Lecture 15

Question 1

What are all properties of materials related to at all levels?

Answer 1

structure

Question 2

What does internal structure determine?

Answer 2

Properties

Question 3

What are the differences in diamond and graphite when it comes to
1. structure
2. atom arrangement
3. physical properties
4. electrical properties
5. optical properties
6. color

Answer 3

Structure
- diamond: 3D
- graphite: layered

Atom arrangement
- diamond: tetrahedral
- graphite: planar arrangement

physical properties
- diamond: strong, rigid, hard
- graphite: soft, good lubricant

electrical properties
- diamond: insulator
- graphite: conductor (and with heat)

optical properties
- diamond: disperses light
- graphite: absorbs light

color
- diamond: transparent
- graphite: grey/black

Question 4

What did the discovery of X-ray and electron diffraction techniques do?

Answer 4

Made us realize that most materials are crystalline (or partly) even w/o external evidence

Question 5

Who discovered the X-ray and how?

Answer 5

Wilhelm Conrad Rontgen

observed that electrons couldn’t be lighting up a glowing up a tube so had to be new

Question 6

What are x-rays? what are their wavelength?

Answer 6

electromagnetic radiation

wavelength = Å

Question 7

When does diffraction of light happen?

Answer 7

When the wave in motion encounters a regular array of scattering objects

Question 8

What is the diffraction phenomenon due to?

Answer 8

constructive/destructive interaction between scattered waves

Question 9

Do X-rays have a wavelength shorter or longer than visible light?

Answer 9

shorter wavelength

Question 10

What new possibilities did X-rays present? What can this be used for?

Answer 10

Investigate the fine structure of matter. Used to solve crystal structure

Question 11

What is Bragg’s law?

Answer 11

Question 12

What is interference? What is the difference in the path travelled?

Answer 12

a diffraction phenomenon due to constructive/destructive interaction between scattered waves

difference in phase

Question 13

What do waves in phase look like? Out-of-phase? Out-of phase but not completely?

Answer 13

In-phase
Intensity max
λ & λ

Out-of-phase
Intensity max =0
λ and λ/2

Out-of-phase but not completely
λ and λ/4

Question 14

What does a change in path length correspond to?

Answer 14

Change in phase

Question 15

What is an important formula for intensity

Answer 15

Question 16

When are two rays completely in phase?

Answer 16

When their path lengths differ either by zero or by a whole number of wavelengths

Question 17

What is a diffracted beam?

Answer 17

A beam composed of scattered rays that reinforce one another

Question 18

What is the relationship between the incident beam, the normal to the diffraction plane, and the scattered beam?

Answer 18

They’re co-planar

Question 19

What’s the angle between diffracted beam and incident

Answer 19

2 theta