Proton Exchange Method Research Articles

High-responsivity and high-speed black phosphorus photodetectors integrated with proton exchanged thin-film lithium niobate waveguides.

We present a high-performance broadband (450-1550 nm) black phosphorus photodetector based on a thin-film lithium niobate waveguide. The waveguides are fabricated by the proton exchange method with flat surfaces, which reduces the stress and deformation of two-dimensional materials. At a wavelength of 1550 nm, the photodetector simultaneously achieves a high responsivity and wide bandwidth, with a responsivity as high as 147 A/W (at an optical power of 17 nW), a 3-dB bandwidth of 0.86 GHz, and a detectivity of 3.04 × 1013 Jones. Our photodetector exhibits one of the highest responsivity values among 2D material-integrated waveguide photodetectors.

Short-period domain patterning by ion beam irradiation in lithium niobate waveguides produced by soft proton exchange

The lithium-niobate-based waveguides have emerged as one of the key platforms for enabling integrated optical technologies. The most common method for creating waveguides in lithium niobate is soft proton exchange (SPE) method. The range of the waveguides applications can be expanded further by creation of near-surface periodical structure of stripe ferroelectric domains within a waveguide (periodical poling) to realize various types of nonlinear optical interactions for creation of frequency conversion devices. However, the joint use of these two procedures (SPE and periodical poling) remains a challenging task. In this paper, we propose a focused ion beam (i-beam) periodical poling technique realized after SPE process for creation of an integrated optical frequency conversion device. The choice of i-beam poling parameters is based on the study of the features of domain structure evolution in lithium niobate after SPE process. We have found that SPE process leads to formation of shallow structure of isolated nanodomains. The revealed isotropic domain growth was caused by the sideways domain wall motion by step generation as a result of merging with these nanodomains. This type of domain kinetics is preferable for periodical poling as it decreases the probability of fast merging of stripe domains due to formation of fast domain walls. Eventually, we have created the 1-mm-long 2-μm-period domain structure in a channel waveguide. The obtained second harmonic generation efficiency for pulse pumping at 756 nm was up to 6·107% W−1 cm−2 for average power and 300 % W−1 cm−2 for peak power indicating the high quality of periodical poling.

Optimization of the annealed proton exchange method with controlled annealing for multifunctional integrated optical chip production.

The main objective of our study is to develop a new approach to the annealed proton exchange (APE) method for the fabrication of the multifunctional integrated optical chip (MIOC) used in fiber-optic gyro systems and to eliminate the loss of time and material, especially in mass production applications. In this work, self-polarized waveguides, which are the basic components of a MIOC device, were produced by the APE method and studied. With the developed method, controlled annealing trials have been carried out from a certain region on the LiNbO3 substrate used in waveguide production, and the annealing time specific to the annealing process was determined. By utilizing a special setup for the hot acid process, the proton exchange process was accomplished without a sudden temperature change of the substrate. Using prism coupling measurements of the fabricated waveguides, annealing times were determined to obtain index change values suitable for 45%-50% optical throughput. Mode profiles of devices with high optical throughput that were produced by the proposed method were measured, and it was seen that devices from different proton exchange runs had similar profiles. As a result, many undamaged substrates were fabricated, and their optical quality was found to be within the expected values.

Investigation of near-surface layer dislocation density of lithium niobate single crystal wafers using chemical etching

Using chemical etching it was shown that the density of dislocation in lithium niobate (LN) single crystal wafers is higher near the surface in depth about 20 um than in the depth of crystal. It caused to change of diffusion coefficient during the waveguide formation with proton exchange (PE) method and can increase DC-drift of intensity optical modulators based on PE-waveguides.

Effect of the Structure of the Lithium Niobate Surface Layer on the Characteristics of Optical Waveguides

The surface and surface layer of X-cut plates of congruent lithium niobate (produced by OAO Fomos Materials) have been investigated by structural and optical methods. It is shown that the plate surface is of high optical quality, comparable with that of foreign analogs. The existence of an oxygen-saturated (and, correspondingly, niobium-deficient) damaged surface layer with a depth of up to 20 μm is demonstrated. Ooptical waveguides have been designed based on the investigated crystal using the proton exchange method. The optical characteristics of these waveguides are comparable with those for Crystal Technology lithium niobate crystals; however, the proton exchange and annealing processes should be corrected. A comprehensive analysis of the Fomos Materials samples showed that they can be used to design integrated optical circuit elements for various instrumentation tasks.

