IR Absorption Spectroscopy Research Articles

Compositional Homogeneity and Optical Properties of Stoichiometric Lithium Niobate Crystals of Various Geneses

It is shown that the method of high temperature top-seeded solution growth (HTTSSG) can be used to obtain near stoichiometric LiNbO3 crystals from a congruent melt with the addition of 6.0 wt.% of the K2O flux. The structure of complex defects containing OH− groups in these crystals is close to those in stoichiometric crystals grown from a melt containing ∼ 58.6 mol.% of Li2O. However, the former are significantly superior to the latter in terms of total optical and structural homogeneity. The obtained crystals are studied using laser conoscopy, photoinduced light scattering, measuring the fundamental absorption edge, IR absorption spectroscopy in the region of OH− stretchings, Raman spectroscopy in the region of two-particle states of acoustic phonons with zero total wave vector.

Synthesis of Homogeneous Doping with Zinc Charge of Lithium Niobate and Comparative Study of LiNbO3:Zn Crystals of Different Genesis

Abstract—The congruent charge LiNbO3:Zn (2.44 wt %) was synthesized using precursor Nb2O5:Zn (2.83 wt %) by the method of homogeneous doping. The LiNbO3:Zn crystal (2.12 wt %) was grown from this charge by the Czochralski method. The crystal demonstrates high chemical uniformity of Zn dopant distribution along the growth axis. The same distribution is characteristic of crystals obtained by usual direct doping. The homogeneously doped LiNbO3:Zn crystal (2.12 wt %) and the LiNbO3:Zn (2.02 wt %), LiNbO3:Zn (2.05 wt %), and LiNbO3:Zn (2.12 wt %) crystals close to this composition obtained by method of direct doping, as well as LiNbO(3cong), were compared to study defectiveness and optical and structural homogeneity. The method of IR absorption spectroscopy, photoinduced light scattering, and laser conoscopy were used for the study. All studied crystals show no photorefractive response, as can be seen from photoinduced light scattering. The conoscopic patterns of a crystal LiNbO3: Zn (2.12 wt %, homogeneous doping) are strained, which can be connected with a greater photoinduced ability to scatter light than in other crystals. The ability is caused by microstructures, clusters, and residual domain structures. However IR spectra demonstrate narrowing of bands, which can be explained by the fact that homogeneous doping of a Nb2O5 precursor with zinc contributes to the ordering of the lithium sublattice of a LiNbO3:Zn crystal and ordering of H+ protons compared to the ordering in a LiNbO3cong crystal. This effect is highly unusual at this concentration of the dopant.

SYNTHESIS AND STUDY OF Zn COMPLEXES WITH N'-ACYL-SALICYLHYDRAZIDES

Zn complexes with potentially tridentate (carbonyl and hydroxyl oxygen atoms of the salicylic fragment and nitrogen atom of the amide group) were synthesized by the ligand N'-phthalimido-salicylamide (H2L) and potentially heptadentate (carbonyl and hydroxyl oxygen atoms of the salicylic fragment, two nitrogen atoms of the hydrazide moiety and two oxygen atoms of the carbonyl and carboxyl groups of the maleic fragment) with the ligand N'-maleoal-salicylhydrazide (H4L) with 78% and 86% yield, respectively. The structural features of the N'-phthalimido-salicylamide (H2L) and N'-maleoyl-salicylhydrazide (H4L) obtained were established by IR and 1H and 13C NMR spectroscopy. In the 1H NMR spectra, signals from proton-containing groups are detected in the expected region. Also the structure of the ligands confirms 13C NMR spectroscopy. The yield of ligands is 92% and 95%, respectively. It was found that both ligands, in the conducted synthesis reactions, behave as bidentate, are in the enol form. Ligand-N- (salicylamide) -phthalimide is coordinated with zinc ion through the oxygen atoms of the phenol and nitrogen amide groups. The N’-maleoyl-salicylhydrazide ligand is coordinated with the zinc ion through the oxygen atoms of the salicylic residue and the nitrogen atom of the amide group of the maleic residue. The structures of synthesized Zn coordination compounds with H2L and H4L have been studied by IR and electronic absorption spectrometry, elemental analysis and thermogravimetry. These analyzes helped to establish that the metal ion in complex compounds is bound to two water molecules by a hydrogen bond and forms a distorted octahedral geometry. Coordination with water molecules is also confirmed by the TG curves, in which the first and second stages of weight loss are attributed to the removal of solvent molecules — coordinated water molecules and DMF.

The Photoaddition of a Psoralen to DNA Proceeds via the Triplet State.

