Abdelaziz M. Gouda

Efficient fabrication methodology of wide angle black silicon for energy harvesting applications

In this paper, we report an easy and relatively cost effective fabrication technique of a wide band omnidirectional antireflective black silicon surface based on silicon nanowires (SiNWs). An effective and economical one step silver electroless catalytic etching method in an aqueous solution of AgNO3 and HF is used for the synthesis of the black silicon surface. The formation mechanism for SiNW arrays is explained in terms of a localized nanoelectrochemical cell. The length and diameter of the nanowires were controllable as we found a commensurate relationship between dimensions and the etching time. Different sample sizes were used to prove the techniques large scale production potential. Wide range near zero reflection is reported in the visible region due to the strong trapping and antireflective properties in addition to a wide angle up to ±60°. Raman scattering measurements confirmed the quantum size effect and phonon scattering in the fabricated structure with different diameters. A black silicon surface based on solid and porous SiNWs shows promising potential for photovoltaic, optoelectronic and energy storage applications.

Silicon-based nanostructures as surface enhanced Raman scattering substrates

We report surface enhanced Raman scattering substrates that are low cost and easy to fabricate using silver nanoparticles on silicon wafer and silicon nanowires decorated with the nanoparticles. Numerical simulations showed enhancement factors around 107 to 108 at the hot spots, enabling single molecule detection. We demonstrated experimentally the substrates using reduced Graphene oxide solution.

Facile omnidirectional black silicon based on porous and nonporous silicon nanowires for energy applications

High reflection losses and low photon absorption combined with high velocity large area surface recombination are the main obstacles for boosting the efficiency of solar cell. We report a simple large-scale one step catalytic room temperature fabrication approach of black silicon (B-Si) in an aqueous solution of HF and AgNO3. B-Si based on porous and nonporous Silicon nanowires (SiNWs) shows a superior optical properties with low reflectance <;0.1% and unprecedented absorption > 99.9% in the solar irradiance peak (wavelength range 400 to 800 nm). The black silicon reflects <;2% at different incident angles up to ±60°. The black silicon consists of nonporous and porous SiNWs of tuned filing ratio from 130 to 750 nm, matching the wavelength of the incident light for improved light trapping inside the nanostructure.

Lithography-free wide-angle antireflective self-cleaning silicon nanocones

Low-cost, wideband, and wide-angle antireflective layers are of prime importance to photovoltaic and other optoelectronic applications. We report a novel fabrication methodology of random textured silicon nanocones (SiNCs) array through metal-assisted chemical etching combined with oxidation. The optical properties of the fabricated structure are studied theoretically and experimentally. The random textured SiNCs array showed very promising broadband antireflective properties through the entire visible wavelength range at different incident angles up to ±60°. In addition, the nanostructures inherently could become self-cleaning due to the high contact angle. This random cheap textured SiNCs array increases the absorption efficiency of photodetectors and reduces its cost.

Black silicon based on simple fabrication of mesoporous silicon nanowires for solar energy harvesting

We report large-scale fabrication of black silicon based on mesoporous silicon nanowires (SiNWs) with reflectance <;0.1% in the solar irradiance peak (wavelength range 400 to 800 nm). The black silicon reflects <;2% at different incident angles up to ±60°. The black silicon consists of mesporous SiNWs of diameters in the range 130-750 nm, matching the wavelength of the incident light for improved light trapping inside the nanostructure. SiNWs were synthesized through catalytic wet chemical etching. This study shows that black silicon surfaces based on mesoporous SiNWs can be used as an efficient broadband absorber for solar energy harvesting without any need for antireflective coating.