Superhydrophilic and underwater superoleophobic Ti foam with robust nanoarray structures of TiO2 for effective oil-in-water emulsion separation

In this work, a superhydrophilic and underwater superoleophobic Ti foam with TiO2 nanoarrays was facilely fabricated via the hydrothermal treatment and proton exchange method. Taking advantages of the constructed hierarchical structures and the high surface energy of TiO2, the Ti foam exhibits excellent superwetting behaviors to water and ultralow oil adhesion property with the underwater oil contact angle (OCA) of 166° and the sliding angle (OSA) lower than 3°. Meanwhile, the as-prepared foam can be applied for separating various oil-in-water emulsions with 99% separation efficiency and high permeation fluxes. Additionally, it performed good anti-fouling and self-cleaning property, which had stable separation performance even for 50 cycles of repeated use. Importantly, the hierarchical structured sample showed outstanding chemical stability and robust mechanical durability under various chemical corrosions, physical abrasion and vibration without obvious reduction of the separation efficiency. It is expected that superhydrophilic Ti foam with nanoarray structures constructed by this facile method would be a practical candidate in oily wastewater purification, due to its excellent wetting property, good self-cleaning capacity, robust mechanical durability, as well as superior chemical stability.

Computational kinetic modeling of the selenol catalytic activity as the glutathione peroxidase nanomimic

Density functional theory and solvent-assisted proton exchange methods have been applied for computational modeling of the catalytic cycle of selenol zwitterion anion from the kinetic and thermodynamic viewpoints. Selenol zwitterion anion has been represented as an effective glutathione peroxidase nanomimic. It reduces peroxides through a three-step pathway. In the first step, seleninic acid is produced through deprotonating of the selenol zwitterion anion in the presence of the hydrogen peroxide. Seleninic acid reacts with a thiol to form selenylsulfide in the second step. In the last step, selenylsulfide is reduced by the second thiol and regenerates selenolate anion through disulfide formation. Selenol zwitterion anion in comparison to more widely studied compounds such as ebselen has a good activity to react with hydrogen peroxide and producing seleninic acid. The energy barrier of this reaction is 11.7kcalmol−1 which is smaller than the reported enzyme mimics. Moreover, the reactions of seleninic acid and selenylsulfide with methanethiol, which is used as a nucleophile, are exothermic by −18.4 or −57.0kcalmol−1, respectively. Based on the global electron density transfer value of −0.507 e from the natural atomic charge analysis, an electronic charge depletion at the transition state (TS), electron-donor substitutions on the selenolate facilitates the reduction reaction, effectively. Finally, the nature of the bond formation/cleavage at the TS has been quantitatively described by using the topological analyses.

Fabrication of Optical Modulator Based on Proton Exchange

<p>For the investigation of optical modulator, the optical wave-guide was fabricated on x-cut LiNbO<sub>3</sub> substrate using proton exchange method with self-aligned electrode. The electrode pattern was designed using a self-aligned thin film electrode method. After proton exchange process, the wave-guide could be prepared by annealing process to control the width and depth of the optical wave-guide. The initial crossover state of the fabricated 1´2 optical switch was observed with controlling the annealing process variables and the structure of self-aligned thin film electrodes. As the results in the present work, the measured cross talk and minimum detectable switching voltage were obtained at the values of -29.5dB and 8.0V, respectively, with good merits.</p>

Properties and Photocatalytic Activity of Rutile TiO$lt;inf$gt;2$lt;/inf$gt; Nanosheets

