Stretching Mode Absorption Research Articles

Quantitative analysis of boron–hydrogen pair dynamics by infrared absorption measurements at room temperature

The ability of hydrogen quantification in crystalline silicon in concentrations as low as 1014cm−3 becomes fairly important in regard to hydrogen-related degradation phenomena in silicon devices generally and solar cells particularly. The method presented here allows for direct boron–hydrogen pair quantification and, therefore, allows inference on total hydrogen content. Hydrogen-rich amorphous silicon nitride was deposited on stripes of boron-doped float-zone silicon (1 Ωcm), which were exposed to a rapid high temperature step to introduce relatively high amounts of hydrogen into the wafer. Infrared absorption spectra, which have been corrected for multiple reflection and free-carrier absorption, show absorption related to the boron–hydrogen stretching mode at ν~=1868cm−1 with varying strengths during formation and subsequent dissociation of boron–hydrogen pairs triggered by annealing in the dark at 220°C. Since the measurements were performed at room temperature, this method allows investigations with little effort and standard laboratory equipment. Furthermore, the change in free-carrier absorption (described by Drude’s theory) is used to derive the change in hole concentration concurring with the formation and dissociation of boron–hydrogen pairs. The latter is found to fairly match not only the changing strength in absorption of the stretching mode, but also the change in hole concentration obtained by highly sensitive resistivity measurements. The comparison of stretching mode absorption strength and change in resistivity allows for a calibration of specific absorption, yielding a calibration factor ABH. This calibration was performed with the absorption α [ABHα=(4.2±0.3)×1015cm−1] as well as with the quotient of absorption and wavenumber α/ν~ [ABHα/ν~=(7.8±0.6)×1018cm−2].

Chemometry-assisted Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) method for quantification of a novel antipsychotic agent in pharmaceuticals: A case study on ICH Q 14 concept

A robust and reliable Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) method was developed and validated for the quantification of a novel antipsychotic agent pimavanserin tartarate. A holistic novel concept of Analytical Procedure Development (APD) was implemented for establishing the robust nature of the method while aiming to achieve analytical excellence. Experiment room temperature (°C), number of scans and resolution (cm−1) were identified as the critical method variables for quantitative measurements performed in the 1614 cm−1 region for the carbonyl i.e. CO group stretching mode absorption. Infrared absorption intensity was considered as the critical analytical attribute of the analytical method. Risk-based investigation and optimization exercises revealed that resolution was found significantly affecting the measurements and control strategy was defined to control the variation due to it. The optimized method was validated as per ICH norms for Beer’s range (1.0–3.5 μg/mg), accuracy (>100 %) and precision (RSD < 1 %), LOD (0.5 μg/mg), LOQ (1.0 μg/mg), specificity and selectivity. Further, the design of the experimental approach was implemented for precision studies leading to excellent method preciseness. Overall, this new analytical method effectively identified the various key functional groups of the novel analyte and performed a robust quantification of pimavanserin in pharmaceutical tablets.

Mercury Cyanides and Isocyanides: NCHgCN and CNHgNC as well as NCHgHgCN and CNHgHgNC: Simple Molecules with Short, Strong Hg−Hg Bonds

AbstractMercury atoms, laser‐ablated from an amalgam dental filling target, react with cyanogen in excess argon during condensation at 4 K to form two major products in the 2200 cyanide M−C−N stretching region of the IR spectrum, which were assigned to NCHgCN and NCHgHgCN from their antisymmetric C−N stretching mode absorptions at 2213.8 and 2180.1 cm−1. Two broader bands in the isocyanide region at 2098.2 and 2089.6 cm−1 were assigned to CNHgNC and CNHgHgNC. The N‐bonded isomers were computed to be 603/33 and 823/69 times more intense IR absorbers than the C‐bonded isomers at the CCSD level of theory. The dissociation energy for the NCHg−HgCN molecule into two HgCN molecules was calculated to be 296 kJ mol−1 and that for CNHg−HgNC into two HgNC molecules is 304 kJ mol−1. These simple molecules with two cyanide or two isocyanide ligands have two of the shortest and strongest known Hg−Hg single bonds as the two electronegative CN ligands withdraw antibonding electron density from the bonding region.

Mercury Cyanides and Isocyanides: NCHgCN and CNHgNC as well as NCHgHgCN and CNHgHgNC: Simple Molecules with Short, Strong Hg-Hg Bonds.

