Introduction to Scanning Probe Microscopy

1. Introduction to Scanning Probe Microscopy Brandon Weeks Texas Tech University

2. Introduction to Nanotechnology As soon as I mention this, people tell me about miniaturization, and how far it has progressed today. They tell me about electric motors that are the size of the nail on your small finger. And there is a device on the market, they tell me, by which you can write the Lord's Prayer on the head of a pin. But that's nothing; that's the most primitive, halting step in the direction I intend to discuss. It is a staggeringly small world that is below. In the year 2000, when they look back at this age, they will wonder why it was not until the year 1960 that anybody began seriously to move in this direction. Feynman, Richard; "Theres Plenty of Room at the Bottom An Invitation to Enter a New Field of Physics (1960); Engineering and Science Magazine; © California Institute of Technology

3. Is there a definition for “nanotechnology” National Nanotechnology Initiative Definition Research and technology development at the atomic, molecular or macromolecular levels, in the length scale of approximately 1 - 100 nanometer range, to provide a fundamental understanding of phenomena and materials at the nanoscale and to create and use structures, devices and systems that have novel properties and functions because of their small and/or intermediate size. The novel and differentiating properties and functions are developed at a critical length scale of matter typically under 100 nm. Nanotechnology research and development includes manipulation under control of the nanoscale structures and their integration into larger material components, systems and architectures. Within these larger scale assemblies, the control and construction of their structures and components remains at the nanometer scale. In some particular cases, the critical length scale for novel properties and phenomena may be under 1 nm (e.g., manipulation of atoms at ~0.1 nm) or be larger than 100 nm (e.g., nanoparticle reinforced polymers have the unique feature at ~ 200-300 nm as a function of the local bridges or bonds between the nano particles and the polymer).

4. What is Nanotechnology • Top Down vs. Bottom Up approach • Who does Nanotechnology • Chemists • Physicists • Materials Science • Biologists • Movers and shakers of Nanotechnology • Richard Feynman (Nobel prize winning author) • Eric Drexler (Unbounding the Future – The Nanotechnology Revolution)

5. Nanotechnology Initiative funding ($ millions)

6. Industrial Revolution Industrial Revolution This is the period of time that occurred after developments such as the steam combustion engine allowed for more efficient production of goods. The advent of the assembly line etc. occurred. It basically changed production from single goods to mass production. Mid 1800s to early 1930s.

7. Steam Engine James Watt (1736-1819)In 1765, James Watt while working for the University of Glasgow was assigned the task of repairing a Newcomen engine, which was deemed inefficient but the best steam engine of its time. That started the inventor to work on several improvements to Newcomen's design. Most notable was Watt's 1769 patent for a separate condenser connected to a cylinder by a valve, unlike Newcomen's engine the condenser could be cool while the cylinder was hot.

8. Measuring and Machining • What measuring instruments and machining tools were required to develop the steam engine?and • When were they developed ?

9. Atomic Force Microscope The AFM is a measuring and fabrication instrument (tool) that is facilitating the nanotechnology revolution - just as the milling machine and calipers were necessary for the industrial revolution.

10. AFM Instrumentation Atomic resolution on silicon

11. Comparison of AFM to other imaging techniques • Scanning Tunneling Microscopy (STM) • STM has higher resolution but can only image conducting samples • Optical Microscopy • Diffraction limited, images can be complex due to reflectivity and diffraction within differing materials • Transmission Electron Microscopy (TEM) • Expensive, complex sample prep.

12. Comparison of AFM vs. Scanning Electron Microscopy Similar lateral resolution Comparable is cost SEM AFM Wide range of sample roughness Samples must be relatively flat (few microns in Z) Large field of view Maximum scan range ~70-100 microns 2 dimensional images Unambiguous 3D images Can provide elemental analysis Minimal chemical information obtained Operated in low to high vacuum Operates from UHV – ambient - fluid Photoresist 3 m

13. Investigation of micro/nanoscale defects on surfaces Using AFM we can visualize in 3D defects and structures on surfaces In addition measurements can be obtained on the height, depth, surface area, volume

14. Contact mode imaging • Tip is scanned in feedback to maintain constant deflection • Tip contacts surface through adsorbed fluid layer • Forces range from nano Newtons to micro Newtons • Advantages • High scan speeds and ease of use • Disadvantages • Shear force can damage sample • Delicate samples can be difficult to image

