Fourier Transform Infrared Absorption Spectra Research Articles

In Situ Synthesis of PVA-PAA-HA Interpenetrating Composite Hydrogel

A composite hydrogel with interpenetrating network structure was prepared via in-situ synthesis of calcium phosphates during the physical-chemical crosslinking of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA). The hydrogel water content was tested. Fourier transform infrared absorption spectrum (FT-IR), X-ray diffraction and scanning electron microscopy were employed to evaluate the characteristics of the composite hydrogel. The results showed that the composite hydrogel had high water content and that the inorganic phase was poorly crystalline calcium phosphates. FT-IR confirmed that the interpenetrating network structure was formed between PVA and PAA. The chemical interactions between inorganic and organic phases were further investigated and discussed. The composite hydrogel with an interpenetrating network achieved using the present novel method could be a promising material for tissue engineering.

Microstructural Evolution of Thermally Treated Low-Dielectric Constant SiOC : H Films Prepared by PECVD

Low-dielectric constant amorphous- films were prepared by using plasma-enhanced chemical vapor deposition technique and then treated in vacuum at temperatures ranging between 400 and 900°C for 30 min. The evolution of the film microstructure was investigated by means of vibrational spectroscopy, i.e., by Raman scattering and Fourier transform infrared (FTIR) absorption. FTIR absorption spectra consist of several vibrational bands: namely, Si–O–Si rocking at , Si–O–Si asymmetric stretching at , symmetric deformation of – group in configuration at , C–H stretching of – groups in the region between 2750 and , and –OH related vibrational bands in the range between 3150 and . On annealing the samples up to 500°C, it is observed that both spectral shape and intensity exhibit minor changes with increasing temperature, indicating that this material exhibits a good thermal stability. In samples undergoing thermal treatments at temperatures higher than 500°C a progressive hydrogen release occurs which is evidenced by the intensity decrease of the related bands. A deeper inspection of the evolution of these spectral features evidenced that thermal treatment of samples induces a preferential release of hydrogen than of – groups, which results in the transformation of – groups into – groups. Raman spectroscopy carried out on the same samples evidences the presence of carbon nanoclusters. In fact, in the films treated at temperatures higher than 500°C both D and G bands, typical of -hybridized carbon, are observed, due to the formation of C–C bonds within the film following the hydrogen release. The intensity of these D and G bands becomes more pronounced in samples annealed at higher temperatures, thus indicating a progressive precipitation of carbon within the amorphous matrix of films. In conclusion, the H-release process is accompanied by a structural rearrangement with the formation of an amorphous silicon oxide matrix, and free-carbon inclusions embedded in it.

Effect of light germanium doping on thermal donors in Czochralski silicon wafers

In this paper, the effect of light Germanium (Ge-) doping on thermal donors (TDs) in Czochralski silicon (CZ-Si) has been investigated by four-point probe and low-temperatures Fourier transform infrared (FTIR) spectrometer. After 650 °C, 30 min annealing to eliminate the grown-in TDs, conventional CZ-Si and germanium-doped CZ-Si (GCZ-Si) samples were further subjected to isothermal annealing at about 450 °C to generate TDs. It was found that Ge-doping suppressed the formation of TDs. Moreover, the low temperature FTIR absorption spectra of the TDs in GCZ-Si were found to agree quite well with that of TDs in CZ-Si, which was not the case for the heavily Ge-doped silicon. Therefore, it is considered that the light Ge-doping suppresses the formation of TDs but does not affect the microscopic structure of TDs.

TR-FTIR absorption spectroscopy of transition metal carbonyl radicals generated by photodissociation of metal–metal bonds, by halogen abstraction or by radical ligand substitution

Three methods of obtaining time-resolved Fourier-Transform infrared (TR-FTIR) absorption spectra of transition metal carbonyl radicals in hexane are reported here. For the first method, CpM(CO) 2L and Cp*M(CO) 2L (M = Mo, W; L = CO, PR 3) radicals have been generated by photodissociation of the corresponding metal–metal bonded dimers. Radicals of formula M(CO) 4L (M = Mn, Re; L = CO, PR 3, AsPh 3, SbPh 3) and CpM(CO) n (M = Fe, Mo; n = 2, 3) have been produced via the second method which is halogen abstraction of the transition metal carbonyl halides using CpMo(CO) 3 radical. For the third method, fast radical ligand substitution kinetics has been exploited to generate CpMo(CO) 2PR 3 radicals from CpMo(CO) 3 in the presence of free phosphines. An assessment of the three methods with respect to TR-FTIR spectroscopic detection of radicals was also discussed.

