CCMR - RET 2008WEEK 5

SEM (scanning electron microscope)

• A type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern.

How does SEM work?

• Electron beam interacts with the material, causing a variety of signals to be emitted-revealing details of the material’s shape, homogeneity and elemental composition.

SEM Images

• Low accelerating voltages– finer surface structure

images can generally be obtained.

SEM Images

• High accelerating voltages– the beam penetration

and diffusion area become larger, resulting in unnecessary signals being generated from within the specimen.

SEM Images

Lichen Unknown

Electron Microprobe

1149 Snee Hall

probelab.geo.umn.edu/electron_microprobe.html

A. Electrons are generated by heating a tungsten filament similar to the one in a light bulb.

B. Electrons pass through lenses that condense the beam, remove aberrations and focus the beam

C. The electrons hit the sample - This knocks out inner electrons in the sample - The atom is now in an excited state. An outer electron drops down to the inner energy level releasing energy in the form of x-rays at the same time.

D. X-rays are then reflected through a crystal

E. The reflected rays are then counted and recorded by a detector.

Electron Microprobe Uses• Non - destructive• Compositional Analysis

– Quantitative– Qualitative

• Precise X-Ray intensities• High Spectral Resolution

http://www.authorstream.com/Presentation/Janelle-19809-Electron-Beam-MicroAnalysis-Geol-619-1-History-Electrons-as-Entertainment-ppt-powerpoint/

Applications of the Electron Microprobe

Case Study One – What is under the fingernails?

Clay?

Paint?

Lichen?

SEM image

Insect Wing?

SEM image

Electron Microprobe Analysis

Since the fingernail is an organic compound, there was alarge carbon peak. Other elements such as calcium and sulfur

might be found in fingernails normally.

Other Applications of Electron Microprobe

GEOLOGY-

Chemical analysis of rocks, dating, plate tectonics

ArcheologyCompositional distinctions between 16th century ‘fac¸on-de-

Venise’ andVenetian glass vessels excavated in Antwerp, Belgium†

I. De Raedt,a K. Janssens*a and J. VeeckmanbaDepartment of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.

E-mail: koen@uia.ua.ac.bebExcavation Department of the City of Antwerp, Godefriduskaai 36, B-2000 Antwerp, Belgium

Received 29th October 1998, Accepted 10th December 1998At

JEOL 6300 SEM/EDX

Based on chemical analysis,50% of the glassware was from Italy

FORENSIC SCIENCESEMGSR

The SEM solution for AutomatedAnalysis and Classification of

Gunshot Residue

SEM/ Microprobe is used to analyze inorganic compounds in gunshot residue

STUDY POTENTIAL ELECTROCATALYSTS FOR FUEL CELLS

1. Sputter different concentrations of metals onto a substrate

(Based on lecture by Hector Abruna)

2. Perform Thermal imaging to determine areas of higher electrochemical activity

3. Use scanning electrochemical microscopy (SECM) to test sample’s ability to oxidize hydrogen/formic acid

and reduce oxygen.

Now we need to determine the chemical composition Of the product before bulk manufacture

Obtain composition with microprobe and Rutherford backscattering (RBS)

SEM-Observe texture and crystal grain size

GADDS-Determine crystal structure

Niobium/Tin Film Studies

Unannealed Sample- 2 to 1 Niobium to Tin

Element Line

Net Counts

Weight % Atom % Atom % Error

Compnd %

Nb L 64150 67.40 72.53 +/- 0.47 67.40 Nb M 0 --- --- --- --- Sn L 17107 32.60 27.47 +/- 0.33 32.60 Sn M 0 --- --- --- ---Total 100.00 100.00 100.00

Annealed Sample -

Oxygen accountedthe missing mass- the niobium was probably oxidized.

Large peak seen for Niobium. About 10% of mass unaccounted for.

Butterfly Wings-The Sequel-

Light Microscope Images

Butterfly Scales showing overlapping pattern

10µ

20µ

Individual scales showing ribbing

pattern

Light Microscope views

Fringe Scales Tips of Fringe scales

10 µ20 µ

Fringe Scales of Wing

100 µ 50µ

Optical Microscope -Transmitted Light

Optical Microscope – Reflected Light

Unpolarized vs Polarized Light

Wing Scale Unpolarized Light 50x objective lens

Wing Scale Polarized Light 50x objective

lens

10 µ 10µ