High Energy Electron Reflection Essay

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Reflection High-Energy Electron Refraction Intensity Oscillations

Reflection high-energy electron refraction (RHEED) has been used as a surface probe for in situ observation of monolayer growth using molecular beam epitaxy (MBE) because of its high surface sensitivity and a near grazing incidence. It utilizes diffraction of electrons by surface atoms[1] and the RHEED intensity oscillation can convey morphological information of the growth surface if the intensity oscillation pattern is properly interpreted[2].

The wave properties of electrons make techniques like RHEED feasible. Low-energy electron diffraction (LEED) has also been used to determine the surface structure as well. But RHEED is more preferable to LEED because of its forward
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4. Schematic diagram of the correlation of surface coverage of 2-D clusters with idealized RHEED oscillations. (Adapted from J.R. Arthur, Surface science 500 (2002) 189-217)

There are similar in situ surface studies techniques used by means of optics, such as reflectance difference spectroscopy (RDS), which also known as reflectance anisotropy (RAS). This technique measures the difference in reflectance between two orthogonal polarization states of light falling at near-normal incidence on the sample surface[8]. The typical setup of RAS spectrometer is shown in Fig. 5. The details of how RAS works are given somewhere else[8]. Fig. 5. Typical setup of RAS spectrometer. (Adapted from Z. Sobiesierski et al, Journal of Physics: Condensed Matter 10 (1998)
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Besides, the overall intensity decreases as the mole fraction of Ge increases. K. Sakamoto et al[9] also did a comparison experiment to find a more favorable condition for Ge growth on Si, the result is shown in Fig. 7. More than 10 periods of oscillations can be seen at room temperature, so K. Sakamoto et al[9] concluded that lower temperature is more preferable because the surface migration would be suppressed. Fig. 7. RHEED intensity oscillations during the Ge growth on Si(001) (a) at 450°C and (b) at room temperature. The RHEED patterns during growth at 450°C are also shown. (Adapted from K. Sakamoto et al, Japanese journal of applied physics 26 (1987) 666)

By interpreting the RHEED intensity oscillation patterns, the surface structure can be approximated. In this paper, they did an approximation of what the structure looks like at different stages. Fig. 8 shows the Schematic illustration of Ge growth on Si(001) at 450°C, derived from the RHEED intensity oscillation shown in Fig. 7 (a). Fig. 8. Schematic illustration of Ge growth on Si(001) at 450°C, derived from the RHEED intensity oscillation shown in Fig. 7 (a). (Adapted from K. Sakamoto et al, Japanese journal

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