Interaction of PMMA–silica in PMMA–silica hybrids under acid catalyst and catalyst-less conditions

PMMA–silica hybrids were prepared by the sol–gel process polymerization from methyl methacrylate (MMA) and tetraethyl orthosilicate (TEOS) and hydroxypropyl acrylate (HPA). The mechanisms of interaction between the organic PMMA and inorganic silica in the PMMA–silica hybrids prepared under acid catalyst and catalyst-less conditions were analyzed by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). By FTIR absorption spectra, and XPS spectrum analyses, it was found that the covalent bond (Si–O–C) between the organic component and the inorganic component was formed even under catalyst-less condition. The catalyst had a great influence on yielding Si–O–C bonds.The ratio of the covalent bond, Si–O–C, between the organic component and the inorganic component under the acid catalyst condition was higher than that under the catalyst-less condition. With the results of FTIR and XPS analyses, a chemical reaction process was made clear and with this process the differences of the recation vecocitry, the formation of Si–O–Si bonds and Si–O–C bonds and their amount under the acid catalyst condition and/or catalyst-less condition could be predicted quantatively.

Nano-patterned Growth of Ge Quantum Dots for Infrared Detector Applications

ABSTRACTQuantum dot infrared photodetectors (QDIPs) have been studied widely for normal-incidence infrared detection. The 3D confinement provided by quantum dots allows for the elimination of gratings that are typically required for normal-incidence detection in quantum well infrared photodetectors (QWIPs). Furthermore, the growth of Ge dots on Si substrates offers the potential for integration with existing CMOS platforms. To date, however, Ge QDIPs have typically been grown epitaxially by Stranski-Krastonov growth – producing pancake-like dots with base dimensions of 50-100 nm, heights of 7-10 nm, and an aerial dot density of 109–1010 cm−2. Such dots have poor lateral confinement, causing them to have non-ideal normal-incidence absorption characteristics, similar to quantum wells. In this work, we demonstrate infrared absorption in Ge dots with base dimensions of approximately 15 nm. These dots are epitaxially grown on pre-patterned Si substrates, with an aerial dot density of approximately 1011 cm−2. The substrates are prepared by using diblock copolymers to create a nano-pattern on the substrate surface which is transferred to the substrate by dry etching. The size of this pattern determines the base dimensions of the Ge dots. After growth, these dots are then tested for their infrared absorption properties using Fourier Transform Infrared (FTIR) Spectroscopy. The normal-incidence absorption of the dots can be studied with FTIR by varying the polarization angle of the infrared light. We present FTIR absorption spectra for samples grown with various conditions (e.g., different dot doping levels, numbers of layers, and dot base dimensions) and investigate the effects of different growth conditions on infrared absorption properties. We also report on the normal-incidence absorption characteristics of these dots by presenting absorption spectra for various polarization angles of infrared light.

Leuco Crystal Violet as a Dopant for n-Doping of Organic Thin Films of Fullerene C60

The triphenylmethane dye crystal violet (CV) and its leuco base, leucocrystal violet (LCV), are investigated as dopants for n-type doping of fullerene C60. Conductivities up to 8 × 10-3 S/cm at 30 °C are achieved when C60 is doped with CV. Mass spectroscopy and optical spectroscopy (UV/VIS/NIR absorption and Fourier transform infrared transmission) confirm that the leuco base LCV is formed during sublimation of the cationic CV dye. When the commercially available LCV was directly used as a dopant in C60, a maximum conductivity of 1.3 × 10-2 S/cm was obtained at 30 °C. We found that in both cases, the leuco base became reoxidized to the cationic form by electron transfer to electron-accepting matrixes, leading to the doping effect. The donor properties of LCV in a charge-transfer complex with 7,7,8,8-tetracyanoquinodimethane (TCNQ) were confirmed by UV/VIS/NIR absorption and Fourier transform infrared (FTIR) spectroscopy. C60 anions were observed in the FTIR or NIR absorption spectra of the mixed films of C60 and LCV. Photoinduced charge transfer between LCV and C60 provides free electrons, which increase the n-type conductivity. The electron transfer becomes irreversible by hydride abstraction.

Highly moisture-resistive silicon nitride films prepared by catalytic chemical vapor deposition and application to gallium arsenide field-effect transistors

Moisture resistivity for silicon nitride (SiNx) films prepared by catalytic chemical vapor deposition (Cat-CVD) was examined. SiNx films prepared by Cat-CVD and those by plasma-enhanced chemical vapor deposition (PECVD) were subjected to the pressure cooker test (PCT) in H2O vapor at 2 atm and 121°C for 96 h. It was confirmed after PCT that the intensity of the signal due to Si–O bonds in Fourier-transform infrared absorption spectra remarkably increases for PECVD films although little increase is observed for Cat-CVD films. Low stress of the order of 10 MPa was also obtained for SiNx films prepared by Cat-CVD. SiNx passivation by Cat-CVD brings about low leakage current and high mutual conductance for gallium arsenide self-align-gate field-effect transistors.

