Quantum mechanics

Question 1

what is quantum confinement?

Answer 1

qunatisisation of a materials energy levels due to its small size in one of more directions

Question 2

What is quantisisation?

Answer 2

process of mapping continuous infinte values to a smaller set of discrete finite values

Question 3

quantum

Answer 3

property takes discrete values

Question 4

what does the energy of an electron depend on?

Answer 4

its location with respect to the nucleus, higher energy electrons are further away from the nucleus

Question 5

what does the Pauli exclusion principle state?

Answer 5

No two electrons in an atom can have indentical values for all 4 of their quantum numbers

Question 6

When 2 atoms are bonded/brought together?

Answer 6

The electrons in the 1s level cannot have the same energy when they are next to each other, therefore the suborbital must split into 2 branches.

Question 7

What happens if N atoms are added?

Answer 7

A given energy level will split into N different energy levels. In bulk material their are so many energy levels that the number of levels is called a “band”
- Because there are so many levels, the levels are effectively continuous in the band and all energies are possible

Question 8

Therefore when you have a low dimensionality particle of structure the electrons can only have what?

Answer 8

certain discrete values

Question 9

What are quantum dots?

Answer 9

• small semiconducting nanocrystals
• Range from 2nm - 10nm
• Able to absorb light, when released they transform it into a different colour of light

Question 10

What does the colour that a quantum dot produces depend on?

Answer 10

The size and the material

Question 11

What waves and light do larger dots emit?

Answer 11

low energy waves and redder light

Question 12

What waves and light do smaller dots emit?

Answer 12

high energy waves and bluer light

Question 13

Why is quantum confinement useful?

Answer 13

alters the properties of the semiconductor such that photons are absorbed at 1 discrete wavelength and transmitted at another, hence they are useful in light emitting devices and in solar cells.

Question 14

Quantum dots have a bandgap that is?

Answer 14

tunable across a wide variety of energy levels by changing their size. In bulk, band gap is fixed by choice of material

Question 15

what is bandgap?

Answer 15

the difference in energy between the valence band and the conduction band

Question 16

Band gap in conductors?

Answer 16

conductors have no band gap between their valence and conduction bands since they overlap. Their is no barrier for electrons to move between the bands.

Question 17

what is the conduction band?

Answer 17

delocalized band of energy levels in a crystalline solid that is partially filled with electrons. These electrons are highly mobile and cause electrical conductivity
- the band that electrons can jump up to from the valence band when excited
- they now have enough energy to move freely in the material

Question 18

what is the valence band?

Answer 18

the band of electron orbitals that electrons can jump out of, moving into the conduction band when excited. Simply the outmost electron orbital of an atom of material

Question 19

List the reasons that nanomaterials are different from the bulk?

Answer 19

• Quantum effects, quantum confinement
• larger surface area
• reactivity
• sensitivity
• increased dissolution

Question 20

What properties change at the nanoscale?

Answer 20

melting point, fluorescence, electrical conductivity, magnetic, chemcial reactivity

Question 21

What are the advantage of quantum dots as fluorescent dyes instead of typical organic dyes.

Answer 21

• Precise colour and higher peak brightness
• better energy efficiency
• less photobleaching
• more robust to degradation
• multi-color property(due to size) allows the use of many probes to track simultaneously
• have a broader excitation spectra
• narrower more sharply defined emission peak
• fluorescent intensity last for a longer time than fluorophores

Question 22

1 disadvantage of QDs as fluorescent dyes?

Answer 22

The time for fluorescence is longer than in fluorphores

Question 23

Basic operating principle of scanning tunneling microscopy?

Answer 23

STM works by scanning a very sharp metal wire tip over a surface. By bringing the tip very close to the surface, and by applying an electrical voltage to the tip or sample, we can image the surface at an extremely small scale, down to indiviudal atoms.
- Uses the concept of tunneling