Mercury atoms, laser-ablated from an amalgam dental filling target, react with cyanogen in excess argon during condensation at 4 K to form two major products in the 2200 cyanide M-C-N stretching region of the IR spectrum, which were assigned to NCHgCN and NCHgHgCN from their antisymmetric C-N stretching mode absorptions at 2213.8 and 2180.1 cm-1 . Two broader bands in the isocyanide region at 2098.2 and 2089.6 cm-1 were assigned to CNHgNC and CNHgHgNC. The N-bonded isomers were computed to be 603/33 and 823/69 times more intense IR absorbers than the C-bonded isomers at the CCSD level of theory. The dissociation energy for the NCHg-HgCN molecule into two HgCN molecules was calculated to be 296 kJ mol-1 and that for CNHg-HgNC into two HgNC molecules is 304 kJ mol-1 . These simple molecules with two cyanide or two isocyanide ligands have two of the shortest and strongest known Hg-Hg single bonds as the two electronegative CN ligands withdraw antibonding electron density from the bonding region.

Si nanorod length dependent surface Raman scattering linewidth broadening and peak shift

Enhanced Stoke Raman scattering of large-area vertically aligned Si nanorod surface etched by metal-particle-catalytic is investigated. By enlarging the surface area with lengthening Si nanorods, the linear enhancement on Stoke Raman scattering intensity at 520 cm(-1) is modeled to show well correlation with increasing quantity of surface Si dangling bonds. With Si nanorod length increasing from 0.19 to 2.73 μm, the Raman peaks of the as-etched and oxidized samples gradually shift from -4 cm(-1) and from -4.5 cm(-1) associated with their linewidth broadening from 3 to 9 cm(-1) and from 7 to 18 cm(-1), respectively. The peak intensity of Raman scattering signal from Si nanorod could be enhanced with the increase of interaction area as the number of phonon mode directly corresponds to the tetrahedrally coordinated Si vibrations in the bulk crystal lattice. The asymmetric linewidth broadening and corresponding Raman peak shift is affected by the strained Si nanorod surface caused by etching and the crystal quality. Fourier transform infrared spectroscopy corroborates the dependency between nanorod length and Si-O-Si stretching mode absorption (at 1097 cm(-1)) on oxidized Si nanorod surface, elucidating the increased transformation of surface dangling bonds to Si-O-Si bonds for passivating Si nanorods and attenuating Stoke Raman scattering after oxidation.

Annealing studies of substoichiometric amorphous SiOx layers for c‐Si surface passivation

AbstractWe investigate thermal stability of amorphous substoichiometric silicon‐oxide alloys with oxygen concentrations from 0 to 10 at‐%. Annealing experiments, including effective lifetime measurements, hydrogen effusion, and infrared absorption spectroscopy, yield a surface passivation on p‐type float‐zone crystalline silicon wafers with maximum effective lifetimes up to 1.5 ms. The thermal stability of the passivation increases with increasing oxygen concentration of the films. For oxygen concentrations above 5%, we observe a decrease of passivation due to the formation of voids in the material, which shows in a low temperature peak of the H effusion spectra. Annealing leads to a structural transition of the material which is accompanied by an increase in effective lifetime. The stretching mode absorptions of Si– O–Si molecular vibrations near 1000 cm–1 shift towards higher wavenumbers, both with increased oxygen concentration and upon annealing of the films. For increased oxygen concentrations, the Si–H stretching modes shift from predominantly 2000 cm–1 to 2090 cm–1(© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim) (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Reflectance and emission spectroscopy study of four groups of phyllosilicates: smectites, kaolinite-serpentines, chlorites and micas

AbstractCoordinated visible/near-infrared reflectance/mid-infrared reflectance and emissivity spectra of four groups of phyllosilicates were undertaken to provide insights into the differences within and among groups of smectites, kaolinite-serpentines, chlorites and micas. Identification and characterization of phyllosilicates via remote sensing on Earth and Mars can be achieved using the OH combination bands in the 2.2–2.5 μm region and the tetrahedral SiO4 vibrations from ~8.8–12 μm (~1140–830 cm–1) and ~20–25 μm (500–400 cm–1). The sharp and well resolved OH combination bands in the 2.2–2.5 μm region provide unique fingerprints for specific minerals. Al-rich phyllosilicates exhibit OH combination bands near 2.2 μm, while these bands are observed near 2.29–2.31, 2.33–2.34 μm and near 2.35–2.37 μm for Fe3+-rich, Mg-rich and Fe2+-rich phyllosilicates, respectively. When a tetrahedral substitution of Al or Fe3+ for Si occurs, the position of the Si(Al,Fe)O4 stretching mode absorption shifts. Depending on the size of the cation, the Si(Al,Fe)O4 bending mode near 500 cm–1 is split into multiple bands that may be distinguished via hyperspectral remote sensing techniques. The tetrahedral SiO4 vibrations are also influenced by the octahedral cations, such that Al-rich, Fe-rich and Mg-rich phyllosilicates can be discriminated in reflectance and emissivity spectra based on diagnostic positions of the stretching and bending bands. Differences among formation conditions for these four groups of phyllosilicates are also discussed. Hyperspectral remote sensing can be used to identify specific phyllosilicates using electronic and vibrational features and thus provide constraints on the chemistry and formation conditions of soils.

