Lithium Niobate Single Crystals Research Articles

Monolithic deformable mirror based on lithium niobate single crystal for high-resolution X-ray adaptive microscopy

X-ray microscopy is very promising not only for nondestructive and high-spatial-resolution observation of the internal structure of a sample but also for elemental distribution and chemical state analysis. However, the spatial resolution of microscopes remains unsatisfactory owing to the fabrication error in the objective lens. To realize an ultra-high-resolution, we propose and develop a monolithic deformable mirror based on a lithium niobite single crystal and a novel adaptive imaging system based on it. An X-ray interferometer confirmed that shape modification is possible with an accuracy of 0.67 nm in peak to valley under high stability (0.17 nm over 7 h) and hysteresis-free deformation control. Introducing this adaptive mirror into an X-ray microscope based on advanced Kirkpatrick-Baez mirror optics and correcting the wavefront aberration demonstrated that the X-ray image quality could be significantly improved.

Lithium Niobate MEMS Antisymmetric Lamb Wave Resonators with Support Structures.

The piezoelectric thin film composed of single-crystal lithium niobate (LiNbO3) exhibits a remarkably high electromechanical coupling coefficient and minimal intrinsic losses, making it an optimal material for fabricating bulk acoustic wave resonators. However, contemporary first-order antisymmetric (A1) Lamb mode resonators based on LiNbO3 thin films face specific challenges, such as inadequate mechanical stability, limited power capacity, and the presence of multiple spurious modes, which restrict their applicability in a broader context. In this paper, we present an innovative design for A1 Lamb mode resonators that incorporates a support-pillar structure. Integration of support pillars enables the dissipation of spurious wave energy to the substrate, effectively mitigating unwanted spurious modes. Additionally, this novel approach involves anchoring the piezoelectric thin film to a supportive framework, consequently enhancing mechanical stability while simultaneously improving the heat dissipation capabilities of the core.

Enhancing the electric charge output in LiNbO3-based piezoelectric pressure sensors.

Lithium niobate (LiNbO3) single crystals are a kind of ferroelectric material with a high piezoelectric coefficient and Curie temperature, which is suitable for the preparation of piezoelectric pressure sensors. However, there is little research reporting on the use of LiNbO3 single crystals to prepare piezoelectric pressure sensors. Therefore, in this paper, LiNbO3 was used to prepare piezoelectric pressure sensors to study the feasibility of using LiNbO3 single crystals as a sensitive material for piezoelectric pressure sensors. In addition, chemical mechanical polishing (CMP) technology was used to prepare LiNbO3 crystals with different thicknesses to study the influence of these LiNbO3 crystals on the electric charge output of the sensors. The results showed that the sensitivity of a 300 μm sample (0.218 mV kPa-1) was about 1.23 times that of a 500 μm sample (0.160 mV kPa-1). Low-temperature polymer heterogeneous integration and oxygen plasma activation technologies were used to realize the heterogeneous integration of LiNbO3 and silicon to prepare piezoelectric pressure sensors, which could significantly improve the sensitivity of the sensor by approximately 16.06 times (2.569 mV kPa-1) that of the original sample (0.160 mV kPa-1) due to an appropriate residual stress that did not shatter LiNbO3 or silicon, thus providing a possible method for integrating piezoelectric pressure sensors and integrated circuits.

Electrophysical properties, memristive and resistive switching of charged domain walls in lithium niobate

Charged domain walls (CDWs) in ferroelectric materials raise both fundamental and practical interest due to their electrophysical properties differing from bulk ones. On a microstructure level, CDWs in ferroelectrics are 2D defects separating regions with different spontaneous polarization vector directions. Screening of electric field of the CDW's bound ionic charges by mobile carriers leads to the formation of elongated narrow channels with an elevated conductivity in initially dielectric materials. Controlling the position and inclination angle of CDW relative to the spontaneous polarization direction, one can change its conductivity over a wide range thus providing good opportunities for developing memory devices, including neuromorphic systems. This review describes the state of art in the formation and application of CDWs in single crystal uniaxial ferroelectric lithium niobate (LiNbO3, LN), as resistive and memristive switching devices. The main CDWs formation methods in single crystal and thin-film LN have been described, and modern data have been presented on the electrophysical properties and electrical conductivity control methods of CDWs. Prospects of CDWs application in resistive and memristive switching memory devices have been discussed.

Ferroelectric Domain Wall p-n Junctions.

