RHEED pattern

Figure 3 (c) Photograph of a RHEED pattern from cleaved GaAs(IIO) obtained using a... 

What gives rise to streaks in a RHEED pattern from a real surface For integral-order beams, die explanation is atomic steps. Atomic steps will be present on nearly all crystalline surfaces. At the very least a step density sufficient to account for any misorientation of the sample from perfeedy flat must be included. Diffraction is sensitive to atomic steps. They will show up in the RHEED pattern as streaking or as splitdng of the diffracted beam at certain diffraction conditions that depend on the path difference of a wave scattered from atomic planes displaced by an atomic step height. If the path difference is an odd muldple of A./2, the waves scattered... 

Figure 4 (a) Photograph of a RHEED pattern for 4 monolayers of In deposited on... 

RHEED is a powerful tool for studying the surface structure of crystalline samples in vacuum. Information on the surface symmetry, atomic-row spacing, and evidence of surfece roughness are contained in the RHEED pattern. The appearance of the RHEED pattern can be understood qualitatively using simple kinematic scattering theory. When used in concert with MBE, a great deal of information on film growth can be obtained. 

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])...

Emersion resulting in substantial amounts of electrolyte remaining on the (hydrophilic) electrode is much more commonly observed. When the solvent evaporates from the surface, the electrolyte is left behind as small crystallites. These can distort LEED and RHEED patterns and, more importantly, can render quantitative evaluation of the surface cation and anion concentrations by ESCA impossible. 

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).

Figure 7.9 shows RHEED patterns obtained with 30keV electrons impinging on clean surfaces of optimized ZnO thin films grown on r-, a-, and c-plane sapphire. The azimuthal directions of the two types of RHEED images of the c-axis oriented ZnO films (on a- and c-sapphire) are [flOO] (top) and [2110] (bottom) [52]. 

Fig. 7.9. RHEED images of optimized ZnO thin film surfaces on r-plane, a-plane, and c-plane sapphire, in the two azimuthal orientations (top and bottom) separated by 45° (left) or 30° (middle and right), respectively. The RHEED patterns of the a-axis textured film on r-plane sapphire (left) indicate an epitaxial and three-dimensional, island-like growth. The ZnO films on a-plane (middle) and c-plane sapphire (right) exhibit a smoother surface structure, as indicated by the streaky RHEED patterns and the observation of additional weak reflections in the top images due to 3 x 3 surface reconstruction [51]...

Figure 4.5, An 80-keV reflection high-energy electron-diffraction (RHEED) pattern from a single layer of the nitrostilbene molecule shown in Structure 4.1b. The substrate is 111 silicon.

Cubic boron nitride (cBN) has a zinc blende-type crystal structure with a lattice constant of 3.615 A, which is very close to that of diamond (3.567 A). The difference is only about 1.3%. According to RHEED measurements with the electron beam parallel to the 111 layer of cBN, a growth of diamond by DC plasma CVD on cBN(lll) [150] using c = 0.5%CH4/H2, T = 900°C, and F=180Torr led to a result that a smooth (111) layer of diamond was epitaxially deposited in such a way that the [110] direction of diamond was parallel to that of cBN. Namely, D 111 //cBN(lll and D[110]//cBN[110]. In the RHEED pattern, however, extra spots were observed, which were presumably due to the twinnings of (111 diamond layers. In the Raman spectra, there were two lines due to cBN at 1054.5 and... 

The atomic structure of HOD film surface was investigated using electron microbeam diffraction in Ref. [259]. The substrate used was a 500-nm thick P-SiC(lOO) that had been heteroepitaxially grown on Si(lOO) and was tilted about the [1 lOj-axis by 4° from the exact (100) orientation. The thickness of the HOD film was -20 pm. According to the RHEED pattern, using the electron micro-beam (the spatial resolution as observed by SEM was 0.1 pm), the length of the surface dimer rows was 1.5nm, which was significantly shorter than that of the homoepitaxial layer, 7 to 10 nm. 

Figure 6.25 Structures of different Me deposits on GaAs (hk ) [6.181], (a) RHEED pattern of Ni deposit on GaAs (111) (b) TEM image (replica technique) of a Pt deposit on photo-etched GaAs (100) (c) TEM image of Ru deposit on photo-etched GaAs (100).

Figure 11 Experimental (left panel) and schematic (right panel) RHEED pattern of the Pt3Sn(001)-surface after low temperature annealing. The main features are transmission spots lying on horizontal lines rather than Laue-circles. The Laue-circles are indicated in the schematic pattern. Electron energy is l2keV, direction of incidence is along [100]. From Ref. [27].

Figure 7.1 TEM (a), SEM (b-e) and AFM (f) images of PSC samples cross-sectional images of the samples prepared at = 8 mA cm 2 (a), / = 30 mA cm 2 (c), and (e) / = 80 mA cm-2, present nanoporous, mixed- and microporous PSC structures, respectively (b, d) are plan-view images of nanoporous and microporous SiC. The insets in (b) and (d) are the RHEED patterns obtained from the corresponding samples, which illustrate changes in surface perfection (f) is an AFM image of the surface opening marked by an arrow in (d). (a) Reproduced from M.G. Mynbaeva et al., Pbys. Sol. State, 47, 1630-1636. Copyright (2005), with permission from Elsevier...

Figure 2 gives the experimental current transient with the best fitting (Fig. 2a) and the RHEED pattern (Fig. 2b) corresponding to the electrodeposition of CdSe on (II1) GaAs. The parameters which have been deduced from the fitting are the following ... 

Fig. 30. RHEED patterns of CdS chemically deposited on InP single crystals, (from [170])...

---