Unraveling the structure of hydrogen bond stretching mode infrared absorption bands: An anharmonic density functional theory study on 7-azaindole dimers

The structure of the linear infrared absorption spectrum of the N-H stretching mode in 7-azaindole dimers is analyzed by quartic anharmonic vibrational force field calculations based on density functional theory. It is demonstrated that a multiple Fermi resonance model including contributions from 12 fingerprint vibrational modes, most of them containing considerable contributions of N-H bending motions, combined with a single low-frequency mode satisfactorily explains the complex line shape of N-H stretching mode absorption band.

Effects of low-fluence swift iodine ion bombardment on the crystallization of ion-beam-synthesized silicon carbide

Ion beam synthesis using high-fluence carbon ion implantation in silicon in combination with subsequent or in situ thermal annealing has been shown to be able to form nanocrystalline cubic SiC (3C-SiC) layers in silicon. In this study, a silicon carbide layer was synthesized by 40-keV C12+ implantation of a p-type (100) Si wafer at a fluence of 6.5×1017 ions∕cm2 at an elevated temperature. The existence of the implanted carbon in Si substrate was investigated by time-of-flight energy elastic recoil detection analysis. The SiC layer was subsequently irradiated by 10–30 MeV I127 ions to a very low fluence of 1012 ions∕cm2 at temperatures from 80 to 800 °C to study the effect on the crystallization of the SiC layer. Infrared spectroscopy and Raman scattering measurement were used to monitor the formation of SiC and detailed information about the SiC film properties was obtained by analyzing the peak shape of the Si-C stretching mode absorption. The change in crystallinity of the synthesized layer was probed by glancing incidence x-ray diffraction measurement and transmission electron microscopy was also used to confirm the results and to model the crystallization process. The results from all these measurements showed in a coherent way that the synthesized structure was a polycrystalline layer with nanometer sized SiC crystals buried in a-Si matrix. The crystallinity of the SiC layer was enhanced by the low-fluence swift heavy ion bombardment and also favored by higher energy, higher fluence, and higher substrate temperature. It is suggested that electronic stopping plays a dominant role in the enhancement.

Assignment of Carbon Chain Molecules in Cryogenic Matrices by Selective Laser-Induced Oxidation

We tested and applied a laser-induced oxidation method for identifying the IR-active stretching mode absorptions of linear C(2)(n)(+1) molecules which have known strong UV-vis absorptions. For this purpose, we trapped the molecules of carbon vapor in non-inert matrices (pure O(2) and Ar-O(2) mixtures) at temperatures providing molecular growth. The matrix was exposed to laser light tuned to the wavelength of the UV-vis transition of a specific carbon species. We observed a bleaching of that UV-vis absorption and a correlated decrease of lines in the IR spectra for C(9), C(11), C(13), C(15), and C(21). The data suggest that the strongest IR absorptions of the C(2)(n)(+1) (n > or = 4) chains form a regular pattern with increasing n. To obtain information about IR absorptions of carbon chain oxides, oxygen matrices with replaced (16)O --> ( 18)O isotopes were applied. Our data revise some of the IR assignments existing in the literature.

Surfactant Removal and Silica Condensation during the Photochemical Calcination of Thin Film Silica Mesophases

