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(Color online) Reciprocal space geometry of an azimuthal RHEED experiment. During the sample rotation, the intensity is recorded in regular intervals along the recording line parallel to the sample surface, ideally through the specular spot. These lines can then be plotted as a function of azimuthal angle to construct the measured intensity in the reciprocal plane. The constructed plane shown as a horizontal disk is a planar cut of a large area of reciprocal space.
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![FIG. 9. (Color online) Radial (h À 2h) scans along the GaAs [110]...](profile/Bernd-Jenichen/publication/234838706/figure/fig15/AS:667086313517064@1536057179395/Color-online-Radial-h-A-2h-scans-along-the-GaAs-110-direction-during-the-deposition_Q320.jpg)
![FIG. 11. (Color online) Intensity profiles (a) along the MnAs [0001]...](profile/Bernd-Jenichen/publication/234838706/figure/fig17/AS:667086313508869@1536057179660/Color-online-Intensity-profiles-a-along-the-MnAs-0001-direction-recorded-at-k-14-0_Q320.jpg)
![FIG. 13. (Color online) (a) Radial (h À 2h) scan along the GaAs [110]...](profile/Bernd-Jenichen/publication/234838706/figure/fig18/AS:667086313508877@1536057179933/Color-online-a-Radial-h-A-2h-scan-along-the-GaAs-110-direction-showing-the-d11_Q320.jpg)
Azimuthal reflection high-energy electron diffraction (ARHEED) and in situ grazing incidence synchrotron x-ray diffraction techniques are employed to investigate the growth, epitaxial orientation, and interfacial structure of MnAs layers grown on GaAs(001) by molecular beam epitaxy (MBE). We demonstrate the power and reliability of ARHEED scans as...
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... by the formation of secondary defects that introduce additional planes into the coincidence lattice. 12 In this article, we present ARHEED patterns recorded while rotating the substrate about the surface normal during MnAs film growth. This technique allows us to construct a planar cut through reciprocal space parallel to the surface (see Fig. 1) and provides two-dimensional real time informa- tion on the nucleation and interface formation of the MnAs film. The technical details of this method are described in the following section. We then discuss the strain state of the film during growth of MnAs, followed by an analysis of the inter- facial structure along the c-axis ...Context 2
... is similar to the diffrac- tion patterns recorded by low-energy electron diffraction (LEED) measurements, except that the LEED pattern is a spherical cut through reciprocal space, whereas our azi- muthal scans are planar. Such a planar cut of the reciprocal lattice plane, which can be measured by ARHEED, is illus- trated as a horizontal disk in Fig. 1. The x-ray diffraction profiles we compare with the RHEED data are measured in a grazing incidence-grazing exit geometry using 10 keV synchrotron x-rays. The high brilliance of the primary beam allows us to investigate very thin epitaxial layers starting from the monolayer thickness regime. ...Context 3
... One such Gaussian fit to the (01) peak is shown as an inset. The resolution defined as the FWHM is much higher than in conventional RHEED; only about 15% less than the values of a corresponding x-ray measurement. The FWHM of the GaAs (220) substrate reflection measured in grazing incidence geometry is used here for comparison and is shown in Fig. 13(a). This very high longitudinal reso- lution is a result of the energy resolution of around DE=E ¼ 5 Â 10 À4 which is approximately the same in our system for x-ray diffraction 15 and RHEED. 19 For the high quality substrate used here, both values are still instrument- limited for the substrate reflections used for this ...Context 4
... study the interfacial structure between MnAs and GaAs along the c-axis direction where the misfit is about 30%. An ARHEED scan from the sample (sample C) taken af- ter the growth is shown in Fig. 10. To study the interface by RHEED, we have grown an ultra-thin film having a thickness below 10 nm. The surface morphology studied by AFM (not shown) indicates the presence of well-developed islands which are not yet connected. The formation of epitaxial MnAs crystallites at such a low thickness is confirmed by the rectan- gular 2 Â 1 ...Context 5
