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MindMap Gallery Scanning electron microscopy

Scanning electron microscopy

This is a mind map about scanning electron microscopy analysis, image display recording system: convert the signal output from the signal collector into changes in the electron beam intensity of the cathode ray picture tube in proportion, so as to obtain an image on the fluorescent screen with A scanned image of a physical signal generated by a sample scanning point that is proportional to the change in brightness is recorded photographically or stored in a computer in digital form.

Edited at 2022-12-13 20:26:53

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Scanning electron microscopy

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Outline

Scanning electron microscopy

composition structure

Electronic optical system

It consists of electron gun, condenser lens, objective lens, diaphragm, astigmatism absorber and sample chamber

effect

Provide a scanning electron beam with a small enough diameter and high enough brightness to focus the electron beam from the electron gun into an incident beam with high brightness and small diameter (the diameter is generally 10nm or less) to bombard the sample, causing various physical phenomena to occur in the sample. The signal actually serves as the excitation source of sample information.

Scan system

composition:

Scan signal generator

Scan amplification controller

scanning deflection coil

effect

Make the incident electron beam scan the surface of the sample, and make the electron beam of the cathode ray picture tube scan the fluorescent screen synchronously;

Change the scanning amplitude of the incident beam on the sample surface, thereby changing the magnification of the scanned image.

Signal detection amplification system

The signals are converted into electrical signals, amplified, and finally imaged on a picture tube and recorded as digital images.

image display recording system

The signal output by the signal collector is proportionally converted into changes in the electron beam intensity of the cathode ray picture tube, so that a scanning image with brightness changes proportional to a certain physical signal generated by the sample scanning point is obtained on the fluorescent screen. At the same time Record it photographically or store it in digital form on a computer.

Specimen placement system

Vacuum system

The function is to ensure the normal operation of the electronic optical system

Power Systems

working principle

Features

(1) Simple sample preparation method

(2) The depth of field is large, the image has a strong three-dimensional sense, and it is easy to identify and interpret.

(3) The magnification range varies widely, from 15 to hundreds of thousands of times

(4) Has quite high resolution

(5) The quality of images can be controlled and improved conveniently and effectively through electronic methods

(6) Comprehensive analysis can be carried out

Imaging principle

It is formed point by point in a certain time and space sequence and displayed on the picture tube outside the mirror.

Imaging process (taking secondary imaging as an example)

The electron gun emits an electron beam, and the converging lens and objective lens shrink and focus it to form an electron beam with a certain energy, intensity, and spot diameter on the surface of the sample. Under the influence of the magnetic field of the scanning coil, the incident electron beam will perform a raster point-by-point scan on the sample surface in a certain time and space sequence. Due to the interaction between the incident electrons and the sample, secondary electrons will be excited from the sample. Due to the function of the secondary electron collector, the secondary electrons emitted in all directions can be gathered together, and then accelerated to the scintillator to become optical signals, and then reach the photomultiplier tube through the light guide and become electrical signals. The electrical signal is amplified by the video amplifier to form a secondary electron image.

performance

Resolving power: The resolution of the scanning electron microscope is the resolution of the secondary electron image

Depends on factors

The diameter of the incident electron beam spot

Scattering of electrons by the sample

gain

Expression M=A2/A1

In the formula, A1 is the scanning amplitude of the electron beam on the sample, and A2 is the scanning amplitude of the electron beam on the fluorescent screen in the cathode ray tube (the side length of the fluorescent screen).

SEM image contrast

Surface topography contrast

Using physical signals (secondary electrons) that are sensitive to the surface topography of the sample as the modulation signal of the picture tube, the resulting image contrast

Atomic number contrast

Signals such as backscattered electrons, absorbed electrons, and characteristic X-rays generated when the scanning electron beam is incident on the sample are very sensitive to differences in the atomic number or chemical composition of the microregions on the surface of the sample.

Characteristic X-rays

Moselle's law

λ=1/(Z-σ)2, σ is a constant

Scope of application

X-ray energy spectrometers (EDS) used in transmission electron microscopes and scanning electron microscopes can perform micro-element analysis on samples.

Two imaging modes

secondary electron image

Mainly used for observation of surface morphology

Features

High-resolution

No obvious shadow effect

Large depth of field and strong three-dimensional effect

The electrons escaping from the sample have less energy

Backscattered electron image

It can not only observe the morphology but also reflect the changes in composition.

Features

low resolution

The electrons in the electron beam have higher energy

Analytical sample preparation methods

Sample requirements

Block or powder solid

Can remain stable in vacuum with low volatile content

Does not contain moisture

The surface is not contaminated

new fracture

Appropriate erosion is required to expose certain structural details

Demagnetize

application

Polymer Materials

The influence of the phase structure and the interaction between phase interfaces on the performance of multi-composite systems is mainly studied by observing the fracture surface of the composite system.

Analyze material fracture processes

Research on toughening and strengthening mechanisms through composite material morphology analysis

Study the morphological structure of crystalline polymers

X-ray microanalysis

SEM was used combined with X-ray energy spectroscopy (EDS) to analyze the formation process and chemical composition of the inorganic coating on the metal surface.

Schematic diagram