1. NANOFABRICATION TECHNOLOGIES
Nanotechnology Products
Introduction to Nanoscience
Nanofabrication Processes
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

2. Nanotechnology
Fabrication and application of entities whose feature sizes are in the range from about 1 nm to 100 nm
1 nm = 10-3 m = 10-6 mm = 10-9 m
Entities include structures, films, coatings, dots, lines, tubes, and systems
Nanoscience – the field of scientific study that is concerned with objects in the 1 to 100 nm range
Nanoscale – refers to dimensions within this range and slightly below
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

3. Some Examples of Nanoscale Entities
Helium atom – diameter about 0.1 nm
Uranium atom – diameter about 0.22 nm
Molecules tend to be larger because they consist of multiple atoms
Molecules made up of about 30 atoms are roughly 1 nm in size
Depending on the atoms involved
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

4. Nanotechnology Products
Cosmetics and sun lotions
Car polishes and waxes
Coatings for eyeglass lenses
Scratch-resistant paints
Carbon nanostructures
Buckyballs
Carbon nanotubes
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

5. Buckyballs (Fullerines)
Carbon molecules containing exactly 60 atoms (C60) and shaped like a soccer ball
Originally named buckministerfullerene, after R. Buckminister Fuller, designer of the geodesic dome (shortened to fullerene)
Can be bonded together to form crystals whose lattice structure is face-centered cubic
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

6. Buckyballs Structure of C60 molecule 12 pentagonal faces
20 hexagonal faces
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

7. Properties and Applications of Fullerines
Electrical properties of insulator, but can be doped (e.g., K3C60) to become conductor
Exhibits properties of a superconductor and very low temperatures (around 18K)
Possible medical uses because they possess many possible attachment points for drugs
Other medical applications include antioxidants, burn creams, and diagnostic imaging
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

8. Carbon Nanotubes
Another nanostructure of interest, consisting of carbon atoms bonded together in the shape of a long tube
Depending on structure and diameter, can have conducting or semiconducting properties
Conductivity superior to copper due to fewer defects that increase electrical resistance
Thus, high currents do not increase temperature as in metals
Elastic modulus and tensile strength of carbon nanotubes much greater than steel
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

9. Carbon Nanotubes
Carbon nanotube structures: (a) armchair and (b) zigzag
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

10. Introduction to Nanoscience
Nanoscience and nanotechnology are interdisciplinary fields
Chemistry, physics, various engineering disciplines, computer science, biology, and medical science
Biology operates in the nanoscale range
Proteins – large molecules ranging in size between about 4 nm and 50 nm
Chlorophyll in plants – about 1 nm
Hemoglobin in blood – about 7 nm
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

11. Size Matters
As the size of an object becomes smaller and smaller, approaching nanoscale, the surface molecules become increasingly important relative to internal molecules
Because of the increasing proportion of surface molecules relative to internal molecules
Thus, the surface properties of materials of nanoscale objects become more influential in determining the behavior of the objects
And the influence of bulk properties is reduced
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

12. Some Size Effects: Atomic Bonding
Two types of atomic bonds:
Primary bonds –combining atoms into molecules
Secondary bonds – attraction between molecules to form bulk materials
Secondary bonds become more important for nanoscale objects because their shapes and properties depend on these secondary bonding forces
Thus, material properties and behavior of nanoscale objects are different from those of much larger objects
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

13. Size Effects: Quantum Mechanics
Branch of physics concerned with the notion that all forms of energy occur in discrete units when observed on a small enough scale
Example: electricity is conducted in units of electrons
Quantum mechanics are significant for nanoscale entities
One implication: As microelectronic devices reach nanoscale, we approach the limits of technological feasibility of current fabrication processes for integrated circuits
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

14. Scanning Probe Microscopes
Conventional optical microscopes
Magnification ~ 1000 times
Resolutions ~ 200 nm
Electron microscopes
Magnification ~ 1,000,000 times
Resolutions ~ 1 nm
Scanning probe microscopes
Magnifications ~ 10 times greater than electron microscopes
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