... The weak spots corresponding to the surface reconstruction are clearly visible; for example, see the spot at the midpoint of the line connecting the (00) and (01) observed for a layer thickness of more than $1.5 nm by the in situ GID as a result of high misfit. 14 The magnified (2 Â 1) reconstructed MnAs unit cell from the ARHEED scan is shown in Fig. 10(b). Due to the high resolution of ARHEED, we can resolve two orders of satellites associated with the (01) streak marked by black arrows in the image. This is even more evident in the line profiles extracted from the ARHEED scan which are shown in Fig. 11. The line profile taken along the MnAs [0001] direction at k ¼ 1 and drawn in Fig. ...Context 6
... 14 The magnified (2 Â 1) reconstructed MnAs unit cell from the ARHEED scan is shown in Fig. 10(b). Due to the high resolution of ARHEED, we can resolve two orders of satellites associated with the (01) streak marked by black arrows in the image. This is even more evident in the line profiles extracted from the ARHEED scan which are shown in Fig. 11. The line profile taken along the MnAs [0001] direction at k ¼ 1 and drawn in Fig. 11(b) shows clear periodic satellites to the (01) RHEED spot, whereas in a similar line profile taken at k ¼ 0 through the ori- gin, no satellites are present. This means that the resolution on a line through the origin is insufficient to resolve these ...Context 7
... in Fig. 10(b). Due to the high resolution of ARHEED, we can resolve two orders of satellites associated with the (01) streak marked by black arrows in the image. This is even more evident in the line profiles extracted from the ARHEED scan which are shown in Fig. 11. The line profile taken along the MnAs [0001] direction at k ¼ 1 and drawn in Fig. 11(b) shows clear periodic satellites to the (01) RHEED spot, whereas in a similar line profile taken at k ¼ 0 through the ori- gin, no satellites are present. This means that the resolution on a line through the origin is insufficient to resolve these satel- lites. In other words, by using conventional RHEED, it is impossible to resolve ...Context 8
... taken at k ¼ 0 through the ori- gin, no satellites are present. This means that the resolution on a line through the origin is insufficient to resolve these satel- lites. In other words, by using conventional RHEED, it is impossible to resolve such fine periodic features. The line pro- file along the MnAs ½11 20 direction at h ¼ 1 shown in Fig. 11(c) also does not show the presence of these satellites asso- ciated with the (10) reflection. It is worth mentioning that the resolution for the line profiles taken at k ¼ 1 and h ¼ 1 is the same. Hence, the splitting of only the (01) RHEED spot indi- cates a periodicity along the MnAs [0001] direction or along the c-axis of MnAs. The ...Context 9
... satellites next to the (01) spot in ARHEED are seen at all temperatures within this range. Figure 10(c) shows the same area as in Fig. 10(b) recorded at 383 K, without the disappearance of the (01) streak. Therefore, we can rule out the possibility of the satellites being due to the strain-medi- ated coexistence of periodic domains of a and b MnAs near room temperature. ...Context 10
... have performed ARHEED scans within a wide tem- perature range from 383 to 303 K, while cooling down the sample. The satellites next to the (01) spot in ARHEED are seen at all temperatures within this range. Figure 10(c) shows the same area as in Fig. 10(b) recorded at 383 K, without the disappearance of the (01) streak. Therefore, we can rule out the possibility of the satellites being due to the strain-medi- ated coexistence of periodic domains of a and b MnAs near room temperature. 26 Again, we emphasize the advantage of ARHEED scans over conventional RHEED, where it is practically ...Context 11
... may appear. We have investigated the presence of different epitaxial orientations of the MnAs film grown on GaAs(001) using ARHEED. The sample used for this investigation was grown in slightly As- deficient conditions and the total thickness of the MnAs layer is estimated to be below 10 nm. An ARHEED scan of the MnAs surface is shown in Fig. 12. It clearly demonstrates the presence of both the A 0 and B 0 orientations of MnAs. The nomenclature of these orientations is in accordance with the report by Iikawa et al. 27 The unit cells of A 0 and B 0 ori- entation are rotated by 90 around the surface normal with respect to each other and marked in Fig. 12. The presence of both A ...Context 12
