Mid-infrared Absorption Spectra Research Articles

Scanning near-field infrared microscopy and spectroscopy with a broadband laser source

A scanning near-field microscope that allows the fast acquisition of midinfrared absorption spectra is described. The microscope couples the nanoscale spatial resolution of a scanning probe microscope with the chemical specificity of vibrational spectroscopy. Key design elements of the microscope include a tunable broadband infrared light source; an infrared focal plane array-based spectrometer which allows parallel detection of the entire pulse bandwidth (200 cm−1); and a single mode, fluoride glass, near-field probe fabricated with a chemical etching protocol. Infrared transmission images of a micropatterned thin gold film are presented that demonstrate spatial resolution conservatively estimated to be λ/7.5 at 3.4 μm, in the absence of optical artifacts due to topography. Constant height mode images of a polymer nanocomposite demonstrate instrumental sensitivity to fractional transmission changes of 1×10−3. Near-field absorption spectra (λ=3.4 μm) of a 2 μm thick polystyrene film are presented which demonstrate the instrumental sensitivity required for high spatial resolution, near-field absorption imaging. These spectra are acquired in 2 s and indicate a film thickness detection limit for polystyrene of 200 nm. Measurements exploring the coupling between the infrared absorption magnitude and changes in tip–sample separation suggest that near-field absorption imaging is relatively insensitive to topographic artifacts.

Characterization of inorganic and biogenic magnesian calcites by Fourier Transform infrared spectroscopy

The effect of cationic substitution on the mid-infrared absorption spectra of synthetic, and natural inorganic and biogenic MgCO 3-CaCO 3 solid solutions (Mg calcites; space group R3̄c; 0–23 mol% MgCO 3) is investigated, and the results are compared to disordered proto-dolomite (Ca 0.5Mg 0.5CO 3; space group R3̄c), ordered dolomite (Ca 0.5Mg 0.5CO 3; space group R3̄), huntite (Ca 0.25Mg 0.75CO 3; space group R32), and magnesite (MgCO 3; space group R3̄c). The measurements show that significant frequency shifts of the vibrational bands of the carbonate ion group occur as a function of chemical composition. The Mg 2+ content of all Mg calcites correlates linearly with the position of the sharp v4 mode according to: v4 (cm −1) = 39.40 X Mg + 712.20 ( r = 0.97).

A peculiar temperature dependence of infrared absorption spectra of semiconducting BaBiO 3 and Ba 0.93K 0.07BiO 3 crystals

Mid-infrared absorption spectra of BaBiO 3 and Ba 0.93K 0.07BiO 3 crystals were measured in the temperature range 5–500 K. The absorption coefficient in the band gap region for both semiconducting compounds was found to be almost temperature independent below 150 K and to increase substantially upon heating above 150 K. The applicability of bipolaran and exciton models for the explanation of the data is discussed.

Theory of optical spectra in 1D Mott insulators

Optical spectra of one-dimensional Mott insulators including CuO chains are studied theoretically. The midinfrared absorption spectrum has an asymmetric cusp-like singularity. We analyze this spectrum in terms of the phonon-assisted absorption in the quantum spin chain model. A good agreement between theory and experiments is obtained, and the singularity is identified with the van Hove singularity of the des Cloizeaux-Pearson modes.

Phonon softening and MIR absorption in superconducting

The temperature evolution of the far-infrared (FIR) and mid-infrared (MIR) absorption spectra of (2223 phase) superconductors show a large softening of phonon frequencies in the superconducting phase . The onset of the softening is at 130 K which is well above the superconducting transition temperature at 106 K. A change of the MIR absorption near is reported and compared with earlier observations in .

Above Tc phonon renormalization in Bi1.7Pb0.3Sr2Ca2Cu3Ox: an infrared spectroscopic study

The far infrared (FIR) and mid infrared (MIR) absorption spectra of Bi1.7Pb0.3Sr2Ca2Cu3Ox superconductors were recoded in the spectral ranges 220–680 cm−1 and 500–4000 cm−1 at temperatures between 7 K and 300 K, respectively. The phonon signal near 598 cm−1 showed a Lorentzian line profile and its temperature dependence could be analysed in great detail. When the sample was cooled, the frequency softening started well above the superconducting phase transition at 106 K. The overall energy shift was 4 cm−1.

