TY - JOUR AB - The crystal family of potassium titanyl phosphate (KTiOPO4) is a promising material group for applications in quantum and nonlinear optics. The fabrication of low-loss optical waveguides, as well as high-grade periodically poled ferroelectric domain structures, requires a profound understanding of the material properties and crystal structure. In this regard, Raman spectroscopy offers the possibility to study and visualize domain structures, strain, defects, and the local stoichiometry, which are all factors impacting device performance. However, the accurate interpretation of Raman spectra and their changes with respect to extrinsic and intrinsic defects requires a thorough assignment of the Raman modes to their respective crystal features, which to date is only partly conducted based on phenomenological modelling. To address this issue, we calculated the phonon spectra of potassium titanyl phosphate and the related compounds rubidium titanyl phosphate (RbTiOPO4) and potassium titanyl arsenate (KTiOAsO4) based on density functional theory and compared them with experimental data. Overall, this allows us to assign various spectral features to eigenmodes of lattice substructures with improved detail compared to previous assignments. Nevertheless, the analysis also shows that not all features of the spectra can unambigiously be explained yet. A possible explanation might be that defects or long range fields not included in the modeling play a crucial rule for the resulting Raman spectrum. In conclusion, this work provides an improved foundation into the vibrational properties in the KTiOPO4 material family. AU - Neufeld, Sergej AU - Gerstmann, Uwe AU - Padberg, Laura AU - Eigner, Christof AU - Berth, Gerhard AU - Silberhorn, Christine AU - Eng, Lukas M. AU - Schmidt, Wolf Gero AU - Rüsing, Michael ID - 47997 IS - 10 JF - Crystals KW - Inorganic Chemistry KW - Condensed Matter Physics KW - General Materials Science KW - General Chemical Engineering SN - 2073-4352 TI - Vibrational Properties of the Potassium Titanyl Phosphate Crystal Family VL - 13 ER - TY - JOUR AB - Potassium titanyl phosphate (KTP) is a nonlinear optical material with applications in high-power frequency conversion or quasi-phase matching in submicron period domain grids. A prerequisite for these applications is a precise control and understanding of the poling mechanisms to enable the fabrication of high-grade domain grids. In contrast to the widely used material lithium niobate, the domain growth in KTP is less studied, because many standard methods, such as selective etching or polarization microscopy, provides less insight or are not applicable on non-polar surfaces, respectively. In this work, we present results of confocal Raman-spectroscopy of the ferroelectric domain structure in KTP. This analytical method allows for the visualization of domain grids of the non-polar KTP y-face and therefore more insight into the domain-growth and -structure in KTP, which can be used for improved domain fabrication. AU - Brockmeier, Julian AU - Mackwitz, Peter Walter Martin AU - Rüsing, Michael AU - Eigner, Christof AU - Padberg, Laura AU - Santandrea, Matteo AU - Silberhorn, Christine AU - Zrenner, Artur AU - Berth, Gerhard ID - 23826 JF - Crystals SN - 2073-4352 TI - Non-Invasive Visualization of Ferroelectric Domain Structures on the Non-Polar y-Surface of KTiOPO4 via Raman Imaging ER - TY - JOUR AU - Spychala, K. J. AU - Mackwitz, P. AU - Rüsing, Michael AU - Widhalm, A. AU - Berth, Gerhard AU - Silberhorn, Christine AU - Zrenner, Artur ID - 22056 JF - Journal of Applied Physics SN - 0021-8979 TI - Nonlinear focal mapping of ferroelectric domain walls in LiNbO3: Analysis of the SHG microscopy contrast mechanism ER - TY - JOUR AU - Padberg, Laura AU - Santandrea, Matteo AU - Rüsing, Michael AU - Brockmeier, Julian AU - Mackwitz, Peter AU - Berth, Gerhard AU - Zrenner, Artur AU - Eigner, Christof AU - Silberhorn, Christine ID - 25920 JF - Optics Express SN - 1094-4087 TI - Characterisation of width-dependent diffusion dynamics in rubidium-exchanged KTP waveguides ER - TY - JOUR AB - In recent years, Raman spectroscopy has been used to visualize and analyze ferroelectric domain structures. The technique makes use of the fact that the intensity or frequency of certain phonons is strongly influenced by the presence of domain walls. Although the method is used frequently, the underlying mechanism responsible for the changes in the spectra is not fully understood. This inhibits deeper analysis of domain structures based on this method. Two different models have been proposed. However, neither model completely explains all observations. In this work, we have systematically investigated domain walls in different scattering geometries with Raman spectroscopy in the common ferroelectric materials used in integrated optics, i.e., KTiOPO4, LiNbO3, and LiTaO3. Based on the two models, we can demonstrate that the observed contrast for domain walls is in fact based on two different effects. We can identify on the one hand microscopic changes at the domain wall, e.g., strain and electric fields, and on the other hand a macroscopic change of selection rules at the domain wall. While the macroscopic relaxation of selection rules can be explained by the directional dispersion of the phonons in agreement with previous propositions, the microscopic changes can be explained qualitatively in terms of a simplified atomistic model. AU - Rüsing, Michael AU - Neufeld, Sergej AU - Brockmeier, Julian AU - Eigner, Christof AU - Mackwitz, P. AU - Spychala, K. AU - Silberhorn, Christine AU - Schmidt, Wolf Gero AU - Berth, Gerhard AU - Zrenner, Artur AU - Sanna, S. ID - 4769 IS - 10 JF - Physical Review Materials SN - 2475-9953 TI - Imaging of 180∘ ferroelectric domain walls in uniaxial ferroelectrics by confocal Raman spectroscopy: Unraveling the contrast mechanism VL - 2 ER - TY - JOUR AB - In this work we study the impact of ion implantation on the nonlinear optical properties in MgO:LiNbO3 via confocal second-harmonic microscopy. In detail, we spatially characterize the nonlinear susceptibility in carbon-ion implanted lithium niobate planar waveguides for different implantation energies and fluences, as well as the effect of annealing. In a further step, a computational simulation is used to calculate the implantation range of carbon-ions and the corresponding defect density distribution. A comparison between the simulation and the experimental data indicates that the depth profile of the second-order effective nonlinear coefficient is directly connected to the defect density that is induced by the ion irradiation. Furthermore it can be demonstrated that the annealing treatment partially recovers the second-order optical susceptibility. AU - Spychala, Kai J. AU - Berth, Gerhard AU - Widhalm, Alex AU - Rüsing, Michael AU - Wang, Lei AU - Sanna, Simone AU - Zrenner, Artur ID - 3434 IS - 18 JF - OPTICS EXPRESS SN - 1094-4087 TI - Impact of carbon-ion implantation on the nonlinear optical susceptibility of LiNbO3 ER - TY - CONF AU - Hett, Thomas AU - Frers, Torsten AU - Widhalm, Alex AU - Berth, Gerhard AU - Hilleringmann, Ulrich AU - Zrenner, Artur ID - 3798 T2 - Smart Systems Integration 2016 - International Conference and Exhibition on Integration Issues of Miniaturized Systems, SSI 2016 TI - Silicon oxynitride microdisk resonators for integrated waveguide coupling ER - TY - JOUR AB - Confocal Raman spectroscopy is applied to identify ferroelectric domain structure sensitive phonon modes in potassium titanyl phosphate. Therefore, polarization-dependent measurements in various scattering configurations have been performed to characterize the fundamental Raman spectra of the material. The obtained spectra are discussed qualitatively based on an internal mode assignment. In the main part of this work, we have characterized z-cut periodically poled potassium titanyl phosphate in terms of polarity- and structure-sensitive phonon modes. Here, we find