... of the MnAs surface is shown in Fig. 12. It clearly demonstrates the presence of both the A 0 and B 0 orientations of MnAs. The nomenclature of these orientations is in accordance with the report by Iikawa et al. 27 The unit cells of A 0 and B 0 ori- entation are rotated by 90 around the surface normal with respect to each other and marked in Fig. 12. The presence of both A 0 and B 0 orientations is confirmed by grazing incidence x-ray diffraction measurements on the same sample shown in Fig. 13. The radial GID scans recorded along both the GaAs [110] and ½1 10 directions show the pres- ence of the MnAs (11 20) reflections corresponding to the A 0 and B 0 orientations. The ...Context 13
... these orientations is in accordance with the report by Iikawa et al. 27 The unit cells of A 0 and B 0 ori- entation are rotated by 90 around the surface normal with respect to each other and marked in Fig. 12. The presence of both A 0 and B 0 orientations is confirmed by grazing incidence x-ray diffraction measurements on the same sample shown in Fig. 13. The radial GID scans recorded along both the GaAs [110] and ½1 10 directions show the pres- ence of the MnAs (11 20) reflections corresponding to the A 0 and B 0 orientations. The Gaussian fits to the ð11 20Þ peaks are shown as thick solid blue lines. We determine the relative ...Similar publications
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We study the role of a Ti surface treatment applied to the As-terminated GaAs (001) substrate surface prior to SrTiO3 (STO) epitaxial growth by comparing STO/GaAs samples prepared with and without Ti interlayers. Reflection high energy electron diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy are used to assess the...
We report on photoluminescence
(PL) emission with long wavelength for quantum structure by the sub-monolayer (SML) growth technique on GaAs (001) substrate. It is found that the PL emission wavelength can be controlled by controlling the SML InAs deposition amount. At 12 K, the PL peak position of the grown samples changes from about 1.66 to 1.78 μ...
![Figure 3: Diffraction features near the position along the [01L]...](publication/310466771/figure/fig1/AS:429785575890952@1479480274327/Diffraction-features-near-the-position-along-the-01L-GaAs111-CTR-for_Q320.jpg)
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We have investigated the growth by molecular beam epitaxy (MBE) of GaAs on MnSb. MnSb epilayers on GaAs(111), GaAs(001) and of thickness 50 nm were used as substrates for GaAs films. The MBE growth of GaAs was monitored in situ using synchrotron X‐ray diffraction and reflection high energy electron diffraction. We show data on strain relaxation and...
Citations
... One collects 100 patterns covering 360 • to construct 3D reciprocal space structure. The application of substrate rotation and capture of RHEED patterns of reconstructed GaAs have been demonstrated by Braun et al. [47,48] and Satapathy et al. [49]. ...
... RHEED patterns acquired at different azimuths are utilized to map the reciprocal space structure of surfaces and monitor the growth of epitaxial thin films (Braun et al., 1998a;Satapathy et al., 2011). The entire reciprocal space structure of a 2D material can be obtained by rotating the sample around the surface normal and acquiring the RHEED patterns as a function of the azimuthal angle. ...
Reflection high-energy electron diffraction (RHEED) is widely used to characterize surface structure of single crystals. Moreover, RHEED has become a standard tool to monitor thin film growth in molecular beam epitaxy and is used to monitor other vapor deposition techniques including evaporation, sputtering, and pulsed laser deposition. With the rapid development of the fabrication methods and use of nanoparticles, RHEED operating in the transmission mode is being applied to characterize nanoparticles on surfaces. In this review, the fundamentals needed to interpret RHEED patterns from the top few atomic layers, in its reflection mode, and from nanoparticles and nanofeatures, in its transmission mode, are discussed based on the geometric kinematic approximation. Examples are provided on the interpretation of RHEED patterns from unreconstructed and 2×1-reconstructed Si(100), InP(100), highly oriented pyrolytic graphite, indium nanoparticles, and indium growth on Si(100)-2×1.
