The Wisconsin Institutes for Discovery (Nano + Bio + Info)

1. Nanoscience and Nanotechnology The Wisconsin Institutes for Discovery (Nano + Bio + Info)

2. Universe (largest length) 1027 Taking a human as reference, the Sun is a billion times larger, a nanometer a billion times smaller. 10–3 mm 10–6 m 10–9 nm 10–35 Planck Length (smallest length) How small is a Nanometer?

3. How small is a Nanometer ? Each panel 10x smaller Each time something different Two more steps to reach one nanometer 125 nm Hewlett-Packard molecular memory

4. l Consider devices operating at room temperature. Their energy levels have to be separated by more than the thermal energy kBT = 25 meV.Convert this energy scale to a length scale by fundamental constants. Fundamental Length Scales Quantum Electric Magnetic Quantum Well:Quantum Well Laser Capacitor:Single Electron Transistor Magnetic Particle:Data Storage Media E1 E0 a= V1/3 d Energy Levels3h2/8ml2 Charging Energy2e2/d Spin Flip Barrier ½M2a3 l< 7 nm d< 9 nm a> 3 nm

5. Quantum Length Scale: The Quantum Well Laser 6nm optimum thickness, comparable to the electron wavelength

6. Confinement in Nanocrystals Quantum confinement: Crystal size determines the color (blue-shifted when smaller)

7. When Does Silicon Cease to be Silicon? The band gap of silicon nanoclusters GaAs Bulk Silicon 3 nm : Gap begins to change

8. Electric Length Scale: Single Electron Transistor e- e- dot Cg Vg Vg  e/Cg N-½ N+½ N Electrons on the dot N-1 To add one extra electron to the dot requires the voltage Vg e/Cg (Cg=Qg/Vg= gate/dot capacitance). This costs the charging energy UC=eVg = e2/Cg . The smaller the dot, the smaller the capacitance, the larger the charging energy per electron. This effect can be observed when the charging energy becomes larger than the thermal energy: UC > kBT For room temperature operation (kBT =25 meV) this happens when the dot is smaller than 10nm.

9. Magnetic Length Scale:Superparamagnetic Size Limit Energy Barrier E When ferromagnetic particles become smaller than about 10nm, they lose their magnetism over time (a few years at room temperature). The thermal energy can flip all the spins in a particle (see Lect. 24, Slide 10). If one measures magnetic hysteresis loops (Lect. 23, Slide 4) at various temperatures, they switch rather suddenly from ferromagnetic loops to paramagnetic lines at a temperature called the blocking temperature. This looks like the magnetic phase transition at the Curie temperature, but it depends on how fast the measurement is performed.