Reflection High Energy Electron Diffraction WeiLi Chen 11152007
- Slides: 31
Reflection High Energy Electron Diffraction Wei-Li Chen 11/15/2007
RHEED • Reflection High Energy Electron Diffraction, RHEED, is an important real time analytical tool to monitor growth front condition. Substrate thermal cleaning monitoring ØControlling initial growth stage ØMonitoring surface structure and growth dynamics ØGrowth rate measurement Ø • The small incident angle makes it sensitive to the structure of top monolayers.
Bravais Lattice • A Bravais lattice is an infinite arrays of discrete points with an arrangement and orientation that appears exactly the same, from whichever of the points the array is viewed. • A Bravais lattice consists of all points with position vectors R of the form
Crystal Structure • The atom group, which builds complete crystal structure by translational operations is called crystallographic unit cell • Crystal structure = Lattice + Basis In General: a ≠ b ≠ c and α≠ß≠γ
Reciprocal Lattice
Miller Indices Plane Vector in Bravais lattice Crystal symmetry equivalent plane sets Crystal symmetry equivalent vector sets
Bragg’s and von Laue’s Formula
The Edwald Construction
The Geometry of RHEED • The geometry of RHEED is quite simple, Fig. 1. An accelerated electron beam (5 – 100 ke. V) is incident on the surface with a glancing angle (< 3 deg) and is reflected. The high energy of the electrons would result in high penetration depth. However, because of the glancing angle of incidence, a few atomic layers are only probed. This is the reason of the high surface sensitivity of RHEED. Upon reflection, electrons diffract, forming a diffraction pattern that depends on the structure and the morphology of the probed surface.
“Molecular Beam Epitaxy “ edited by R. F. C. Farrow
Fourier Transform
Ideal smooth surface 3 D clusters real smooth surface polycrystal
Powder or Polycrystal diffraction spots rings Rotation of crystal
Growth Calibration by RHEED Oscillation The reflection intensity of the specular point is related to the roughness of the surface, which changes periodically with the accumulation of film thickness. “Molecular Beam Epitaxy “ edited by R. F. C. Farrow
Ga. N RHEED Oscillation Growth rate reduction due to thermal decomposition
Surface Reconstruction • In order to minimize the energy of the near-surface region of the crystal, the atoms rearrange themselves in a regular fashion which exhibits long range order. Each ordered arrangement of the near surface region is known as a surface reconstruction. • Surface reconstruction reflects the stoichiometry of the growth process and influences the growth mechanism. • RHEED is used to monitor the surface reconstruction of the growth front since it is sensitive to atomic layers near the surface. • Usually surface reconstruction is affected by substrate temperature, impinging fluxes, III/V flux ratio, and the existence of surfacants.
“Molecular Beam Epitaxy” edited by R. F. C. Farrow “Molecular Beam Epitaxy “ edited by R. F. C. Farrow
Polarity of Ga. N c-plane surface
Ga. N Surface Reconstruction 2 -fold 3 -fold
As as a Surfacant
- Color 11152007
- Reflection refraction diffraction interference
- Reflection refraction diffraction
- Reflection wave behavior
- Electron diffraction experiment results
- Electron diffraction
- Chen chen berlin
- Plano convex lens
- Energy energy transfer and general energy analysis
- Energy energy transfer and general energy analysis
- Thin film formula
- Multiple slits diffraction
- Magnets for neutron diffraction
- Absent spectra in diffraction grating
- Dispersive power of grating equation
- Difference between fresnel and fraunhofer diffraction
- Sound diffraction
- Fresnel and fraunhofer diffraction difference
- Diffraction
- Diffraction by circular aperature
- Missing order in diffraction
- Diffraction grating
- Diffraction in a sentence
- Von laue
- Diffraction and polarization
- For viewing tiny objects in a microscope diffraction is
- Bragg's law in reciprocal lattice
- Diffraction examples
- Powder diffraction database
- Fresnel and fraunhofer diffraction difference
- Laser diffraction spectroscopy
- Diffraction of waves