Bragg-surface Diffraction Research Articles

Depth profiles of the interfacial strains of Si0.7Ge0.3/Si using three-beam Bragg-surface diffraction.

Interfacial strains are important factors affecting the structural and physical properties of crystalline multilayers and heterojunctions, and the performance of the devices made of multilayers used, for example, in nanowires, optoelectronic components, and many other applications. Currently existing strain measurement methods, such as grazing incidence X-ray diffraction (GIXD), cross-section transmission electron microscope, TEM, and coherent diffractive imaging, CDI, are limited by either the nanometer spatial resolution, penetration depth, or a destructive nature. Here we report a new non-destructive method of direct mapping the interfacial strain of [001] Si0.7Ge0.3/Si along the depth up to ~287 nm below the interface using three-beam Bragg-surface X-ray diffraction (BSD), where one wide-angle symmetric Bragg reflection and a surface reflection are simultaneously involved. Our method combining with the dynamical diffraction theory simulation can uniquely provide unit cell dimensions layer by layer, and is applicable to thicker samples.

Realizing in-plane surface diffraction by x-ray multiple-beam diffraction with large incidence angle

Based on rigorous dynamical-theory calculations, we demonstrate the principle of an x-ray multiple-beam diffraction (MBD) scheme that overcomes the long-lasting difficulties of high-resolution in-plane diffraction from crystal surfaces. This scheme only utilizes symmetric reflection geometry with large incident angles but activates the out-of-plane and in-plane diffraction processes simultaneously and separately in the continuous MBD planes. The in-plane diffraction is realized by detoured MBD, where the intermediate diffracted waves propagate parallel to the surface, which corresponds to an absolute Bragg surface diffraction configuration that is extremely sensitive to surface structures. A series of MBD diffraction and imaging techniques may be developed from this principle to study surface/interface (misfit) strains, lateral nanostructures, and phase transitions of a wide range of (pseudo)cubic crystal structures, including ultrathin epitaxial films and multilayers, quantum dots, strain-engineered semiconductor or (multi)ferroic materials, etc.

X-ray n-beam diffraction to study nanodefects of Xe+ implantation in Si(001)

Investigations about the nanocavities/bubbles formation by inert gas ion implantation in Si matrix and its properties have constituted an ongoing challenge in material science. Dislocation/extended defects (likely the {113} defects) are produced by post-implant annealing, which affect directly the nanocavities/bubbles structural evolution. In this work, the formation of defects induced by Xenon gas ion implantation in a Si sample (#Si-pristine) was studied by high-resolution reciprocal space mappings (RSM) and non-conventional X-ray Multiple Diffraction (XRMD) using synchrotron radiation. For this, Xe+ ions (80 keV; 5x1015 cm-2) were implanted in Si(001) at room temperature. Subsequently, the as-implanted samples were thermally annealed in air atmosphere at 600, 700 and 800 °C for 30 min in order to nucleate Xe nanobubbles that were detected in annealed samples by TEM images. Differences in the diffracted intensity pattern, along the crystal truncation rod, were detected in the Si (113) asymmetrical RSM for as-implanted and annealed samples, in comparison to pristine Si, indicating defect contribution along in-plane an out-of-plane directions. The ω(incident):Φ(azimuthal) coupled scans of two XRMD cases: 3-beam Bragg-Surface-Diffraction (BSD) (000)(002)(1-11) and the 4-beam (000)(002)(1-1-1)(1-13) have shown expected broader peaks (as-implanted sample) in comparison to the pristine sample, besides the ω-axis intensity asymmetry (c-axis strain induced). Furthermore, the analysis of all BSD mappings has provided: i) the annealing effect of reducing the lattice strain (600 and 700 °C samples), and ii) a huge surface effect through the diffuse scattering (800 °C-sample). As to the 4-beam case, a strong streak (diffraction condition trace) was observed for annealed sample patterns. This remarkable effect can be associated to the {113} defects, which are in the same direction of the secondary/coupling diffracting planes (XRMD phenomenon). It is believed that these defects break the spatial coherence, increasing the streak intensity. On the other hand, the streak is suppressed by the primary extinction effect in the pristine-Si and as-implanted samples. Financial support by Brazilian Synchrotron Light Laboratory (LNLS), CAPES, CNPq and FAPEMA.

