The sample surface diffracts electrons, and some of these diffracted electrons reach the detector and form the RHEED pattern.

In the RHEED setup, only atoms at the sample surface contribute to the RHEED pattern.

Figure 2 shows a RHEED pattern.

A RHEED pattern obtained from electron diffraction from a clean TiO2 ( 110 ) surface.

The diffraction pattern at the screen relates to the Ewald's sphere geometry, so RHEED users can directly calculate the reciprocal lattice of the sample with a RHEED pattern, the energy of the incident electrons and the distance from the detector to the sample.

The size and position of the detector determine which of the diffracted electrons are within the angular range that reaches the detector, so the geometry of the RHEED pattern can be related back to the geometry of the reciprocal lattice of the sample surface through use of trigonometric relations and the distance from the sample to detector.

The specular point has the greatest intensity on a RHEED pattern and is labeled as the ( 00 ) point by convention.

The other points on the RHEED pattern are indexed according to the reflection order they project.

The RHEED pattern is a collection of points on the perimeters of concentric Laue circles around the center point.

The RHEED pattern would be different for each azimuth angle.

Users sometimes rotate the sample around an axis perpendicular to the sampling surface during RHEED experiments to create a RHEED pattern called the azimuthal plot.

Kikuchi patterns are characterized by lines connecting the intense diffraction points on a RHEED pattern.

Figure 6 shows a RHEED pattern with visible Kikuchi lines.

A RHEED pattern from a TiO < sub > 2 </ sub > ( 110 ) surface with visible Kikuchi lines.

Contaminants on the sample surface interfere with the electron beam and degrade the quality of the RHEED pattern.

Diffraction conditions are fulfilled over the entire intersection of the rods with the sphere, yielding elongated points or ‘ streaks ’ along the vertical axis of the RHEED pattern.

Streaked RHEED pattern from the TiO < sub > 2 </ sub > ( 110 ) surface.

The sample had a terraced surface, which caused noticeable streaking compared to the RHEED pattern from the flat TiO < sub > 2 </ sub > ( 110 ) surface shown above.

The intensities of individual spots on the RHEED pattern fluctuate in a periodic manner as a result of the relative surface coverage of the growing thin film.

The reflection high energy electron diffraction ( RHEED ) technique uses the reflection of a beam of electrons fired at various low angles to characterize the surface of crystalline materials.

The RHEED construction of the Ewald's Sphere at the sample surface.

Users generally index at least 2 RHEED scans at different azimuth angles for reliable characterization of the crystal ’ s surface structure.

The RHEED system must operate at a pressure low enough to prevent significant scattering of the electron beams by gas molecules in the chamber.

Figure 8 shows an example of the intensity fluctuating at a single RHEED point during MBE growth.

A RHEED system requires an electron source ( gun ), photoluminescent detector screen and a sample with a clean surface, although modern RHEED systems have additional parts to optimize the technique.

Systematic setup of the electron gun, sample and detector / CCD components of a RHEED system.

Many of the reciprocal lattice rods meet the diffraction condition, however the RHEED system is designed such that only the low orders of diffraction are incident on the detector.

This technique is typically coupled with reflection high energy electron diffraction ( RHEED ) and reflection high-energy loss spectroscopy ( RHELS ).

Reflection high-energy electron diffraction ( RHEED ) is a technique used to characterize the surface of crystalline materials.

The Ewald's sphere analysis is similar to that for bulk crystals, however the reciprocal lattice for the sample differs from that for a 3D material due to the surface sensitivity of the RHEED process.

The electron gun is the most important piece of equipment in a RHEED system.

RHEED is an extremely popular technique for monitoring the growth of thin films.

In particular, RHEED is well suited for use with molecular beam epitaxy, a process used to form high quality, ultrapure thin films under ultrahigh vacuum growth conditions.

The curve is a rough model of the fluctuation of the intensity of a single RHEED point during MBE deposition.

The oscillation period is highly dependent on the material system, electron energy and incident angle, so researchers obtain empirical data to correlate the intensity oscillations and film coverage before using RHEED for monitoring film growth.

During operation, reflection high energy electron diffraction ( RHEED ) is often used for monitoring the growth of the crystal layers.

The principle is the same as that of other electron diffraction methods such as LEED and RHEED, but the obtainable diffraction pattern is considerably weaker than those of LEED and RHEED because the density of the target is about one thousand times smaller.

In many electron diffraction techniques like reflection high energy electron diffraction ( RHEED ), transmission electron diffraction ( TED ), and gas electron diffraction ( GED ), where the incident electrons have sufficiently high energy (> 10 keV ), the elastic electron scattering becomes the main component of the scattering process and the scattering intensity is expressed as a function of the momentum transfer defined as the difference between the momentum vector of the incident electron and that of the scattered electron.

Thus in the case of gas electron diffraction, reflection high-energy electron diffraction ( RHEED ), and transmission electron diffraction, because the energy of the incident electron is high, the contribution of inelastic electron scattering can be ignored.

RHEED systems gather information only from the surface layer of the sample, which distinguishes RHEED from other materials characterization methods that also rely on diffraction of high-energy electrons.

However, only the first few layers of the material contribute to the diffraction in RHEED, so there are no diffraction conditions in the dimension perpendicular to the sample surface.