vibrations whose intensities are linked to the ferroelectric domain walls. We interpret this in terms of changes in the polarizability originating from strain induced by domain boundaries and the inner field distribution. Hence, a direct and 3D visualization of ferroelectric domain structures becomes possible in potassium titanyl phosphate. AU - Rüsing, Michael AU - Eigner, Christof AU - Mackwitz, P. AU - Berth, Gerhard AU - Silberhorn, Christine AU - Zrenner, Artur ID - 4239 IS - 4 JF - Journal of Applied Physics SN - 0021-8979 TI - Identification of ferroelectric domain structure sensitive phonon modes in potassium titanyl phosphate: A fundamental study VL - 119 ER - TY - JOUR AB - We report the fabrication of periodically poled domain patterns in x-cut lithium niobate thin-film. Here, thin films on insulator have drawn particular attention due to their intrinsic waveguiding properties offering high mode confinement and smaller devices compared to in-diffused waveguides in bulk material. In contrast to z-cut thin film lithium niobate, the x-cut geometry does not require back electrodes for poling. Further, the x-cut geometry grants direct access to the largest nonlinear and electro-optical tensor element, which overall promises smaller devices. The domain inversion was realized via electric field poling utilizing deposited aluminum top electrodes on a stack of LN thin film/SiO2 layer/Bulk LN, which were patterned by optical lithography. The periodic domain inversion was verified by non-invasive confocal second harmonic microscopy. Our results show domain patterns in accordance to the electrode mask layout. The second harmonic signatures can be interpreted in terms of spatially, overlapping domain filaments which start their growth on the þz side. AU - Mackwitz, P. AU - Rüsing, Michael AU - Berth, Gerhard AU - Widhalm, A. AU - Müller, K. AU - Zrenner, Artur ID - 4237 IS - 15 JF - Applied Physics Letters SN - 0003-6951 TI - Periodic domain inversion in x-cut single-crystal lithium niobate thin film VL - 108 ER - TY - JOUR AB - Cubic gallium nitride (GaN) films are analyzed with highresolution X-ray diffraction (HRXRD) and Raman spectroscopy. Several cubic GaN layers were grown on 3C-SiC (001) substrate by radio-frequency plasma-assisted molecular beam epitaxy. The layer thickness of the cubic GaN was varied between 75 and 505 nm. The HRXRD analysis reveals a reduction of the full-width at half-maximum (FWHM) of omega scans for growing layer thicknesses, which is caused by a partial compensation of defects. The Raman characterization confirms well-formed c-GaN layers. A more detailed examination of the longitudinal optical mode hints at a correlation of the FWHM of the Raman mode with the dislocation density, which shows the possibility to determine dislocation densities by Ramanspectroscopy on a micrometer scale, which is not possible by HRXRD. Furthermore, this Raman analysis shows that normalized Raman spectra present an alternative way to determine layer thicknesses of thin GaN films. AU - Rüsing, Michael AU - Wecker, T. AU - Berth, Gerhard AU - As, Donat Josef AU - Zrenner, Artur ID - 4240 IS - 4 JF - physica status solidi (b) KW - cubic gallium nitride KW - dislocation density KW - HRXRD KW - Raman spectroscopy SN - 0370-1972 TI - Joint Raman spectroscopy and HRXRD investigation of cubic gallium nitride layers grown on 3C-SiC VL - 253 ER - TY - JOUR AB - Congruent lithium niobate and lithium tantalate mixed crystals have been grown over the complete compositional range with the Czochralski method. The structural and vibrational properties of the mixed crystals are studied extensively by x-ray diffraction measurements, Raman spectroscopy, and density functional theory. The measured lattice parameters and vibrational frequencies are in good agreement with our theoretical predictions. The observed dependence of the Raman frequencies on the crystal composition is discussed on the basis of the calculated phonon displacement patterns. The phononic