Lattice strain distribution resolved by X-ray Bragg-surface diffraction in an Si matrix distorted by embedded FeSi2nanoparticles

Out-of-plane and primarily in-plane lattice strain distributions, along the two perpendicular crystallographic directions on the subsurface of a silicon layer with embedded FeSi2nanoparticles, were analyzed and resolved as a function of the synchrotron X-ray beam energy by using ω:φ mappings of the ({\overline 1}11) and (111) Bragg-surface diffraction peaks. The nanoparticles, synthesized by ion-beam-induced epitaxial crystallization of Fe+-implanted Si(001), were observed to have different orientations and morphologies (sphere- and plate-like nanoparticles) within the implanted/recrystallized region. The results show that the shape of the synthesized material singularly affects the surrounding Si lattice. The lattice strain distribution elucidated by the nonconventional X-ray Bragg-surface diffraction technique clearly exhibits an anisotropic effect, predominantly caused by plate-shaped nanoparticles. This type of refined detection reflects a key application of the method, which could be used to allow discrimination of strains in distorted semiconductor substrate layers.

Measuring lattice parameter of iron silicides using x-ray Bragg-surface diffraction

We investigated the strain field of the β-FeSi2 semiconductor on a Si(001) substrate, where FeSi in a grain form coexists with β-FeSi2 during the growth of β-FeSi2. The lattice-parameter variations in silicon due to the presence of β-FeSi2, FeSi and the grain boundary between β-FeSi2 and FeSi were detected by using the x-ray three-beam, Si(002)/(1¯11), Bragg-surface diffraction, where (002) is a symmetric Bragg reflection and (1¯11) a surface diffraction. The diffraction images of (1¯11) reflection as a function of the azimuth rotation angle around the reciprocal lattice vector of (002) provide information of lattice-parameter variation in Si. The surface nature of the (1¯11) reflection makes the (1¯11) diffraction images extremely sensitive to the interfaces between Si, β-FeSi2 and FeSi. With the penetration (detection) depth calculated from the dynamical theory of x-ray diffraction, the strain field versus the depth in the Si substrate near the interfaces is determined with the resolution of 0.002 Å for lattice variation. The largest strain detected is about 0.4% up to 15–70 Å below the interfaces.

X-ray Bragg-Surface Diffraction: A Tool to Study In-Plane Strain Anisotropy Due to Ion-Beam-Induced Epitaxial Crystallization in Fe+-Implanted Si(001)

In-plane strain anisotropy was clearly observed by the X-ray Bragg-surface diffraction technique in the silicon lattice surrounded by nanoparticles that were synthesized by an ion-beam-induced epitaxial recrystallization process of Fe-implanted amorphous Si layer. High resolution transmission electron microscopy images have shown the occurrence of metallic spherical and plate-like γ-FeSi 2 nanoparticles in the implanted/recrystallized region. These were found in different orientations within the sample, being responsible for the strain anisotropy detected. The striking anisotropy effect, due to mainly the plate-like nanoparticles in the recrystallized region, appears when comparing two (-6.04° and 83.96°) (002) rocking curves at Bragg-surface diffraction exact condition. Furthermore, the mappings of the (111) Bragg-surface diffraction reflections show an evident anisotropy between φ -6.04° and 83.96° mappings and also a marked broadening of the implanted sample profile as compared to that of the Si (matrix). Reciprocal space maps obtained for both perpendicular directions clearly exhibit this anisotropic effect in the q x direction, thus confirming the Bragg-surface diffraction results.

Synchrotron x-ray multiple diffraction in the study of Fe+ ion implantation in Si(0 0 1)

In this work, x-ray multiple diffraction has been used as a three-dimensional high-resolution probe to study the Fe+ ion implantation process in Si(0 0 1). The semiconducting β-FeSi2 crystallographic phase has been synthesized by Fe ion co-implantation in Si(0 0 1) followed by ion-beam-induced epitaxial crystallization (IBIEC) and thermal treatment. This phase was clearly detected by the conventional techniques, micro-Raman scattering spectroscopy, transmission electron microscopy (TEM) and grazing incidence x-ray diffraction. Synchrotron radiation rocking curves (ω-scans) and mapping of the Bragg surface diffraction (BSD) of the Si matrix, as-implanted, after the IBIEC process and thermally treated, have enabled the detection of co-implanted regions formation that present distinct lattices in comparison with the matrix one clearly observed by TEM. Also, the compressive strain of both regions in depth by rocking curve and in-plane has been determined by using BSD, which is one order of magnitude smaller.

Growth and capping of InAs/GaAs quantum dots investigated by x-ray Bragg-surface diffraction

An x-ray diffraction method, based on the excitation of a surface diffracted wave, is described to investigate the capping process of InAs/GaAs (001) quantum dots (QDs). It is sensitive to the tiny misorientation of (111) planes at the surface of the buffer layer on samples with exposed QDs. After capping, the misorientation occurs in the cap-layer lattice faceting the QDs and its magnitude can be as large as 10° depending on the QDs growth rates, probably due to changes in the size and shape of the QDs. A slow strain release process taking place at room temperature has also been observed by monitoring the misorientation angle of the (111) planes.

