Unit 1, Part 1: Introduction to Nanotechnology (Read Chapter

2 in Di Ventra)

Dr. Brian Grady-Lecturerbpgrady@ou.edu

Four Units

• Synthesis: Dr. Warren Ford wtford@okstate.edu• Characterization: Dr. Brian Grady

bpgrady@ou.edu• Applications/Microscopy: Dr. Alan Cheville• Presentation of Review Papers

Mechanics Issues (On-line quizzes, laboratory issues etc.): Chris Young: nanotechta@gmail.com

Format of Class

• On-line lectures, assigned reading

• On-line quizzes: Purpose is to be sure you have read and comprehended material– Multiple attempts if necessary; not graded

except pass-fail

Format of the Class-Continued

• Three laboratories– Read material in advance– On-line video showing you how to do the experiments– On-line quiz to be completed PRIOR to laboratory or

you will not be allowed in the laboratory– Complete laboratory- on site on Saturday

• Logistical transportation issues will be dealt with later– Lab report: Important part of your grade– In order to be allowed to do the lab and get anything

but a failing grade for that lab: you must successfully complete ALL of the on-line quizzes for that unit (unless indicated as not necessary by an instructor) PRIOR to being allowed to enter the laboratory

Format of the Class (cont.)

• Comprehensive review paper– Topics must be approved by Dr. Grady no

later than November 1st.

• Papers due December 7th

• You will also prepare and give a 15-20 minute presentation at a mini-conference that will be held on Dec 1st. Location of miniconference will be at TU

Format of the Class (continued)

Read the Syllabus

What is nanotechnology

• Nanomaterials are materials where at least one dimension is very small (i.e. on the order of nanometers)– 1 nanometer=10 Angstroms=.001 microns=10-9

meters– Almost always talking about solids (not liquids or

gases)

• Nanotechnology is the study of the synthesis/manufacture of those materials, the characterization of those materials and the application of those materials

Why Nanotechnology

• Materials having very small sizes have unique properties– See Figure 1.19 in the text

• The size of the particles controls the colors that are emitted when the particles are exposed to UV light

• Only certain chemical compositions will have this property (i.e. this behavior is not generic to all nanoparticles)

• Materials with small sizes can be packed into small areas and can do lots of stuff– Integrated circuits: Millions of electrical components (resistors,

transistors) per square inch• Materials with small sizes can be packed in a regular

arrangement and do interesting things– See Figure 1.21 on inverse opals (unique colors due to a regular

arrangement of spheres)• By and large, the chemical identity of the spheres is irrelevant to the

effect; this is strictly a size effect.

Inverse Opals

• If spheres in regular pattern as shown to the right, and the spheres are the size of the wavelength of light (400-700 nm) get unique colors and can change color by changing sphere size

Why is nanotechnology unique?• Certain phenomena occur only when characteristic

dimensions reach the nanometer scale– Quantum tunnelling effects: If you put a voltage across an

insulator, then the current is given by V=IR. If the insulator becomes small; less than 100 nm; the current is much higher (orders of magnitude!) than that predicted by the formula due to tunnelling

• Surface effects are very important (surface to volume ratio is extremely large)– One sense: how atoms are arranged at the surface have a very

large influence on all properties, not just surface properties– 2nd sense: Certain phenomena that are “surface” phenomena

become dominant phenomena at nanoscale. For example, in flow through a pipe (think of water flowing through your garden hose!) the fluid right near the wall acts very differently than the rest of the fluid. This fact has a negligible effect though on the behavior of the water coming out of the hose end. If the garden hose becomes of nanoscale dimensions, all of the fluid is “near the wall” and all of the laws that tell you (for example) how much fluid comes out of your garden hose as a function of the pressure of the water do not apply.

Why study nanotechnology?

• Today there is a large amount of research, but, outside of integrated circuits, not a large number of commercial applications of nanotechnology

• Still primarily in the realm of start-up companies, and in the research departments of large companies

Is nanotechnology the wave of the future?

