1. The pore diameter at the pore mouth is always equal to that of the initial noble metal particle.
a) True
b) False
Explanation: The conical effect in the pores formed by metal-assisted approach can be more or less pronounced, depending on the etching conditions, and the pore diameter at the pore mouth can be bigger or smaller than that of the initial noble metal particle
2. The diameter of the pores can be said to be dependant on the diffusion of electronic holes injected from the noble metal-silicon interface.
a) True
b) False
Explanation: The conical effect can be associated with the diffusion of electronic holes injected from the noble metal-silicon interface to the side walls, the partial dissolution of silicon by the etchant and the progressive dissolution and re-deposition of noble metal in the course of the etching process
3. _____ is/are obtained when a homogeneous noble metal film is deposited on the surface of silicon.
a) Conical structure
b) Distorted and rough surfaces
c) Honey-comb structure
d) Wire-like structure
Explanation: Silicon wires with well-defined geometry and shape are obtained when a homogeneous noble metal film featuring holes is deposited on the surface of a silicon substrate and subsequently etched in a suitable etchant solution.
4. Lithographic approach along with noble metal is used to produce highly ordered pores.
a) True
b) False
Explanation: Silicon wires can be produced with highly ordered distribution and precisely controlled geometry if the surface of the silicon is patterned by lithographic approaches prior to the deposition of the noble metal film.
5. The morphology of the resulting pSi structures is dependent on the noble metal film.
a) True
b) False
Explanation: The thickness of the noble metal film has a direct effect on the morphology of the resulting pSi structures as well. For instance, 3 and 5 nm thick films of gold lead to pores and wires, respectively. In the case of silver films, 5 nm thick films yield pores while films of 20–50 nm thickness result in silicon wires
6. The configuration of the noble metal film is dependent on the deposition method used.
a) True
b) False
Explanation: It is important to bear in mind that the morphology of the resulting noble metal films can vary with the deposition technique and the nature of the noble metal
7. The stability of the noble metal in the etchant is dependent on its nature.
a) True
b) False
Explanation: Regarding the stability of the noble metal in the etchant, this is highly dependent on its nature and some noble metals can be oxidised and dissolved in the course of the etching process according to the existing relationship between the electrochemical potentials of the noble metal and the oxidant
8. Which of the following particles, leads to pores or wires with heterogeneous geometric features?
a) Ag
b) Au
c) Cu
d) Cr
Explanation: Ag particles dissolve and re-deposit during the etching process as a result of the relatively low electrochemical potential of silver. Therefore, Ag particles can change their shape and morphology during this process, leading to pores or wires with heterogeneous geometric features and morphologies with depth.
9. Which of the following particles are used to produce pSi structures with well-defined geometric features?
a) Zn
b) Cd
c) Pd
d) Au
Explanation: Usually, Au particles and films are preferably used to produce pSi structures with well-defined and precisely controlled geometric features and morphologies due to its stability in the etchant. For instance, Au meshes have been used to fabricate silicon wires of high aspect ratio (i.e. >200).
10. Illumination of light in metal-assisted etching of silicon affects the etching rate.
a) True
b) False
Explanation: As far as the effect of light illumination in metal-assisted etching of silicon, this has a direct effect on the etching rate. It has been reported that the etching rates for p-type and n-type (100) silicon substrates of resistivity 1–10 Ω cm differ whether the etching process is conducted with or without illumination.