Rutile TiO2 nanosheets were prepared by Sol-Gel method, proton exchange and delamination method. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), UV-Vis diffuse re- flectance spectroscope, X-ray photoelectron spectroscope (XPS) and photoluminescence (PL). The transference of photogenerated charge carriers was studied. It is revealed that the rutile TiO2 nanosheets (thickness 5 nm) exhibit in- creased specific surface area (185.7 m 2 /g) and enlarged energy band gap, resulting in enhanced redox ability, when compared with rutile TiO2 samples. In addition, the photogenerated charge carriers are able to transfer to the surface of nanosheets, due to their unique structure enabling photogenerated charge carriers to be effective separation during photocatalytic reactions. Therefore, the rutile TiO2 nanosheets can enhance photocatalytic activity. Forthermore, the rutile TiO2 nanosheets exhibite higher photocatalytic activity than rutile and anatase TiO2 samples on the photocata- lytic degradation of 4-chlorophenol under ultraviolet irradiation.

Aqueous acidities of primary benzenesulfonamides: Quantum chemical predictions based on density functional theory and SMD.

Aqueous pK(a) of selected primary benzenesulfonamides are predicted in a systematic manner using density functional theory methods and the SMD solvent model together with direct and proton exchange thermodynamic cycles. Some test calculations were also performed using high-level composite CBS-QB3 approach. The direct scheme generally does not yield a satisfactory agreement between calculated and measured acidities due to a severe overestimation of the Gibbs free energy changes of the gas-phase deprotonation reaction by the used exchange-correlation functionals. The relative pK(a) values calculated using proton exchange method compare to experimental data very well in both qualitative and quantitative terms, with a mean absolute error of about 0.4 pK(a) units. To achieve this accuracy, we find it mandatory to perform geometry optimization of the neutral and anionic species in the gas and solution phases separately, because different conformations are stabilized in these two cases. We have attempted to evaluate the effect of the conformer-averaged free energies in the pK(a) predictions, and the general conclusion is that this procedure is highly too costly as compared with the very small improvement we have gained.

Dependence of Stereoelectronic and Charge Effects on pKa Values of 1,3‐Dithiane‐Derived Sulfides, Sulfoxides, and Sulfones: An Experimental and Computational Investigation

AbstractThe pKa values of conformationally fixed 1,3‐dithianes were investigated with experimental and theoretical methods to gain an insight into the influence of the relative orientation of the acidic proton and the stabilising S=O or S–C bonds. Experimental values were determined with a modification of the spectrophotometric method using overlapping indicators developed by Bordwell; theoretical values were obtained with the proton exchange methods using DFT calculations. It turned out that stereoelectronic stabilisation is important for sulfides and sulfoxides, whereas charge effects become dominant in sulfones. Deprotonation of the equatorial proton is favoured for most of the compounds except for the equatorial/axial bis‐sulfoxide.

Interference Lithography Patterned Nanogratings in LiNbO<sub>3</sub> Fabricated by Dry Etching

Channel waveguides have been fabricated in x-cut lithium niobate (LiNbO3) by proton exchange (PE) method and optically measured. The thickness and the optical constants of the thin PE layer were characterized using a prism coupling technique. The PE area was plasma etched and a 2.775-μm total etching depth was achieved. The measured average etching rate is 92.5 nm/min. One-and two-dimensional dense arrays of LiNbO3 nanostructures have also been fabricated by using interference lithography (IL) and inductively coupled plasma reactive ion etching (ICP-RIE) techniques.Intorduction

Fabrication and characterization of single mode annealed proton exchanged waveguides in -x-cut lithium niobate

Lithium niobate is a key, well-known material in optical communication that maintains its importance due to its high speed in electro-optical modulators and other optical devices. Using a benzoic acid proton exchange method and annealing in wet O2, we have fabricated waveguides along the y-axis of -x-cut lithium niobate substrate. We have optimized proton exchange and annealing time to make waveguides with the highest transmission we observed to date. The optical transmission was measured in waveguides between 3μm and 7μm in width, and 10mm in length. The near-field mode properties of the waveguides were also examined. In addition, we discovered that the transmission through waveguides is reduced by the surface residues which are underestimated in most fabrication processes. This paper outlines the full fabrication process as well as characterization methods in detail, including a supercontinuum laser source.

