Properties on the Nanoscale

1. Properties on the Nanoscale

2. Why Miniaturize? Activity: Nail polish! Properties start to change as size decreases!

3. DRIVING FORCE Make things smaller so one device can do everything for you and make your life easy.

4. This 17 minute video highlights useful and some novel properties that occur on the nano scale. When a property is mentioned, please write it down. http://www.youtube.com/watch?v=70ba1DByUmM p.s. Steven Fry, an English actor, is a HOOT as the narrator.  p.p.s. The movie was filmed at Cambridge University and won several awards in 2010.

5. Why “nano” is interesting • Because the particles are small… • High surface-to-volume ratio • React differently • Act differently (new properties) • Interact with light differently • Are on the scale of small biological structures • Interesting “new” structures • Classical Physics meets Quantum Physics • (Neither applies!) • - Discussion question: What is classical physics? • What is quantum physics?

6. In a nutshell… Classical physics = physics at the macroscale Quantum physics = physics at the microscale

7. Classical physics is a branch of physics in which matter and energy are two separate concepts. • Classical physics is generally divided into several different areas: • Mechanics (looking at motion, objects and the forces that act on them) • Dynamics • Hydrodynamics • Statics • Optics • Thermodynamics (studying energy and heat) • Acoustics • Magnetism • Electricity.

8. Quantum physics (also known as quantum mechanics)is a branch of science that deals with discrete, indivisible units of energy called quanta as described by the Quantum Theory. • There are five main ideas represented in Quantum Theory: • Energy is not continuous, but comes in small but discrete units. • The elementary particles behave both like particles and like waves. • The movement of these particles is inherently random. • It is physically impossible to know both the position and the momentum of a particle at the same time. The more precisely one is known, the less precise the measurement of the other is. • The atomic world is nothing like the world we live in. "Anyone who is not shocked by quantum theory has not understood it.“ ~Niels Bohr

9. Physical Structure  Physical Property What do you think this means?

10. Physical Structure  Physical Property • Some physical structure differences on the nano scale: • High % surface atoms • Large surface energy • Reduced imperfections

11. Surface Area and Surface Energy Surface atoms (%) • Surface energy increases with surface area. diameter (nm) • Large surface area  Instability …So these small structures are driven to grow to lower their energy to a stable state. (This can cause problems if you’re trying to keep structures small!)

12. Reduced imperfections The bigger the structure, the more chances there are for error! (And vice versa!)

13. What properties are affected by physical structure? What can properties can we tune? • Melting point • Mechanical properties • Electrical properties • Light properties • Optical properties

14. Melting Points • Nanostructures <100 nm have a lower MP than their macroscopic version • - Why? It has to do with the higher surface energy these • smaller structures have—it takes less energy to melt them! Melting point (K) Particle diameter (nm)

15. Mechanical Properties • Improve also as size decreases • - Why? The high internal and external perfection of structure Strength (kg/mm) d (µm) Mechanical Strength of NaCl whiskers

16. Electrical Properties • In a regular wire, electron scattering increases resistance (electrons are flowing less efficiently). - Electrons scatter because the ions within the wire are moving around and because of imperfections in the lattice. • In nano wires, electron scattering decreases. • Why? Smaller size = fewer defectslessscattering • However, there are other side effects nano wires have that are not favorable that scientists have to deal with.

17. BAND THEORY (Background info) When electrons get excited (gain energy) they can jump up to a higher energy level.

18. BAND THEORY (Background info) When this happens in metals and semiconductors, electrons are moving from the valence band to the conduction band (to conduct electricity!)

19. Electrical Properties In nanoparticle semi-conductors, band gap decreases as particle size increases. E Metal Insulator Semi-conductor NP Semi-conductor THIS IS AN INTERESTING NANO SCALE EFFECT!

20. What’s so great about semiconductors ANYWAYS???? Semiconductors like silicon are used in electronics because we know the exact amount of energy it takes to turn “them” on and off.

21. Light Properties Nanoparticles interact differently with light - Why? The structures are smaller than the wavelength of light. 1X 220X 5000X 20,000X Photonic Crystals Militaries Study Animals for Cutting-Edge Camouflage. James Owen in England for National Geographic News March 12, 2003, Proc. R. Soc. Lond. B (1999) 266, 1403-1411

22. Light Properties (cont’d) • Surface Plasmon Resonance (METALS) • Sea of electrons gets excited and vibrates • Because light interacts differently with NPs, they use this property for sensors (like pregnancy tests).

23. Light Properties (cont’d) Quantum dots (SEMICONDUCTORS) E Metal Insulator Semiconductor 10 nm QD 50 nm QD QDs have a promising future in medical imaging and disease detection

24. http://news.sciencemag.org/sciencenow/2004/07/20-03.html