Psoralens are natural compounds that serve in the light dependent treatment of certain skin diseases (PUVA therapy). They are DNA intercalators that upon photoexcitation form adducts with thymine bases. For one psoralen derivative, 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT), the photoreactions are characterized here by nanosecond UV-vis and IR absorption spectroscopy. The triplet state of AMT is identified as the reactive one. On the 1-10 μs time scale this local triplet state transforms into a triplet biradical bearing one single bond between the addends. Within ∼50 μs this biradical forms the final adduct featuring a cyclobutane ring. This kinetic behavior is in stark contrast to the closely related photoaddition of two thymine moieties within the DNA. Origins of the differences are discussed.

From Thorium to Plutonium: Trends in Actinide(IV) Chloride Structural Chemistry.

A series of eighteen tetravalent actinide (An = Th, U, Pu) compounds were synthesized from acidic aqueous solutions containing thorium, uranium, or plutonium and a series of protonated nitrogen heterocycles. The compounds were characterized using Raman, IR, and optical absorption spectroscopies. The structures were determined using single-crystal X-ray diffraction and found to consist of [An(H2O)xCly]4-y (x = 4-7 and y = 2-4) or AnCl62- molecular units. Breaks in the structural chemistry of the early actinides were observed, with Th adopting exclusively Th-aquo-chloro species and Pu forming only PuCl62-; U crystallized as both U-aquo-chloro and UCl62-. The relationship between the solid-state structural units and the solution species was interrogated using UV-vis-near-IR absorption spectroscopy. A comparison of the solution and solid-state spectra suggested that, although prevalent in the solid state, particularly for U and Pu, AnCl62- does not exist to an appreciable extent in the reaction solution. Despite the identification of U-aquo-chloro species in solution, there are limited reports of these complexes in the solid state. Isolation of these unique actinide(IV) chlorides as reported in this work may point to the importance of nonbonding interactions in the stabilization and precipitation of AnIV structural units.

Composite films of single-walled carbon nanotubes with strong oxidized graphene: Characterization with spectroscopy, microscopy, conductivity measurements (5–291 K) and computer modeling

The hybridization of 1D carbon nanotubes and 2D graphene family is able to form 3D nanostructures with significantly improved electrical, mechanical and thermal properties, which make them very useful for huge potential applications. In this work the graphene oxide-single walled carbon nanotube (GO-SWNT) hybrids prepared in aqueous suspension and films obtained by vacuum filtration are studied with UV–IR absorption spectroscopy, scanning electron microscopy (SEM) and computer simulation. Low-temperature measurements of conductivity of these films in the temperature range 5–291 K were also performed. For hybrid preparation SWNTs with prevailing content of semiconducting nanotubes (up to 95%) and graphene oxide with small C:O ratio (about 1.3) were selected. SEM analysis of a cutoff of the composite GO-SWNT film showed that the film is formed by composition of thin layers which are preferably located along the surface of the film with laminar, rather dense package. We have found spectroscopic manifestation of the interaction between GO and SWNT in the hybrid, estimated the interaction energy between components, revealed the conductivity in the composite film although in the GO film we have not observed a noticeable conductivity. It was also demonstrated that the behavior of the temperature dependence of the conductivity in the film of pure SWNTs and in the composite one is different. The decrease in the conductivity with lowering of temperature indicates that this dependence is similar with the conductivity observed in semiconducting systems.

The influence of UV light on the azathioprine photodegradation: New evidences by photoluminescence

Abstract In this work, we report a photodegradation process of azathioprine (AZA) highlighted by correlated studies of photoluminescence (PL) and the UV-VIS and IR absorption spectroscopy. The photodegradation process of AZA is observed by the gradual increasing in the intensity of the PL spectrum recorded under the excitation wavelength of 300 nm. This behaviour is accompanied, in the photoluminescence excitation (PLE) spectra, by a gradual intensity decreasing of the PLE band situated in the 250–320 nm spectral range simultaneous with the intensity increasing of the PLE band localized in the 325–425 nm spectral range. Regardless if the immunosuppressive compound is in the state of powder, tablet or solution, the PL and UV-VIS absorption spectroscopy studies have demonstrated that a photodegradation process under UV light takes place. According to the PL studies carried out in ambient and vacuum condition, the photodegradation process of AZA was demonstrated to be influenced by the oxygen from air. The presence of a new IR band with maximum at 1745 cm−1 confirms the AZA photodegradation pathway proposed in this work.

