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Introduction to Scanning Probe Microscopy Brandon Weeks Texas Tech University Introduction to Nanotechnology

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Introduction to scanning probe microscopy l.jpg
Introduction to Scanning Probe Microscopy

Brandon Weeks

Texas Tech University


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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


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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).


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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)



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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.


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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.


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Measuring and Machining

  • What measuring instruments and machining tools were required to develop the steam engine?and

  • When were they developed ?


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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.


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AFM Instrumentation

Atomic resolution on silicon


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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.


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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


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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


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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


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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


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AC imaging contact mode

  • 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


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Phase imaging contact mode

  • 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


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Techniques Spurred From AFM Technology contact mode

Very sensitive detector for changes in mass,

temperature, etc.

  • Artificial nose

  • Biological detection

  • Explosive sensor

Thiol added

Unfolding of protein domains


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Concentrated Areas of Nanoscience contact mode

  • 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


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High Technology contact mode

  • Manmade materials:

    • Hard Disk (MFM)

    • Micro Optics

    • Others


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Low Technology contact mode

  • Man Made but not controlled on short length scale

    • Polymers

    • Paper


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Biological contact mode

  • Cells/Virus

  • DNA Proteins


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rms roughness contact mode

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


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Movie of the phase transition of HMX contact mode

  • 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


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Nanolithography contact mode

  • 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


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Surface manipulation with AFM contact mode

  • 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


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Dip-Pen Nanolithography contact mode

  • AFM tip “inked” with molecule of interest

  • Transport occurs through meniscus formed between tip and substrate


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Tagged antibodies contact mode

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)



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Nano Materials contact mode

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


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High resolution imaging (nanotube tips) contact mode

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


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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)


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Imaging restrictions enzymes and DNA mapping  processes

  • 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)


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Is smaller better always better processes

  • Data Storage

    • Tb/cm2

  • Molecular devices

    • Motors

    • Transistors

    • Happening now!

  • Medicine

    • Sensors

    • Robotics

    • Genetic

  • Government

    • Military

    • Space


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