We have used high-voltage Kelvin probe force microscopy to map the spatial distribution of electrical potential, dropped along curved current-carrying conducting domain walls, in x-cut single-crystal ferroelectric lithium niobate thin films. We find that in-operando potential profiles and extracted electric fields, associated with p-n junctions contained within the walls, can be fully rationalized through expected variations in wall resistivity alone. There is no need to invoke additional physics (carrier depletion zones and space-charge fields) normally associated with extrinsically doped semiconductor p-n junctions. Indeed, we argue that this should not even be expected, as inherent Fermi level differences between p and n regions, at the core of conventional p-n junction behavior, cannot occur in domain walls that are surrounded by a common matrix. This is important for domain-wall nanoelectronics, as such in-wall junctions will neither act as diodes nor facilitate transistors in the same way as extrinsic semiconducting systems do.

Theoretical studies and structural analysis of the Nd3+ centers with trigonal symmetry in congruent lithium niobate single crystals

In this paper, the superposition model (SM) and complete diagonalization procedure of energy matrix (CDM method) were used for a few selected Nd3+ (4f3) paramagnetic centers with trigonal symmetry in congruent lithium niobate (LN, LiNbO3) single crystals. Additionally, the g-shift method was applied to these systems. In general, the calculated g-factors (parallel and perpendicular) match the measured values very well. The displacements of the Nd3+ ions calculated by g-shift method are also fit very well to the experimental values. A detailed structural analysis of paramagnetic Nd3+ centers with trigonal symmetry in congruent LN single crystals was also performed. The charge compensation mechanism and its role in establishing Nd3+ centers in congruent LN are also debated.

New insights into refractive indices and birefringence of undoped and MgO-doped lithium niobate crystals at high temperatures

The lithium niobate single crystal is a well-known optical material that has been employed in a wide range of photonic applications. To realize further applications of the crystal, the birefringence properties need to be determined over a large range of temperatures. We report refractive indices and birefringence properties of undoped and MgO-doped lithium niobate crystals with high accuracy using spectroscopic ellipsometry in the spectral range from 450 to 1700 nm and a temperature range from ambient temperature to 1000 °C. The birefringence results indicate a transition temperature, where the crystal transforms from an anisotropic to isotropic property, and the advance of MgO doping in the crystal, which is related to the optical damage threshold of the materials. In addition, the lattice dynamics of the crystals have been analyzed by revisiting the Raman spectroscopy. The results establish the foundation of optical properties of lithium niobate crystals, providing pathways for their photonic applications.

Preparation and Characterization of Lithium Niobate Single Crystals Doped with 4.02–5.38 mol % Zn

Preparation and Characterization of Lithium Niobate Single Crystals Doped with 4.02–5.38 mol % Zn

Time-domain Brillouin scattering for evaluation of materials interface inclination: Application to photoacoustic imaging of crystal destruction upon non-hydrostatic compression

Time-domain Brillouin scattering (TDBS) is a developing technique for imaging/evaluation of materials, currently used in material science and biology. Three-dimensional imaging and characterization of polycrystalline materials has been recently reported, demonstrating evaluation of inclined material boundaries. Here, the TDBS technique is applied to monitor the destruction of a lithium niobate single crystal upon non-hydrostatic compression in a diamond anvil cell. The 3D TDBS experiments reveal, among others, modifications of the single crystal plate with initially plane-parallel surfaces, caused by non-hydrostatic compression, the laterally inhomogeneous variations of the plate thickness and relative inclination of opposite surfaces. Our experimental observations, supported by theoretical interpretation, indicate that TDBS enables the evaluation of materials interface orientation/inclination locally, from single point measurements, avoiding interface profilometry. A variety of observations reported in this paper paves the way to further expansion of the TDBS imaging use to analyze fascinating processes/phenomena occurring when materials are subjected to destruction.

Hybrid structure for vortex beam generation and propagation in LN crystal based on femtosecond laser direct writing

We report a q-plate-waveguide hybrid optical vortex emitter processed by femtosecond laser directly writing the lithium niobate (LN) single crystal. Both simulation and experimental results show that by utilizing the geometric phase of the q-plate, the fabricated device can convert the incident Gaussian beam into the vortex beam with orbital angular momentum (OAM) and realize the low-loss transmission of the vortex beam in the double-cladding waveguide. Our results demonstrate that the q-plate-waveguide hybrid structure has great prospects for promoting the development of photonic integrated chips (PICs) by generating and propagating a vortex beam with a certain topological charge.