First Principles pKa Calculations on Carboxylic Acids Using the SMD Solvation Model: Effect of Thermodynamic Cycle, Model Chemistry, and Explicit Solvent Molecules

Aqueous pK(a) values are calculated from first principles for a set of carboxylic acids using the SMD solvation model with various model chemistries, thermodynamic cycles, and treatments of explicit solvation. In all, 108 unique theoretical protocols are examined. The direct (D) and water proton exchange (PX) cycles are trialled along with a new approach, termed the semidirect (SD) cycle. The SD thermodynamic cycle offers some improvements over the D and PX schemes, as it bypasses the gas-phase heterolytic bond dissociation calculation required in the conventional D approach while also avoiding an aqueous OH(-) calculation required by the PX method when using water as the reference acid. With all three cycles, the recommended model chemistry employs M05-2X/cc-pVTZ Gibbs energies of solvation with a single discrete water molecule and a high-level composite method for the gas-phase reaction energies. With the SD cycle, these calculations result in a mean unsigned error of less than 1 pK(a) units, with respective mean signed error and maximum unsigned error of less than 0.5 and 2 pK(a) units. Similar results are obtained with the D and PX cycles, and further improvement is required in both the gas and aqueous phase ab initio energy calculations before we can truly discriminate between the thermodynamic cycles investigated here.

DFT and AIM Study of the Protonation of Nitrous Acid and the pKaof Nitrous Acidium Ion

The gas phase and aqueous thermochemistry, NMR chemical shifts, and the topology of chemical bonding of nitrous acid (HONO) and nitrous acidium ion (H(2)ONO(+)) have been investigated by ab initio methods using density functional theory. By the same methods, the dissociation of H(2)ONO(+) to give the nitrosonium ion (NO(+)) and water has also been investigated. We have used Becke's hybrid functional (B3LYP), and geometry optimizations were performed with the 6-311++G(d,p) basis set. In addition, highly accurate ab initio composite methods (G3 and CBS-Q) were used. Solvation energies were calculated using the conductor-like polarizable continuum model, CPCM, at the B3LYP/6-311++G(d,p) level of theory, with the UAKS cavity model. The pK(a) value of H(2)ONO(+) was calculated using two different schemes: the direct method and the proton exchange method. The calculated pK(a) values at different levels of theory range from -9.4 to -15.6, showing that H(2)ONO(+) is a strong acid (i.e., HONO is only a weak base). The equilibrium constant, K(R), for protonation of nitrous acid followed by dissociation to give NO(+) and H(2)O has also been calculated using the same methodologies. The pK(R) value calculated by the G3 and CBS-QB3 methods is in best (and satisfactory) agreement with experimental results, which allows us to narrow down the likely value of the pK(a) of H(2)ONO(+) to about -10, a value appreciably more acidic than literature values.

Searching for Computational Strategies to Accurately Predict pKas of Large Phenolic Derivatives

Twenty-two reaction schemes have been tested, within the cluster-continuum model including up to seven explicit water molecules. They have been used in conjunction with nine different methods, within the density functional theory and with second-order Møller-Plesset. The quality of the pKa predictions was found to be strongly dependent on the chosen scheme, while only moderately influenced by the method of calculation. We recommend the E1 reaction scheme [HA + OH(-) (3H2O) ↔ A(-) (H2O) + 3H2O], since it yields mean unsigned errors (MUE) lower than 1 unit of pKa for most of the tested functionals. The best pKa values obtained from this reaction scheme are those involving calculations with PBE0 (MUE = 0.77), TPSS (MUE = 0.82), BHandHLYP (MUE = 0.82), and B3LYP (MUE = 0.86) functionals. This scheme has the additional advantage, compared to the proton exchange method, which also gives very small values of MUE, of being experiment independent. It should be kept in mind, however, that these recommendations are valid within the cluster-continuum model, using the polarizable continuum model in conjunction with the united atom Hartree-Fock cavity and the strategy based on thermodynamic cycles. Changes in any of these aspects of the used methodology may lead to different outcomes.

