Luis H. Avanci

Piezoelectric coefficients d14, d16, d34 and d36 of an L-arginine hydrochloride monohydrate crystal by X-ray three-beam diffraction

Previous work employed X-ray three-beam diffraction techniques to obtain part of the L-arginine hydrochloride monohydrate (L-AHCL.H(2)O) piezoelectric coefficients, namely d(21), d(22), d(23) and d(25). Those coefficients were obtained by measuring the shift in the angular position of a number of secondary reflections as a function of the electric field applied in the [010] piezoelectric direction. In this paper a similar procedure has been used to measure the remaining four piezoelectric coefficients in L-AHCL.H(2)O: with the electric field applied in the [100] direction, d(14) and d(16) were measured; with the electric field applied in the [001] direction, d(34) and d(36) were obtained. Therefore the entire piezoelectric matrix of the L-AHCL.H(2)O crystal has been successfully measured.

Habit modification of nearly perfect single crystals of potassium dihydrogen phosphate (KDP) by trivalent manganese ions studied using synchrotron radiation X-ray multiple diffraction in Renninger scanning mode

The X-ray multiple diffraction technique using synchrotron radiation is applied in the preliminary study of the habit modification of KDP samples as induced by incorporation of the trivalent transition metal cation Mn 3+ . High-resolution Renninger scans of pure and doped KDP were carried out using 400 as the primary reflection, echoing the fact that these impurity species were segregated in the {100} growth sector. The analysis of the Renninger scans of the doped KDP crystals is consistent with the presence of the impurity species chemically bound within the KDP crystal structure, as confirmed through the suppression of the huge observed peak asymmetry, characteristic of perfect crystals. In addition, an extra Renninger-scan peak measured for the doped material is indicative of the impurity atoms occupying interstitial crystallographic sites in the lattice, a result consistent with X-ray standing-wave measurements. Renninger-scan reflection curve widths and lattice parameter measurements reveal the decrease in crystalline perfection (increased mosaic spread, η) and lattice contraction of ca 0.4% in the a and c lattice directions at the surface plane for the Mn 3+ -doped KDP samples in comparison with the undoped crystals.

Strength tuning of multiple waves in crystals

In this work, the linear polarization of synchrotron radiation is explored as a tuning key for the strength of the simultaneously diffracted X-ray waves in crystals. The relative strength of the waves has been defined by the reflectivities of the Bragg reflections involved in each multiple-diffraction case and it has limited the applicability of the multiple-diffraction phenomenon. With a proper choice of the wavelength and the polarization direction of the incident synchrotron radiation, it is demonstrated how the intensity ratios of the simultaneously diffracted beams can be drastically changed.

Two-dimensional intensity profiles of effective satellites

The observation of a new X-ray scattering process with synchrotron radiation is reported. The phenomenon is analogous to three-beam diffraction in a single crystal; however, the features in the azimuthal scans are provided by superlattice-satellite reflections instead of bulk reflections. These features were named effective satellites and they are observed over the ordinary satellite reflections as a function of the azimuthal angle. Their occurrences have been monitored in completely different superlattices by mapping the incidence and azimuthal angles of the incident X-ray beam. Effects of structural parameters of the superlattices on the effective satellites as well as the information that can be extracted by measuring their positions are discussed.

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.

Strain field of InAs QDs on GaAs (001) substrate surface: characterization by synchrotron X-ray Renninger scanning

Precise lattice parameter measurements in single crystals are achievable, in principle, by X-ray multiple diffraction (MD) experiments. Tiny sample misalignments can compromise systematic usage of MD in studies where accuracy is an important issue. In this work, theoretical treatment and experimental methods for correcting residual misalignment errors are presented and applied to probe the induced strain of buried InAs quantum dots on GaAs (001) substrates.

Energy conservation in approximated solutions of multi-beam scattering problems

Scattering of particles by time-independent potentials is describable by wave solutions in the form of series expansion. As mathematically demonstrated here, such form of solutions when applied to multi-beam scattering phenomena can lead to energy violation where the incident and scattered numbers of particles are not preserved. In this work, we outline a general basic requirement for developing consistent solutions of time-dependent multi-beam scattering problems by extended potentials.

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 Laboratorio Nacional de Luz Sincrotron (LNLS) to study KDP phase transition induced by electric field is discussed. A Huber three-axis (w, f, 2q) 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)( 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 f = 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.