研究目的
To study the structural and optical properties of silicon nanowire arrays fabricated by metal-assisted chemical etching with ammonium fluoride, focusing on the mechanism of the etching process and the effect of pH values on these properties.
研究成果
The replacement of HF with NH4F in MACE successfully produces SiNWs with desirable structural and optical properties. The shape and length of nanowires depend on pH, with optimal properties at specific pH values. Impedance measurements indicate facilitated charge transport with silver catalysis. Optical properties show reduced reflectance and enhanced photoluminescence and Raman scattering due to light localization, making these SiNWs promising for applications in photovoltaics, photonics, and sensorics.
研究不足
The study is limited to specific etching conditions (e.g., 10 min etching time, room temperature) and p-type silicon wafers. The use of NH4F may have different etching kinetics compared to HF, and scalability for large-scale production is not fully addressed. Optical measurements are conducted in air at room temperature, which might not represent all environmental conditions.
1：Experimental Design and Method Selection:
The study uses metal-assisted chemical etching (MACE) with ammonium fluoride (NH4F) instead of hydrofluoric acid (HF) to fabricate silicon nanowires (SiNWs). The pH of the etching solution (H2O2:NH4F) is varied to investigate its effects. Methods include SEM for structural analysis, impedance and Mott-Schottky measurements for electrical characterization, and optical measurements (total reflectance, photoluminescence, Raman scattering) for optical properties.
2：Sample Selection and Data Sources:
p-type crystalline silicon (c-Si) wafers with (100) orientation and resistivity of 10–20 Ω·cm are used. Samples are prepared by depositing silver nanoparticles and etching in NH4F/H2O2 solutions with pH controlled by adding H2SO
3：List of Experimental Equipment and Materials:
Equipment includes SEM (Carl Zeiss SUPRA 40 FE-SEM), electrochemical interface (Solartron 1287), frequency response analyzer (Solartron 1255B), spectrometer with integrating sphere (Perkin Elmer Lambda 950), FTIR spectrometer (Bruker IFS 66v/S with FRA-106 unit), and Nd:YAG laser. Materials include AgNO3, NH4F, H2O2, H2SO4, HNO3, and de-ionized water.
4：Experimental Procedures and Operational Workflow:
c-Si wafers are rinsed in HF, coated with Ag nanoparticles in AgNO3/NH4F solution, etched in H2O2/NH4F solution with varying pH for 10 min, rinsed, dried, and Ag is removed with HNO3. Structural, electrical, and optical measurements are performed at room temperature.
5：Structural, electrical, and optical measurements are performed at room temperature.
Data Analysis Methods:
5. Data Analysis Methods: SEM images are analyzed for shape and length. Impedance data is fitted with equivalent circuits. Mott-Schottky plots are used to determine flat band potentials. Optical data is normalized and compared to c-Si substrate; Bruggeman model is used for porosity calculation.
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