IR Transmission Spectroscopy Research Articles

IR-active vibrational modes of CdTe, CdSe, and CdTe/CdSe colloidal quantum dot ensembles

The frequencies of the vibrational modes of CdTe and CdSe quantum dots and CdTe/CdSe core/shell nanoparticles prepared by the colloidal chemistry method are determined using IR transmission and IR reflection spectroscopy. The experimental IR transmission spectrum of CdTe and CdSe nanocrystals exhibits a broad minimum located between the frequencies of the transverse (TO) and longitudinal (LO) optical phonons of bulk CdTe and CdSe crystals. The frequencies of the modes for ensembles of CdTe and CdSe quantum dots are considerably shifted toward lower frequencies as compared to those calculated for single quantum dots. This is explained by the dipole-dipole interaction between quantum dots. The frequencies of modes for the structures with core/shell nanoparticles differ little from the calculated frequencies. This suggests a weakening of the interaction in these structures due to the enhancement of dielectric screening.

Two-Phase Coexistence in CMR Manganite Thin Films

The consequence of the metal-insulator coexisting state in CMR manganite thin films in the macroscopic properties has been studied. Conventional transport measurement together with microcontact probe measurement and IR transmission spectroscopy revealed that the two phases coexist even far away from the transition temperature, that the coexistence is very robust, and that the inhomogeneity can be large scale. The use of untextured films allows us to show that the inhomogeneity is not pinned by defects and hence genuine thermodynamic phenomenon.

IR-active vibrational modes of CdTe and CdSe colloidal quantum dots and CdTe/CdSe core/shell nanoparticles and coupling effects

The frequencies of the vibrational modes of CdTe and CdSe quantum dots and CdTe/CdSe core/shell nanoparticles prepared by the colloid chemistry method are determined using IR transmission and IR reflection spectroscopy. The experimental IR transmission spectrum of CdTe and CdSe nanocrystals exhibits a broad minimum located between the frequencies of the transverse optical (TO) and longitudinal optical (LO) phonons of bulk CdTe and CdSe crystals. The frequencies of the modes for ensembles of CdTe and CdSe quantum dots are considerably shifted toward lower frequencies as compared to those calculated for single quantum dots. This is explained by the dipole-dipole interaction between quantum dots. The frequencies of modes for the structures with core/shell nanoparticles differ little from the calculated frequencies. This suggests a weakening of the interaction in these structures due to the enhancement of dielectric screening.

Optical constants of industrial polymers in the IR region

The optical constants have been measured by the techniques of IR transmission and ATR spectroscopy in the range 4000–400 cm−1 for four industrial polymers: polymethyl methacrylate, polystyrene, polyethylene, and polytetrafluorethylene.

Hydrolysis of ZrF 6 2− anions in solutions of copper(II) ammine and synthesis of Cu x Zr(OH) y F z nanolayers by the ionic layering method

The possibility to synthesize M1xM2(OH)yFz nanolayers by the ionic layering method with the use of soluble anionic complexes of metal fluorides was demonstrated. The influence of the concentration and pH of reagent solutions and of the number of ionic layering cycles on the kinetics of layer growth was studied using the example of CuxZr(OH)yFz layers. The composition of the synthesized layers was studied by X-ray photoelectron (XPE) spectroscopy, ellipsometry, and electronic and Fourier transform IR (FT-IR) transmission spectroscopy.

Zr and Hf oxoclusters as building blocks for the preparation of nanostructured hybrid materials and binary oxides MO2–SiO2(M = Hf, Zr)

Silica materials embedding ZrO2 or HfO2 were prepared by copolymerisation of organically modified oxozirconium or oxohafnium clusters M4O2(OMc)12 (M = Zr, Hf and OMc = methacrylate) with (methacryloxymethyl)triethoxysilane or (methacryloxypropyl)trimethoxysilane. Free radical copolymerisation of the oxoclusters bearing 12 methacrylate groups with the methacrylate-functionalized siloxanes allows stable anchoring of the clusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. This route represents a valuable strategy to yield a very homogeneous dispersion of the MO2 precursors inside the silica matrix. The composition and the microstructural features of the starting hybrid gels were studied by solid state 13C and 29Si NMR spectroscopy and FT IR transmission spectroscopy. Their evolution upon mild heating (up to 180 °C) was followed by FT-IR Attenuated Total Reflectance spectroscopy (ATR), while their thermal behaviour was studied by thermogravimetric analysis (TGA). The covalent incorporation of the clusters into the silica hybrid matrix was studied at several temperatures. Through X-Ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) it is demonstrated that temperatures above 800 °C yield binary oxides MO2–SiO2 (M = Zr, Hf). Delayed crystallisation of HfO2 and tetragonal ZrO2 from 450 °C to at least 800 °C was detected, which is ascribed to the presence of a homogeneous dispersion of the guest oxide in the silica matrix.

