Polycrystalline Lithium Niobate Research Articles

Microstructure and characteristics of Zn and Mg-doped LiNbO3 materials for electrochromic devices

In this investigation, polycrystalline targets of lithium niobate (LN), zinc-doped lithium niobate (Zn:LN), and magnesium-doped lithium niobate (Mg:LN) were synthesized utilizing the Hot Isostatic Pressing (HIP) and Cold Isostatic Pressing (CIP) sintering technique. Subsequently, amorphous thin films of LN, Zn:LN, and Mg:LN and electrochromic devices were fabricated via radio frequency (RF) magnetron sputtering. Comprehensive characterization of the microstructure and optoelectronic properties of the targets, films and devices was conducted employing scanning electron microscopy, X-ray diffraction, spectrophotometry, atomic force microscopy, and an electrochemical workstation. Studies have shown that doping with zinc and magnesium enhances the sintering quality of ceramics, reducing lithium vacancies in polycrystalline lithium niobate ceramics. Zinc doping increases the resistance of lithium niobate, whereas magnesium doping introduces a secondary phase that decreases the resistance. The resistances of LN, Zn:LN, and Mg:LN polycrystalline ceramics are 8.35 GΩ, 9.80 GΩ, and 7.61 GΩ, respectively. The doping process refines the growth of the target and film particles, enhancing the microstructural quality. Notably, the ionic conductivity of the Mg:LN film escalates to 1.7 × 10−5 S/cm. Using doped lithium niobate thin films as electrolytes, the electrochromic devices showed a 38 % increase in coloration efficiency and a 46 % improvement in bleaching efficiency, significantly enhancing device performance.

Microdisk resonators with lithium-niobate film on silicon substrate.

In this paper, we report the fabrication of lithium niobate (LN) microdisk resonators on a pulsed-laser deposited polycrystalline LN film on a silicon substrate rather than commercially provide LN film on insulator. The quality factor of these polycrystalline LN microdisks were measured above 3.4×104 in the 1550-nm band. Second harmonic generation was demonstrated in the fabricated microresonators. Because the properties of homemade LN film can be easily tuned by doping various ions, LN devices on homemade LN film may have more flexible functions and broad applications.

Determination of optical parameters of lithium niobate films by srectrophotometry

Lithium niobate films on silicon substrates were synthesized by high−frequency magnetron sputtering of a target. The resultant film was a layer of polycrystalline lithium niobate. By the method of spectrophotometry we obtained the spectral dependences of the reflectance in the wavelength range 300—700 nm at small angles of incidence. The angular dependence of p− and s− polarized light were measured for a discrete set of wavelengths from 300 to 700 nm increments of wavelength 50 nm and increments for angles of 1°. The values of the refractive indicies, film thickness and extinction coefficients were determined using a numerical method for solving inverse problems. As the film is absorbing we accepted the simulation optical system as an isotropic monolayer absorbing film on a semi-infinite absorbing substrate with a sharp interface. Initial approximation for the solution of inverse problems were defined by the methods based on the estimation of the interference extrema position in the reflection-angular spectra. Values of the refractive indicies of the film differ from the values typical for LiNbO3 single crystals obtained both from the reference literature, and by refractive indices direct goniometric method measurements of a certified standard enterprise sample (SES) made from a lithium niobate single crystal. We additionally studied the specimens with X−ray diffraction and scanning probe microscopy. These deviations are attributed to the film inhomogeneity, the presence of the second phase, and disordering of the structure. Inclusions of the second phase in the form of crystallites with a predominant orientation along the Z axis are observed.

Charge phenomena at the Si/LiNbO3 heterointerface after thermal annealing

Polycrystalline lithium niobate (LiNbO3) films were deposited onto Si substrates by radio-frequency magnetron sputtering method in an Ar environment and an Ar+O2 gas mixture. All as-grown films manifested ferroelectric properties with the remnant polarization of Pr = 69μC/cm2 and the internal field of Ei = 2.8 kV/cm. Thermal annealing (TA) of as-grown Si-LiNbO3 heterostructures leads to decrease in the internal field of LiNbO3 films grown in an Ar atmosphere and results in the change of sign of Ei for the films, grown in an Ar+O2 gas mixture. Analysis of the capacitance-voltage and current voltage characteristics of the studied heterostructures revealed that oxygen vacancies and electron trapping on border traps with energy of about Et = 1.7 eV below the conduction band are responsible for this effect. TA results in decline of conductivity of LiNbO3 films, affected by the phonon scattering of electrons, making these films close to single crystal lithium niobate.

Lithium‐Niobate–Silica Hybrid Whispering‐Gallery‐Mode Resonators

Lithium-niobate-silica hybrid resonators with quality factors higher than 10(5) are fabricated by depositing a layer of polycrystalline lithium niobate on the flat top surfaces of inverted-wedge silica microdisk resonators. All-optical modulation with improved performance over silica-only resonators and electro-optic modulation not achievable in silica-only resonators are realized in the hybrid resonators.

Multilayer-MoS2-microsheet/(Nano-Au:LiNbO3) for all-optical tunable metamaterial-induced transparency

All-optical tunable metamaterial-induced transparency is realized using polycrystalline lithium niobate doped with gold nanoparticles and multilayer molybdenum disulfide microsheets as a third-order nonlinear optical material. A low threshold pump intensity of 90 kW cm−2 is obtained based on nonlinearity enhancement associated with the quantum confinement effect, the local-field enhancement effect, and reinforced interaction between photons and the multilayer molybdenum disulfide microsheets. An ultrafast response time of 27.4 ps is maintained owing to the fast relaxation dynamics of bound electrons in the polycrystalline lithium niobate. This work may pave a way for the realization of ultrahigh speed information processing chips based on metamaterials.