... It exhibits a first-order phase transition from the FM α-MnAs to the orthorhombic paramagnetic structure (β-MnAs) at T c = 313 K [14]. Several studies have shown that the α-MnAs can be grown on different semiconductor substrates, for example, on the GaAs (0 0 1) surface, indium phosphide or silicon [15][16][17][18]. Some works report α and β MnAs phase coexistence whereas, in others, it is indicated that the epitaxial growth of pure α-MnAs is only possible on GaAs and InP (1 1 1) B substrates [10,19,20]. ...
Spin-polarized first-principles total-energy calculations have been done in order to investigate the epitaxial growth of MnAs on the InP (0 0 1) surface. The epitaxial growth is carried out on the mixed dimer reconstructed InP (0 0 1)-(2 × 4) surface. The initial stage of the MnAs epitaxial growth is stable under P-rich and intermediate conditions. Also, InAs growth is stable under In-rich conditions. We have deposited extra MnAs layers on top of the structure to build four stable interfaces: one constructed by 50% MnP and 50% InP, an ideal formed by MnP, the ideal interface of InAs and an interface built by alternating layers of InAs and InP. Under In-rich conditions, the epitaxial growth of InAs remains stable. We have investigated the magnetic and electronic properties of the four stable interfaces. Results show semiconductor-ferromagnetic interfaces in all cases, with the structure having spin up magnetization. The density of states shows that the interfaces are half-metallic, where the conduction channels of majority spin come from the P-p and Mn-d orbitals, and the minority spin exhibits an energy gap. Our results suggest that MnAs may allow the generation of spin-polarized current in InP semiconductors, which makes this system suitable for applications in spintronic devices.
... The shown rectangle is slightly mismatched with the reflexes due to the wobble of the sample rotation during measurement of RHEED images. A more detailed description of this technique and clear polar plots of GaAs are presented in the works of Satapathy et al.68 and Braun et al. 67 ...
Spin electronics or spintronics is identified as one of the potential technologies to replace the currently prevailing metal-oxide-semiconductor field-effect transistor (MOSFET) technology for information processing. For realization of spintronic devices like spin-valves in which spin currents are injected and detected, a large combination of ferromagnet-semiconductor (fm-sc) interfaces are being investigated. To replace the current MOSFET technology with the spin-transistors, high spin-injection efficiency is necessary which is not yet reported. Therefore, understanding the structural state of these fm-sc interfaces is essential for fabricating highly efficient future spintronic devices.
This dissertation describes the investigation of structural properties of Fe/III-V semiconductor interfaces. This work also encompasses the correlation of the observed structural state to the measured spin-injection across the interface. These investigations are performed on three material systems, namely Fe on moderately doped GaAs (001), Fe on InGaAs/InAs quantum wells and Fe on MgO/GaAs surfaces. Spin injection across the first two material systems is successfully measured by using an all electrical non-local spin-valve setup. In this work the emphasis is on the structural studies conducted on Fe layers under the influence of intrinsic and extrinsic strain.
Structural investigations are performed on Fe/GaAs interfaces that are grown as a function of Fe layer deposition temperature and subjected to post growth annealing cycles. These investigations are performed by utilizing various X-ray scattering geometries available at both laboratory and third generation synchrotron facilities. The Fe layers in this system are found to be compressively strained and this strain state is observed to be influenced by post-growth annealing at 200°C. In addition, grazing incidence diffraction measurements reveal the existence of a Fe3GaAs phase at the interface which is also observed to be influenced by post-growth annealing. In correspondence, the spin-injection efficiency across the interface is also affected by the post-growth annealing which was non-existent before annealing. But, after first annealing cycle, it increased to a value of 5.5%. However, after a second annealing cycle, the spin-injection efficiency is reduced to 2.6%.
