1. The pores produced by RIE etching can have a thin defective region.
a) True
b) False
Explanation: The pores produced by RIE etching can have a thin defective region, which can prevent or hinder the metal-assisted etching process. To overcome this drawback, the same authors used a slight modification of the traditional NAA approach in order to avoid the use of RIE etching.
2. In the aforementioned approach (modified approach), which of the following metals is used?
a) V
b) Cr
c) Pt
d) Ag
Explanation: In this new approach, a film of Ag is deposited on the NAA mask and the whole system etched. In this way, the Ag film with holes was transferred from the top of the NAA mask to the surface of the silicon substrate as a result of the dissolution of the NAA mask. Then, the etching occurred on the surface of the silicon by metal-assisted etching catalysed by the Ag film.
3. The use of NAA mask technique to produce pSi structures need simple wet chemistry laboratory.
a) True
b) False
Explanation: The main advantage of the use of NAA masks to produce pSi structures by metal-assisted etching is that it can be carried out in a simple wet chemistry laboratory without expensive facilities.
4. Self-ordered NAA structures do not present any defects and domains.
a) True
b) False
Explanation: Self-ordered NAA structures present defects and domains, which are inevitably transferred to the patterned structure on the silicon substrate and thus to the resulting arrays of silicon nanowires.
5. The NAA approach can produce silicon nano-wires of _____ cross-section.
a) triangular
b) circular
c) square
d) needle like
Explanation: Along with the production of self-ordered pores, another limitation of this approach is that only silicon nanowires featuring circular section can be obtained
6. Nanosphere lithography method is another lithographic approach extensively used to produce pSi structures.
a) True
b) False
Explanation: Nanosphere lithography method is another lithographic approach extensively used to produce pSi structures by metal-assisted etching. Huang et al. developed an approach where a monolayer of self-assembled polystyrene (PS) nanospheres was first deposited on the surface of a silicon substrate. After this, the size and distance between adjacent nanospheres were increased by RIE etching and a noble metal film was deposited on the silicon surface by thermal evaporation.
7. At high aspect ratio, silicon nanowires tend to form bundles.
a) True
b) False
Explanation: It is worthwhile mentioning that silicon nanowires of high aspect ratio trend to form bundles or collapse as a result of surface tension forces during the drying process. This drawback can be overcome by supercritical drying approach
8. Porous silicon can be used as carriers for drug delivery.
a) True
b) False
Explanation: Its biocompatibility and degradability properties have enabled the use of porous silicon structures as micro and nanocarriers for drug delivery. While it’s outstanding optical properties make porous silicon a unique material to develop optical structures suitable for optical sensing.
9. Micro machining processes (MMPs) are used to increase selectivity, accuracy, performance, etc. parameters.
a) True
b) False
Explanation: Micro machining processes (MMPs) are used for;
(1) Minimizing energy and materials used in manufacturing Reduction of power budget
(2) Faster devices
(3) Increased selectivity and sensitivity
(4) Improved accuracy and reliability
(5) Cost/ performance advantages
(6) Integration with electronics, simplifying systems.
10. Choose the odd one out.
a) micro-AJM
b) micro-USM
c) micro-AWJM
d) micro-EDM
Explanation: Among all the processes, micro-AJM (micro abrasive jet machining), micro-USM (micro ultrasonic machining) micro-AWJM (micro abrasive water jet machining) use mechanical energy to remove the material; whereas, micro-EDM (micro eletro discharge machining) process uses thermal energy to remove the material.