contribution to the static dielectric tensor is calculated by means of the generalized Lyddane-Sachs-Teller relation. Due to the pronounced dependence of the optical response on the Ta concentration, lithium niobate tantalate mixed crystals represent a perfect model system to study the properties of uniaxial mixed ferroelectric materials for application in integrated optics. AU - Rüsing, Michael AU - Sanna, Simone AU - Neufeld, Sergej AU - Berth, Gerhard AU - Schmidt, Wolf Gero AU - Zrenner, Artur AU - Yu, H. AU - Wang, Y. AU - Zhang, H. ID - 10026 JF - Physical Review B SN - 2469-9950 TI - Vibrational properties of LiNb1−xTaxO3 mixed crystals ER - TY - JOUR AB - LiTaO3 and LiNbO3 crystals are investigated here in a combined experimental and theoretical study that uses Raman spectroscopy in a complete set of scattering geometries and corresponding density-functional theory calculations to provide microscopic information on their vibrational properties. The Raman scattering efficiency is computed from first principles in order to univocally assign the measured Raman peaks to the calculated eigenvectors. Measured and calculated Raman spectra are shown to be in qualitative agreement and confirm the mode assignment by Margueron et al. [J. Appl. Phys. 111, 104105 (2012)], thus finally settling a long debate. While the two crystals show rather similar vibrational properties overall, the E-TO9 mode is markedly different in the two oxides. The deviations are explained by a different anion-cation bond type in LiTaO3 and LiNbO3 crystals. AU - Sanna, Simone AU - Neufeld, Sergej AU - Rüsing, Michael AU - Berth, Gerhard AU - Zrenner, Artur AU - Schmidt, Wolf Gero ID - 4332 IS - 22 JF - Physical Review B SN - 1098-0121 TI - Raman scattering efficiency in LiTaO3 and LiNbO3 crystals VL - 91 ER - TY - JOUR AB - Atomistic simulations in the framework of the density functional theory have been used to model morphologic and vibrational properties of lithium niobate–lithium tantalate mixed crystals as a function of the [Nb]/[Ta] ratio. Structural parameters such as the crystal volume and the lattice parameters a and c vary roughly linearly from LiTaO3 to LiNbO3, showing only minor deviations from the Vegard behavior. Our ab initio calculations demonstrate that the TO1, TO2 and TO4 vibrational modes become harder with increasing Nb concentration. TO3 becomes softer with increasing Nb content, instead. Furthermore, the investigated zone center A1 -TO phonon modes are characterized by a pronounced stoichiometry dependence. Frequency shifts as large as 30 cm−1 are expected as the [Nb]/[Ta] ratio grows from 0 to 1. Therefore, spectroscopic techniques sensitive to the A1 modes (such as Raman spectroscopy), can be employed for a direct and non-destructive determination of the crystal composition. AU - Sanna, Simone AU - Riefer, A. AU - Neufeld, Sergej AU - Schmidt, Wolf Gero AU - Berth, Gerhard AU - Rüsing, Michael AU - Widhalm, A. AU - Zrenner, Artur ID - 13520 IS - 1 JF - Ferroelectrics KW - Ferroelectrics KW - vibrational properties KW - LiNbO3 KW - LiTaO3 KW - mixed crystals SN - 0015-0193 TI - Vibrational Fingerprints of LiNbO3-LiTaO3Mixed Crystals VL - 447 ER - TY - JOUR AB - Copper oxide and cobalt oxide (CuO, Co3O4) nanocrystals (NCs) have been successfully prepared in a short time using microwave irradiation without any postannealing treatment. Both kinds of nanocrystals (NCs) have been prepared using copper nitrate and cobalt nitrate as the starting materials and distilled water as the solvent. The resulted powders of nanocrystals (NCs) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements. The obtained results confirm the presence of the both of oxides nanopowders produced during chemical precipitation using microwave irradiation. A strong emission under UV excitation is obtained from the prepared CuO and Co3O4 nanoparticles. The results show that the nanoparticles have high dispersion and narrow size distribution. The line scans of atomic force microscopy (AFM) images