Chapter 3 Why Properties Change on the Nanoscale: An Introduction to Nanoscale Physics NANO 101 Introduction to Nanotechnology 1

The Original Physics Classical physics Largely developed by Isaac Newton (late 1600s) Doesn’t explain observations of atoms, molecules, subatomic particles…. 2 Action = reaction Still relevant to our world today

Quantum Mechanics “I think I can safely say that nobody understands quantum mechanics” - Richard Feynman, The Character of Physical Law (1965) “For those who are not shocked when they first come across quantum theory cannot possibly have understood it.” -Nils Bohr 3

Quantum Mechanics Explains phenomena not explained by Classical Mechanics (early 1900s) Based on probability and statistics Correspondence Principle – not one or the other Components: Electromagnetic Waves Photoelectric Effect Atomic Orbitals Wave-Particle Duality Uncertainty Principle 4

wavelength Electromagnetic Radiation Speed of light = 3.0 x 10 8 m/s = 670 million mph Frequency (f): number of cycles/second (s -1 = Hz) Wavelength ( ): distance between 2 identical spots on wave crest to crest 5

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Light is a Wave 7 Waves can interfere constructively or destructively Double slit experiment shows wave like nature

Photoelectric Effect e- 8 Light as a wave: –Energy of emitted electrons should be proportional to intensity of incident light –An electron should be emitted eventually if light of a low frequency is shone at a high intensity for a long period of time –There should be a lag time associated with lights of lower frequency

Photoelectric Effect e- 9 Einstein - Light as a particle: –Energy of light is proportion to its frequency –Light of a lower frequency will never have enough energy to eject an electron –Increasing intensity increases amount of electrons ejected but not their energy –No lag time associated with transfer of energy from particle to electron

Light is a Particle: Photons Light “particles” Discrete (not continuous) fixed quantity bundles of energy What is the E of one photon of microwave radiation with a wavelength of 1.20 cm? 10 C = 3 x 10 8 m/s

The Double Slit Experiment 11

Wavelength of an Electron 12 h = x J s m = mass v = velocity What is the wavelength of : Usain Bolt (m = 94 kg) running the 100 meter dash at avg speed of 25 mph 1 mile = 1.61 km An electron (m = 9.1x kg) in a TEM accelerated at 3 x 10 8 m/s

Heisenberg Uncertainty Principle Impossible to know exact position and momentum of a particle at same time ∆x: uncertainty in position m: mass ∆u: uncertainty in speed h: Planck’s constant Why can we be certain about larger particles (i.e. baseball)? 13

Heisenberg Uncertainty Principle 14

A radar gun measures Felix Hernandez’s fastball at 94 mph ± 0.1 mph, what is the uncertainty in position? –A baseball weights ~ 145 g –1 mile = 1.61 km What is the uncertainty in position of one of the electrons that make up the baseball? –An electron weight 9.1 x kg 15

Reminder: HW#2: 2.1, 3.8, 3.10abd, 3.20, 3.21 Electrons have particle and wave like properties Atoms are the building blocks - > Chemistry and Nanotechnology 16

Models of the Atom J.J. Thomson 17 RutherfordCurrent model ProtonNeutronElectron Charge Mass (kg) ~1.673* ~1.675* ~9.11* Locationnucleus “clouds”

Schrodinger Equation Electrons as standing waves 18

Where are electrons? Atomic Orbital: volume of space where an e- is most likely to be found each orbital can hold a maximum of 2 e- orbitals closer to the nucleus have lower energy 19 Cloud around nucleus Each e- is associated with a specific energy Always some uncertainty

Quantum Numbers Each atomic orbital can be described by three numbers: (n, l, m l ) 1.Principal quantum number (n) Energy level, shells Probable distance from nucleus 2.Angular momentum quantum number ( l ) Subshells, sublevels Shape 3.Magnetic quantum number (m l ) Orientation 20

Orbital Shapes s orbitals p orbitals functions%20 and%20probability%20distributions/z51.htm 21

d orbitals More Orbital Shapes f orbitals int.ch.liv.ac.uk/Lanthanide/Ln_Chemistry_folder/ Miscellaneous%20folder/Miscellaneous.html#f_orbitals 22

Quantization of Energy Atoms can only contain certain amount of energy (discrete values – not continuous) 23 White light is a continuous spectrum

Quantization of Energy Atoms can only contain certain amount of energy (discrete values – not continuous) 24 Electrons in an atom move between energy states

Quantization of Energy Atoms can only contain certain amount of energy (discrete values – not continuous) 25 Electrons in an atom move between energy states

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Chapter 3 Overview Electrons in atoms are found in orbitals. Each orbital has an energy level and sublevel (shape) The closest energy level to the nucleus is the ground state; higher levels are excited states Electrons can act like particles or waves (double-slit expt) Radiation can act like energy or waves (photoelectric effect; photons are packets of light energy) Atoms emit or absorb photons when their electrons change energy levels The Uncertainty Principle states that the more you know an object’s position, the less you know its momentum (and visa versa). 27

Langmuir Film/Self Assembled Monolayer 28

Langmuir-Blodgett Technique 29

Fatty Acids 30 Lauric acid Pentadecanoic acid Stearic acid

Lycopodium Powder 31 - Very hydrophobic -Help to see the monolayer -Very fine powder Primary use of lycopodium powder (not in this lab)

For Thursday No food or drink in lab Bring a print out of lab sheet Record all significant figures from measurements Potential for lab based question on quiz 32