Point defects substitution mechanism in indium-doped LiNbO3 single crystals revealed by UV–Visible and Micro-Raman analysis

This work reveals relevant information about the mechanism of substitution of point defects by In ions in lithium niobate single crystals doped with In in moderate concentrations ranging from 0.5 to 4 mol % in the melt. It was found that the In ions, first replace Nb ions at Li sites, and then Li ions. However, it does not occur continuously because while the doping concentration approaches a given critical value (0.65 mol % into the crystal), the Li concentration reaches a maximum, and the Li vacancies and niobium antisites remain practically constant. At this critical doping concentration point, the crystal stops the introduction of indium into its structure. After this critical value, as the doping concentration increases, the In replaces the Li but also the Li vacancies and niobium antisites. The niobium antisite is not the most stable point defect due to as the In-doping increases it takes values between five and fourteen times lower than the Li vacancies. From a compressive strain in the lattice of LN crystals induced by the In ion, the phonon modes with a Raman shift in the range from 300 to 500 cm−1 were appreciably attenuated. Close to the peaks centered at 151 cm−1 and 878 cm−1 appeared one extra vibration mode for crystals doped with 2.0 mol % and 1.3% mol of In in the melt, which reveals important structural changes induced by the In ion.

Zeta potential and nanodiamond self assembly assisted diamond growth on lithium niobate and lithium tantalate single crystal

This study focuses on the self-assembly and subsequent diamond growth on SiO2 buffered lithium niobate (LNO) and lithium tantalate (LTO) single crystals. The zeta-potential of LNO and LTO single crystal were measured as a function of pH. They were found to be negative in the pH range 3.5–9.5. The isoelectric point for LNO was found to be at pH ∼ 2.91 and that of LTO to be at pH ∼ 3.20. X-ray photoelectron spectroscopy performed on the surfaces show presence of oxygen groups which may be responsible for the negative zeta potential of the crystals. Self-assembly of nanodiamond particles on LTO and LNO, using nanodiamond colloid, were studied. As expected, high nanodiamond density was seen when self-assembly was done using a positively charged nanodiamond particles. Diamond growth was attempted on the nanodiamond coated substrates but they were found to be unsuitable for direct growth due to disintegration of substrates in diamond growth conditions. A ∼100 nm thick silicon dioxide layer was deposited on the crystals, followed by nanodiamond self assembly and diamond growth. Thin diamond films were successfully grown on both coated crystals. The diamond quality was analysed by Raman spectroscopy and atomic force microscopy.

Magnetoelectric MEMS Magnetic Field Sensor Based on a Laminated Heterostructure of Bidomain Lithium Niobate and Metglas.

Non-contact mapping of magnetic fields produced by the human heart muscle requires the application of arrays of miniature and highly sensitive magnetic field sensors. In this article, we describe a MEMS technology of laminated magnetoelectric heterostructures comprising a thin piezoelectric lithium niobate single crystal and a film of magnetostrictive metglas. In the former, a ferroelectric bidomain structure is created using a technique developed by the authors. A cantilever is formed by microblasting inside the lithium niobate crystal. Metglas layers are deposited by magnetron sputtering. The quality of the metglas layers was assessed by XPS depth profiling and TEM. Detailed measurements of the magnetoelectric effect in the quasistatic and dynamic modes were performed. The magnetoelectric coefficient |α32| reaches a value of 492 V/(cm·Oe) at bending resonance. The quality factor of the structure was Q = 520. The average phase amounted to 93.4° ± 2.7° for the magnetic field amplitude ranging from 12 to 100 pT. An AC magnetic field detection limit of 12 pT at a resonance frequency of 3065 Hz was achieved which exceeds by a factor of 5 the best value for magnetoelectric MEMS lead-free composites reported in the literature. The noise level of the magnetoelectric signal was 0.47 µV/Hz1/2. Ways to improve the sensitivity of the developed sensors to the magnetic field for biomedical applications are indicated.

Abnormal Domain Growth during Polarization Reversal in Lithium Niobate Crystal Modified by Proton Exchange

The results of an experimental study of the abnormal domain structure kinetics in lithium niobate single crystals with a surface layer modified by soft proton exchange are presented. Domain switching in a wide field range allowed two qualitatively different types of domain structure evolution to be revealed: (1) the traditional growth of hexagonal domains in fields higher than 21.5 kV/mm and (2) the abnormal growth of stripe domains oriented along the Y crystallographic directions in the field range from 3.8 to 21.5 kV/mm. The stripe domains had a width up to 4 µm and depth up to 30 µm. It was shown that the time dependence of the total length of stripe domains could be analyzed in terms of the modified Kolmogorov–Avrami approach, taking into account the transition from the one-dimensional β-model to the one-dimensional α-model. The possibility of the controllable creation of a quasi-periodic structure of stripe domains with an average period of 5 µm by a two-stage polarization switching process was demonstrated. The formation and growth of stripe domains were considered in terms of the kinetic approach to the evolution of the domain structure as a result of the domain walls’ motion under inefficient screening conditions caused by the presence of a modified surface layer. The abnormally low threshold fields were attributed to a presence of a “built-in” field facilitating switching, created by a composition gradient induced by soft proton exchange.

