Lecture 3: Hardware, real nanobots and nanocircuits.

1. Dr Heidi Fearn CSUF Physics 1 Lecture 3: Hardware, real nanobots and nanocircuits. Details on nanomachines, motors and mechanical parts, built from “hard” man made materials. CLE lecture series Spring 2005 Dr. Heidi Fearn.

2. 2 Dr Heidi Fearn CSUF Physics

3. 3 Dr Heidi Fearn CSUF Physics Contents of Lecture 3: Why can’t we just scale down machines, build the same mechanical parts only smaller? Stickiness, Brownian motion, surface to volume ratio, weird quantum forces. Where are we with respect to self assembly of machine parts? Drexlers dream machines. What about components for circuits and the promise of Terahertz CPU’s in the future? (1000x faster than today’s Pentium 4 chip, 3 or 4 GHz).

4. 4 Dr Heidi Fearn CSUF Physics Viscosity at the nanoscale“Soft Machines” by R. L. A. Jones, Oxford U. Press. Water, at the nanoscale, is not the free flowing liquid we are used to in the macroscale. Tiny objects in water are surrounded by a sticky viscous fluid- more like molasses, or treacle. The properties of fluids at the nanoscale become dominated by viscosity. In order to move forward, the volume of fluid we have to move out of the way, in a given time, varies like the velocity (v) times the area (a). Momentum (p) is mass times velocity. Mass is density (?) times volume. Inertial force is; Force = dp/dt ~ ?a²v² Force of viscosity is; F= ?av, where ? is the liquid viscosity. The ratio gives Reynolds number; Force/F = ?av/ ?

5. 5 Dr Heidi Fearn CSUF Physics The lower the Reynolds number the more is the effect of viscosity! The ratio gives Reynolds number; (Inertial Force)/(Viscous Force) = ?av/ ? As you can see for a smaller surface area (a), the ratio gets smaller and hence the effect of viscosity gets greater and will effect the motion of the small object more. A bacterium is a million times smaller than a human, so the bacterium feels water one million times more viscous than we do!

6. 6 Dr Heidi Fearn CSUF Physics Swimming on the nanoscale.“Soft Machines” by R. A. L. JonesOxford Univ. Press. In treacle or molasses, even an expert swimmer would expend a lot of energy moving backward and forward and not getting anywhere fast! A fast motion on the downward stroke gives us a sharp kick forward, but the return stroke in treacle, would simple move us back to where we started. Hence we don’t move much at all… So how do nanoscale biological objects get around? They do the TWIST- twisting movement seems most efficient.

7. 7 Dr Heidi Fearn CSUF Physics Can nanobots really fly?“Soft Machines” p58, by Jones Oxford press. Viscosity is 10,000 times more of a problem for insects than for planes. A reasonable value for the lift/drag ratio of a wing for a plane is 25, whereas for a fruit fly it is 1.8 An insect can compensate by flapping its wings faster, a fruit fly can manage 200 times a second, a midge can manage 1000 times per second. The power consumption is prodigious and it is very unlikely that a smaller robot could have directed flight and overcome the air viscosity.Viscosity is 10,000 times more of a problem for insects than for planes. A reasonable value for the lift/drag ratio of a wing for a plane is 25, whereas for a fruit fly it is 1.8 An insect can compensate by flapping its wings faster, a fruit fly can manage 200 times a second, a midge can manage 1000 times per second. The power consumption is prodigious and it is very unlikely that a smaller robot could have directed flight and overcome the air viscosity.

8. 8 Dr Heidi Fearn CSUF Physics

9. 9 Dr Heidi Fearn CSUF Physics Brownian Motion Objects under a microscope appear to be undergoing continuous random motion- jiggling. This is due to the constant bombardment of a microscopic object by atoms and molecules. Atoms and molecules are always in constant motion and they collide frequently with other larger objects, making the object, look like it is jiggling around by itself. You cannot see the atoms bombarding the larger object. The discrete nature of atoms means that is it possible for there to be an imbalance in the number of impacts from one direction, hence the object moves one way and then another in an apparent random motion or “random walk”.

10. 10 Dr Heidi Fearn CSUF Physics More on Brownian motion… The smaller the object being bombarded the greater the effect of a single impact. The effect is greatest when the size of the object is nearly the same as the atoms bombarding it. Brownian motion is greatest with very small objects. It persists even in a vacuum due to temp being transmitted by photons. Photon absorption and emission will cause Brownian motion. Building a machine very small will be like trying to assemble a building in a hurricane, with the winds swirling and pushing in every possible direction.. (wind will be like the action of the atoms, 600 mile an hour winds possibly!!) water at room temp will have a speed of 260 m/s nearly 600 miles an hr. Kinetic theory- statistical physics. Average energy of a particle due to its Brownian motion depends on the temp. Kinetic energy depends on mass and velocity mv^2/2 the mass and hence the size of an object determines its velocity. Small things go very fast but not very far. In a dense crowd of other particles they soon hit something and bounce back from where they started. The nanoscale is dominated by never ending pointless motion. Transport of matter by random walk is known as diffusion. This will have a great impact on the design of microscopic objects, And has had a great influence on the ways cells work and move about.water at room temp will have a speed of 260 m/s nearly 600 miles an hr. Kinetic theory- statistical physics. Average energy of a particle due to its Brownian motion depends on the temp. Kinetic energy depends on mass and velocity mv^2/2 the mass and hence the size of an object determines its velocity. Small things go very fast but not very far. In a dense crowd of other particles they soon hit something and bounce back from where they started. The nanoscale is dominated by never ending pointless motion. Transport of matter by random walk is known as diffusion. This will have a great impact on the design of microscopic objects, And has had a great influence on the ways cells work and move about.