of the nanocrystals (NCs) sprayed on GaAs substrates confirm the results of both X-ray diffraction and transmission electron microscopy. Furthermore, vibrational studies have been carried out using Raman spectroscopic technique. Specific Raman peaks have been observed in the CuO and Co3O4 nanostructures, and the full width at half maximum (FWHM) of the peaks indicates a small particle size of the nanocrystals. AU - Rashad, M. AU - Rüsing, Michael AU - Berth, Gerhard AU - Lischka, K. AU - Pawlis, A. ID - 47940 JF - Journal of Nanomaterials KW - General Materials Science SN - 1687-4110 TI - CuO and Co3O4 Nanoparticles: Synthesis, Characterizations, and Raman Spectroscopy VL - 2013 ER - TY - CONF AB - The structural and vibrational properties of lithium niobate (LN) – lithium tantalate (LT) mixed crystals (LNT, LiNb1-xTaxO3) are investigated over the whole composition range by first-principles simulations. The crystal volume grows roughly linearly from LT to LN, whereby the lattice parameters a and c show minor deviations from the Vegard behavior between the end compounds, LiNbO3 and LiTaO3. Our calculations in the framework of the density functional theory show the TO1, TO2 and TO4-modes to become harder with increasing Nb concentration. TO3 becomes softer with increasing Nb content, instead. The frequency shifts of the zone center A1-TO phonon modes for crystals with different compositions are found to be as large as 30 cm-1. Raman spectroscopy, which is sensitive to the A1 modes, can be therefore employed to determine the crystal composition. AU - Sanna, Simone AU - Riefer, Arthur AU - Neufeld, Sergej AU - Schmidt, Wolf Gero AU - Berth, Gerhard AU - Widhalm, Alex AU - Zrenner, Artur ID - 4380 KW - Ferroelectrics KW - Vibrational properties KW - LiNbO3 KW - LiTaO3 KW - Mixed Crystals T2 - Proceedings of ISAF-ECAPD-PFM 2012 TI - Vibrational fingerprints of LiNbO3-LiTaO3 mixed crystals ER - TY - JOUR AB - The existence of localized vibrational modes both at the positive and at the negative LiNbO3 (0001) surface is demonstrated by means of first-principles calculations and Raman spectroscopy measurements. First, the phonon modes of the crystal bulk and of the (0001) surface are calculated within the density functional theory. In a second step, the Raman spectra of LiNbO3 bulk and of the two surfaces are measured. The phonon modes localized at the two surfaces are found to be substantially different, and are also found to differ from the bulk modes. The calculated and measured frequencies are in agreement within the error of the method. Raman spectroscopy is shown to be sensitive to differences between bulk and surface and between positive and negative surface. It represents therefore an alternative method to determine the surface polarity, which does not exploit the pyroelectric or piezoelectric properties of the material. AU - Sanna, S. AU - Berth, Gerhard AU - Hahn, W. AU - Widhalm, A. AU - Zrenner, Artur AU - Schmidt, W. G. ID - 4544 IS - 9 JF - IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control SN - 0885-3010 TI - Vibrational properties of the LiNbO3 z-surfaces VL - 58 ER - TY - JOUR AB - Laser irradiation damage in ZnTe epilayers was analyzed in situ by power-density-dependent and time-resolved micro-Raman spectroscopy. Damage by ablation or compound decomposition on the sample surface was revealed by the decrease of the ZnTe–nLO mode intensity with the increase of laser power density. The appearance of the peaks associated with the stronger crystalline-tellurium modes, tellurium aggregates and second-order Raman scattering at room temperature μ-Raman spectra was observed for higher power densities than 4.4 × 105 W cm−2. The Raman signal time transients of ZnTe–nLO and crystalline-tellurium modes reveal an exponential evolution of the laser irradiation damage and a fast formation of crystalline tellurium aggregates on the layer surface. AU - Wiedemeier, V AU - Berth, Gerhard AU - Zrenner, Artur AU - Larramendi, E M AU - Woggon, U AU - Lischka, K AU - Schikora, D ID - 4545 IS - 10 JF - Semiconductor Science and Technology SN - 0268-1242 TI - In situ characterization of ZnTe epilayer irradiation via time-resolved and power-density-dependent Raman spectroscopy VL - 26 ER - TY - CONF AB - Silicon oxynitride (SiON) layers for telecommunication device application are grown by Plasma Enhanced Chemical Vapor Deposition (PECVD) for various gas compositions of SiH4, N2O and NH3. Processing and annealing effects on the oxynitride films were studied by Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM) measurements. By reduction of the silane (SiH4) gas flow and enhancement of the PECVD deposition temperature, the absorption loss due to NH bands can be nearly completely erased. Furthermore the surface roughness can be reduced by decreasing the gas flow and rising the deposition temperature. First waveguide structures are introduced and their characterization is presented. AU - Frers, Torsten AU - Hett, Thomas AU - Hilleringmann, Ulrich AU - Berth, Gerhard AU - Widhalm, Alex AU - Zrenner, Artur ID - 4546 SN - 9781457704314 T2 - 2011 Semiconductor Conference Dresden TI - Characterization of SiON integrated waveguides via FTIR and AFM measurements ER - TY - JOUR AB - Confocal Raman spectroscopy was performed as an archetype imaging method to study the ferroelectric domain structure of periodically poled lithium niobate. More precisely, the linkage out of spatial resolution and spectral information proved itself as very useful. Here a specific modulation of the Raman lines by the local variation of polarity and a non-symmetric measuring-signal across the domain structure were found, which allows for imaging of domain boundaries as well as oppositely orientated domains. The high potential of this method is demonstrated by the visualization of the ferroelectric domain structures based on various phonon modes. AU - Berth, Gerhard AU - Hahn, Wjatscheslaw AU - Wiedemeier, Volker AU - Zrenner, Artur AU - Sanna, Simone AU - Schmidt, Wolf Gero ID - 4377 IS - 1 JF - Ferroelectrics KW - Raman spectroscopy KW - ferroelectric domains KW - LiNbO3 KW - confocal imaging SN - 0015-0193 TI - Imaging of the Ferroelectric Domain Structures by Confocal Raman Spectroscopy VL - 420 ER - TY - JOUR AB - Uniform mesoporous Si double layers are formed on 4 inch p-type < 100> wafers with an off orientation of 6º towards < 111> by means of electrochemical etching in ethanoic-based HF electrolytes. These substrates are of interest for the epitaxial growth of III–V compound semiconductor stacks on their top for the production of multi-junction solar cells and very thin electronic devices. We demonstrate transfer of porous layers after an annealing process in hydrogen atmosphere. Electron Back-Scatter Diffraction analysis confirms that the substrate orientation is conserved during the etching and annealing steps. Confocal μ-Raman spectroscopy analysis shows a decrease in the Raman signal intensity after etching and a subsequent increase after annealing while no shift is observed. By means of Atomic Force Microscopy, analysis the surface appearance after the etching and annealing steps can be visualized. The mean surface roughness varies during the process from 0.55 nm for the unprocessed wafers to 0.27 nm after etching and 0.78 nm after annealing. The decrease of average roughness after etching is caused by an electropolishing step prior to porous formation. Despite of slight increase of mean surface roughness after annealing the samples are still appropriate for high quality epitaxial growth and subsequent lift-off. AU - Garralaga Rojas, E. AU - Terheiden, B. AU - Plagwitz, H. AU - Hensen, J. AU - Wiedemeier, V. AU - Berth, Gerhard AU - Zrenner, Artur AU - Brendel, R. ID - 4379 IS - 1 JF - Thin Solid Films KW - Porous Si KW - Layer transfer KW - Thin-film KW - Photovoltaics SN - 0040-6090 TI - Lift-off of mesoporous layers by electrochemical etching on Si (100) substrates with miscut of 6° off towards (111) VL - 520 ER -