RHEED electron diffraction

RHEED Reflection high-energy electron diffraction [78, 106] Similar to HEED Surface structure, composition... 

As the table shows, a host of other teclmiques have contributed a dozen or fewer results each. It is seen that diffraction teclmiques have been very prominent in the field the major diffraction methods have been LEED, PD, SEXAFS, XSW, XRD, while others have contributed less, such as NEXAFS, RHEED, low-energy position diffraction (LEPD), high-resolution electron energy loss spectroscopy (HREELS), medium-energy electron diffraction (MEED), Auger electron diffraction (AED), SEELFS, TED and atom diffraction (AD). 

Fig. 4. Schematic of an ultrahigh vacuum molecular beam epitaxy (MBE) growth chamber, showing the source ovens from which the Group 111—V elements are evaporated the shutters corresponding to the required elements, such as that ia front of Source 1, which control the composition of the grown layer an electron gun which produces a beam for reflection high energy electron diffraction (rheed) and monitors the crystal stmcture of the growing layer and the substrate holder which rotates to provide more uniformity ia the deposited film. After Ref. 14, see text.

Reflection High-Energy Electron Diffraction (RHEED)... 

This chapter contains articles on six techniques that provide structural information on surfaces, interfeces, and thin films. They use X rays (X-ray diffraction, XRD, and Extended X-ray Absorption Fine-Structure, EXAFS), electrons (Low-Energy Electron Diffraction, LEED, and Reflection High-Energy Electron Diffraction, RHEED), or X rays in and electrons out (Surfece Extended X-ray Absorption Fine Structure, SEXAFS, and X-ray Photoelectron Diffraction, XPD). In their usual form, XRD and EXAFS are bulk methods, since X rays probe many microns deep, whereas the other techniques are surfece sensitive. There are, however, ways to make XRD and EXAFS much more surfece sensitive. For EXAFS this converts the technique into SEXAFS, which can have submonolayer sensitivity. 

Alternatives to XRD include transmission electron microscopy (TEM) and diffraction, Low-Energy and Reflection High-Energy Electron Diffraction (LEED and RHEED), extended X-ray Absorption Fine Structure (EXAFS), and neutron diffraction. LEED and RHEED are limited to surfaces and do not probe the bulk of thin films. The elemental sensitivity in neutron diffraction is quite different from XRD, but neutron sources are much weaker than X-ray sources. Neutrons are, however, sensitive to magnetic moments. If adequately large specimens are available, neutron diffraction is a good alternative for low-Z materials and for materials where the magnetic structure is of interest. 

RHEED Reflection high-energy electron diffraction... 

In the process of MBE, the surface structure can be investigated by reflected high energy electron diffraction (RHEED). During MBE growth, one often observes an oscillation in the intensity of the specular reflected beam as a function of time. This is interpreted to be due to the layer-by-layer growth of a two-dimensional island. 

Surface morphology Reflection high-energy electron diffraction (RHEED) Atomic force microscopy (AFM)... 

Fig. 4.1 Reflection high-energy electron diffraction (RHEED) patterns corresponding to the best epitaxial conditions of CdSe deposited on a (111) InP face (thickness 85 nm). (a) Observation under the (112) azimuth (b) observation under the (110) azimuth. (With kind permission from Springer Science-l-Business Media [6])...

For single crystal substrates which are not in the form of thin films, the techniques of transmission microscopy and nanodiffraction can not be used. For such cases, the techniques of reflection electron microscopy (REM) or its scanning variant (SREM) and reflection high energy electron diffraction (RHEED), in the selected area or convergent beam modes, may be applied (18). 

Fig. 2. Reflection high energy electron diffraction (RHEED) patterns taken from [110] azimuth, (a) Low-temperature grown GaAs at 250°C. (b) (Ga,Mn)As at 250°C. (c) I70°C, and (d) 320°C (Shen ei al. 1997a).

The structure, crystallinity and phase of the films were studied by X-ray diffraction (Cu Ka filtered radiation) and by reflection and transmission high energy electron diffraction (RHEED and THEED), with 50 keV incident electron beams. The composition and the purity of the films was determined by Auger electron spectroscopy (AES). A cylindrical mirror analyser with a coaxial electron gun was placed at 30° with respect to the normal surface. 

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