Room Temperature Atomic Layer Deposition of ZnO Observed By in Situ IR Absorption Spectroscopy

Zinc oxide (ZnO) is an attractive material for flexible electronics since it has various merits of nontoxicity, wide bandgap, low resistivity, and a high optical transmittance. The ZnO deposition has been intensively studied as transparent conductive films for the liquid crystal displays and thin film solar cells. Furthermore, ZnO has been used as buffer layers for gas barrier films on organic electronics devices. The ZnO deposition has been already reported by DC magnetron sputtering, chemical vapor deposition (CVD), and metal organic CVD (MOCVD). However, it was difficult to control the film thickness with a nanometer precision. In addition, these require high-temperature treatments exceeding 300 ºC, which might be problems for organic electronics and micromachines. To achieve the room temperature growth with a nanometer scale precision, we developed RT atomic layer deposition (ALD). In this study, we report a new RT ALD with dimethyl zinc (DMZ) and an oxidation gas of plasma excited humidified Ar. We used an in-situ multiple-internal-reflection IR absorption spectroscopy (MIR-IRAS) equipped ALD system to investigate the saturation behavior in precursor adsorption and oxidization. We determined injection conditions of the precursor and oxidization gas for the RT ALD based on the IRAS experiment. The RT ALD of ZnO was performed to confirm the ZnO formation on a silicon substrate. In figure 1, we show ZnO thicknesses as a function of ALD cycle which were measured by spectroscopic ellipsometry. The growth per cycle was estimated as 0.046 nm/cycle. We evaluate its composition by using X-ray photoelectron spectroscopy and confirmed that it was fully oxidized. We assume that the deposited film was amorphous from the X-ray diffraction pattern. In addition, we discuss the reaction mechanism in this ALD with Langmuir equation fitting applied to the saturation curve plotted from the result of IR absorption spectroscopy. We depict the surface reaction scheme of the ZnO RT ALD in this paper. Acknowledgment; This work was partly supported by JST-CREST Grant Number JPMJCR14F3, Japan. It was also partly supported by JSPS KAKENHI Grant Numbers 15H03536 and 16K17494. Figure 1 Growth thicknesses of ZnO as a function of the ALD cycle number. Figure 1

Temperature-Dependent Rate Coefficient for the Reaction of CH3SH with the Simplest Criegee Intermediate

The kinetics of the reaction of the simplest Criegee intermediate CH2OO with CH3SH was measured with transient IR absorption spectroscopy in a temperature-controlled flow reaction cell, and the bimolecular rate coefficients were measured from 278 to 349 K and at total pressure from 10 to 300 Torr. The measured bimolecular rate coefficient at 298 K and 300 Torr is (1.01 ± 0.17) × 10-12 cm3 s-1. The results exhibit a weak negative temperature dependence: the activation energy Ea ( k = Ae- Ea/ RT) is -1.83 ± 0.05 kcal mol-1, measured at 30 and 100 Torr. Quantum chemistry calculations of the reaction rate coefficient at the QCISD(T)/CBS//B3LYP/6-311+G(2d,2p) level (1.6 × 10-12 cm3 s-1 at 298 K; Ea = - 2.80 kcal mol-1) are in reasonable agreement with the experimental results. The experimental and theoretical results of the reaction of CH2OO with CH3SH are compared to the reactions of CH2OO with methanol and hydrogen sulfide, and the trends in reactivity are discussed. The results of the present work indicate that this reaction has a negligible influence to atmospheric CH2OO or CH3SH.

Photoconductive detection of a hydrogen-related donor in SnO2

Hydrogen defects in single-crystalline SnO2 are studied by combined photoconductivity and IR absorption spectroscopy. Our results indicate that a defect with an O–H local vibrational mode at 3272 cm−1 (10 K) is a donor with a level less than 300 meV below the conduction band. Annealing experiments demonstrate that the defect is stable up to approximately 450 °C and therefore may contribute to persistent n-type conductivity of SnO2.

Defect Complexes in Stoichiometric Lithium Niobate Crystals Prepared by Different Processes

Using IR absorption spectroscopy in the stretching region of OH groups and Raman spectroscopy in the region of two-particle states of acoustic phonons, we have demonstrated that high-temperature top-seeded solution growth from a melt of congruent composition containing 6.0 wt % K2O flux in Kristall-2 commercially available growth units makes it possible to obtain nearly stoichiometric LiNbO3 crystals having approximately the same perfection of the proton sublattice as in stoichiometric crystals grown from a melt containing 58.6 mol % Li2O, but considerably surpassing them in general optical and structural homogeneity.

