Infrared Reflectivity Measurements Research Articles

Effect of ageing on optical and thermal properties of YBa2Cu3O7–δ

Abstract Photoacoustic phase and amplitude spectra of YBa2Cu3O7 – δ samples synthesised 18 years ago were measured and numerically analysed. The value of thermal diffusivity obtained on the aged samples was lower than the values obtained for fresh samples. Far infrared spectra of YBa2Cu3O7 – δ samples synthesised 18 years ago were recorded and analysed enabling determination of reflectivity peak phonon frequencies present at room temperature. X-ray diffraction analysis and far infrared reflectivity measurements enabled determination of a slight change of the oxygen content with time. The YBa2Cu3O7 – δ samples synthesised 18 years ago still remained superconducting, which was confirmed by resistivity measurements of the samples between 50 K and room temperature where the critical temperature was reduced from 93 to 73 K. Atomic force microscopy, scanning electron microscopy and energy dispersive X-ray microanalytical measurements were also performed confirming the composition of the sample.

Carrier concentration and surface electron accumulation in indium nitride layers grown by high pressure chemical vapor deposition

Electronic and structural properties of InN layer grown by high pressure chemical vapor deposition have been studied by high-resolution electron energy loss spectroscopy (HREELS) and room temperature infrared reflection measurements. HREEL spectra after atomic hydrogen cleaning exhibit N–H bending and stretching vibrations with no indications of an indium overlayer or droplet formation. Broad conduction band plasmon excitations are observed centered at 3100–4200cm−1 at various locations across the surface in HREEL spectra acquired with 25eV incident electron energy. The plasmon excitations are shifted about 300cm−1 higher in spectra acquired using 7eV electrons due to higher plasma frequency and carrier concentration at the surface than in the bulk which indicates surface electron accumulation. Infrared reflectance data acquired at various spots across the surface showed a similar variation in bulk plasma frequency. A three phase thin film reflection model fitted to the infrared data yielded carrier concentrations from 8.2×1019to1.5×1020cm−3 and carrier mobilities from 105 to 210cm2∕Vs.

Optical phonons via oblique-incidence infrared spectroscopy and their deformation potentials in In1−xGaxAs

The concentration dependence of optical phonons in In1−xGaxAs epilayers grown by chemical beam epitaxy and lattice matched to InP(100), where the epilayer strain is zero for x=0.46809, has been characterized for 0.25<x<0.8 with polarized far infrared reflectivity measurements at an oblique angle of incidence. In this method, the reflectance spectra contain sharp Berreman peaks exactly at the optic phonon frequencies. For radiation polarized in the plane of incidence (p polarized), Berreman peaks for both transverse optic (TO) and longitudinal optic (LO) modes are observed, whereas for s polarization only TO modes are seen. The derivatives of the measured spectra were fitted to Lorentzian line shapes to evaluate the various phonon modes, which included GaAs-like TO and LO phonons, disorder induced TO and LO modes, and InAs-like TO and LO phonons. The concentration dependences of the phonon frequencies were used to estimate the phonon deformation potentials of the bulk alloy. Indirect evidence is obtained for LO mode repulsion at low x values from the concentration dependences of the GaAs-like modes in both strained and bulk In1−xGaxAs and from an unphysical variation with x of the GaAs-like LO phonon deformation potential.

Infrared absorption in Li-intercalated tungsten oxide

Thin films of amorphous and polycrystalline tungsten oxide were produced by reactive dc magnetron sputtering and nanocrystalline films were deposited by advanced gas evaporation. The films were submitted to electrochemical intercalation of Li ions before infrared reflectance measurements were carried out. For crystalline films, the reflectance in the wavelength region 10–30 μm increases upon intercalation, indicating an increasing free-electron contribution. On the other hand, all the films display an increased absorption at wavelengths less than 10 μm when intercalated. The thermal emittance could be varied from about 0.5 to 0.7–0.75 by intercalation in films with thicknesses in excess of 1 μm. Both absorption and interference contribute to the emittance contrast.