Highly moisture-resistive silicon nitride films prepared by catalytic chemical vapor deposition and application to gallium arsenide field-effect transistors

Moisture resistivity for silicon nitride (SiN x ) films prepared by catalytic chemical vapor deposition (Cat-CVD) was examined. SiN x films prepared by Cat-CVD and those by plasma-enhanced chemical vapor deposition (PECVD) were subjected to the pressure cooker test (PCT) in H 2O vapor at 2 atm and 121°C for 96 h. It was confirmed after PCT that the intensity of the signal due to Si–O bonds in Fourier-transform infrared absorption spectra remarkably increases for PECVD films although little increase is observed for Cat-CVD films. Low stress of the order of 10 MPa was also obtained for SiN x films prepared by Cat-CVD. SiN x passivation by Cat-CVD brings about low leakage current and high mutual conductance for gallium arsenide self-align-gate field-effect transistors.

From polymer–metal complex framework to 3D architectures: growth, characterization and formation mechanism of micrometer-sized α-NiS

A complex-ion reaction route under solvothermal conditions was investigated for the preparation of micrometer-sized NiAs-type α-NiS with complex architectures, on the basis of the strategy that the framework structure of PEG-NiCl2 complex could provide orientation for the growth of 3D NiAs-type α-NiS crystals. The as-prepared NiS powders with flower-like architectures were characterized by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet, visible light (UV-Vis) and photoluminescence (PL) spectra. Fourier transform infrared absorption (FT-IR) spectra as functions of temperature were recorded to investigate the coordinative chemical effect in the PEG–NiCl2 complex. When PEG-6000 was substituted with poly(vinyl alcohol) (PVA) or poly(vinyl pyrrolidone) (PVP), two other complex architectures (i.e. tennis-ball shaped or urchin-like) were produced. On the basis of a series of supplementary experiments and the result of FT-IR spectra, it was found that both the framework structure of the polymer–metal complex and the functional groups on the polymers had a considerable effect on the final architectures of α-NiS crystals.

Electrochemical formation and characterization of copper oxygenous compounds in alumina template from ethanolamine solutions

Peculiarities of Cu, Cu(OH) 2, Cu 2O, and CuO a.c. deposition into the porous alumina template from various triethanolamine (TEA) solutions were studied using anodic stripping, Fourier transform infrared (FTIR), XRD and Raman spectroscopy. Copper deposition into the porous alumina template mainly in the metallic form and, as a consequence, coloring them in cherry tints was found only from the acid solutions. The Raman vibrational spectrum of porous alumina a.c. treated in weakly acidic Cu(II)–TEA solutions (pH 4.1–5.3) and colored in greenish tint was found to be consisted of two main peaks located at 519–522 and 613–619 cm −1 what is characteristic of Cu 2O lattice vibrations. The additional peak located at about 365 cm −1 was detected in the spectrum of alumina colored in gray, obtained from neutral to alkaline solutions, what is indicative of CuO codeposition with Cu 2O. These results were confirmed by FTIR and X-ray absorption spectra clearly discernible absorption peaks of Cu 2O, CuO, and Cu(OH) 2 depending on the composition of Cu(II)–TEA solution used.

Fourier-transform infrared spectroscopy of Pediastrum duplex: characterization of a micro-population isolated from a eutrophic lake

Fourier-transform infrared (FTIR) spectroscopy was carried out on single colonies of Pediastrum duplex present in air-dried preparations of mixed phytoplankton samples isolated from a eutrophic freshwater lake. FTIR absorption spectra had 12 distinct bands over the wavenumber range 3300–900 cm−1 which were tentatively assigned to a range of chemical groups, including –OH (residual water, wavenumber 3299 cm−1), –CH2 (lipid, 2924), –C=O (cellulose, 1739), amide (protein, 1650 and 1542), >P=O (nucleic acid, 1077) and –C–O (starch, 1151 and 1077). Measurement of band areas identified residual water, protein and starch as the major detectable constituents. Areas of single bands and combined bands of –CH2, –C–O and >P=O species normalized to protein (to correct for differences in specimen hydration and thickness) showed wide variation between colonies, indicating environmental heterogeneity. Correlation analysis demonstrated close statistical associations between different molecular species. Particularly high levels of correlation between bands 3/4 (CH2), 6/7 (amide) and 8/9 (–CH3) was consistent with their joint origin from the same molecular species. The isolation of bands 11 and 12 in the correlation pattern was confirmed by factor analysis, suggesting that variation in the level of starch is statistically unrelated to other macromolecules being monitored. The use of FTIR spectroscopy to characterize an algal micro-population within mixed phytoplankton has potential for future studies on biodiversity and environmental interactions at the species level.

