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Silicon/polymer composite nanopost arrays
Published in Klaus D. Sattler, Silicon Nanomaterials Sourcebook, 2017
Xueyao Liu, Wendong Liu, Bai Yang
Metal-assisted chemical etching (MACE) is simple, inexpensive, and the morphology parameter can be finely controlled. The first MACE applied on Si was reported in 1997, and the porous silicon was obtained by stain etching in the mixture of HNO3, HF, and H2O with the help of the predeposited Al layer [1]. However, the thickness of the as-prepared porous Si was limited to a rather thin scope (less than 1.5 nm). The most widely used MACE nowadays is proposed by Li and Bohn [11]: the Si will be etched in the mixture of HF, H2O2, and EtOH with the etching process catalyzed by patterned noble metal layer deposited onto the Si surface. As a result, the Si surface will be etched into nanopost or nanopore arrays. Huang et al. [1] reviewed MACE in detail, including the basic mechanism and various influence factors, such as noble metal, etchant, temperature, illumination, and intrinsic properties of Si on MACE. To ensure the high reproducibility and controllable fabrication of Si nanopost, ordered structural fabrication is essential. Template-based MACE endows the structure high ordering and excellent controllability. The most common templates include nanosphere, AAO, block-copolymer, and mask obtained by interference lithography [1]. Based upon the template category, the obtained nanoposts are endowed with morphologically distinguished characteristics.
Advances in 1D Materials
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Javier Palomino, Brad R. Weiner, Gerardo Morell
The processes of metal-assisted chemical etching (MACE) are represented in Figure 1.13, and they use noble metals (such as Au, Pt, and Ag) as a hole (h+) catalyst deposited on the surface of a semiconductor (Si). MACE is described briefly in the following: (i) In an acidic solution (such as HF), the metal accelerates the hole (h+) generation from an oxidant (such as H2O2) by providing electrons to the oxidant and producing holes at the metal (local oxidation and reduction reactions). (ii) The holes diffuse through the noble metal toward the metal–silicon interface, and the holes (h+) are injected from metal catalyst to silicon by transferring electrons from silicon to metal. (iii) This process results in the oxidation and dissolution of silicon at the metal–silicon interface by hydrofluoric acid (HF), without net consumption of the metal. Subsequently, HF and the byproducts diffuse along the interface to be removed. (iv) Due to high concentration of holes under the noble metal, at the metal–silicon interface, the silicon is etched preferentially below the metal catalyst. As a result, metal descends into the semiconductor as the semiconductor is being etched right underneath. (v) Afterward, the excess of holes diffuses from the Si under the interface to off-metal areas. Ultimately, metal byproducts on the structures can be washed off with deionized water after the synthesis was completed. In addition, nitric acid bath for at least 1 h can be used to remove all residual metals from the surface of the fabricated nanostructures (Huang et al., 2011). In order to achieve tailored nanostructures with high aspect ratio like arrays of vertical NWs, the catalyst metal must be systematically patterned on the silicon substrate, to be etched into the semiconductor and produce the engineered nanostructure.
The emergence of nanoporous materials in lung cancer therapy
Published in Science and Technology of Advanced Materials, 2022
Deepika Radhakrishnan, Shan Mohanan, Goeun Choi, Jin-Ho Choy, Steffi Tiburcius, Hoang Trung Trinh, Shankar Bolan, Nikki Verrills, Pradeep Tanwar, Ajay Karakoti, Ajayan Vinu
Porous silicon (pSi), as the name suggests, is a form of elemental silicon-containing a porous structure. pSi is usually synthesised by an electrochemical perforation etching method or metal assisted chemical etching method [220]. pSis formed by electrochemical etching depicts high porosity with a surface area between 200 and 300 m2/g, with a size less than 500 nm [221]. It has several promising characteristics for drug delivery. pSi nanoparticles are biocompatible with minimal side effects, as they decompose into orthosilicic acid over a period in the body. However, this biodegradable and biocompatible material has disadvantages such as lower colloidal stability, less retention time in blood circulation, and unstable behaviour in both in vitro and in vivo systems. In 2016, Nissinen et al. reported a functionalised pSi with dual PEGylation (DPEG), which increased the circulation half-life of the nanoparticle from 1 to 241 minutes in the lung mouse models (Figure 5A) [222]. A 10 nm thick DPEG coating was achieved by utilizing silane coupling chemistry. Similarly, Nakki et al. moved a step further by modifying the pSi with both magnetic and pH-responsive agents and loaded chemo drug DOX in the pSi platform followed by triple PEGylation. The pore-blocking ability and pH responsiveness of CaCO3 was combined with the iron oxide magnetic nanoparticles.
Silicon nanowires obtained by metal-assisted chemical etching for photonic applications
Published in Radiation Effects and Defects in Solids, 2022
Antonio Alessio Leonardi, Maria José Lo Faro, Emanuele Sciuto, Sabrina Conoci, Barbara Fazio, Alessia Irrera
Recently, several approaches based on a metal-assisted chemical etching (MACE) are emerging as new promising fabrication methods due to the low-cost fabrication, control of the Si NW structural properties, large area scalability, and compatibility with Si technology. Metal-assisted chemical etching is a wet etching anisotropic approach using a high electronegative metal as a catalyst. MACE was first proposed and demonstrated in 2000 by Li and Bohn as a high anisotropic etching approach to obtain porous silicon (27). The method used by these authors is also known as the silver salts approach and takes advantage of silver nanoparticle random precipitation onto the Si surface to catalyze the etching. The average diameter of the realized NWs is usually about 50 ± 20 nm (27,28). This method is fast, does not need complex sample preparation, and is scalable on a wafer. With respect to VLS (29,30), it is simpler to obtain a high density of Si NWs and it does not require complicated equipment and a high temperature. The MACE approach arises as a cost-effective approach, as highlighted by several groups (31–33).
Surface-enhanced Raman scattering for biosensing platforms: a review
Published in Radiation Effects and Defects in Solids, 2022
M. J. Lo Faro, A. A. Leonardi, D. Morganti, E. L. Sciuto, A. Irrera, B. Fazio
The final plasmon material consisted of silver nanoparticles of 15–20 nm in diameter spread onto the very large surface exposed by the silicon nanowire material obtained by metal-assisted chemical etching (MACE). This latter technique is a top-down and low-cost approach allowing for a dense forest of silicon wires of tunable length and that can be decorated at will or combined with other materials (55,56). The reported method allowed for a SERS enhancement factor of 108, as measured on aqueous solution of a probe molecule (Rhodamine 6G), increasing by one order of magnitude the one of Ag NPs deposited with the same procedure on a flat substrate; see Figure 2 for a sketch of this 3D sensor. This additional amplification was due to the huge surface of Ag-covered Si NW arrays increasing the number of hot spots intercepted by the laser spot.