Silver-decorated silicon nanowires array as surface-enhanced Raman scattering (SERS) substrate

Raman scattering is an excellent analysis tool because a wealth of information can be obtained using a single measurement. It can also be configured as a diagnostic tool as a label free sensing method. In that case, enhancing the Raman signal is important to improve the sensitivity and detect low concentrations of analytes. A nanoparticle showing a particular Raman enhancement shows a much higher enhancement when it is on a nanowire. This was also confirmed experimentally. We report on a simple fabrication method of silver nanoparticles and silicon nanowires decorated with these nanoparticles. The nanowires were fabricated using metal assisted chemical etching. The nanoparticles were formed using electrodeposition. Samples were then immersed in Pyridine. An enhancement factor of around 6 to 8×105 was observed for silver nanoparticles alone. By depositing the same nanoparticles on silicon nanowires, the enhancement factor jumped 10-fold to 7×106. Finite Difference Time Domain simulations showed that a range of enhancement factors is possible up to 109.

Simple scalable fabrication method of wide-angle black silicon surface for energy-harvesting applications

In this study, we report an easy and cheap fabrication technique of wide band omnidirectional antireflective black silicon surface based on porous and non-porous silicon nanowires (SINWs). This technique depends on one step silver electroless catalytic etching method (EMACE) in an aqueous solution of AgNO3 and HF. We found a commensurate relationship between the dimensions and the etching time. The fabrication technique was examined for large scale production potential. Wide band and angle near zero reflection is reported in the visible region due to the strong trapping and antireflection properties. Quantum size effect and phonon scattering is confirmed for the fabricated structure through Raman measurement. Black silicon based on porous and non-porous SINWs shows promising potential for photovoltaic, optoelectronic and energy storage applications.

Random textured silicon oxide nanocones for high-performance thin silicon solar cells

High reflection losses combined with low absorption capabilities and high velocity surface recombination are the main problems that deteriorate the efficiency of thin silicon solar cells. Therefore, Low cost and easy scalable fabrication of wide band, angle and self-cleaning antireflection coatings are of great importance for different optical applications especially solar cells. Random textured silicon nanocones are fabricated through electroless metal assisted chemical etching (EMACE) combined with ambient oxidation. Theoretical studies using Finite difference Time Domain (FDTD) simulation guided the experimental procedures in terms of dimensions and tolerance to reach the optimum dimensions and superior optical properties. The Optical numerical and experimental studies are revealed wide antireflection properties and strong trapping effects up to 60° through the entire visible wavelength. The textured structure modified the hydrophobicity of the solar cell into hydrophobic surface with self-cleaning properties.

Surface enhanced Raman scattering as a sensing technique using silicon nanowires and plasmonic nanoparticles

To overcome the classic sensitivity vs selectivity trade-off often associated with sensors used in diagnostic applications, signature spectroscopic information that is characteristic of the molecules to be sensed can be exploited. Raman spectroscopy offers such information and is suitable for biological fluids. It is considered a label-free sensing method that inherently has excellent specificity. Sensitivity on the other hand is generally low unless amplification of the generally weak Raman signal is achieved. Surface enhanced Raman Scattering (SERS) employs localized surface plasmons on metallic nanoparticles to amplify this signal by several order of magnitude. In this work, SERS substrates were prepared by growing silver nanoparticles using electrodeposition on silicon nanowires that were prepared using metal assisted chemical etching. Experimental results agree with finite difference time domain (FDTD) simulation results. Using pyridine as a probe molecule, Raman signal intensity was found to correlate well with the pyridine concentration in the range 10-6 M to 10-9 M, indicating its applicability as a quantitative sensor. Very low concentration of pyridine, 10-11 M, was detected although at this low concentration the detection is only qualitative. The enhancement factor was calculated to reach 1011. Spot-to-spot, sample-to-sample, and batch-to-batch variation was studied to ensure repeatability, which had been a long-standing issue of low-cost SERS substrates. In addition, experiments over several days highlight the robustness of these SERS substrates. This work bolsters the use of SERS as a low cost sensing method with good sensitivity and specificity for a plethora of applications without compromising on repeatability or robustness.

Self-cleaning wideband antireflective Silicon nanocones for solar cell applications

Theoretical studies guided the experimental work for a novel fabrication methodology of asymmetric textured Silicon nanocones (SiNCs) through Metal-assisted chemical etching followed by oxidation. Optical numerical and Experimental studies showed a promising antireflective broadband property at angles up to ±60° combined with an inherent self-cleaning Property.