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薄膜材料的表征方法(二)


薄膜材料的表征方法(二)
ANALYTICAL TECHNOLOGIES OF THIN FILMS(2) FILMS(

谭永胜 2004.11.20

Abstract
Electronic beam analytic techniques. Low energy electron diffraction(LEED) and Reflection high energy electron diffraction(RHEED). Scanning electron microscopy(SEM) and Transmission electron microscopy(TEM).

Electronic beam analytic techniques
Properties of electrons:
An inelastic mean free path(MFP) of a few tenth of nm. Electrons are easily focused into beams and the energy may be varied. Electrons are efficiently detected and counted. Electrons may be analyzed angular and energy distribution. Electrons disappear from the vacuum system after being used for analysis.

Electronic beam analytic techniques
The interaction of an incident electron beam with a solid sample.

Electronic beam analytic techniques
Energy distribution of the secondary electrons.

Low energy electron diffraction(LEED)
According to the de Broglie relation, the wavelength of the electrons is given by: λ =h/p When the electrons are accelerated by a voltage V, the kinetic energy of electrons is eV, and the electron momentum can be expressed by p = (2 m e V)1/2 Thus the electron wavelength is determined by: λ = h / (2 m e V)1/2 = (150.4/V)1/2. LEED:E<1000eV RHEED: 5-100keV

Low energy electron diffraction(LEED)
Schematic apparatus of LEED.

Low energy electron diffraction(LEED)
Atomic arrangement on surface.

Low energy electron diffraction(LEED)
LEED patterns of Si clean surfaces.

Low energy electron diffraction(LEED)

Reflection high energy electron diffraction(RHEED).
Schematic diagram of RHEED optics.

Reflection high energy electron diffraction(RHEED).

Reflection high energy electron diffraction(RHEED).
The intensity of specular RHEED beam varied with the surface coverage.

Reflection high energy electron diffraction(RHEED).
The arrow-like arrowstreaks.

Reflection high energy electron diffraction(RHEED).

Conclusion
Principle: (a): the de Broglie material wave of electrons. (b): Bragg diffraction. Properties: (a):surface analysis. (b):RHEED is well suited for situ monitoring in MBE. (c):need UHV.

Scanning electron microscopy(SEM)
The principle of light microscopy and electron microscopy.

Scanning electron microscopy(SEM)

Scanning electron microscopy(SEM)

Scanning electron microscopy(SEM)

Scanning electron microscopy(SEM)

Scanning electron microscopy(SEM)

Transmission electron microscopy(TEM)
Schematic diagram of TEM.

Transmission electron microscopy(TEM)

Transmission electron microscopy(TEM)
The electron diffraction images of amorphous and Single crystal.

Transmission electron microscopy(TEM)

Transmission electron microscopy(TEM)
Crystallite at the interface Si/SiO2.

Conclusion
Principle: SEM:secondary electrons or backscatter electrons. TEM:diffraction of the transmission electrons. Purpose: SEM:surface topography. TEM:crystal structure.


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