Infrared Absorption Spectra and Their Correlation with the Ti-O Bond Length Variations for TiO2 (Rutile), Na-Titanates, and Na-Titanosilicate (Natisite, Na2TiOSiO4)

The mid-infrared absorption spectra (400–1200 cm−1) of four TiO2-bearing crystalline solids, in the form of rutile (TiO2), Na-titanates (Na2Ti6O13/ Na2Ti3O7), and natisite (Na2TiOSiO4), are presented, providing a clear illustration of their differences in IR band structure (band pattern). Two sharp characteristic peaks of IR absorption bands of natisite have been noted at 725 and 624 cm−1, representing the internal vibration modes of TiO5 (normal) and SiO4 structural units, respectively, and obtainable by comparison with that of Ca-titanosilicate (CaTiOSiO4), NTS glass (Na2O-TiO2-SiO2), and low-cristobalite (SiO2). The tested series of TiO2-bearing crystalline solids has been helpful in presenting a case study in support for the generalization of IR spectra/structure correlations, showing that vibrational spectroscopy can be useful for understanding the crystal chemistry of crystalline solids in terms of the geometric setting of molecular structural units and chemical bonds. It has been qualitatively demonstrated that the Ti-O bond length variations may be broadly correlated with the complexity of IR absorption bands of four TiO2-bearing solids having great diversity in both chemical composition and crystalline structure.

High-pressure synthesis, characterization, and equation of state of cubic C-BN solid solutions.

Synthesis of several samples across the cubic ${\mathrm{C}}_{\mathit{x}}$(BN${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ solid solution (x=0.3--0.33,0.5,0.6) at pressures in excess of 30 GPa and temperatures above 1500 K indicates that they are isostructural with diamond and cubic BN (borazon). Measurement of the lattice parameters of C-BN samples quenched to ambient conditions shows that the solid solution between C (diamond) and cubic BN is nonideal, with unit-cell volumes up to 1% larger than predicted based on ideal mixing (Vegard's law). In addition, we have measured the zero-pressure, 300-K vibrational spectra for ${\mathrm{C}}_{0.3}$(BN${)}_{0.7}$. In the midinfrared absorption spectrum, we observe a reststrahlen band ranging from 1000--1120 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and the Raman spectrum has a longitudinal optic mode at 1323(\ifmmode\pm\else\textpm\fi{}2) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Based on a comparison of the spectrum with that of diamond and cubic BN, we conclude that the bonding in cubic C-BN is partially ionic. In addition to these measurements on quenched samples, we have measured the isothermal bulk modulus of ${\mathrm{C}}_{0.33}$(BN${)}_{0.67}$ by x-ray diffraction through a diamond cell to over 100 GPa at 300 K. The bulk modulus is 355(\ifmmode\pm\else\textpm\fi{}19) GPa, which is lower than those of diamond, cubic BN and the value predicted from ideal mixing between the end members, but is consistent with the nonideal expansion observed for the cubic C-BN lattice parameters.

Determination of Methanol and Methyl tert-Butyl Ether in Gasoline by Infrared Spectroscopy Using the CIRCLE® Cell and Multivariate Calibration

The feasibility of predicting concentrations of methanol and methyl tert-butyl ether (MTBE) in gasolines from the mid-infrared absorption spectra was investigated. The C-O bond stretching band region was related to these oxygenated compounds' levels with the aid of multivariate statistics. The sample spectra were taken with the use of a circular internal reflectance (CIRCLE®) cell. With the use of partial least-squares (PLS) regression a model with 18 samples was built and used to predict a set of 10 gasolines with good agreement. Two additional samples prepared with other brands of gasoline were analyzed with the same model and no matrix effects were found.

Multivariate FTIR analysis of substrates for protein, polysaccharide, lipid and microbe content: potential for solid-state fermentations.

