Scanning electron microscopy methods in study of micro objects - - PowerPoint PPT Presentation

Scanning electron microscopy methods in study of micro objects

STUDENTS: CIUCĂ Andrei, PLĂMĂDEALĂ Cristina SUPERVISOR: O.L. ORELOVICH

Table of contents

• Introduction to SEM
• Equipment
• Sample preparation
• Charging of sample
• Tilted sample
• Different types of samples:

 CD  Salt  Plant

Introduction to SEM

• Electron source = thermo emission tungsten filament;
• Electrons are accelerated and focused using magnetic

lenses;

• The beam is focused in 5-9 nm spot that scans the probe;
• Secondary electrons are detected and analyzed, forming

the image;

• Electron microscopes allow the visualization of structures

that would normally be not visible by optical microscope;

• SEM offers higher resolution and depth of field when

compared to optical microscopes.

• Fig. 1. Schematics of scanning electron

microscope.

Equipment

• JSM-840 is an analog SEM capable of high

resolution images

• Accelerating voltage can be varied from 1 kV

up to 40 kV;

• The uses of multiple detectors ensures a

wide range of structural investigations: a backscattered electron detector, a secondary electron detector and a X-ray spectrometer;

• Large specimen goniometer allows tilting

and rotating of the sample in order to obtain a more detailed image.

• Fig. 2. JSM-840 electron microscope

Equipment

• Hitachi TM3000 is a tabletop electron
• microscope. It is very portable and easy to
• perate.
• 5 or 15 kV accelerating voltage can be used

which leads to magnification range from 15 to 30000x;

• It uses a semiconductor backscattered electron

detector;

• The software used on the control PC/notebook
• ffers fast digital images which can be easily

analyzed and transferred.

• Fig. 3. Hitachi TM3000 electron microscope

Sample preparation

• Sample is fixed on specimen stages using silver glue, carbon or copper band depending on

sample type;

• For nonmetallic samples a thin layer of gold is applied to increase the coefficient of secondary

electron emission, reduce sample charging and increase thermal conductivity;

• An ion sputter uses plasma to coat the samples in gold.
• Fig. 4. Ion sputter schematics and sample placement.

Charging of sample

• Fig. 5a. Charging of sample due to lack of gold coating.
• Fig. 5b. Higher resolution due to gold coating.

Tilted sample

• Fig. 6a. Increase in contrast due to sample tilt (15, 60 degrees)

Tilted sample

• Fig. 6b. Better topographical details due to sample tilt (0 and 60 degrees).

Porous membranes measurements

• Fig. 7. Calculation of pore dimension and pore density used for porosity determination. High number of pores is required to reduce errors

CD

• Fig. 8 Structural difference between empty and written CD (10x magnification).

Salt

• Fig. 9 NaCl crystals at different magnifications (50x and 150x)

Salt

• Fig. 10 NaCl crystal structural details. (600x and 5000x magnifications)

Plant

• Fig. 11 Plant sample preparation and SEM images of different structures.

Stalk

• Fig. 12 Plant stalk details.

Flower

• Fig. 13 Flower, and pollen structure.

Leaf

• Fig. 14 Leaf structure and topography.

Conclusions

• Scanning electron microscopy offers high resolution images (up to 3 nm) which cannot be
• btained in conventional optical microscopy and allow the visualization of structures that would

normally be not visible by optical microscope;

• The large depth of field of SEM (30 μm), compared with optical microscopes (0.1 μm), produce

realistic 3D images which permit observation of multiple details;

• The use of multiple detectors offer the possibility of observing not only topographical

information but also of physical and chemical properties;

• SEM is an invaluable tool whose practical applications can be employed in many fields of

research

Thank you for your attention !