Transmission Electron Microscopy

Question 1

What does TEM detect?

Answer 1

Electrons that have had high enough energy to travel completely through the sample

Question 2

What information does TEM provide?

Answer 2

Local map of electron density of sample

Question 3

What information does diffraction analysis of TEM provide?

Answer 3

Information of crystalline structures as well as density maps.

Question 4

What does TEM involve?

Answer 4

1. Thin specimen irradiated with an electron beam of uniform current density.
2. Electrons emitted from electron gun and illuminate sample through 2 or 3 stage condenser lens system.
3. Objective lens: provides formation of either image or diffraction pattern
4. Electron intensity distribution behind specimen is magnified with a 3 or 4 stage lens system and viewed on a fluorescent screen.
5. Image recorded by direct exposure of a CCD camera.

Question 5

Give 5 different TEM techniques and a brief description of each.

Answer 5

-TEM energy-dispersive X-ray spectroscopy: provides information of different elements within structure

-Thin sectioning: Sample cut into v thin sections using ultramicrotomy and then studied using TEM. Useful for complex samples

-Cryo-TEM: can see dispersion of NPs when sample is frozen. Useful when imaging delicate materials

-Scanning Transmission Electron Microscopy (STEM): Electron beam focused to a sharp spot and scanned over the sample. Useful for obtaining internal chem composition of nanomaterials and the specific location of elements.

-TEM-tomography: obtains 3D images -> several TEM images taken at different angles and stacked together