Components of fermentation processes such as protein, polysaccharide and lipid, as well as microbes, such as fungi grown on solid substrates, are difficult to measure in situ. The potential of Fourier Transform Infrared (FTIR) analysis of solid-state fermentations from mid-infrared absorption spectra has been investigated. The problem under consideration was to build a calibration model containing no irrelevant information to enable a multivariate mathematical approach for prediction of component concentrations. Methods for solid sample preparation and preprocessing of FTIR data were developed to assure Beer-Lambert law compliance and produce a well-conditioned multivariate system. The model was tested using composite samples of zein protein, corn starch and azolectin lipid, and corn samples containing known levels of fungal contamination. Preliminary concentration estimates were remarkably close to the correct values, with less than 5% standard error of prediction for all components measured.

Detection of fungal contamination in corn: potential of FTIR-PAS and -DRS

Evaluation of agricultural grains, such as corn, suffers from a lack of techniques that can analyze solid materials. Two techniques, photoacoustic spectroscopy (PAS) and diffuse reflectance spectroscopy (DRS), were coupled to a Fourier transform infrared (FTIR) spectrometer to provide information about the mid-infrared absorption spectra of corn. Spectra generated from corn that was infected with Fusarium moniliforme or Aspergillus flanus, two mycotoxin producers, were dramatically different from those of uninfected corn

Infrared Studies of the Double Acceptor Zinc in Silicon

AbstractIn the present paper, optical absorption studies on the neutral charge state of the double acceptor zinc in silicon are presented. Measurements were carried out in the mid infrared (MIR) and in the near infrared (NIR) region. The MIR absorption spectra show the excitation series of an effective-masslike hole, from which the Zn° level position is calculated to be at Ev + 319. 1 meV. A splitting of the ground state into 3 sublevels is assigned to hole-hole coupling and crystal-field splitting. Absorption spectra obtained in the NIR are interpreted in terms of an A° X-type bound exciton.

Infrared spectra of the natural zeolite heulandite

The mid-infrared (4 000-200 cm-1) absorption spectra, far infrared (400-40 cm-1) absorption spectra, infrared (1 400-200 cm-1) reflection spectra, and Raman spectra (3 600-50 cm-1) were measured at room temperature for polycrystalline heulandite, a natural zeolite from Poonah, India.

Vibrational spectra, electronic transitions and short order structure of rare earth—gallium sulphide glasses

Absorption spectra of chalcogenide glasses of general formula Ln 2S 3-1,8 Ga 2S 3 (Ln = La +3, Ce +3, Pr +3, Nd +3, Gd +3) were investigated from the far infrared to ultra-violet region. Raman spectra were recorded in the 5 cm −1–600 cm −1 range. Vibrational spectra of glasses have been compared with those of polycrystalline compounds Ln 10 3 Ga 6S 14 (Ln = La +3, Ce +3) and Ln 6Ga 10 3 S 14 (Ln = La +3 to Gd +3). From the observed spectra it could be concluded that the short distance order around gallium atom is strongly modified in going from crystalline to glassy state. Electronic transitions of Ce +3, Pr +3 and Nd +3 ions have been also identified in the visible region and in the mid infrared absorption spectra.

Spectres vibrationnels, transitions electroniques et structures a courtes distances dans les verres: Sulfures de terres rares - sulfure de gallium

Absorption spectra of chalcogenide glasses of general formula Ln 2S 3-1,8 Ga 2S 3 (Ln = La +3, Ce +3, Pr +3, Nd +3, Gd +3 were investigated continously from far infrared to ultra-violet region. Raman spectra were recorded in the 5cm −1–600 cm −1 range. Vibrational spectra of glasses have been compared to those of polycrystalline compounds Ln 10 3 Ga 6 S 14 (Ln = La +3, Ce +3) and Ln 6 Ga 10 3 S 14 ( Ln = La +3 to Gd +3) . From the observed spectra it could be concluded that the short distance order around gallium atom is strongly modified in going from crystalline to glassy state. Electronic transitions of Ce +3, Pr +3 and Nd +3 ions have been also identified in the visible region and in the mid infrared absorption spectra.