Study of the Fourier-Transform Infrared Spectra of InAs/GaAs Quantum Dot Superlattices for Far-Infrared Photodetectors

Fourier-transform infrared (FTIR) spectra were studied to characterize the self-assembled InAs/GaAs quantum dot superlattices for long-wavelength infrared photodetectors. The superlattices, grown on (001)-oriented GaAs semi-insulating substrates by a solid-source molecular-beam epitaxy system, are composed mainly of 20 layers of Si-doped (5×1018 cm-3) InAs quantum dot layers and undoped GaAs spacer films. The composition, structural properties and surface morphologies of the InAs quantum dots were evaluated by secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM) and atomic force microscopy (AFM), respectively. The far-infrared absorption signals were observed using the FTIR technique. The analysis of FTIR absorption spectra revealed that the InAs quantum dot superlattices possess an unpolarized absorption feature and only a slight temperature-dependent change of absorption index.

A New, Low-Thermal-Budget Planarization Scheme for Pre-Metal Dielectric Using Electron-Beam Cured Hydrogen Silsesquioxane in Device

Employing an electron-beam (E-beam) cured hydrogen silsesquioxane (HSQ) based inorganic spin-on-glass as a pre-metal dielectric (PMD) material, we developed a simple planarization process with low thermal budget and good planarity in stacked capacitor dynamic random access memory (STC DRAM) device. We observe the basic E-beam cured HSQ film characteristics such as Fourier-transform infrared absorption spectra (FTIR), wet etch rate, film shrinkage, refractive index (RI), X-ray photoelectron spectroscopy (XPS), and electron spin resonance spectroscopy (ESR) in non-patterned wafer. No degradation of device characteristics such as Vth change, hot carrier hardness, and gate oxide quality has been observed. This process resulted in lower leakage current and higher capacitance for Ta2O5 capacitor as well as better planarization performance compared with the conventional undoped silicate glass (USG) etch back process. These results show that E-beam curing process as a low thermal budget PMD scheme would be a promising process for high capacitor dielectric materials.

The Effect of Surface Roughness on Photoluminescence of Porous Silicon

AbstractWe studied the effect of surface roughness of Si wafers on porous silicon by means of photoluminescence (PL), Fourier transformed infrared (FTIR) absorption and Raman spectroscopy. We prepared several kinds of Si wafers with a different surface roughness, and then the anodization was performed at a same condition. PL spectra show a blue shift with the increase of surface roughness. The particle size of porous silicon nanostructure becomes the smaller with increasing surface roughness at the same time. On the other hand, FTIR absorption spectra show no difference regardless of surface roughness. The PL emission dependent on the surface roughness originates from a quantum size effect. We infer that the surface roughness causes the concentration of the current during anodization in the area where the radius of the curvature at the surface is small.

Post-annealing effect in reactive r.f.-magnetron-sputtered carbon nitride thin films

Thin films of CN x were deposited by reactive r.f.-magnetron sputtering on Si(100) substrates. The effect of annealing temperatures on the structural properties of the films has been studied by Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Both FTIR and XPS results show that the population of the C≡N phase decreases upon annealing in a vacuum. The XPS N Is peaks indicate the component due to the C≡N bond to be significantly weaker than the others. An increase of the annealing temperature leads to a more prominent peak corresponding to the C-N phase in the FTIR absorption spectra. These results suggest a substantial decrease of the weakly bound nitrogen and carbon dangling bonds. Electron diffraction measurements reveal the existence of polycrystalline C 3 N 4 structures in films annealed at 700°C in a vacuum. The XPS studies confirmed that these crystalline phases are composed exclusively of carbon and nitrogen.

Crystallization kinetics of a low melting PbO-ZnO-P 2O 5 glass

A low-melting water-resistant 40P 2O 5-50PbO-10ZnO glass with a glass transition temperature T g ≅ 338°C has been prepared. Differential thermal analysis (DTA), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) absorption spectroscopy techniques were applied for both qualitative and quantitative characterization and crystallization of (Pb 5/6Zn 1/6) 3P 4O 13 in glass. Kinetics of crystallization was analyzed based on the Johnson-Mehl-Avrami model. It was found that the surface nucleation mode, having the morphology index n ≅ 1, is dominant. The activation energy of crystallization was found to be 312 kJ mol −1 by a non-isothermal DTA method, while 363 and 344 kJ mol −1 by isothermal XRD and FTIR methods, respectively. These values agree with each other to a reasonable extent. Peak intensity of a specific vibrational mode in FTIR absorption spectra was found to be applicable for quantitative kinetic analysis should suitable calibration using a standard specimen be done.