The evolution of photochemical surfactant removal and silica condensation from organically templated thin film silica nanocomposites with mesoscopic ordering has been probed using a combined application of Fourier transform infrared (FT-IR) spectroscopy and single wavelength ellipsometry. Thin films of silica nanocomposites were prepared by a previously reported evaporation-induced self-assembly process. Specifically, oxidized silicon and gold substrates were withdrawn at 25 mm/min from a subcritical micelle concentration solution containing an ethylene oxide surfactant as a structure-directing agent and tetraethyl orthosilicate as a silica precursor. Real-time grazing incidence difference FT-IR spectra of the nanocomposite films on gold taken during exposure to short-wavelength ultraviolet light (184-257 nm) show that surfactant removal and silica condensation occur gradually and concomitantly. Surfactant removal and silica reconstructions were found to be nearly complete after 90 min of exposure. Further, a transient feature was observed in the FT-IR spectra around 1713 cm(-1) during the UV exposure process and was assigned to a carbonyl (C=O) stretching mode absorption, reflecting the transient formation of a partially oxidized surfactant intermediate. From these data we propose a stepwise model for surfactant removal from the nanocomposite films. Ellipsometrically determined index of refraction values collected as a function of UV exposure are also shown to support such a stepwise mechanism of surfactant removal from the ordered nanocomposite silica thin film mesophases studied here.

Separation of contributions to the third-order signal: ultrafast frequency-selected vibrational echo experiments on a metalloporphyrin-CO

Abstract One-dimensional and frequency-selected vibrational echo experiments on the CO stretching mode of a metalloporphyrin carbonyl compound (model heme) in poly-methylmethacrylate (PMMA) and in 2-methylteterahydrofuran (2-MTHF) are compared. Spectrally resolving the vibrational echo signal and observing the decay at selected wavelengths, permits the independent detection of the 0–1 and 1–2 vibrational level dephasing dynamics, eliminating cross terms and anharmonic beats. In the high temperature 2-MTHF liquid, 0–1 and 1–2 dephasing dynamics are identical within experimental error. The decays are non-exponential, demonstrating that the CO stretching mode absorption spectrum is not a completely homogeneous, motionally narrowed line.

FTIR stretching-mode measurements and calculations of equal and unequal pairs of SH− and SD− defects in KCI

The fundamental stretching-mode absorption of molecular defects (nSH− or nSD−, where n = 32, 33, 34, 36) in KCI has four clear isotope-split lines. Due to the resonance interaction of the defects in pairs the absorption band of pair defects does not show the same isotope structure. We present here a theoretical approach for studying this phenomenon in KCI:SH:SD. The ions are assumed to preserve the [111] orientation of isolated defects and occupy the nearest neighbour anion sites. The results of the calculation show that the SH− ions in the pair should have parallel or antiparallel directions to agree with the experimental spectrum.

Coherent vibrational ground-state dynamics of an intramolecular hydrogen bond

We present direct evidence for coherent vibrational motions of low frequency in the v=0 ground state of the high-frequency O–D stretching mode of an intramolecular hydrogen bond. Femtosecond mid-infrared pump–probe studies of hydroxy-deuterated 2-(2 ′-hydroxyphenyl)benzothiazole in toluene reveal an oscillatory change of O–D stretching mode absorption persisting for several picoseconds after excitation. An infrared resonantly enhanced stimulated Raman process within the bandwidth of the pump pulse creates a vibrational wave packet which is made up of quanta of a 118 cm −1 mode modulating the length of the hydrogen bond and thus the O–D stretching absorption band.

Anomalous isotope dependence of tunnel splitting of OH(-) and OD(-) defects in KCl and NaCl crystals.

We report low temperature high resolution Fourier-transform infrared stretching mode absorption and dielectric susceptibility measurements of OH(-) and OD(-) defects in potassium chloride and sodium chloride crystals. Although very low concentrated samples have been used in this investigation, we find in all cases significant deviations from the behavior expected for isolated tunneling defects. The most interesting result is the observation that the tunneling of hydroxide and deuteroxide defects in both host crystals exhibits a rather unusual isotope dependence, since the level splitting associated with the tunneling motion of the heavier defect ion OD- is larger than that due to OH- defects.

Structural and electronic differences between deuterated and hydrogenated amorphous silicon

Both as-deposited and plasma-treated hydrogenated and deuterated amorphous silicon (a-Si:H and a-Si:D) films are prepared by plasma-enhanced chemical vapor deposition. Their structural and electronic characteristics are studied and compared. It is found that the deuterium concentration of a-Si:D is higher than the hydrogen concentration of a-Si:H in as-deposited samples, but is less in plasma-treated samples, which is consistent with the photoluminescence spectra. Besides, the proportionality constants relating the integrated stretching mode absorption to the concentrations of Si–D and Si–H bonds were determined, i.e., 1×1020 for Si–D and 6.9×1019 for Si–H, by means of secondary ion mass spectrometry.