Mesoporous α-MnO 2/Pd catalyst air electrode for rechargeable lithium–air battery

Rechargeable lithium–air battery is studied using Pd/mesoporous α-MnO 2 air composite electrode. In the present work, we have studied the preparation and electrochemical performance of ordered mesoporous α-MnO 2 as a cathode catalyst for rechargeable Li–air batteries. α-MnO 2 was prepared by reduction of KMnO 4 solution in acidic aqueous solution followed by successive proton and alkali-ion exchange method. α-MnO 2 with high surface area of 33–133.0 m 2 g −1 was successively synthesized and used as an electrode catalyst for Li–air battery. It was found that the mixture of Pd and mesoporous α-MnO 2 electrode shows the high activity to oxidation and reduction of Li to form Li 2O 2 or Li 2O. Application of Pd/mesoporous α-MnO 2, which is mixed with teflonized acetylene binder (TAB), for air electrode is effective for decreasing the charge potential and also improved the energy efficiency as well as cyclability.

NANOSCALE ARRAYS IN LITHIUM NIOBATE FABRICATED BY INTERFERENCE LITHOGRAPHY AND DRY ETCHING

Channel waveguides have been fabricated in x-cut lithium niobate (LiNbO3) by proton exchange (PE) method and optically measured. The thickness and the optical constants of the thin PE layer were characterized using a prism coupling technique. The PE area was plasma etched and a 2.775-μm total etching depth was achieved. The measured average etching rate is 92.5 nm/min. One- and two-dimensional dense arrays of LiNbO3 nanostructures have also been fabricated by using interference lithography (IL) and inductively coupled plasma reactive ion etching (ICP-RIE) techniques.

PKa Calculation of Some Biologically Important Carbon Acids - An Assessment of Contemporary Theoretical Procedures.

In this study, the aqueous pKa values for 13 neutral, 10 cationic, and 5 anionic carbon acids, including amino acids, peptides, and related species have been calculated using the high level ab initio composite procedure, G3MP2+//BMK, combined with solvation energies that were calculated using the CPCM-(UAKS/UAHF), COSMO-RS, and SM6 continuum models. The pKas were further calculated using three schemes, namely the direct method and the proton exchange method as well as the inclusion of an explicit solvent water molecule. The results of this study indicate that the direct method is unsuitable for computing the pKa of carbon acids, whereas the other two schemes perform significantly better with varying degrees of success, depending on the charge of the carbon acid. Specifically, the combination of the proton exchange scheme and CPCM-UAKS model performed particularly well for neutral species, with mean absolute deviations (MADs) of ∼1 pKa unit. The ionic species were more problematic, though the combination of the proton exchange scheme and the SM6 and CPCM-UAKS models performed reasonably well for the cationic and anionic acids, respectively. The inclusion an explicit water molecule generally improved the calculated values for anionic carbon acids.

고온 양자교환법으로 제작된 LiNbO3도파로의 굴절률 분포

저손실의 높은 편광 소멸비를 갖는 LiNbO<TEX>$_3$</TEX> 도파로를 만들기 위하여 고온 양자교환 방법을 이용하였다. 이 방법으로 제작된 도파로의 굴절률 특성을 분석하기 위하여 프리즘 결합기 방법으로 도파 모드를 측정하고 IWKB(inverse WKB) 방법을 사용하여 표면 굴절률 변화와 깊이에 대한 굴절률 분포 특성을 관찰하였다. 이러한 방법으로 고온 양자교환법의 주요 인자인 양자교환 온도, LS 농도, 양자교환 시간에 대한 굴절률 변화를 분석하였다. The high temperature proton exchange (HTPE) method was used to fabricate optical waveguides based on LiNbO<TEX>$_3$</TEX>, which gives rise to low propagation loss and high polarization extinction ratio. To characterize the refractive index distribution of the fabricated waveguides, the guided modes of each waveguide were observed using the prism coupling method and then the refractive index profile was calculated by the inverse WKB method with the least square fitting. Finally, we showed how the HTPE parameters such as the temperature of PE, the concentration of lithium additive, and the time of PE effect the refractive index profile.