Crystal structures, spectroscopic studies and photodenitrosylation reactions of stereoselectively formed dinitrosyl-molybdenum [Mo(bidentate-N,S)2(NO)2] complexes with 2-pyrimidinethiolate derivatives

For the first time, the cis(NO,NO)-trans(S,S)-[Mo(dapymt)2(NO)2] (dapymt = 4,6-diamino-2-pyrimidinethiolate) (1) and cis(NO,NO)-trans(N,S)-[Mo(dmpymt)2(NO)2] (dmpymt = 4,6-dimethyl-2-pyrimidinethiolate) (2) complexes have been prepared by the reaction of [Mo(NO)2]2+ with thiolate ligands. These complexes were characterized using UV–Vis absorption spectroscopy, IR absorption spectroscopy and X-ray crystallography. The dapymt complex exhibits a trans(S,S)-type configuration similar to that of our briefly reported dinitrosyl complexes cis(NO,NO)-trans(S,S)-[Mo(pymt)2(NO)2] (pymt = 2-pyrimidinethiolate) (3) and cis(NO,NO)-trans(S,S)-[Mo(pyt)2(NO)2] (pyt = 2-pyridinethiolate) (4). The dmpymt complex is a novel example of cis(NO,NO)-trans(N,S) coordination. This new isomer was selectively formed based on the use of a sterically hindered ligand that lacked the ability to form hydrogen bonds. Under ambient light, the prepared dinitrosyl complexes released one of two nitric oxide (NO) molecules to yield the following μ-OH dinuclear complexes: [{(ON)Mo(L)2}(μ-OH)2] (L = dmpymt (2p), pymt (3p), or pyt (4p)). Following irradiation of the parent complex with visible light, one NO ligand was eliminated and the Mo atoms were bridged by two hydroxo ligands to form a symmetric Mo2O2 core. Over time, the complexes exhibited a drastic decrease in absorbance of the MLCT (Mo → π*(NO)) band. It was found that the presence of a pyri(mi)dine nitrogen atom in the ligand was important for this photoreaction. The primary coordination sphere of the central molybdenum ion changed from a six-coordinate geometry to a seven-coordinate geometry, and the coordination geometry around the Mo atom was observed to be that of a distorted pentagonal bipyramid. Further, the oxidation states of the Mo atoms also varied from 0 to +II with this reaction. The E1/2 values of 1–4, [Mo(o-atp-N,S)2(NO)2] (o-atp = o-aminothiophenolate) (5), [Mo(o-ap-N,O)2(NO)2] (o-ap = o-aminophenolate) (6) and [Mo(pic-N,O)2(NO)2] (pic = 2-picolinate) (7)) indicated that the [Mo(NO)2]2+ moiety could be easily oxidized according to the following reaction order: 6 < 5 < 1 < 4 < 2, 3, 7. The E1/2 value of the [Mo(NO)2]2+ moiety in the dinitrosyl complexes is considered to be related to the denitrosylation reaction rate.

Surface reaction kinetics of room temperature atomic layer deposition of ZnO observed by in situ IR absorption spectroscopy

Room temperature (RT) atomic layer deposition (ALD) of ZnO is developed by using a precursor of dimethyl zinc (DMZ) and plasma excited humidified argon. Surface reactions of RT ALD of ZnO are investigated by an in situ observation of multiple internal reflection IR absorption spectroscopy. The saturation condition of DMZ and plasma excited humidified argon is discussed by the IR absorbance spectra measured from the sample surface. In the ALD experiment, the grown film is identified as the fully oxidized ZnO by x-ray photoelectron spectroscopy. The growth per cycle is measured to be 0.046 nm/cycle. In this paper, the authors will discuss the mechanism of surface reaction in the ALD process.

Vibrational and photoluminescence properties of polydiphenylamine doped with silicotungstic acid heteropolyanions and their composites with reduced graphene oxide

In this work, the influence of silicotungstic acid concentration on the diphenylamine (DPA) electropolymerization in the absence and the presence of reduced graphene oxide (RGO) is studied. The optical properties of the composites based on polydiphenylamine (PDPA) doped with the H4SiW12O40 heteropolyanions and RGO are investigated by Raman scattering, IR absorption spectroscopy and photoluminescence (PL). The presence of RGO induces an up-shift of the oxidation maximum of the DPA, as a result of a covalent functionalization process of graphene sheets with the polymer in the doped state. The deposition of PDPA onto RGO sheets surface is confirmed by the Raman scattering studies. Regardless of the H4SiW12O40 concentration, an up-shift of the IR bands from 910 to 1014 cm−1 to ∼920 and 1022 cm−1 is reported as a consequence of the compensation of positive charges of PDPA macromolecular chains with of the H4SiW12O40 heteropolyanions. An enhancement in the absorbance of the IR bands situated in the spectral range 750–1050 cm−1 accompanied of a decrease in the relative intensity of the PL bands of PDPA and their composites with RGO, as increasing the H4SiW12O40 concentration, is reported. In the presence of RGO, a change in the PDPA PL spectra profile is also highlighted.