IR-study of a-SiC x:H and a-SiC xN y:H films for c-Si surface passivation

Amorphous intrinsic silicon carbide (a-SiC x :H(i)) films and amorphous silicon carbonitride (SiC x N y :H) films have been deposited by plasma enhanced chemical vapor deposition from CH 4/SiH 4/(N 2) plasma on n-type (1.5 Ω cm) crystalline silicon (c-Si). These films have evidenced excellent surface passivation properties with a best result for the surface recombination velocity S eff≈2–3 cm s −1 for amorphous SiC x N y :H films, which is the lowest reported value for n-type c-Si with resistivity of 1.5 Ω cm so far. IR transmission spectroscopy was performed to get more detailed information about the structural composition of the films. Integrated absorption of the bands typical for SiC and SiN bonds reveals that N 2 addition to the plasma leads to nitrogen incorporation into the films but also enhances the incorporation of carbon. From IR analysis it is found that the characteristic minimum of the S eff for a certain CH 4/SiH 4 gas flow ratio is not correlated with the bulk properties of the amorphous films. However, first analysis of injection level dependent lifetime measurements indicates that the minimum in S eff is related to good interface properties of the silicon carbon alloy deposited in the composition range of x≈0.2.

Comparative Study of an Anisotropic Polymer Layer by Infrared Spectroscopic Techniques

Infrared spectroscopic ellipsometry (IRSE), reflection absorption IR spectroscopy (RAIRS), IR transmission spectroscopy, and best-fit calculations are applied in a cooperative study to determine the anisotropic optical properties of a thin polyimide layer in the spectral range 4000–500 cm−1. The employed anisotropic uniaxial optical layer model afforded very good agreement between the calculated and the experimental spectra obtained by the different complementary IR methods. The main advantage of IRSE is that it is possible to obtain data for the optical constants and the thickness ( d = 1.81 μm) of the polyimide layer simultaneously within one experiment. From the ellipsometric spectra it was concluded that the layer structure can be regarded as possessing uniaxial symmetry where the layer is isotropic in directions (x, y) parallel to the sample surface. A qualitative determination of the anisotropic parameters of vibrational bands is possible by calculation of the ellipsometric spectra. The evaluation procedure can be improved by evaluation of polarized reflection spectra, provided the reference standard has been calibrated by ellipsometry. The oscillator parameters are then derived more accurately from the separate s- and p-polarized reflection spectra rather than from their ratio, which is measured in ellipsometry.

Covalently bound CdTe nanocrystals

Two different species of CdTe nanocrystals stabilized with thioacids or aminothiols have been prepared. These were used in order to build up a superstructure by covalent binding via an amide bond using water soluble carbodiimides acting as a mediating agent. The resulting structure has been characterized by UV/vis absorption, emission, and IR transmission spectroscopy. The IR spectra indicate the existence of amide bonds between the stabilizing ligands.

Investigation of the Orientation of Amphiphiles in Langmuir-Blodgett Films Using IR Spectroscopy

A facile method for investigating the orientation of amphiphiles in the LB films using IR transmission and reflection-absorption spectroscopy (RAS) was presented. This method does not require the estimation of the enhancement factor in the RAS measurements or that of the difference in quantities of the molecules in the LB films on different substrates. The application of the present method to the actual LB films gave better results compared with the conventional method.

An IR-transmission spectroscopical study of the influence of substrate surface defects on the morphology and the electronic structure of ultrathin Fe grown on MgO(001)

IR broad-band properties are sensitive to electronic transport and charge localization. This allows to investigate the electronic structure of ultrathin metal films by means of IR-transmission spectroscopy. As this electronic structure is determined by the interfaces of the film, the dynamic conductivity also reflects its morphology. We performed in-situ transmission spectroscopy in the middle infrared (MIR) during the evaporation of Fe on MgO(001) at room temperature in ultrahigh vacuum. We varied the quality of the substrate surface by using MgO(001) cleaved in air and cleaved in ultrahigh vacuum. The difference in the thicknesses for the onset of continuous transport properties of the growing films is well detected by their different IR-spectroscopical behavior. For continuous films, we calculate the thickness dependent scattering of electrons and the thickness dependent effective IR-optical oscillator strength from their IR-optical data. For MgO cleaved in air compared with cleavage in ultrahigh vacuum, the continuous thin film model becomes relevant at a smaller thickness, i.e. the substrate is covered faster in this case.