Determination of three-dimensional interfacial strain — A novel method of probing interface structure with X-ray Bragg-surface diffraction

A new X-ray diffraction technique is developed to probe structural variations at the interfaces between epitaxy thin films and single-crystal substrates. The technique utilizes three-wave Bragg-surface diffraction, where a symmetric Bragg reflection and an asymmetric surface reflection are involved. The propagation of the latter along the interfaces conveys structural information about the interfacial region between the substrate and epi-layers. The sample systems of Au/GaAs(001) are subject to the three-wave diffraction investigation using synchrotron radiation. The GaAs three-wave Bragg-surface diffractions, (006)/(11¯3) and (006)/(1¯1¯3), are employed. The images of the surface diffracted waves are recorded with an image plate. The obtained images show relative positions of diffraction spots near the image of the interfacial boundary, which give the variation of lattice constant along the surface normal and in-plane directions. With the aid of grazing-incidence diffraction, three-dimensional mapping of strain field at the interfaces is possible. Details about this diffraction technique and the analysis procedures are discussed.

Measuring interface strains at the atomic resolution in depth using x-ray Bragg-surface diffraction

A generic x-ray diffraction method, using three-wave Bragg-surface diffraction, is developed to measure strains at the interface of molecular beam epitaxial Au∕GaAs(001), where grazing-incidence diffraction cannot be applied due to the difference in refractive index between Au and GaAs. Changes in diffraction images of the surface reflection (1−13) of GaAs(006)∕(1−13) three-wave Bragg-surface diffraction and the (−1−13) of GaAs(006)∕(−1−13) at different azimuth and Bragg angles give the depth penetration of 2Å resolution and variations of lattice constant, −49%, −27%, and 2%, along the surface normal [001] and in-plane directions [−1−10] and [1−10] within the depths of 18, 72, and 72Å, respectively.

Probing interface strain with X-ray Bragg-surface diffraction

Probing interface strain with X-ray Bragg-surface diffraction

Synchrotron radiation multiple diffraction in the characterization of the PrAl2 magnetocaloric compound

Abstract X-ray multiple diffraction technique using synchrotron radiation is applied to characterize the PrAl 2 magnetocaloric compound. Renninger scans ( φ -scans) of the (0 0 2) primary reflection were measured in the Brazilian Synchrotron Laboratory (LNLS). The (5 3 3 ) (5 3 5) four-beam case provided a =8.0277(5) A and the sample surface polishing effect was clearly observed through the measurement of Bragg-surface diffraction (BSD) peak and the mapping (MBSD) of its multiple diffraction condition.

Structural characterization of TiO2/TiNxOy (δ-doping) heterostructures on (1 1 0)TiO2 substrates

TiO2/TiNxOy δ-doping structures were grown on the top of (110)TiO2 rutile substrates by low pressure metal-organic vapor phase epitaxy (LP-MOVPE) technique at 750°C. The samples were analyzed by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and X-ray diffraction techniques (rocking curves and φ-scans). The presence of satellites in the (110)TiO2 rocking curve revealed the epitaxial growth of 10 period δ-doping structures. The thickness of the TiO2 layers, 84nm, was deduced from the satellites period. HRTEM observations showed around 1.5nm thick δ-doping layers, where the presence of nitrogen was detected by EELS. The analysis of the Bragg surface diffraction peaks observed in the φ-scans points to an almost negligible strain in this sample which was confirmed by substrate curvature radius measurements.

Synchrotron radiation X-ray multiple diffraction in the study of KDP phase transition induced by electric field

In this work, the application of the X-ray multiple diffraction technique using synchrotron radiation at Laboratório Nacional de Luz Síncrotron (LNLS) to study KDP phase transition induced by electric field is discussed. A Huber three-axis (omega, phi, 2theta) diffractometer mounted on a table which rotates around the incident beam allows to measure Renninger scans (RS) at the XRD station of LNLS using the adequate polarization for the experiments. Prior results indicated (080) as the best choice for the KDP primary reflection and the (440)(<img src="http:/img/fbpe/mr/v4n1/quatro.gif" alt="quatro.gif (94 bytes)"> 40) four-beam case for the secondary. Two Bragg-surface diffraction (BSD) reflections, where the secondary beam is propagated parallel to the sample surface, are involved in this multiple diffraction case. A RS interval of 3.3° around phi = 0° position was measured while the electric field was increased up to 6 kV/cm. At this value, a phase transition was observed and the secondary peaks became narrower and changed their RS position indicating possible occurrence of a metastable ferroelectric phase.