IR absorption spectroscopy of deposition process of amorphous carbon film due to ethylene plasma

AbstractChanges in chemical states of amorphous carbon film during ethylene (C2H4) plasma in the floating potential were investigated with multiple‐internal‐reflection infrared absorption spectroscopy (MIR‐IRAS) and deposition rates. IRAS spectra showed that the peaks due to the sp3‐CHX were observed, but no peaks due to sp2‐CHX were observed. The deposition rate due to ethylene plasma was nearly twice that due to methane plasma, in the same way that the number of carbons in an ethylene molecule is twice as that in a methane molecule. It is suggested that the film growth due to ethylene plasma is the same manner of that due to methane plasma; the plasma‐generated hydrocarbon species such as C2H3 and C2H5, which are generated in ethylene plasma, are adsorbed on dangling bonds that are generated by hydrogen abstraction from the deposited film surface. As a result, the deposited film is composed of sp3‐hydrocarbon components.

Application of IR spectra of two successive isotope labeled residues to the evaluation of dihedral angles of polyproline II structure

The method to evaluate the dihedral angles of a polypeptide using IR absorption spectroscopy was applied to a polyproline type II (PPII) structure. We have prepared 1PPPPPPG7-NH2 with the two successive residues labeled by 13C18O. The doublet of the 13C18O stretching band due to the two successive labeled residues was observed, which comes from the vibrational coupling between the labeled residues. The differences in the peak wavenumber and the intensity of the doublet band were analyzed using the GF matrix method and ab initio molecular orbital calculations. The obtained dihedral angles of the labeled residues were compared with the reported values.

Effect of surface-bound sulfide on oxygen reduction reaction on Pt: Breaking the scaling relationship and mechanistic insights.

A combined in situ electrochemical attenuated total reflection-surface enhanced IR absorption spectroscopy, microkinetic simulation, and density functional theory calculation study shows that not only can the adsorbed sulfide disproportionally affect the surface binding of OOH* (EOOH* ) vs OH* (EOH* ), i.e., breaking the original scaling relationship of pure metals (Ir, Pd, Pt, Au), to enhance oxygen reduction reaction (ORR) activity but can also be used as a reaction pathway alternating species to help deepen our mechanistic understanding of ORR.

Optical Properties and Defects of Congruent Crystals of Doubly Doped Lithium Niobate

The effect of complex defects, associated with the presence of protons, on the optical characteristics of LiNbO3:Y(0.24):Mg:(0.63 wt.%) and LiNbO3:Gd(0.25):Mg(0.75 wt.%) crystals was investigated by IR absorption spectroscopy in the region of the stretching vibrations of the OH groups, by photoinduced and Raman light scattering, and by laser conoscopy. It was shown that the LiNbO3:Y(0.24):Mg:(0.63 wt.%) crystal has a larger photorefraction effect than the LiNbO3:Gd(0.25):Mg(0.75 wt.%) crystal and a congruent crystal. It was found that the speckle structure in the indicatrix of photoinduced light scattering for the LiNbO3:Y(0.24):Mg:(0.63 wt.%) crystal appeared anomalously quickly (<1 s).

IR Absorption Spectroscopy of Deposition Process of Amorphous Carbon Film due to Ethylene Plasma

IR Absorption Spectroscopy of Deposition Process of Amorphous Carbon Film due to Ethylene Plasma

Defect Complexes and Optical Properties of Doubly Doped Lithium Niobate Crystals

The effect of defect complexes related to the presence of protons on the optical properties of LiNbO3:Y(0.24):Mg(0.63) and LiNbO3:Gd(0.25):Mg(0.75) (wt %) crystals has been studied using IR absorption spectroscopy, photoinduced light scattering, and laser conoscopy. The results indicate that the absorption bands at frequencies of 3483 and 3486 cm–1 correspond to vibrations of a V Li - –OH− defect complex. To a Mg Li + - Mg Nb 3- –OH−defect complex in the LiNbO3:Gd(0.25):Mg(0.75) crystal correspond bands at frequencies of 3526 and 3535 cm–1. In the LiNbO3:Y(0.24):Mg(0.63) crystal, we have detected an anomalous opening of the speckle structure of the photoinduced light scattering indicatrix.