Fourier Transform Infrared Absorption Spectra Research Articles

In Situ Mass Spectral and Infrared Studies of the Gas‐Phase Evolution and Decomposition Pathways of Cu II ( hfac ) 2: Application in the Development of Plasma‐Assisted Chemical Vapor Deposition of Copper

Results are presented from in situ, real‐time, mass spectral, and infrared studies of the gas‐phase evolution and decomposition pathways of the copper(II) β‐diketonate precursor bis(1,1,1,5,5,5‐hexafluoroacetylacetonato)copper(II),, during plasma‐assisted CVD (PACVD) of copper. Quadrupole mass spectrometry (QMS) investigations focused on determining the ionization efficiency curves and appearance potentials of under real CVD processing conditions. The resulting curves and associated potentials were then employed to identify the most likely precursor decomposition pathways and examine relevant implications for thermal and plasma‐assisted CVD of copper from . The QMS studies were complemented with real‐time Fourier‐transform infrared (FTIR) spectroscopy of the CVD processing environment to establish a basic understanding of plasma effects on copper precursor evolution and decomposition, and to determine optimum plasma CVD processing windows. Real‐time FTIR absorption spectra of the gas‐phase species in the CVD reactor were collected and analyzed for various plasma power densities. Key changes in precursor stretching and bending infrared (IR) bands were subsequently identified through a systematic comparison of the spectra of hydrogen plasma‐exposed , collected as a function of varying plasma power density, and the fingerprint spectra of non‐plasma‐exposed H(hfac) and . The resulting FTIR findings were used to develop optimum plasma processing conditions for providing the high concentration of reactive hydrogen species needed for the clean and efficient reduction of the precursor, without inducing undesirable gas‐phase reactions. The results demonstrated that FTIR does provide a reliable in situ, accurate, and nonintrusive technique for monitoring the gas‐phase evolution of metallorganics and associated reactants in the CVD reactor and allowing critical adjustments for optimal copper film quality.

FT-IR spectrometry in materialography

Fourier transform infrared (FT-IR) spectroscopy was utilized in the analysis of various materials as a complementary technique to scanning electron microscopy during microstructural characterization. Applications included: (1) the identification of resin and filler additives in organometallic cements; (2) differentiation between resin type, and quantification of their degree of conversion; (3) identification of the fracture pathway in resin-bonded glass-filled resin composites; (4) characterization of resin degradation due to air and ethanol exposure; (5) detection of thin lubricating oil films on stainless steel; (6) characterization of the oxidation of stainless steel as a function of temperature and exposure time at room temperature; and (7) characterization of the aqueous corrosion of stainless steel during exposure in 0.1M sodium chloride. The results presented include scanning electron micrographs for the relevant structural details together with the FT-IR absorbance versus wavenumber spectra for the phase or component of interest. FT-IR techniques included diffuse reflectance, microtransmission with the FT-IR microscope, and polarization-modulated external reflection-absorption techniques. The results showed (1) that polymethyl methacrylate and alumina are additives in some dental cements; (2) that one type of bonded composite fractures entirely through the adhesive bonding resin; and (3) that ethanol degradation of resin occurs via an increase in the concentration of carbonyl C  O bonds. The extreme sensitivity with the external reflection technique was demonstrated by (1) the continued detection of thin oil films on polished stainless steel after numerous attempts to wipe the oil from surface; (2) the ability to differentiate the surface of stainless steel due to different exposure times to room temperature air; and (3) the ability to distinguish corroded surfaces after immersion for varying times in a chloride solution.

Rovibrationally resolved, Fourier-transform near infrared spectroscopy of the ν1 and ν2 vibrations of the HCl dimer in a supersonic jet

We have recorded the high-resolution (0.007 cm−1) Fourier-transform near infrared absorption spectrum of the symmetric 35Cl–35Cl, and the mixed 35Cl–37Cl isotopomers of the hydrogen chloride dimer in a supersonic jet. The spectrum was recorded under a low effective rotational temperature (≊20 K). Rovibrational analysis of the observed spectra has been performed for the K″a=0 subbands of the ν+1 and ν−1 perpendicular-type bands centered at 2890 and 2879 cm−1, respectively. The K″a=0 and 1 parallel-type subbands of the ν−2 at 2839 cm−1 and ν+2 at 2857 cm−1 have also been analyzed. Furthermore, we have observed and investigated the (H 35Cl)2ν+1, K″a=1, ΔK=−1 rovibrational transition centered near 2869 cm−1. The results are compared with spectra previously recorded using difference frequency tunable laser spectrometers both in a supersonic slit jet and in an equilibrium gas phase mixture to demonstrate the advantages and limitations of the FTIR technique.