15. Lateral force images can be obtained simultaneously with contact mode • Measure the twisting of the cantilever while scanning • Data is a convolution of topography and lateral force Topography Friction Alkane thiols on gold (acid bright, methyl dark) Can obtain some information beyond topography

16. AC imaging • The cantilever is oscillated near its resonant frequency • A constant amplitude/tip sample interaction is maintained (typical amplitude is 20-100 nm) • Forces are typically 200 pN or less • Advantages • Higher lateral resolution (typically 1-5 nm) • Lower forces (virtually no lateral force) • Disadvantages • Much slower

17. Phase imaging • Measure the phase lag of the cantilever driving frequency vs. actual oscillation • contrast depends on the physical properties of the material Polymer blend (Polypropylene & EDPM) Topography Phase Method of measuring relative elastic properties of complex samples

18. Techniques Spurred From AFM Technology Very sensitive detector for changes in mass, temperature, etc. • Artificial nose • Biological detection • Explosive sensor Thiol added Unfolding of protein domains

19. Concentrated Areas of Nanoscience • Dry Nanotechnology • Surface Science, Fabrication of structures • Semiconductiors, metals, nanotubes, etc. • Wet Nanotechnology • Biological systems • Genetic material, membranes, enzymes, etc. • Computational Nanotechnology • Modeling and simulation of complex structures

20. High Technology • Manmade materials: • Hard Disk (MFM) • Micro Optics • Others

21. Low Technology • Man Made but not controlled on short length scale • Polymers • Paper

22. Biological • Cells/Virus • DNA Proteins

23. rms roughness Surface Area 2 m b 67 nm phase 109 m 2 m d 299 nm phase 123 m Observe kinetic processes • Topographic images showing surface reconstruction of HMX (high explosive) at 185oC

24. Movie of the phase transition of HMX • Voids appear to grow along crystallographic planes • Slow growth of the voids followed by a fast transition • Well organized layers • By observing the rate at different temperatures kinetics can be measured

25. Nanolithography • Advantages • High resolution • Precise manipulation of single molecules • Inexpensive compared to similar high resolution techniques • Imaging capabilities allow real-time manipulation • Can be performed in ambient conditions (including fluids) • Disadvantages • Currently a serial process • Scanner nonlinearities

26. Surface manipulation with AFM • Surface manipulation of colloidal gold on mica • Data storage • Sensors • Single electron transistors • J. Vacuum Sc. & Tech. B, Vol. 15, No. 4, pp. 1577-1580, 1997 • Manipulation of Nanotubes • Single molecule logic circuit • Science, Vol. 292, Issue 5517, April 27, 2001

27. Dip-Pen Nanolithography • AFM tip “inked” with molecule of interest • Transport occurs through meniscus formed between tip and substrate

28. Tagged antibodies 6 m Electroluminescent polymers Examples of DPN inks include thiols, antibodies, polymers Thiol ‘Ink’ on gold (Friction Image) Chemical ‘Ink’ on glass (Confocal Images) Human Hair (80 mm width) Noy et al., Nano Letters (2002)

29. Applications of nanolithography

30. Nano Materials Tip broadening Si)-CC(C6H5) Nanocrystals on mica h=2 nm width~60 nm Why the difference in measurements? Tip effects Paper nucleopore filter (pore diameter ~ 250 nm) Holes appear V shaped in line scan images Poor aspect ratio

31. High resolution imaging (nanotube tips) Pick-up method attached nano-tube after growth on substrate CVD process grows nano-tubes directly onto tips Nanotubes on Si 15x7.5 mm iIlustration of pick-up Force curves used to detect pick-up Regular tip Bends Mixture of hydrocarbon gas and oxygen reacts in furnace Nanotubes nucleate on Fe catalyst Cantilever deflection Nanotube Buckles Approach to surface

32. Nanotube-based probes enable observation of molecular scale processes DNA packing by ABF protein Pure 0.001 mg/ml 20nm 20nm 500nm 800nm 0.25 mg/ml 1 mg/ml 100nm 100nm 2000nm 2000nm Klare et al., (In prep)

33. Imaging restrictions enzymes and DNA mapping  • restriction enzymes are valuable for mapping DNA • determine positions of specific elements (e. g. genes or mutations) 50 kb cosmid showing six EcoRI enzyme sites can identify the positions of bound restriction enzymes with an accuracy of about 2% Genomics 41, 379 (1997)

34. Is smaller better always better • Data Storage • Tb/cm2 • Molecular devices • Motors • Transistors • Happening now! • Medicine • Sensors • Robotics • Genetic • Government • Military • Space