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Conventional SEM

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Conventional SEM. Specimen at high vacuum – requires sample fixation and dehydration or freezing. Charging is minimized by coating sample with metal or carbon or lowering the operating kV. Variable Pressure Scanning Electron Microscope. Variable Pressure Scanning Electron Microscope.

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slide1

Conventional SEM

Specimen at high vacuum – requires sample fixation and dehydration or freezing.

Charging is minimized by coating sample with metal or carbon or lowering the operating kV.

slide3

Variable Pressure Scanning Electron Microscope

  • - Vacuum in the sample chamber can range from high vacuum (< 10-6 Pascals) up to 3,000 Pa.
  • - Gas in the sample chamber allows uncoated and unfixed samples to be imaged.
  • Detectors used at higher pressures are backscatter or special secondary detectors.
  • - Moisture on the sample can be controlled by cooling/heating stage and water injection system.
slide8

SEM

Electron/Specimen Interactions

When the electron beam strikes a sample,

both photon and electron signals are emitted.

Incident Beam

Backscattered electrons

X-rays

- composition info

- Atomic number and topographical

Cathodoluminescence

- Electrical

Secondary electrons

Auger electrons

- Surface sensitive compositional

- Topographical

Specimen

Specimen Current

Electrical

slide12

VPSE Detector, Light Pipe and PMT.

Incident Electron Beam

Zeiss VPSE Detector Principle

Photons

BSE’s

The photons are detected and amplified to provide the final image.

Specimen

slide15

Peltier stage

Heats to 50 C

Cools to - 25 C

slide19

Applications

Live centipede

Bacteria on rock

slide20

Fresh moss with

liquid water

slide22

Skyscan 1072

Micro-CT

X-Ray

Tomography

Scanner

slide23

MicroCT

X-ray imaging that reconstructs images to form cross-sections and volumetric information.

Resolution to 5 mm, 3D reconstruction, density measurements.

Any sample works having differential density within sample (e.g. bone vs. tissue, or addition of x-ray contrast agents)

Applications – Bone, insects, food science, material science, substrate/cell distribution.

slide24

Sasov and van Dyck, 1998, J. Microsc.

Object is rotated 180 degrees.

Images captured at one degree increments.

Reconstructions done on aligned images to create volume data.

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