Infrared studies of laser induced oxide on (1 0 0) Si and SiGe layers

Oxide layers have been grown on single crystal (1 0 0) Si and SiGe surfaces with exposure to a pulsed UV laser at 266 nm under various controlled environments. During the growth, sample surfaces were first melted by the laser power. Oxygen related species then diffused into the melt. Oxide was formed after the samples re-solidified. Besides the strong stretching mode absorption at 1080 cm −1 (T 2 mode), there was an intense shoulder around 1200 cm −1 (the A 1 mode) in the Fourier transform infrared spectrum, compared to thermal oxide. The relative intensity of the shoulder decreased with ambient water vapor concentration. The porosity of this oxide leads to the intense shoulder and more water vapor incorporation can decrease the porosity. The porous oxide could be annealed to some extent with a high-temperature thermal process. Because the adsorption and diffusion of water molecules to and in melted silicon are easier than oxygen molecules, ambient water vapor can fill the voids in the oxide more efficiently and leads to less significant absorption shoulder than oxygen molecules. Also because the diffusion of water molecules in Ge is faster than in Si, less voids are formed and hence the absorption shoulder is less prominent in SiGe samples.

New Insights into the Phase Behavior of Lipopolymer Monolayers at the Air/Water Interface. IRRAS Study of a Polyoxazoline Lipopolymer

Lipopolymers are lipids with a polymer chain covalently attached to the lipid. We studied the infrared reflection absorption behavior as a function of molecular area of Langmuir monolayers of an ether lipopolymer, DC18Gly-M35 (35 monomer units). A plateau region was observed in the monolayer isotherm. Within this region the CH2 asymmetric and symmetric stretching mode absorptions shifted toward lower absorption frequencies (6 and 4 cm-1, respectively). This indicates that the plateau is accompanied by strong local ordering in the lipopolymer, which contradicts previous suggestions that the plateau correlates with a mushroom−brush transition in the polymer.

Reorientational tunneling and elastic-dipole properties ofOH−andOD−molecular defects in alkali fluorides

A microscopic model of ${\mathrm{OH}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{OD}}^{\mathrm{\ensuremath{-}}}$ molecular defects and their reorientational tunneling has been determined in alkali fluoride crystals, using high-resolution Fourier transform infrared studies of their stretching mode absorptions. In LiF, NaF, and KF hosts, the measured integrated stress dichroisms yield symmetries and values of their elastic dipoles, which are found to be ``disk-shaped'' $〈111〉$ oriented tensors aligning with a Curie law parallel to an applied $〈111〉$ stress. Analyses of the spectral band shapes and their changes under stress alignment and $T$ variation allow us to estimate their tunneling splittings $\ensuremath{\Delta}$ and vibrational lifetimes $\ensuremath{\tau}$. This is best detectable in LiF:${\mathrm{OH}}^{\mathrm{\ensuremath{-}}}$, for which the separation and width of two well-resolved Lorentzian bands at 2--20 K yield $\ensuremath{\Delta}=1.2$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and $\ensuremath{\tau}\ensuremath{\approx}9$ ps. Isotope variation $\mathrm{H}\ensuremath{\rightarrow}\mathrm{D}$ reduces strongly the tunneling splitting by at least a factor of 6 in LiF and NaF. A general model for $〈111〉$ oriented elastic dipole disks with $70\ifmmode^\circ\else\textdegree\fi{}$ tunneling between nearest neighbor orientations is derived which may become valid for ${\mathrm{OH}}^{\mathrm{\ensuremath{-}}}{/\mathrm{O}\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ in all five alkali fluorides.

FTIR Spectroscopy to Monitor OH‐Impurity Interactions in Insulating Crystals

AbstractHydroxyl ion is a common impurity in insulating crystals: by interacting with other impurities, it gives rise to new complexes. The OH‐stretching frequency is a very sensitive probe of the hydroxyl environment. High resolution (0.04 cm_1) FTIR spectroscopy in the temperature range 9–300 K was applied to study the OH‐cation impurity interaction in alkali halides, fluoroperovskites, and sillenites, suitable for optoelectronic applications. Proper thermal treatments and isotopic substitutions allowed to assign the stretching mode absorption lines to the defects in which OH– is embedded and to supply possible models for them. Anharmonicity effect of the OH– ‐stretching modes, monitored by weak overtone lines, were well described in the framework of the Morse model. Electric anharmonicity was also detected. The phonon coupling of the OH–‐stretching mode in different defects was studied by analysing the temperature dependence of the line‐position and ‐width: in most cases the single‐phonon coupling model accounted for the experimental data and supplied the coupled phonon frequencies.