In-situ investigation of Fe ultrathin film growth by infrared transmission spectroscopy

IR-transmission spectroscopy is sensitive to charge transport and charge localization. Applied to low-dimensional metallic systems, this offers the possibility to investigate morphology on a nanometer scale during thin film growth by IR-optical methods. We performed in-situ IR-transmission spectroscopy during deposition of Fe on UHV-cleaved MgO(001) at 313 K and at 121 K. At thicknesses corresponding to a few monolayers of Fe, we find extremely weak IR-absorption that is due to island morphology as known from our previous helium-atom-scattering results for the same system. For complete substrate coverages, the comparison of IR-transmittance with calculations for homogeneous films indicates significant attenuation of IR-absorption due to additional scattering of charge carriers at the irregular surface as a result of preceding island growth.

Mono- and Dinuclear Silica-Supported Titanium(IV) Complexes and the Effect of TiOTi Connectivity on Reactivity

The room-temperature reactions of excess Ti(OiPr)4 with the hydroxyl groups of a nonporous silica yield dinuclear surface complexes regardless of the degree of partial dehydroxylation of the silica. The surface reactions were studied by in situ IR transmission spectroscopy, 13C CP/MAS NMR, GC/MS, and elemental analysis. The spontaneous stoichiometric formation of both 2-propanol and propene during grafting indicates that interaction of Ti(OiPr)4 with the silica surface induces disproportionation of alkoxide ligands with concomitant formation of Ti−O−Ti bridges. A synthetic route to mononuclear silica-supported Ti alkoxide complexes was developed by reaction of grafted amide complexes (⋮SiO)nTi(NEt2)4-n (n = 1 or 2) with alcohols. Subsequent reactions of the mononuclear surface alkoxide complexes with Ti(OiPr)4 yield dinuclear species identical to those prepared by the direct reaction of Ti(OiPr)4 with silica. Both mono- and dinuclear supported alkoxide complexes undergo ligand-exchange reactions with tert-butylhydroperoxide, but only the dinuclear alkylperoxo titanium surface complexes react with cyclohexene to generate cyclohexene oxide.

Adsorbate induced surface resistivity from IR-transmission spectroscopy: oxygen on Fe/MgO(001)

In situ IR-transmission spectroscopy from 1300 cm −1 to 5900 cm −1 was performed on flat iron ultrathin films on MgO(001) in UHV before and after exposure to oxygen. Spectra of pure Fe films show an absorption that is strongly determined by film–surface scattering of charge carriers. The adsorbate induced IR-optical surface resistivity is observed by a significant broadband increase of transmission. Applying a proper description of the frequency dependent electron scattering rate of iron and including Persson's surface resistivity model we succeed in explaining this broadband spectral change. We calculate an electron–adsorbate scattering rate, which leads to reasonable values for the dc conductivity of the investigated ultrathin films and for the electron-hole lifetime of adsorbate motion.

Effect of hydrogen radicals on properties and structure of a-Si1−xCx:H films

We investigated the effect of hydrogen radicals on properties and structure of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films by the use of a preparation system possessing both hydrogen plasma chamber and silane/methane plasma chamber. The deposition rate, the carbon content, the optical band gap and the film structure investigated with IR transmission spectroscopy remained unchanged with changes in rf power on the hydrogen plasma side. However, the refractive index increased with increasing the rf power on the hydrogen plasma side. The Urbach energy decreased from 67 to 53 meV. The photoconductivity of the films prepared with the rf power on the hydrogen plasma side of 100 W was improved to be 3×10−5 S cm−1, which was by about two orders of the magnitude larger than that without hydrogen plasma. For preparing photoconductive a-Si1−xCx:H films, it is important to generate a number of hydrogen radicals and introduce them onto the growing film surface efficiently.

