Metal-assisted Electroless Chemical Etching Research Articles

Investigation of morphology, reflectance and photocatalytic activity of nanostructured silicon surfaces

One-step metal-assisted electroless chemical etching of silicon substrate in aqueous NH4F/AgNO3/HNO3 solution is investigated. The effects of etching time and AgNO3 concentration on the morphology and reflectance of etched layer are studied. It is found that the morphology and reflectance depend strongly on these parameters. The lowest reflectance is obtained for 0.009–0.01Ω∙cm p-Si(100) etched in 2M NH4F–1.89 M HNO3–0.01M AgNO3 aqueous solution for 15min. Indeed, the reflectance did not exceed the value of 0.63% in the 200–800nm range. In addition, nanostructured silicon surfaces obtained through etching using this solution are decorated with copper and silver nanoparticles and their photocatalytic activity for the degradation of rhodamine B under UV and visible light irradiation is evaluated. The highest catalytic activity is observed for samples decorated with Cu nanoparticles. This is attributed to their ability to facilitate electron–hole separation and to promote electron transfer in the photocatalytic process.

Enhancement of the tartrazine photodegradation by modification of silicon nanowires with metal nanoparticles

In this work we investigated the tartrazine photodegradation by modified and unmodified silicon nanowires (SiNWs). SiNWs were elaborated by one-step metal-assisted electroless chemical etching of silicon substrate in HF/AgNO3 aqueous solution. The modification of SiNWs was carried out by nanoparticles of platinum, palladium, silver, gold and copper in chemical solutions of PtO2, PdCl2, AgNO3, AuCl3 and CuSO4, respectively. The results show that Cu-modified silicon nanowires give the highest photocatalytic activity compared to the unmodified SiNWs and SiNWs modified with nanoparticles of Au, Pt, Pd and Ag.

Tailoring transport and dielectric properties by surface passivation of silicon nanowires with Polyacrylic acid/TiO2 nanoparticles composite

We have presented the composite device including silicon nanowires (SiNWs), Polyacrylic acid (PAA) and Titanium dioxide nanoparticles (TiO2 NPs). SiNWs and TiO2 NPs were synthesized by metal assisted electroless chemical etching (MACE) and co-precipitation method respectively. Solution containing PAA and TiO2 NPs in DI water was spun on already grown vertical SiNW arrays. We have investigated the transport and dielectric properties of p-type SiNWs/PAA/TiO2 NPs (p-SPT) and n-type SiNWs/PAA/TiO2 NPs (n-SPT) composite devices. Presence of PAA/TiO2 NPs on the surface of SiNWs have increased electrical current in p-SPT device than that of n-SPT device. Ohmic like conduction was dominant at lower bias voltages followed by space charge limited current (SCLC) with traps at intermediate voltages. The calculated values of trap densities (Ht) were 7.73×1011 cm−3 and 5.34×1011 cm−3 for p-SPT device and n-SPT device respectively. Similarly p-SPT device shows higher real part of dielectric constant (ε′) and AC conductivity (σac) ∼15 times and ∼85 times respectively than that of n-SPT device. Increment in electrical and dielectric properties can be attributed to the presence of hydrophilic materials (PAA/TiO2 NPs) which may results in enhancement of acceptor like states.

Morphology-dependent optical properties of one-dimensional nanostructure-arrayed silicon

The optical properties of one-dimensional nanostructure-arrayed silicon (1DNSASi), which was fabricated by the metal assisted electroless chemical etching method under different conditions, were characterized in the wavelength range of 220 — 1000 nm. Whether the optical absorption of the 1DNSASi was enhanced relative to that of the polished Si was determined from the detailed morphology of the 1D nanostructures. For the yellow 1DNSASi prepared at a high etchant concentration and high temperatures, its optical absorption was relatively nice in the ultraviolet light region, while a gradual attenuation was shown in the visible and the near-infrared regions, and the optical absorption was lower than that of the polished Si at wavelengths above 800 nm. When the effects of zeroth-order reflectance and zero transmission were combined, the optical absorption of the black 1DNSASi prepared at a low etchant concentration and room temperature was very high (> 99%) in the wavelength range of 220–1030 nm and displayed a slight decrease at wavelengths above 1030 nm. Our results demonstrate that the optical absorption of the black 1DNSASi could be further improved by increasing the etching depth and exhibited its measurable maximum value when the etching depth was large enough. These results indicate that the 1DNSASi may be a promising candidate for high-efficiency photovoltaic devices, high-sensitivity sensors and detectors.