Influence of thermal annealing on structural properties and oxide charge of LiNbO3 films

C-oriented polycrystalline lithium niobate (LiNbO3) films have been deposited on Si substrate by the radio-frequency magnetron sputtering method in an Ar atmosphere and Ar + O2 gas mixture. All as-grown LiNbO3 films manifested positive fixed oxide charge regardless of the sputtering conditions. Donor centers are formed in Si substrate because of diffusion of O2 molecules during sputtering process. Thermal annealing (TA) of the deposited films leads to increase in the surface roughness and grain size as well as formation of LiNb3O8 phase in the studied films. Also, TA resulting in the decline of positive oxide charge due to the diffusion of oxygen molecules into LiNbO3 films from air and out-diffusion from Si substrate.

All-optical switching based on a tunable Fano-like resonance in nonlinear ferroelectric photonic crystals

A low-power all-optical switching is presented based on the all-optical tunable Fano-like resonance in a two-dimensional nonlinear ferroelectric photonic crystal made of polycrystalline lithium niobate. An asymmetric Fano-like line shape is achieved in the transmission spectrum by using two cascaded and uncoupled photonic crystal microcavities. The physical mechanism underlying the all-optical switching is attributed to the dynamic shift of the Fano-like resonance peak caused by variations in the dispersion relations of the photonic crystal structure induced by pump light. A large switching efficiency of 61% is reached under excitation of a weak pump light with an intensity as low as 1 MW cm−2.

Low-power and ultrafast all-optical tunable plasmon-induced transparency in plasmonic nanostructures

We report an ultrafast and low-power all-optical tunable plasmon-induced transparency in a plasmonic nanostructure consisting of a gold nanowire grating embedded in a polycrystalline lithium niobate layer, realized based on strong quantum confinement enhancing nonlinearity. The all-optical tunability is realized based on the third-order nonlinear Kerr effect. A shift of 30 nm in the central wavelength of the transparency window is achieved under excitation of a pump light with an intensity as low as 7 MW/cm2. An ultrafast response time of 69 ps is reached because of ultrafast relaxation dynamics of bound electrons in polycrystalline lithium niobate.

Ultrafast all-optical tunable Fano resonance in nonlinear metamaterials

An ultrafast all-optical tunable Fano resonance is realized in a nonlinear metamaterial composed of arrays of asymmetrically split rings etched in a gold film, coated with a polycrystalline lithium niobate layer. The metamaterial has a large optical nonlinearity because of strong nonlinearity enhancement associated with field reinforcement provided by plasmonic resonance, and quantum confinement effect provided by nanoscale crystal grains. A large shift of 23 nm in the Fano resonance wavelength is achieved under excitation of a weak pump light with an intensity of 15 MW/cm2. While an ultrafast response time of 48 ps is also maintained.

Electrical properties of LiNbO3 (electrolyte)/Cu (anode) bi-layers

In this work specific film structures of Li–Nb–O/Li/Li–Nb–O are investigated by AC Impedance Spectroscopy measurements at different temperatures. This gives the opportunity to investigate properties of the material itself and, at the same time, to consider the influence of the grain boundaries on the ionic behavior of the polycrystalline Lithium Niobate. On the other hand, LiNbO3/Li/Cu multi-layers are studied as electrolyte/anode bi-layers and potential parts of “Li-free” microbatteries. The Li deficiency in the as deposited Li–Nb–O films is cured by forming a “sandwich” of Li–Nb–O/Li/Li–Nb–O, which after annealing becomes ionic conductor. The electrical behavior of an annealed film depends on two sources. The first is due to properties of the material itself and the second is based on the network of the grain boundaries. The average size of the grains is strongly influenced by the structure of the ohmic-contact/substrate. The electrical behavior of the electrolyte/anode interface of the “Li-free” structure LiNbO3/Li/Cu/Au is very similar to the impedance measurements of the single LiNbO3 single films. The whole multilayer structure, though, presents a third relaxation time which is consistent of a small resistance. This resistance is independent of temperature and it seems that is due to the metallic interface Li/Cu/Au.

Combinatorial Chemical Vapor Deposition of Lithium Niobate Thin Films

Combinatorial lithium niobate deposition on 150 mm naturally oxidized silicon (100) wafers in a high-vacuum chemical vapor deposition reactor using Li(OBut) and Nb(OEt)4(dmae) is presented. The novel precursor supply system allows individual spatial control of precursors impinging rates on the substrate. This results in variations of the film properties in a single experiment at a certain substrate temperature due to the influence of different precursors flow rates and ratios. It efficiently leads to deposition conditions to achieve highly <001> oriented polycrystalline lithium niobate films.

Infrared induced red luminescence of Eu3+-doped polycrystalline LiNbO3

Polycrystalline lithium niobate powders were prepared by the sol-gel method. Different grain sizes were obtained by controlling the annealing temperature. The Eu3+ ion was used as a luminescent probe of the nonlinear optical properties of the grains. Strong red emission deriving from Eu3+ ions was observed under pulsed infrared laser irradiation at 936.0nm due to absorption of the light produced in the second harmonic generation process. A measurable emission was observed only for grains having a size of the least 200nm, depending on the annealing temperature.