Question 4 Flashcards
q4a)
In a bottle you have a few grams of graphite powder as starting material.
How would you process this powder into a transparent conducting film?
1: Oxidation of graphite to synthesize graphite oxide: break VdW bonds between sheets: Hummers method (strong acids and oxidants: NaNO3, H2SO4, KMnO4)
2: Sonificate (in water) the graphite oxide to get graphene oxide (GO)
3: Put GO on a substrate (spin coating, dip coating), ideally a single layer 4: Reduce to get reduced GO (transparent & conductive)
5: To lift off: put on a polymer coating on substrate for less adhesion
Possible applications: transparent solar cells, batteries, TVs
q4b)
It is possible to fabricate an optical pressure sensor using gold nanorods (AuNRs) as shown in the Figure below.
What do you think is the underlying working principle of such a sensor?
Nanorods have 2 different absorption peaks (1 for long side and 1 for short side) when aspect ratio is large (long schlacks)
→ if no pressure on matrix, we see both peaks due to the random orientation of the rods
→ pressure on matrix → alignment of the rods in one direction → only see 1 peak
How to produce the AuNRs:
seeds (gold nanoparticles) put in growth solution (more Au and CTAB) → CTAB only binds to 4 out of 6 crystal facets (makes a double layer). on 2 sides: growth possible with reduced Au (by ascorbic acid, step-wise addition of ascorbic acid: risk of nucleation).
q4c)
c) SiO2:SnO2 glass ceramics consist of bulk amorphous silica bodies with embedded SnO2 nanocrystals, and they can be obtained by sol‐gel chemistry, reacting tetraethyl orthosilicate (TEOS) with water in presence of dibuthyltin diacetate (DBTDA).
What are the two parameters, which need to be sufficiently high in order to observe the formation of SnO2 NPs?
- Dopant concentration → needs to be high enough to form clusters
- densification temperature (~1050°C, so hopping can take place)
- densification atmosphere → less O2 in atmosphere -> more vacancies → easier hopping