Fourier transform infrared spectroscopic studies of the secondary structure of spectrin under different ionic strengths

Spectrin, a highly dynamic skeletal membrane protein, plays an important role in maintaining the disk biconcave shape of the human erythrocyte. The sequence of spectrin is mostly composed of repeating segments of 106 amino acids which have been proposed to form unique structural domains. Electronic and vibrational circular dichroism and Fourier transform infrared (FTIR) spectroscopy were used as complementary techniques to study the secondary structure of spectrin. The amide I and II regions of the FTIR absorbance spectra were analyzed using partial least-squares analysis. The secondary structure of spectrin under physiological buffer conditions was estimated to be about 70% alpha-helix, 10% beta-sheet, and 20% other. We believe that this is the first detailed experimental evidence of significant beta-sheet content in spectrin secondary structure. The antiparallel beta-sheet SH3 domain in the center of the alpha-subunit in spectrin accounts for only about 1.5% of the total amino acid residues in the dimer. Hydrodynamic studies have shown spectrin to be sensitive to changes in ionic strength and to addition of denaturing agents. Our FTIR results showed that the secondary structure of spectrin treated with detergent or NaOH changed by 10-20%. The Stokes radii of the spectrin samples used for FTIR measurements were found to vary as a function of the ionic strength, but their secondary structures did not change as a function of ionic strength. These results indicate that while the overall hydrodynamic dimension of spectrin depends on the medium ionic strength, the secondary structure remains essentially constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Overgrowth and strain in MBE-grown GaAs/ErAs/GaAs structures

The molecular-beam epitaxial overgrowth of GaAs on single ErAs layers of varying thickness is studied, as well as the growth of, and strain accommodation in, ErAs/GaAs multilayer films on GaAs substrates. Resonant Raman scattering and Rutherford backscattering are used to characterize the crystal quality of overgrown GaAs layers, while Fourier-transform infrared absorption spectra of the crystal-field-split Er 3+ intra 4f-shell transitions, at 1.54 μm, are exploited as a novel probe of strain accommodation in the ErAs layers. Overgrowth of GaAs of good crystal quality on ErAs, as well as growth of ErAs/GaAs multilayer structures, are both demonstrated, but only for ErAs layers less than about 5 monolayers in thickness. Such thin ErAs layers are found to be tetragonally distorted due to elastic strain accommodation. Single buried ErAs films are found to be electrically continuous down to a thickness of 5 monolayers.

Quantitative Estimation of α-Helix Coil Content in Bovine Serum Albumin by Fourier Transform-Infrared Spectroscopy

Heat denaturation of albumin aqueous solution enables us to control the α-helix content to a reasonable level, and denatured albumin, whose conformation is different, can be obtained. Fourier transform-infrared absorption spectra in the amide I, II, and III band regions of these albumins have been measured and compared with each other. As a result, the characteristic frequencies associated with each conformation of α-helix, β-sheet, and random structure have been observed; moreover it has been newly proved that the intensity ratio of the amide II band to the amide I band depends on the α-helix content in albumin. In this paper, we demonstrate that this intensity ratio is very useful for quantitative estimation of α-helix content in albumin and apply this method to analysis of ATR spectra of albumin adsorbed on polyethylene surface.

Infrared Library Search on Principal-Component-Analyzed Fourier-Transformed Absorption Spectra

Fourier-transformed infrared absorption spectra are compressed by principal-component analysis. Searches using the compressed data demonstrate the success of the compression. A search technique utilizing principal components in a prefilter selection produces the most efficient infrared library search method.