength of 500-3000nm. The pyramidal structures on such solar-blind Si can reduce the reflectance further below 0.1\% in the UV region by conformal growth of granular Al-doped ZnO (AZO) films. X-ray diffraction analyses suggest the growth of polycrystalline AZO on faceted-Si. Moreover, marginal increase in electrical conductivity of AZO is found on textured surfaces, whereas rise in leakage current in Schottky-like Ag/AZO/Si/Ag heterostructure devices is noticed with increasing Si surface area. © 2014 AIP Publishing LLC.