• Certain politicians think so (i.e. money!)• I think most people would agree that the term

“microelectronics” will (or at least should!) eventually be replaced by the term nanoelectronics

• Already niche applications in other areas– Take advantage of small size leading to some unique

characteristic or the fact that the material changes behavior entirely because the surface to volume ratio is so high

• The other logical area that one would think where nanotechnology will be huge is medicine– Blood vessels etc. are pretty small, and to be able to navigate

those vessels without disrupting function, which nanosize things should be able to do, should prove very useful.

Two Important Introductory Concepts

• Bulk vs. Surface Properties

• Arrangement of Atoms

Bulk vs. Surface

• Think of Scotch Tape– Surface Property: Adhesion. Scotch tape sticks to

things– Bulk Property: Strength. How much force does it

take to pull scotch tape apart

• Surface properties are determined by atoms within a few angstroms of the surface

• In nanotechnology: surface properties are much more important relatively than bulk properties than with other materials because surface/volume ratio is so high

Examples

• Examples of Surface Properties– Surface energy (adhesion ability), charge on a

particle (i.e. can it be made to have static electricity), catalytic ability (ability to cause reactions), ability to nucleate (think of putting boiling chips in heated water).

• Examples of Bulk Properties– Mechanical strength, stiffness and flexibility,

electrical conductivity, density etc.

Arrangement of Atoms

• Consider a solid– Three possibilities: atoms are arranged in a regular

pattern, atoms are not arranged in a regular pattern, some atoms are arranged in a regular pattern and some are not

– If atoms are all arranged in a regular pattern: crystalline

– If atoms are not arranged in a regular pattern: amorphous

– If some atoms are arranged in a regular pattern and some are not: semi-crystalline

What do I mean by “regular pattern”• Think of a single type of atom material, e.g.

gold– Gold atoms are arranged in cubes (atoms at

corners and at 6 faces).*

Ball and Stick Model Space Filling Model

* This particular structure is called “face-centered cubic

• Stack Cubes in all three directions to make up repeating structure. This is how atoms lie in “regular patterns”

(Don’t show in and out of page because drawing becomes too confusing)

Crystalline

• All crystalline materials are made up of regular cubic-like structures (cubes, rhombohedrans, cubes with lengths of sides not equal; there are seven total) with atoms at the same positions within every cube. There are only 230 different atom/cube combinations.

• Most of the time, each side of these cubic-like structures have dimensions between 0.5 nm and 2 nm

• Amorphous materials have no such cubes, i.e. if you draw cubes atoms aren’t in the same position within every cube.

Something to Consider• Suppose we make spherical gold

nanoparticles that contains enough volume for 10000 unit cells (which is equivalent to a 5.5 nm diameter particle). Note that in this particle approximately 1/3 of the unit cells have one side touching the surface!

• Since gold forms into cubes, one could easily see how a nanoparticle could be cubic; but how spherical and still have cubic unit cell???

• The answer is that it is not possible; either the outside of the sphere has to look like this or the atoms have to change positions at the surface. If atoms change positions, how deep into the nanoparticle does this go?– It turns out that in some systems, you can make a

material that is normally crystalline into an amorphous material, or even change the crystal structure entirely. Of course, the properties of the material change dramatically if this happens

Surface Composition

• For a single atom material, the arrangement of atoms at the surface can be very different than the arrangement of atoms in the bulk

• For materials with more than one atom, not only can the arrangement of atoms at the surface be different, but the composition can be different – For example, say we have the compound AB. Overall, we have

equal amounts of A and B, but it is possible at the surface we have much more A than B. In non-nanomaterials, this surface enhancement of A does not affect the bulk properties, since the amount of material at the surface is miniscule. In nanomaterials, this surface enhancement not only affects the surface properties, but it also effects the “bulk” properties since there is much more B in the bulk than A, since the amount of material at the surface is NOT miniscule.

On to Synthesis…