Slide 1. Fibres and forensics. Text and images by the Centre for Microscopy & Microanalysis, University of Queensland, Australia, August 2007. Slide 2. Fibres: Natural [animal & mineral] Synthetic [human –made] What we will cover: 1) Scanning Electron Microscopy (SEM).
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Fibres and forensics
Text and images by the Centre for Microscopy & Microanalysis, University of Queensland, Australia, August 2007
Natural [animal & mineral]
Synthetic [human –made]
What we will cover:
1) Scanning Electron Microscopy (SEM).
2) How to identify fibres using the SEM.
3) The identification of a mystery fibre.
What is scale all about?
Resolution (not magnification!) is the ability to separate two objects optically
With enough resolution we can magnify an object many millions of times and still see new detail
This is why we use electron microscopes
If you magnified your thumb nail just 10,000 times it would be about the size of a football pitch.
For example think of the size of Suncorp Stadium in Brisbane
Electron beam produced here
Beam passes down the microscope column
Electron beam now tends to diverge
But is converged by electromagnetic lenses
Cross section of electromagnetic lenses
Diagram of Scanning Electron Microscope or SEM
in cross section - the electrons are in green
Using X-rays and the scanning electron microscope
Electron falls back again to inner ring [lower energy state or valence] & burst of X-ray energy given off that equals this
= Characteristic packet of energy
What the X-rays tell us
Quantity of packets
Characteristic oxygen peak
Energy of packets
in thousands of electron volts come off atoms
Characteristic carbon peak
Characteristic chlorine peak
Some definitions of fibre
Any slender, elongated, threadlike object or structure.
A natural (e.g. plant, animal or mineral) or synthetic filament, capable of being spun into yarn.
Commonly also used in:
Botany: One of the elongated, thick-walled cells that give strength and support to plant tissue.
Anatomy: Any of the filaments constituting the extracellular matrix of connective tissue. Any of various elongated cells or threadlike structures, especially a muscle fiber or a nerve fiber.
Sample preparation for SEM
Fibre samples are dried then mounted on 12mm metal stubs and coated with platinum.
The following images are of various natural (plant and animal) fibres and synthetic fibres imaged using a scanning electron microscope
Note: electrons provide monochrome images.
Natural Fibres (Plant)
(A) Tissue paper at low magnification.
(B) Same tissue paper at higher magnification showing individual fibres.
How wide are these fibres?
Not all hair is the same!
Rabbit hair (A) looks different from
human hair (B) under the SEM.
What are the differences?
(A) Human hair strands at low magnification.
(B) & (C) At higher magnifications showing surface detail (scales).
Fibres can be
natural or synthetic.
But how can we tell them apart quickly and easily?
Coconut fibres (coir)
Shade cloth woven plastic fibres
We can use an SEM to examine the size, shape, surface detail and elemental composition
Synthetic fibre: velcro
(A) Fibre glass at
(B) & (C) Fibre glass at progressively higher magnifications showing individual fibres.
Note smooth fibre surfaces
Asbestos – why is it
dangerous to health?
How many fibres this wide
would fit across 1 mm ?
As seen by a light microscope
As seen by an SEM !