Optical properties and structrue of SiO 2 films prepared by ion-beam sputtering

SiO 2 films were prepared by an ion-beam sputtering (IBS) method and their properties were studied using visible-UV absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and IR transmission spectroscopy. The SiO 2 films prepared with O 2 atmosphere had good transparency in the visible region. Only the XPS signal due to the SiO 2 bond was observed, and the film composition was almost stoichiometric. However, the full widths at half maximum of the XPS peak and each IR band of the SiO 2 films were larger than those of thermally oxidized SiO 2 films. This suggests that the SiO 2 films prepared by the IBS were more disordered than the thermally oxidized SiO 2 films. The IR spectra showed that the structure of the SiO 2 films prepared by the IBS method was mainly coesite like and was different from that of the thermally oxidized SiO 2 which was mainly quartz like.

Annealing of diamond above 800 °C: need for and results of Si3N4 encapsulation

A boron-implanted marker and secondary ion mass spectroscopy analysis were used for diamond etching assessment. Trace amounts of oxygen in argon etch polycrystalline diamond films during annealing at 800 °C. The deposition of a protective PECVD hydrogenated amorphous silicon nitride layer prevents such etching during annealing at least up to 1300 °C. The hydrogen losses of Si 3 N 4 during heating, from 10% after growth to 0.5% at 1000 °C, do not reduce the diffusion barrier efficiency. This is attributed to Si-N bond reconstruction during H effusion. The influence of high temperature annealing on the diamond film was studied by IR transmission spectroscopy and X-ray microanalysis. No carbon compound was found on the diamond surface after annealing and Si 3 N 4 removal. However, a large amount of silicon carbide was observed after annealing above 1100 °C at the interface between the diamond film and the silicon substrate.

Monolayer Formation and Molecular Orientation of Various Helical Peptides at the Air/Water Interface

Ten kinds of helical peptides were synthesized to study interaction between helices in the peptide monolayer formed at the air/water interface. Five of those have a repeating sequence of Ala-Aib and different end groups, other two a repeating sequence of Lys(Z)-Aib, and the rest a repeating sequence of Leu-Aib. All of the peptides take helical conformation in ethanol as confirmed by CD spectroscopy. The surface pressure-area isotherms of the peptide monolayers showed an inflection at the surface area corresponding to the cross section along the helix axis, where the monolayers are considered to collapse. The monolayers were transferred onto substrates and subjected to IR transmission and reflection absorption spectroscopy. By comparison of amide I and II absorbances, the peptides seemed to lie on the substrates. It was concluded that the peptides in the monolayer orient their helical axis parallel to the air/water interface

Deposition and optical properties of amorphous hydrogenated Si xC y layers

Thin films of amorphous hydrogenated silicon-carbon alloys of different compositions were deposited onto silicon and glass substrates by electron cyclotron resonance plasma enhanced chemical vapour deposition using silane and methane as gas precursors. Growth rate dependences were studied for different [ CH] [ CH 4 + SiH 4] gas flow ratios. The films were characterized by optical transmission spectroscopy in the 200–2600 nm wavelength range, Fourier transform IR transmission spectroscopy and Raman spectroscopy. Optical parameters (refractive indices, absorption and extinction coefficients and optical band gap) were extracted from transmission spectra. The refractive index (at wavelength 1300 nm) was found to be between 3.2 and 2.0, and the optical band gap was in the range 1.75 to 2.3 eV, depending on experimental conditions.

Non-isothermal kinetic and thermodynamic study of the decomposition of lead acetate trihydrate

The non-isothermal decomposition of lead acetate trihydrate was studied up to 450°C by means of TG, DTG, DTA and DSC measurements in a dynamic atmosphere of N2 (or dry air).The parent salt was found to undergo melting concurrently with the dehydration process, which takes place in two steps between 30 and 110°C. The anhydrous salt melts at 204°C and later forms two intermediate basic lead acetate salts, namely Pb(CH3COO)2 · PbO (between 230 and 270°C) and Pb(CH3COO)2 · 2PbO (between 275 and 325°C) respectively. The latter basic salt decomposes, between 325 and 380°C in N2 atmosphere, to produce a mixture of PbO and a small amount of metallic Pb. In air, however, the decomposition produces solid PbO only.X-ray powder diffraction and IR transmission spectroscopy were used to identify the solid intermediates and products of the reaction. Gas chromatography was used to identify the volatile products of the decomposition in N2 and in O2. Scanning electron microscopy was also used to investigate the structure changes and possible occurrence of melting during the decomposition.Values of the kinetic (ΔE and ln A) and thermodynamic (ΔH, Cp and ΔS) parameters were calculated for the dehydration and decomposition processes.