# Rugby 2012

The second lecture was “Nanotechnology – Small ideas, Big impacts” by Dr. Yvette Hancock, University of York.

I have written about Dr. Hancock’s lectures before so some of this will be a repeat of that. I’ve included videos of the lecture that she gave at the “Physics in perspective” days last February.

Quantum physics is why technology has got smaller. In 1946 ENLAC (measuring 26 x 9 x 26m) was only capable of simple arithmetic. Today we have tiny IPODS with very large quantities of memory. In the future it is hoped to have flexible electronics where 10000 transistors could fit on something as thin as a human hair (80000 nm thick). However nanoscale is unpredictable. We need quantum theory to understand and be able to make new things.

Quantum effects include electronic transitions, excitation, electronic orbits and probabilistic nature as outlined in the Heisenberg uncertainty principle.

Light is an electromagnetic wave but must have particle behaviour as described by de Broglie. At the macroscopic scale there are two distinct types of phenomena – waves and particles.

Frequency (f) = energy (E)/planck’s constant(h);

Wavelength (λ) = h/momentum (P).

The de Broglie wavelength for a ping pong ball is 6.6xE-21 nm (too small to be detected) and the de Broglie wavelength of an electron is 2nm. The electron is the key player. They bind the atoms together in material systems. The electronic structure determines the fundamental properties of the material (“undressed” electrons don’t feel the environment but “dressed” electrons are sensitive to changes in the environment). The photoelectric effect is evidence for the particle nature of light (photon = quantum particle) and electron diffraction is evidence for the wave nature of electrons.

An application of Schrodinger’s equation is to think of an electron trapped in a box showing wave like properties.

Though oversimplified, this indicates some important things about bound states for particles:
1. The energies are quantized and can be characterized by a quantum number n
2. The energy cannot be exactly zero.
3. The smaller the confinement, the larger the energy required.

If a particle is confined into a rectangular volume, the same kind of process can be applied to a three-dimensional “particle in a box”, and the same kind of energy contribution is made from each dimension. The energies for a three-dimensional box are shown in the diagram above.

This gives a more physically realistic expression for the available energies for contained particles. This expression is used in determining the density of possible energy states for electrons in solids. So for a bigger L value the energy difference between levels is smaller.

The wave like properties can be used to investigate matter. An electron synchrotron is used to get the electrons to the desired energy of 8GeV for the speeds needed.

Dr Hancock mentioned a lecture given by Richard Feynman at an American Physical Society meeting at Caltech on December 29, 1959. Entitled “There’s Plenty of Room at the Bottom” Feynman considered the possibility of direct manipulation of individual atoms. Something that can be done now.

Xenon atoms on Nickel.

Artificial quantum systems include quantum dots where electrons are confined and atoms are trapped in optical lattices.

Dr Hancock continued her talk by explaining an exciting method of cancer treatment, Magnetic hyperthermia. Magnetic nanoparticles.  In each case the magnetic nanoparticles are injected directly into cancerous areas and then a magnetic field is applied to raise the temperature of the nanoparticles and kill the cells that absorb or are close to the nanoparticles.