15. Scanning Probe Microscopes
Utilize a very sharp needle probe to scan a surface from a distance about 1 nm above it
Types of scanning probe microscopes:
Scanning tunneling microscope (STM)
Atomic force microscope (AFM)
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

16. Scanning Tunneling Microscope
A voltage is applied to the probe, causing electrons on the surface to tunnel up to the probe tip
Tunneling electrons can be measured as current
As probe is moved across surface, current is higher at locations immediately above surface atoms and lower in between surface atoms
These variations in current can be used to create topographical maps of surface on an atomic scale
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

17. Atomic Force Microscope
Limitation of scanning tunneling microscope - it can only be used on surfaces of conducting materials
Atomic force microscope can be used on any material
In the AFM, the probe is attached to a delicate cantilever that deflects due to forces exerted by surface atoms as the probe traverses the specimen surface
Forces include van der Waals, capillary, magnetic
Vertical deflection can be measured to construct topographical image of surface
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

18. Atomic Force Microscope Image
AFM image of silicon dioxide letters on a silicon substrate; the oxide letters are about 20 nm wide (photo courtesy of IBM Corp.)
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

19. Nanofabrication Processes
Top-down approaches
Adaptation of microfabrication techniques to make nanoscale objects
Bottom-up approaches
Atoms and molecules are manipulated and combined to form larger nanoscale structures
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

20. Top-Down Processing Approaches
Mostly based on lithographic techniques
Extreme UV – UV wavelengths down to 13 nm
Electron-beam lithography – resolutions ~ 10 nm
X-ray lithography - resolutions ~ 20 nm
Micro-imprint lithography – uses flat mold with desired pattern that physically deforms resist surface to create regions that will be etched
Nano-imprint lithography – same as micro-imprint but adapted to nanoscale
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

21. Micro-Imprint Lithography
(1) Flat mold positioned above resist, (2) mold is pressed into resist surface, (3) mold is lifted, (4) remaining resist removed by etching to expose substrate surface
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

22. Bottom-Up Processing Approaches
Production of carbon nanotubes
Nanofabrication by scanning probe techniques
Self-assembly
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

23. Production of Carbon Nanotubes
Laser evaporation method
Carbon arc techniques
Chemical vapor deposition
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

24. Laser Evaporation Method
Starting material is graphite with traces of Co and Ni that act as nucleation sites in formation of nanotubes
Graphite workpiece is placed in quartz tube filled with argon and heated to 1200°C
A pulsed laser beam is focused on surface, causing carbon atoms to evaporate from the bulk graphite
Argon moves carbon atoms to cool copper surface, where they condense, forming nanotubes with diameters 10 to 20 nm and lengths ~ 100 m
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

25. Carbon Arc Technique If no catalyst – multi-walled nanotubes form
Uses two carbon electrodes that are separated by 1 mm and located in a partial vacuum
25 V is applied across the electrodes, causing carbon atoms to be ejected from positive electrode and carried to negative electrode where they form nanotubes
If no catalyst – multi-walled nanotubes form
If cobalt used as catalyst, single-walled nanotubes with diameters 1 to 5 nm and lengths ~ 1 m
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

26. Chemical Vapor Deposition
Starting material is hydrocarbon gas such as methane (CH4)
Gas is heated to 1100°C, causing it to decompose and release carbon atoms
Atoms condense on cool substrate to form nanotubes
Substrate surface may contain metallic traces that act as nucleation sites for nanotubes
CVD process can be operated continuously, making it attractive for mass production
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

27. Scanning Probe Techniques
The scanning tunneling microscope (STM) can be used to manipulate individual atoms or molecules that adhere to a substrate surface by forces of adsorption (weak chemical bonds)
If the probe tip is moved close enough to the adsorbed atom so that its force of attraction is greater than the adsorption force, the atom will be dragged along the surface
In this way, individual atoms or molecules can be manipulated to create nanoscale structures
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

28. Manipulation of Individual Atoms Using STM Techniques
(a) Probe tip is maintained a distance from the surface that is sufficient to avoid disturbing the adsorbed atom
(b) Probe tip is moved closer to the surface so that the adsorbed atom is attracted to the tip
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

