Lecture 5: Microscopy

PHYS 430/603 material

Laszlo Takacs

UMBC Department of Physics

Light microscopy

The principle and a commercial scope

Useful sites:

http://www.microscopyu.com/articles/optics/components.htmlhttp://em-outreach.ucsd.edu/web-course/toccontents.html

Optical microscope (OM) and transmission electron microscope (TEM)

TEM modes:Composite image, bright field image, dark field image, selected area diffraction

Transmitted and diffracted beams Diffraction patternFirst image

Bright field Bright field, transmitted electrons only Dark field Selected area diffraction pattern

Comparing imaging and diffraction in a TEM.

Electron diffraction from a

monocrystal polycrystal glass

How do scanning microscopies work?

0 2 1 2 2 1 1 1

1 9 7 2 1 8 7 0

2 8 6 1 2 9 8 1

0 8 8 1 8 7 0 1

1 9 7 9 6 0 1 1

1 7 8 8 7 1 1 0

2 9 8 8 6 1 2 1

1 8 9 2 9 7 1 1

0 8 7 1 1 8 3 1

2 1 1 0 2 1 0 1

Image = table of numbers

Measurement generates a value for every location:

• Reflectivity of light (scanner)

• Ejected electrons (SEM)

• Current between tip and surface (STM)

• Force between tip and surface (AFM)

• Any quantity of interest that can produce useful contrast

Interpret numbers as intensitiesfor display or printer.Digital image processing.

How do scanning microscopies work?

0 2 1 2 2 1 1 1

1 9 7 2 1 8 7 0

2 8 6 1 2 9 8 1

0 8 8 1 8 7 0 1

1 9 7 9 6 0 1 1

1 7 8 8 7 1 1 0

2 9 8 8 6 1 2 1

1 8 9 2 9 7 1 1

0 8 7 1 1 8 3 1

2 1 1 0 2 1 0 1

Image = table of numbers

Measurement generates a value for every location:

• Reflectivity of light (scanner)

• Ejected electrons (SEM)

• Current between tip and surface (STM)

• Force between tip and surface (AFM)

• Any quantity of interest

Interpret numbers as intensitiesfor display or printer.Digital image processing.

The principle of the SEM.

There is no image formation in the optical sense.

This is classical analog system. Modern SEMs record the measured intensities in a computer memory rather then project them directly on a CRT screen. This way image processing is possible before the final image is created. TV does the same.

Measurable effect caused by high-energy electrons

Typical morphological contrast by secondary electrons.

It only looks like an illuminated landscape. The contrast comes from how many secondary electrons are generated and how efficiently they are collected by the detector. The illumination comes from above, the detector is n the side.

Magnifications: very different features are seen on different length scales

Depth of field

X-ray analysis

Images of a Lunar rock:

(a) Backscattered electrons(depend on Z)

(c) Fe X-rays(d) P X-rays(b) Sketch of phases;

m = metaltr = trolite, FeSsc = Fe-Ni phosphidewh = phosphate

The principle of STM/AFM