Chemical

Question 1

Clark Cell

Answer 1

Measure Oxygen in a liquid or gas
Main disadvantage of this device is the fact that the electrode (silver) gets oxydized and damaged permanently so it has a short shelf life
Main principle: Oxygen reacts with water forming ions that will react with silver ( the electrode, oxidizing silver), that til form Ag+ that will react with Cl- (generates a current flow)

Question 2

MOS device used as chemical sensor

Answer 2

changing the gate section of the transistor by putting a Ion sensitive membrane or enzimes so that the ions are directed there.

Question 3

Pd-Si Schottky diodes

Answer 3

Problem: due to surface states in the palladium silicon interface, the device fails to show any reponse to hydrogen.
Solved by introducing a very thin oxide layer between the Pd and the silicon. This oxide removes most of the surface states but is thin enough to permit electron tunneling.

Question 4

Physical-chemical sensor

Answer 4

Device that takes advantage of the change in physical properties of materials to measure chemical parameters:
Main advantages: usually don’t need power of any sort, small low cost and mass produced
Tin oxide gas sensor.

Question 5

waveguides

Answer 5

thin cylinders or films made of glassor plastic that efficiently conduct light

Question 6

How can you measure hydrogen ions

Answer 6

using MOS structure: replacing the gate with Pd (Palladium)
this allows the H+ to diffuse through the Pd
you get a potential difference because te ions are being trapped
Problem -> limitation of number of sites the H+ can settle into
Solution- replacing SiO2 with Al2O3.

Question 7

Piezoelectric effect in chemical sensors

Answer 7

• molecules have weight and so when you put them in a cantilever youcan measure the concentration of a material due to the piezoelectric effect and also due to the dielectric constant od the material