Bragg-surface dynamical diffraction

In this work, the dispersion surface of Bragg-surface diffraction (BSD) is presented. A symmetric Bragg reflection plus a secondary diffracted wave nearly parallel to in-plane directions distinguish the BSD from an ordinary three-beam diffraction. The solutions of the fundamental equations of the dynamical theory of X-ray diffraction for the BSD demonstrate that measurable specular-reflected secondary waves are simultaneously excited with the diffracted waves.

Investigation of Bragg surface diffraction in semiconductors and epitaxic structures by reciprocal-space analysis

Bragg surface diffraction (BSD) is a special case of three-beam diffraction, where the secondary beam is scattered in the surface-parallel direction. Under the BSD condition, the surface-detour reflection (secondary plus coupling reflections) transfers some of the secondary-beam intensity into the monitored primary beam. The extinction regime in which such transfer takes place depends on the crystalline perfection of the surface. Based on this fact, the mapping of the BSD profile, in an ω:φ scan technique, has been proposed [Morelhão &amp; Cardoso (1996).J. Appl. Cryst.29, 446–456] as a method to obtain information on the in-plane crystalline quality of the surface. With the X-ray optics for BSD mapping, the diffracting surface thickness that defines the profile could not be measured or compared with those under conventional Bragg diffraction. In this report, the BSD using a triple-axis diffractometer is investigated. Reciprocal-space mapping of the Bragg reflection (primary reflection) was performedinandoutof the BSD condition. It reveals the diffracting surface thickness of BSD in GaAs and Si substrates. The triple axis was also used to investigate the BSD in the SiGe multiple quantum well, and it has demonstrated the existence of effective satellite peaks for such structures.

Electrical Field Effects on Crystalline Perfection of MBA-NP Crystals by Mapping of Bragg-Surface Diffraction

ABSTRACTThe interaction of weak electrical field with the molecular dipole of the MBA-NP crystals is investigated. Such interaction affects the misorientation and size of the perfect diffracting regions of the crystal, which is monitored by mapping the Bragg-surface diffraction condition. This diffraction technique has also confirmed that the diffracting regions are large enough to allow primary extinction and the non-uniform mosaicity along the crystal surface.

Mapping of Bragg-surface diffraction of InP/GaAs(1 0 0) structure

InP/GaAs(1 0 0) heterostructures grown by gas-source molecular-beam epitaxy were analyzed using three-beam bragg-surface diffraction (BSD) of the X-ray multiple diffraction (MD) phenomenon. The angular MD condition is scanned by varying both, the ω incidence angle and the φ rotation angle around [1 0 0] in order to provide the mapping of this condition. From the two-dimensional mapping – ω : φ scan, the crystalline perfection (mosaic spread) parallel ( η φ ) and perpendicular ( η ω ) to the growth direction can be investigated along the layer surface and the substrate interface. The ω: φ scan of the 0 0 0, 2 0 0, 1 1 ̄ 1 BSD is used to analyze the growth processing and post-growth annealing of InP/GaAs samples. The effect of various defect-reduction tools on layer and substrate crystal quality is also investigated.

Sensitivity of Bragg surface diffraction to analyze ion-implanted semiconductors

A special case of the x-ray multiple diffraction phenomenon, the Bragg surface diffraction (BSD), has been investigated under lattice damage due to ion implantation in GaAs (001) samples. The BSD profile is very sensitive to the diffraction regime (dynamical or kinematical) and provides information regarding crystalline perfection and lattice strains in both directions—parallel and perpendicular—to the sample surface. Results from grazing-incidence x-ray diffraction and reciprocal space mapping are also reported.

Bragg-surface three-beam dynamical X-ray diffraction

Three-beam diffraction with a symmetric Bragg reflection and a surface diffraction is studied based on the dynamical theory of X-ray diffraction. The difficulty involved in the boundary conditions for the surface diffraction is overcome by treating the Bragg–surface diffraction as either a Bragg–Laue or a Bragg–Bragg case with the inclination angle α between the crystal surface and the surface-diffracted beam being very small, about 10−5 rad. The geometry of the dispersion surface, the number of permitted modes of wave propagation, the linear absorption coefficient, the excitation of the beam and the diffracted intensity are calculated for the Ge (000) (222) (31\overline 1) Bragg–surface diffraction of Cu Kα1. It is found that the calculated relative integrated intensity ratio among the Bragg–surface 31\overline 1 case and the Bragg–Bragg 113 and 51\overline 1 cases is in good agreement with the integrated intensity ratio obtained experimentally.