lecture 22: chapter 4: surface characterization in biomaterials and tissue engineering

November 14, 2005 EEBE 512/ENEL 619.15 Dr. KE Jones

Lecture 22: Chapter 4: Surface Characterization in Biomaterials and Tissue Engineering

Really just a bunch of Microscopy.

EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005

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It’s from the Greek, mikros (small) and skopeo (look at).


Objectives Starting from the de Broglie equation,

demonstrate that TEM resolution depends on the voltage of the accelerating field

Describe the principle and sample preparation for: TEM, SEM, 2 modes of STM & SFM, XPS, AES, SIMS, ISS,

FT-IR, ATR, FTIR-ATR


Outline

TEM SEM

Electron Microscope

STM SFM

Scanning Probe Microscope

Surface Topography


Why EM?

The topography of biomaterials we are interested in are very small.

• ceramics

• composites

• metals

• polymers


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Why electrons?

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It all started with light, but even with better lenses, oil immersion and short wavelengths, resolution was only about 0.2 mm/1000x = 0.2 micrometers.



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de Broglie equation


TEM invented in 1931Dr. Ernst Ruska at the University of Berlin.


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Fig 4.4 (a) TEM

Condenser

Objective

Projector

Sample

Fluorescent screen

Electron source



• e- can “scatter” or pass thru sample (i.e. slide projector)• transmitted e- (no scat) produce image• The denser parts of the sample scatter more e- > less e- transmitted > appears darker


TEM cont’

1. Chemical (fixation, washing, dehydration, infiltration with solvents & resins, embedding and curing)

2. Ultamicrotomy: 30 - 60 nm

3. Stained with e- dense material


TEM (the end)

• Only unscattered e- are visualized.• No 3D, can’t see surface (although

shadowing)

• Can’t cut everything small enough.

Materials Sciences Division—Lawrence Berkeley National Laboratory

Four images, each taken at 60 second intervals, portray the rightward march of indium atoms along a carbon nantoube under an applied bias of 2 volts. The ends of the nanotube, where the electrical contacts are made, are out of view to the left and right. Reversing the direction of the voltage reverses the direction of motion.

Carbon Nanotubes as Nanoscale Mass ConveyorsAtom Transport at the Nanoscale

A. Zettl , 04-5

100 nm

Model depiction of the motion of atoms along a single-walled carbon nanotube. In principle, this phenomenon could be the basis for arrays of nano-sized conveyor belts delivering mass to specific locations atom-by-atom or picking up material at one site and delivering it to another.

Image created by K. Jensen.


Scanning Electron Microscope

First true SEM, 1942, resolution 50 nm, magnification 8000x.Now, 1 nm & 400 000x.


Fig. 4.4 (b) SEM

Condenser

Condenser

Condenser

Sample

Electron source

Deflector

CRT

Detector



• uses e- that interactinteract with sample• detector• production of 2ndary e- > detector > more 2ndary e- in dense areas• 3D-image of surface features


SEM cont’

1. Dry and stable in vacuum

2. Apply a thin metal coating to specimen to make it conductive

3. Bunch of other stuff not mentioned in text.


UofA Electron Microscope Facility



http://www.ualberta.ca/~mingchen/index.htm




Butterfly wing surface






Origami crane folded by Dr. Ming Chen


Where are we…

TEM SEM

Electron Microscope

STM SFM

Scanning Probe Microscope

Surface Topography


Scanning Tunneling Microscope

• uses e- tunneling effect• apply voltage between probe tip and sample surface• tunneling current develops

• measures mech &/or elec properties at atomic level• images from voltage, current and/or probe position


STM cont’Two Modes

Constant current:

• bumpy surface

• feedback through high gain voltage amps, keeps tunneling current constant by moving probe

• voltage & 3d position

Constant height:

• flat surface

• current & 2d position


Scanning Force Microscope

• also Atomic Force Microscope (AFM)• measures atomic forces between probe and sample surface

• van der Waals (attactive, dominate @ large dist)• exclusion principle (repulsive, dominate @ near dist)

• piezoelectric element controls movement


STM cont’Two Modes

Constant force:

• feedback of force controls piezoscanner that controls sample position

• piezoscanner position

Constant height:

• sample at constant height

• measure deflection of cantilever (optical)

• contact or not (shear force problem)


STM cont’

Laser

Lens

Sample

Piezoscanner

Two-segment photodetector

Mirror Cantilever

Fig 4.9 Optical lever


Objectives Starting from the de Broglie equation,

demonstrate that TEM resolution depends on the voltage of the accelerating field

Describe the principle and sample preparation for: TEM, SEM, 2 modes of STM & SFM, XPS, AES, SIMS, ISS,

FT-IR, ATR, FTIR-ATR

lecture 22: chapter 4: surface characterization in biomaterials and tissue engineering

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