Free-Electron Laser (FEL) Ablation of Ocular Tissues

The purpose of the present study was to investigate the ablation characteristics of free-electron laser (FEL) pulses at 5.3 μm and 6.0 μm on ocular tissues. The advanced FEL was developed by the Los Alamos National Laboratory. It operates in the 4–7 μm range, with a macropulse duration of 10 μs and repetition rate of 10 Hz. Each macropulse consists of a train of micropulses that are 15 ps in pulse duration separated by 10 ns. The output energy of macropulses can be adjusted from 5 to 120 mJ. Five transplant grade corneal-scleral buttons preserved in corneal storage medium were used. Wavelengths 5.3 and 6.0 μm were selected based on Fourier-transform infrared absorption spectra of a type I collagen film. Ocular tissue cuts made at 6.0 μm revealed a well-defined ablation boundary with a lateral tissue damage at 10±2 μm. The ablation boundary of the corneal cuts made at 5.3 μm revealed tissue disruption with thermally denatured tissue constituents with loss of organised structure. The lateral dimension of this effect extended up to 220 μm. It was concluded first that Fourier-transform infrared absorption spectra may be useful in selecting laser ablation wavelengths, and second that lasers emitting near 6 μm achieve excellent spatial confinement of laser energy secondary to both protein and water energy partitioning. This wavelength may have potential for cutting ocular tissue such as cornea, sclera, vitreous or lens, because of energy partitioning.

Laser-photolysis/time-resolved Fourier-transform absorption spectroscopy: Formation and quenching of HCl(v) in the chain reaction Cl/Cl2/H2

A system to measure time-resolved Fourier-transform infrared absorption spectra of gaseous samples using a commercial step-scan spectrometer is described. To increase the signal intensity, the incident infrared light is multipassed within a White cell. Light from a photolysis laser passes through the reaction cell to initiate the reaction in the flowing gaseous sample. The variation of absorbance is obtained from the ac-coupled signal whereas phase information and a reference spectrum are from the dc-coupled signal. The system is tested by probing the temporal evolution of HCl(v) in the chain reaction of H2 and Cl2 initiated by photolysis at 355 nm. Time-resolved absorption spectra of HCl(v=0–2) were obtained with spectral resolution 0.75 cm−1 and intervals down to 5 μs. Kinetic modeling of deduced temporal profiles of HCl(v=0–2) yields rate coefficients of (1.38±0.04)×10−14 and (5.8±0.4)×10−15 cm3 molecule−1 s−1 (in which error limits represent only the uncertainty of the fit) for reactions Cl+H2→HCl(v=0)+H and Cl+H2→HCl(v=1)+H, respectively; the total rate coefficient is in agreement with previous kinetic measurements.

In Situ Fourier Transform Infrared Measurements of Si Surface and Bulk Plasmas in Cl2/O2 and HBr/O2 Electron Cyclotron Resonance Plasma Etching: Influence of Oxygen on Reaction Products

In situ Fourier transform infrared (FTIR) absorption spectroscopy, electrostatic probe measurements and optical emission spectroscopy have been used to investigate reaction products during Si etching in HBr/O2 electron cyclotron resonance plasmas, in comparison with the results obtained in Cl2/O2 plasmas. In HBr/O2 plasmas, the plasma parameters were found to be almost constant within the range of the percentage of O2 gas flow rate to total gas flow rate of 0–10% by electrostatic probe measurements. The ratio of emission intensity of O atom to that of Br atom during Si etching was almost the same as that during SiO2 etching, while the ratio of emission intensity of O atom to that of Cl atom during Si etching was much lower than that during SiO2 etching. In FTIR absorption spectra, silicon bromides SiBrx (x=1–4) were not detected in the gas phase during Si etching in HBr/O2 plasmas at the present level of detection. A chemical shift of the position of a peak related to silicon oxides was observed, indicating the existence of silicon oxybromides on the Si surface. On the Si surface, FTIR absorption spectra revealed asymmetric Si–O stretching vibrational mode after Si etching even in pure HBr plasmas. Thus, Si etching mechanisms in HBr/O2 plasmas were considered to be different from those in Cl2/O2 plasmas.