The structural investigations were also performed on Fe/InGaAs/InAs quantum wells material system to study the local crystallinity of InxAl1-xAs buffer layers on which the active layers containing quantum well are deposited. The structural information of these buffer layers is essential, because the strain relaxation leads to local tilt of lattice planes and composition variation resulting in cross-hatches at the surface of the heterostructure. These cross-hatches in turn determine the non-planar nature of the quantum well. Therefore, the local structural integrity of these layers is probed by using scanning diffractive imaging which revealed two networks of defects that vary as function of Indium content.
The spin-injection measurements performed on InGaAs/InAs quantum wells reveal that spin-transport occurs in the semi-ballistic regime in this system. However, the obtained spin-injection results also indicate that a ballistic model proposed for calculating the spin-injection efficiency is inadequate as it does not take the crystallographic anisotropy of Spin-orbit interaction.
The last system that is investigated in this thesis is the Fe/MgO/GaAs interface. Unlike the other two material systems, the Fe/MgO/GaAs interface is characterized on an atomic scale by high resolution transmission electron microscopy (HRTEM )to reveal the influence of the MgO thickness and its deposition conditions on the morphology and magnetic characteristics of Fe layers. The structural studies including energy dispersive spectroscopy (EDS) mapping and X-ray reflectivity (XRR) analysis are also performed to study the relevance of intermixing at the interface. The magneto-optic Kerr effect (MOKE) investigations reveal that in-plane cubic and uniaxial magnetic anisotropy coexist in Fe/MgO/GaAs samples. The strength of cubic and uniaxial anisotropy contributions are found to vary with the deposition conditions of MgO and Fe.
... Previously, we reported an azimuthal reflection high-energy electron diffraction (RHEED) method that could tell the symmetry of graphene on both conductive and insulating substrates. 34 The principle for this azimuthal RHEED is similar to Satapathy's work. 35 In our previous report, 34 we described the concept, theory, and procedures of the method and tested the feasibility of this method with a commercial polycrystalline graphene sample. ...
... 34 The principle for this azimuthal RHEED is similar to Satapathy's work. 35 In our previous report, 34 we described the concept, theory, and procedures of the method and tested the feasibility of this method with a commercial polycrystalline graphene sample. Herein, we further explore this subject by verifying our theory with single crystalline graphene samples prepared in our laboratory. ...
... 52,53 Alternatively, we have reported that RHEED is capable of revealing the symmetry of the graphene structure as well by constructing the reciprocal space mapping of graphene. 34 For a singlecrystalline two-dimensional (2D) material, its reciprocal space structure consists of vertical rods. 54,55 Due to the relatively large wave vector of the electrons in RHEED, the Ewald sphere is large and cuts through the rods in the reciprocal space like a plane. ...
The possibility of the epitaxial growth of ferromagnetic manganese gallide (Mn3Ga5) layers on the GaAs(100) surface was demonstrated. The ferromagnetic properties of epitaxial Mn3Ga5 at room tem�perature were evaluated from measurements of the anomalous Hall effect. A diode structure based on the
Mn3Ga5/GaAs contact was formed, and the low�temperature electroluminescence of this diode was mea�sured. The possibility of electroluminescence and the high crystal quality of the structures under study showed
promises of their application in light�emitting diodes with spin injection.
Using low energy electron diffraction and low energy ion scattering spectroscopy, we investigated the growth mode of Al on a W(110) surface at room temperature and at 1000 K. We found that Al grew on the W(110) surface in the Frank–van der Merwe mode when the W substrate was kept at room temperature during Al deposition. It was found that at a coverage higher than 2 monolayer (ML) in Al grown at room temperature, Al atoms had a well-ordered face centered cubic (fcc) (111) surface. The [11¯0] direction of the Al grown at room temperature on the (111) surface was parallel to the [001] direction of the W(110) substrate surface. When the temperature of the W substrate was kept at 1000 K, the adsorbed Al atoms grew in the Volmer–Weber mode. The 1.5 ML Al/W(110) surface prepared at 1000 K shows two domains of the fcc Al(111) surfaces along with a W(110) surface. We also found that the early stage of Al film growth shows W(110) structure. However as the film becomes thicker (above 3.5–4 layers) the Al face is turned into fcc (111) face.
