1. The etching rate of silicon wafers under light illumination is much slower than under dark conditions.
a) True
b) False
Explanation: The etching rate of p- and n-type silicon wafers under room light illumination is about 0.05 times faster than under dark conditions. This difference becomes even higher (i.e. 150 times faster) when 20 W illumination is used.
2. The faster etch rates of the silicon wafer under light illumination is due to photo-excited electronic holes.
a) True
b) False
Explanation: The etching rate of p- and n-type silicon wafers under room light illumination is about 0.05 times faster than under dark conditions. This effect can be explained by the fact that under illumination the number of photo-excited electronic holes can be higher than the number of electronic holes injected from the oxidant agent, thus enabling faster etching rates.
3. Metal assisted etching of silicon is dependent on the orientation of silicon atoms in the structure.
a) True
b) False
Explanation: Actually, metal assisted etching of silicon is anisotropic and dependent on the crystallographic orientation of silicon. As an example, slanted porous silicon structures can be produced by etching (111) and (110) silicon wafers.
4. The etching of silicon atoms becomes more difficult for stronger back-bonds.
a) True
b) False
Explanation: The back-bonds of the silicon atoms located on the surface of the substrate must be broken during the oxidation and dissolution of silicon. Therefore, the etching of silicon atoms becomes more difficult for stronger back-bonds. In that respect, it is worth noting that silicon atoms have one, two and three back-bonds in (100), (110) and (111) substrates.
5. Intrinsic properties of silicon substrate have no effect in the metal assisted etching of Si.
a) True
b) False
Explanation: The Important parameter affecting the resulting pSi structures produced by metal-assisted etching are the different intrinsic properties of the silicon substrate, which have a direct effect on the geometric features and characteristics of the resulting pSi structures.
6. In interference lithography (IL) technique, aluminium is used as anode.
a) True
b) False
Explanation: In this system and similar to electrochemical etching of silicon, the anode (i.e. aluminium foil) and cathode (e.g. platinum wire) are immersed in the acid electrolyte
7. In IL technique, nanopores are produced by application of current and voltage.
a) True
b) False
Explanation: The growth of nanopores is produced by the application of current or voltage. Note that the geometric features of pores in NAA can be precisely controlled by the anodization parameters
8.Pore sizes in NAA can range from ____
a) 10—100 nm
b) 20—250 nm
c) 20—400 nm
d) 100—550 nm
Explanation: Typically, pore sizes in nanoporous anodic alumina (NAA) technique can range from 20 to 400 nm, with a pore density from 5 × 108 to 3 × 1010 pores per cm2.
9. The NAA technique can produce silicon nano wires with high crystalline quality.
a) True
b) False
Explanation: This lithographic approach makes it possible to produce silicon wires with controlled geometry, morphology and size with high crystalline quality and smooth surface.
10. The geometric features of the resulting silicon nanowires are independent of the noble-metal thickness.
a) True
b) False
Explanation: The geometric and morphological features of the resulting silicon nanowires are dependent on the thickness of the noble metal film.