Final Reading Assignment: Travels to the Nanoworld: pages pages pages

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1 Final Reading Assignment: Travels to the Nanoworld: pages pages pages Bottom-up nanofabrication Can we assemble nanomachines manually? What are the components (parts)? nanoparticles nanofibers molecules proteins What else? 1

2 The smallest particles atomic clusters If you take a chunk of material and heat it up, or blast it with a laser, small pieces come off. They are called atomic clusters and can be even smaller than the nanoparticles that can be made in commercial quantities. Scientists study the sizes of these clusters by feeding them into an instrument called a mass spectrometer which gives a histogram of the cluster size. Often find that certain sizes are most common. In this case, clusters with 13, 19, 25, 55 atoms, etc. are the most prevalent. Why? Magic numbers Certain clusters correspond to nice close-packed structures which can be formed by packing spheres. These are generally the most stable clusters and since they are common, they correspond to peaks in the mass spectrum. 2

3 The most beautiful cluster In 1985, Richard Smalley at Rice Univ. was looking at carbon clusters. He was making soot. 60, 70, and 118 are not the usual magic numbers. What were these clusters? Buckminster Fuller and Geodesic Domes He showed that curved structures like domes could be constructed by putting together polygons like triangles, pentagons, hexagons, etc. 3

4 Buckerminster Fullerene: the soccer ball molecule Smalley hypothesized that the C60 cluster was actually a special hollow molecule made completely of carbon atoms. The atoms are joined in hexagons and pentagons. < 1 nm diameter Nothing like this had ever been seen before! But he was correct and won the Nobel Prize in Since then, we have learned how to make these Buckyballs in large quantities and that they have some fascinating properties. For example, they are superconducting, i.e. a material made of these balls conducts electricity without any energy loss. They are also ignored by our immune system and are being investigated as drug delivery vehicles. Buckyball cousin: Carbon nanotubes Carbon pentagons wrapped into a cylinder instead of a sphere. Perhaps these will be the wires for the next generation of computers. 4

5 Comparison of directed design technology strategies Technology Construction Advantages Limitations MEMS conventional massively parallel diffraction limit µfabrication production of about 0.2 µm Nanotech molecules, nanoparticles, nm size assembly? proteins, components C nanotubes, etc. Problems for nanoscale construction We have seen ways to manufacture nm size objects, but... How do we see nm size objects? light microscope limited to >500 nm electron microscope limited to >5 nm How do we manipulate nm size objects? 5

6 Analogy: Making Maps Relief map of Colorado taken from satellite images How would you get a more detailed map? Scanning probe microscope Tip also called (AFM) Atomic Force Microscope 6

7 Probe tips and cantilevers microfabricated using conventional photolithography techniques tips are sharpened using clever chemical etching tricks Some AFM images 5nm diameter gold nanoparticles A single strand of DNA 7

8 Images of individual atoms! AFM image of NaCl (sodium chloride), resolving the crystalline atomic structure of the surface. 5.6 nm x 4.8 nm scan. Each atom is about 0.3 nm in size! Nickel atoms on the surface of a crystal 8

9 Can also see molecules C60 molecules on silicon surface Can we manipulate atoms or molecules? 9

10 Lining nanoparticles up into neat rows The manipulation is sophisticated and delicate. Particles 1, 2, and 3, are purposely left in place. Placing atoms and molecules with precision Xenon atoms on Nickel Carbon Monoxide on Platinum Iron atoms on Copper 10

11 Manipulating a nanotube The AFM is first used to obtain an image of the nanotube by scanning the AFM tip, shown in red in the picture, just above the surface. The AFM tip is then brought down to the surface and is used like a tiny plow to move the nanotube. Because of the strong interaction between the nanotube and the surface, the bent Nanotube stays where it has been placed and maintains its shape, rather than snapping back to its preferred straight configuration. An example of how a nanotube can be manipulated to form complex shapes. The 6 frames are a series of AFM images of a nanotube (orange) on a silicon substrate (blue). Not all steps are shown. The AFM tip is used to create the Greek letter "theta" from a 2.5 micron long nanotube. 11

12 Making nanoelectronics A single nanotube (in red) originally on an insulating substrate (silicon oxide, shown in green) is manipulated in a number of steps onto a tungsten film thin wire (in blue), and finally is stretched across an insulating tungsten oxide barrier (in yellow). A nano-transistor Transistors are the basic building blocks of integrated circuits. To use nanotubes in future circuits we must make transistors from them. The width of this nanotube is about 2 nm! The smallest microfabricated transistor is ~180 nm. This could potentially increase transistor density by about 10,000! 12

13 Does it work? An ordinary wire is like a pipe for electrons. Electrical potential (voltage) is like water pressure. Electrical current is analogous to the flow rate. A transistor is like a pipe with a gate, current can only flow when the gate is open. gate open gate closed What s missing? These fabrication techniques are not massively parallel, they are serial (one-at-a-time). The remaining problem is making this economically feasible. How can these nanodevices be made cheaply? AFMs with 1000s of tips working simultaneously self-assembled molecular transistors currently one of the hottest and fastest-moving fields of research and development 13