29. Manipulation of Individual Atoms
Can be classified as:
Lateral manipulation – atoms or molecules are transferred along the substrate surface by the attractive (or repulsive) forces of the probe tip
Vertical manipulation – atoms or molecules are lifted from the substrate surface and deposited at a different location to form a structure
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

30. Limitations of STM Manipulation
Must be carried out in a very high vacuum to prevent stray atoms or molecules from interfering with the process
Surface of substrate must be cooled to temperatures near absolute zero in order to reduce thermal diffusion that would gradually distort the atomic structure being formed
These limitations make STM manipulation of individual atoms and molecules very slow and expensive
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

31. Dip-Pen Lithography (DPN)
An alternative scanning probe technique that does show promise for practical applications
In DPN, the tip of an atomic force microscope is used to transfer molecules to a substrate surface by means of a solvent meniscus
Process is analogous to using an old-fashioned quill pen to transfer ink to a paper surface via capillary forces
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

32. Dip-Pen Lithography
Tip of an atomic force microscope is used to deposit molecules through the water meniscus that forms naturally between the tip and the substrate
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

33. Self-Assembly A fundamental process in nature
Natural formation of a crystalline structure during slow cooling of molten minerals is an example of nonliving self-assembly
Growth of living organisms is an example of biological self-assembly
In both instances, entities at the atomic and molecular level combine on their own into larger entities, proceeding in a constructive manner toward the creation of some deliberate thing
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

34. Self-Assembly in Nanotechnology
Attempts to emulate nature’s self-assembly process to produce materials and systems that have nanoscale features or building blocks
But the final product may be larger than nanoscale
May be micro- or macro-scale, at least in some of its dimensions
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

35. Self-Assembly in Nanotechnology
Desirable features of atomic or molecular self-assembly processes in nanotechnology:
They can be carried out rapidly
They occur automatically and do not require central control
They exhibit massive replication
They can be performed under mild environmental conditions (at or near atmospheric pressure and room temperature)
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

36. Principle of Minimum Energy
Physical entities such as atoms and molecules seek out a state such that the total energy of the system of which they are components is minimized
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

37. Implications for Self-Assembly
There must a mechanism for the movement of the entities, thus causing them to come into close proximity
Diffusion, convection, electrical fields
There must be some form of molecular recognition among the entities
Tendency for one atom or molecule to be attracted to and bind with another
The molecular recognition among the entities causes them to join in such a way that the resulting physical arrangement achieves a state of minimum energy
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

38. Current Processes That Use Self-Assembly
Czochralski process - growing single crystal silicon boule from molten pool of silicon
Lattice structure of the crystal is of nanometer size
Polymerization - joining of individual monomers (e.g., ethylene, C2H4) to form very large molecules (macromolecules such as polyethylene) in the form of long chains, each with thousands of repeating units
Repeating units are of nanometer size
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

39. Self-Assembled Monolayers (SAMs)
Two dimensional array (surface film) that is one molecule thick
Molecules are organized in some orderly fashion
Multi-layered structures also possible that are two or more molecules thick
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

40. Self-Assembled Monolayers
Substrate materials include gold, silver, copper, silicon, silicon dioxide
Substrate material must not form an oxide surface film that would interfere with the layering process
Layering materials include thiols, sulfides, and disulfides
The layering material must be capable of being adsorbed (adhering in the form of a very thin film) onto the substrate surface
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

41. Sequence in Formation of SAMs
Layering molecules move freely above substrate surface and are adsorbed onto the surface
Contact occurs between adsorbed molecules on surface, forming islands
The islands grow and gradually join together through the addition of more molecules on the surface, until the substrate is completely covered
In some cases, SAMs can be formed into desired patterns on the substrate, using techniques such as nano-contact printing and dip-pen lithography
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

42. Sequence in Formation of SAMs
Formation of thiol monolayer on gold substrate: (1) some molecules are attracted to surface, (2) they are adsorbed on surface, (3) they form islands, and (4) islands grow until surface is completely covered
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e