Purpose Porous silicon (Si) was fabricated by using three different wet etching methods, namely, direct current photo-assisted electrochemical (DCPEC), alternating CPEC (ACPEC) and two-step ACPEC etching. This study aims to investigate the structural properties of porous structures formed by using these etching methods and to identify which etching method works best. Design/methodology/approach Si n(100) was used to fabricate porous Si using three different etching methods (DCPEC, ACPEC and two-step ACPEC). All the samples were etched with the same current density and etching duration. The samples were etched by using hydrofluoric acid-based electrolytes under the illumination of an incandescent lamp. Findings Field emission scanning electron microscopy (FESEM) images showed that porous Si etched using the two-step ACPEC method has a higher porosity and density than porous Si etched using DCPEC and ACPEC. The atomic force microscopy results supported the FESEM results showing that porous Si etched using the two-step ACPEC method has the highest surface roughness relative to the samples produced using the other two methods. High resolution X-ray diffraction revealed that porous Si produced through two-step ACPEC has the highest peak intensity out of the three porous Si samples suggesting an improvement in pore uniformity with a better crystalline quality. Originality/value Two-step ACPEC method is a fairly new etching method and many of its fundamental properties are yet to be established. This work presents a comparison of the effect of these three different etching methods on the structural properties of Si. The results obtained indicated that the two-step ACPEC method produced an etched sample with a higher porosity, pore density, surface roughness, improvement in uniformity of pores and better crystalline quality than the other etching methods.

This paper investigates the effects of different etching techniques between direct current electrochemical etching (DCPEC) and integrated pulsed electrochemical etching (iPEC) on the structural and optical characteristics of porous silicon formation. The n-type Si (100) was fabricated using both techniques in an electrolyte that consists of aqueous hydrofluoric acid (HF) and ethanol (C2H5OH) with a ratio of 1:4. An additional pulse cycle of 14 ms with Ton = 10 ms and T off = 4 ms was supplied for iPEC porous silicon sample. The finding from both samples showed that the pore formation was affected by the etching techniques used. The porous silicon etched by the DCPEC technique produced a square-like pore with a porosity of 40% while the iPEC technique formed a mix of square and crossed shape pore with a porosity of 52%. From atomic force microscopy, the sample prepared by DCPEC was identified to have a deeper pore that causes larger crystallite size and better intensity in the Raman and photoluminescence spectra. On the other hand, the iPEC technique produced a higher and larger value of surface porosity and pore diameter but it has a shallower pore. The photoluminescence peak corresponding to red emission (S-band) is observed at 642 and 637 nm for DCPEC and iPEC samples, respectively. This is due to the nanoscaled size of silicon through the quantum confinement effect that was estimated to be around 7.9 nm and 7.8 nm for DCPEC and iPEC samples, respectively, determined from the quantized state effective mass theory.

A study was conducted for production of activated carbon (AC) from industrial bamboo waste using carbonization and Microwave-alkali (Mw-A) activation techniques. The aim of the study is to produce activated carbon with higher surface area via Mw-A activation techniques. The study was focused on the effect of activation (KOH soaking and Mw-A) and carbonization temperature (400oC and 500oC) on the physical and chemical structure of AC. The analysis was conducted using proximate analysis, BET surface area, FESEM and FTIR analysis. The morphology and characteristic study on activated carbon shown that Mw-A activation techniques gave higher BET surface area and well develop pore structure. The results indicated that Mw-A activation of activated carbon gave BET surface area of 950m2g-1, whereas by using steam activation only 719 m2g-1 of BET surface area was recorded. Higher carbonization temperature for Mw-A treated bamboo produced higher surface area of AC. At 500oC, 1578m2g-1 BET surface area of AC was achieved. This work highlighted, Mw-A activation can be applied and further enhanced to obtain higher surface area of activated carbon derived from industrial bamboo waste.

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