Получение серии кристаллов LiNbO3 : Er : Zn различного состава и исследование их оптических и пьезоэлектрических характеристик

New technological approaches to the production of lithium niobate single crystals of double doping LiNbO3 : Er : Zn have been developed. The studies of the optical quality and acoustic characteristics of LiNbO3 : Er : Zn single crystals have been carried out.

Raman scattering of light in single crystals of lithium niobate co-doped with copper and gadolinium

The conditions for the excitation of transverse and longitudinal polar modes in the processes of Raman scattering in lithium niobate single crystals with co-doped with copper and gadolinium are established using a backscattering geometry. A significant increase in the intensity of the Raman lines at 175 and 603 cm−1 was found with an increase in the degree of doping of the crystals with copper due to the photorefractive effect.

Ferroelectric Nanodomain Engineering in Bulk Lithium Niobate Crystals in Ultrashort-Pulse Laser Nanopatterning Regime.

Ferroelectric nanodomains were formed in bulk lithium niobate single crystals near nanostructured microtracks laser-inscribed by 1030-nm 0.3-ps ultrashort laser pulses at variable pulse energies in sub- and weakly filamentary laser nanopatterning regimes. The microtracks and related nanodomains were characterized by optical, scanning probe and confocal second-harmonic generation microscopy methods. The nanoscale material sub-structure in the microtracks was visualized in the sample cross-sections by atomic force microscopy (AFM), appearing weakly birefringent in polarimetric microscope images. The piezoresponce force microscopy (PFM) revealed sub-100 nm ferroelectric domains formed in the vicinity of the embedded microtrack seeds, indicating a promising opportunity to arrange nanodomains in the bulk ferroelectric crystal in on-demand positions. These findings open a new modality in direct laser writing technology, which is related to nanoscale writing of ferroelectric nanodomains and prospective three-dimensional micro-electrooptical and nanophotonic devices in nonlinear-optical ferroelectrics.

Peculiarities of the pyroelectric current generated using a LiNbO3 single crystal driven by low-frequency sinusoidal temperature variation

Lithium niobate (LiNbO3) single crystal is one of the pyroelectric materials, which can be applicable in energy storage and conversion devices. A theoretical and experimental study of the sinusoidal temperature variation of a single crystal of LiNbO3 with ultra-low frequency of 1–80 mHz is presented here. The previously unreported phenomenon of the optimal frequency range with the maximum amplitude of pyroelectric current oscillations is shown. It is noted that the observed effect is very sensitive to the thermal properties of the material. The impact of thermal properties of the crystal on the optimal frequency range is discussed. The accurate calculations of the pyroelectric coefficient using sinusoidal temperature variation are introduced. The observed phenomenon can be applied in pyroelectric energy converters and storage devices having a cycle time of 10–1000 s.

Changing of LiNbO3 Raman spectra under external electric field applying

The results of investigating the effect of an external electric field on the Raman spectrum of the Y-cut of a lithium niobate single crystal are presented. A change in the intensity and position of individual lines of the Raman spectrum that is associated with a change in the parameters of the crystal lattice due to the reverse piezoelectric effect is found. A change in the intensity and a shift in the spectral lines caused by local inhomogeneities of the lithium niobate single crystal have been also observed. In order to determine what contribution each of these effects makes to the change in the Raman spectra, the principal components analysis has been used in the analysis of experimental data.

Ultrahigh Carrier Mobilities in Ferroelectric Domain Wall Corbino Cones at Room Temperature.

Recently, electrically conducting heterointerfaces between dissimilar band insulators (such as lanthanum aluminate and strontium titanate) have attracted considerable research interest. Charge transport and fundamental aspects of conduction have been thoroughly explored. Perhaps surprisingly, similar studies on conceptually much simpler conducting homointerfaces, such as domain walls, are not nearly so well developed. Addressing this disparity, magnetoresistance is herein reported in approximately conical 180° charged domain walls, in partially switched ferroelectric thin-film single-crystal lithium niobate. This system is ideal for such measurements: first, the conductivity difference between domains and domain walls is unusually large (a factor of 1013 ) and hence currents driven through the thin film, between planar top and bottom electrodes, are overwhelmingly channeled along the walls; second, when electrical contact is made to the top and bottom of the domain walls and a magnetic field is applied along their cone axes, then the test geometry mirrors that of a Corbino disk: a textbook arrangement for geometric magnetoresistance measurement. Data imply carriers with extremely high room-temperature Hall mobilities of up to ≈3700 cm2 V-1 s-1 . This is an unparalleled value for oxide interfaces (and for bulk oxides) comparable to mobilities in other systems seen at cryogenic, rather than at room, temperature.