11. 11 Dr Heidi Fearn CSUF Physics Oxygen atoms and diffusion coefficient. Diffusion coeff. of oxygen in water is D=18 x 10 ¯6 cm²/s¯¹ Roughly speaking, the time it takes a molecule to diffuse a given distance, L, is given by L² / D. An Oxygen molecule will move 10nm in a few milliseconds. It takes a minute to move a micron but for it to move a cm or so by diffusion alone would take 100 years!! Bigger molecules have smaller diffusion coeff’s and move more slowly. A bacterium is small enough that Brownian movement alone will transport fuel and oxygen around inside it. It does not need a blood supply. Also Brownian motion brings the meals to the bacterium- meals on wheels in this case is meals by courtesy of Brownian motion.

12. 12 Dr Heidi Fearn CSUF Physics Stickiness at the Nanoscale“Soft Machines” by Jones again. In the nanoworld everything is sticky. Polished glass and metal objects stick together on the macroscale- the only reason large objects do not stick together is that they usually have hard rough surfaces. If a material is soft and flexible it is usually sticky- like cling film. This is because if we press the soft material onto something else- it can deform its shape so that a large surface area is in contact. The soft material conforms to the shape of the hard material it is sticking too. In an engine made of metal, we allow the lubricating oil to leak out, the engine will seize up and the surfaces will stick together- a significant surface area comes into contact.

13. 13 Dr Heidi Fearn CSUF Physics Force of Electromagnetism At the nanoscale electromagnetism rules supreme. Gravity is negligible- too small to worry about. Electromagnetic bonds, bind everything, hence the stickiness. Attraction of two opposite charges. Molecular bonds are electromagnetic in origin. So are Van der Waals forces and Casimir effect forces although they are also quantum mechanical.

14. 14 Dr Heidi Fearn CSUF Physics Surface to volume Ratio For small objects, the surface to volume ratio increases rapidly. Properties of bulk materials are very different from properties of individual atoms and molecules. Microscopic materials tend to be more highly reactive and can more easily access different parts of the body. They are usually more toxic than the bulk material.

15. 15 Dr Heidi Fearn CSUF Physics Weird Quantum Forces at the Nanoscale Van der Waals forces Casimir forces Kondo effect - spintronics. Wave-particle duality Interference effects Quantum mechanical tunneling

16. 16 Dr Heidi Fearn CSUF Physics Self Assembling Machines? Not Yet!! Do we have any kind of mechanical parts for man made nano-machines? We have many computer models care of Drexler and www.imm.org but these are just models and not real atomic constructions.

17. 17 Dr Heidi Fearn CSUF Physics

18. 18 Dr Heidi Fearn CSUF Physics What about assemblers?http://www.imm.org

19. 19 Dr Heidi Fearn CSUF Physics Nano Circuits on the horizon. Do we know how to build the needed circuit components? YES Do we have the materials to build them from? YES Can we mass produce these components and make the venture profitable? NOT YET. Do people really need computers and laptops that small ? YES WE LIKE TOYS.

20. 20 Dr Heidi Fearn CSUF Physics How does a carbon Nanotube switch work?

21. 21 Dr Heidi Fearn CSUF Physics Carbon Nanotubes to the rescue!

22. 22 Dr Heidi Fearn CSUF Physics What properties do the semiconductor variety of Carbon Nanotubes have that makes them so special? Single walled only.“Understanding nanotechnology” Scientific American, Warner Press. The semiconductor type of c-nanotubes have different band gaps. The size of the band gap depends on the diameter of the nanotube. The nanowires will only conduct if they are given enough energy, for the electrons within them, to surmount the band gap. Different sizes of tube give different band gaps- as low as zero (metal), as high as silicon and just about anywhere inbetween.Theory says that a truly nanoscale FET (Field Effect Transisitor) would have switching times 1000 times faster than today. Different band gaps means that different devices are possible. Metal and semiconductors combined can make diodes for example. The multi walled tubes have even more exotic properties- read more about those online and in the books I’ve mentioned. The multi walled tubes have even more exotic properties- read more about those online and in the books I’ve mentioned.

23. 23 Dr Heidi Fearn CSUF Physics Carbon Nanotubes and nanowires“Understanding Nanotechnology” Scientific American, Warner Books. Silicon nanowires are also feasible- they may be easier to attach to existing silicon chip technology. Organic molecule devices are also feasible but they have traditionally been connected via metal wires using lithography techniques. It is not easy to make a connection with the carbon (or silicon) nanowires. Using both devices and wires out of nanotubes may solve that problem.

24. 24 Dr Heidi Fearn CSUF Physics Nanoribbons light the way.http://nanotechweb.org/articles/news/3/8/8/1 Nanowire devices can also emit light and detect photons. Until recently there has been no way to transmit the light from device to device, until 2004. Scientists at the Univ of Berkeley and Lawrence Berkeley National Lab have used nanoribbons of crystalline oxide to channel light between devices. See above article for details. Optical computing come sooner than expected. Carbon nanotubes also have very good optical channeling properties.

25. Dr Heidi Fearn CSUF Physics 25 The End See you on Feb 28th for the LAST talk, Lecture 4: On wetware, biobots and biological manipulation.