Electroless chemical etching of silicon in aqueous NH4F/AgNO3/HNO3 solution

One-step metal-assisted electroless chemical etching of silicon substrate was investigated. The etching was performed in aqueous NH4F/AgNO3/HNO3 solution at room temperature. The effect of several etching parameters on the morphology of etched layer was studied namely: silicon type, doping level and crystallographic orientation. It is shown that the morphology depends strongly on etching parameters. The reflectivity of the nanostructured layers was examined by reflectance spectroscopy and was found to depend on silicon resistivity. Indeed, the lowest average value of reflectance (a few percent) in the range 250–800nm was obtained for 5–10Ωcm p-Si(100), 0.001–0.003Ωcm n++-Si(100) and 5–10Ωcm n-Si(100). Finally, the dissolution mechanism of silicon by Ag-assisted electroless etching is discussed.

Photodetection and transport properties of surface capped silicon nanowires arrays with polyacrylic acid

Efficient hybrid photodetector consisting of silicon nanowires (SiNWs) (∼40 μm) capped with Polyacrylic Acid (PAA) is demonstrated. Highly diluted PAA with deionized (DI) water was spun directly on vertical SiNW arrays prepared by metal assisted electroless chemical etching (MACE) technique. We have observed ∼9, 4 and 9 times enhancement in responsivity, detectivity and external quantum efficiency in SiNWs/PAA hybrid device in comparison to SiNWs only device. Higher electrical current and photodetection may be due to the increment of hydrophilic content (acceptor like states) on SiNWs interface. The higher photosensitivity can also be attributed to the presence of low refractive index PAA around SiNWs which causes funneling of photon energy into SiNWs. Surface roughness of SiNWs leads to immobilization of charge carriers and hence shows persistent photoconductivity.

Far infrared response of silicon nanowire arrays

The reflection, transmission and absorbance spectra of silicon nanowire arrays (NWAs), as a function of the length of the nanowires, are investigated in a wavelength range of 15 μm < λ < 200 μm, using Fourier transform infrared spectroscopy in vacuum. The NWAs are fabricated using metal-assisted electroless chemical etching. The wire length is varied between 20 μm and 140 μm, which is of the same order of magnitude as the wavelength, and their spectra are compared to bulk Si. At high frequencies the absorbance spectra of the NWAs show molecular resonances due to adsorption of molecules involved in the fabrication process but also due to the oxide quality that wraps the nanowires and changes as a function of nanowire length. Transmission characteristics show an increasing shift in absorption band edge towards the far infrared for longer wires and a transition from specular to diffuse reflection at a nanowire length of approximately 60 μm.

Direct Synthesis and Enhanced Catalytic Activities of Platinum and Porous-Silicon Composites by Metal-Assisted Chemical Etching

We demonstrate that Pt/PSi composite powders can be prepared by a simple method involving the metal-assisted electroless chemical etching of Si powders. In X-ray photoelectron spectroscopy and optical measurements, Pt layers are deposited on a Si surface together with the formation of a porous structure. It is found that the oxidation state of Pt layers strongly depends on the conditions for the preparation of Pt/PSi composite powders. Furthermore, Pt/PSi composite powders show an enhanced catalytic activity caused by the Pt metal layer deposited on the nanostructured Pt/PSi surface.

Direct Synthesis and Enhanced Catalytic Activities of Platinum and Porous-Silicon Composites by Metal-Assisted Chemical Etching

We demonstrate that Pt/PSi composite powders can be prepared by a simple method involving the metal-assisted electroless chemical etching of Si powders. In X-ray photoelectron spectroscopy and optical measurements, Pt layers are deposited on a Si surface together with the formation of a porous structure. It is found that the oxidation state of Pt layers strongly depends on the conditions for the preparation of Pt/PSi composite powders. Furthermore, Pt/PSi composite powders show an enhanced catalytic activity caused by the Pt metal layer deposited on the nanostructured Pt/PSi surface.

In-plane control of morphology and tunable photoluminescence in porous silicon produced by metal-assisted electroless chemical etching

Photoluminescent porous silicon (PSi) was produced by Pt-assisted electroless etching of p−-Si (100) in a 1:2:1 solution of HF, H2O2, and methanol. The peak emission wavelength of the PSi could be tuned in the range 500 nm⩽λ⩽600 nm simply by changing the time of etching. The luminescence is sufficiently intense at all wavelengths to be visible by eye. Furthermore, by patterning the metal areas on the surface prior to etching, the luminescence can be controlled spatially. To investigate the relationship among processing variables — principally etch time and spatial proximity to Pt — and morphology, scanning electron microscopy (SEM), true color fluorescence microscopy, and spatially resolved phonon line shape studies were undertaken. SEM images show nanocrystalline features in the region where the luminescence originates, a region which shifts spatially as a function of etch time, as indicated by fluorescence microscopy. Raman scattering measurements of the shift and broadening of the longitudinal optical phonon band interpreted in the context of the phonon confinement model were used to estimate crystallite sizes. As with the luminescence, the crystallite sizes were found to vary as a function of distance from the Pt patterned area and etch time. These results are interpreted in light of an etching mechanism in which H2O2 reduction results in hole injection deep into the valence band, which then drifts spatially and plays a critical role in determining the rate at which Si is removed from the surface.