The classical oscillator model and dielectric constants extracted from infrared reflectivity measurements

The theoretical foundation of the classical oscillator model for the dielectric response of doped semiconductors is reviewed and some errors from the literature are pointed out. Four different modifications of the plasma frequency are identified and their physical significance is given. The influence of the dielectric parameters on reflectivity is discussed. Large changes in the dielectric parameters extracted from experimental reflectivity measurements have been reported, when in fact inappropriate or inadequate reflectivity models have been applied.

Frequency selective IR-filter produced by using EB-lithography

This paper reports on the fabrication of Jerusalem cross diplexer by direct write electron beam (EB) lithography followed by reactive ion etching (RIE) on a phosphorus doped polished silicon wafer substrate. Such structures can be used as frequency selective components in visible, microwave and near infra-red wavelength region. Replication of the patterns is accomplished by micron or sub-micron order mould fabricated from the silicon (Si) master. Fourier transform infra-red reflectance (FT-IR) measurements were performed to characterize the structured patterns. The spectral reflectance from these patterns clearly show a reflection dip due to surface plasmon excitation in the near infra-red wavelength at about 1.42 and 2.5 μm, respectively. Potential applications such as antireflection surface (ARS) can be realized.

Experimental observation of photonic and polaritonic gaps in a silica opal

Experimental observations of the simultaneous presence of a polaritonic and a photonic gap in a three-dimensional photonic crystal is reported, to the best of our knowledge, for the first time. The photonic crystal was made of monodispersed silica microspheres sedimented into a face-centered-cubic structure. Silica has a polaritonic gap for wavelengths between 8 and 9.35 microm. Four different sphere sizes were used, with diameters of d=0.49, 0.73, 0.99, and 1.57 microm. The photonic crystals were studied by normal incidence infrared reflectance measurements in the wavelength interval 0.8-12 microm. Four peaks with the a magnitude of approximately 0.6, originating from the periodicity of the crystal, were recorded in the interval between 1 and 4 microm. Another peak, the polaritonic reflectance peak (approximately 0.4), is observed for wavelengths around 9 microm for all four crystals.

Doping dependence of the optical properties of low-dimensional perovskite-relatedLa1−yCayTiO3.4 ± δ

The doping dependence of the optical properties ofLa1−yCayTiO3.4 ± δ crystals was studied by polarization-dependent infrared reflectivity measurements at room temperature.For y<0.2 the optical conductivity spectra reveal a quasi-one-dimensional conducting character, andthe phonon spectra suggest small changes in the crystal structure and effective chargeinduced by the substitution of trivalent lanthanum with divalent calcium. The pronouncedmid-infrared absorption band observed along the conducting direction shifts to lowerfrequencies with increasing electron concentration. The possible origin of the band isdiscussed in terms of polaronic excitations, Mott–Hubbard excitations, phonon-assisted Tit2g d–dtransitions, and charge-transfer (2p–3d) transitions. Among these interpretations the polaron model is mostlikely. La1−yCayTiO3.4 ± δ with y = 0.2 and δ = 0 exhibits an insulating character and a less anisotropic optical response.The observed differences in the electronic and vibrational excitations inLa0.8Ca0.2TiO3.40 compared to the other studied titanates could be due to local changes of the crystalstructure.

Grating-Coupler Assisted Infrared Reflection Absorption Spectroscopy for the Characterization of Organic Thin Films

We demonstrate how grating-coupler assisted infrared reflection absorption spectroscopy can be used to simultaneously determine the chemical identity and relative thickness of organic thin films. With a grating substrate, a threshold anomaly associated with passing off of the -1 diffracted order occurs at grazing angles of incidence, resulting in a sharp absorbance in the infrared. The position of this peak is sensitive to the grating geometry as well as the dielectric environment near its surface. Thus, shifts in the peak position can be used to determine the relative thickness of adsorbed films or quantify molecular adsorption events. To illustrate the characteristics and sensitivity of this phenomenon, several samples were prepared and tested, including self-assembled alkanethiolate monolayers with 11-mercaptoundecanoic acid, 11-mercapto-1-undecanol, decanethiol, and a covalently linked layer of bovine serum albumin on a commercial, gold-coated grating. For these samples, the position of the threshold absorbance peak shifted to lower wavenumbers as film thickness increased, which is consistent with calculated shifts based upon an increasing refractive index at the interface. The sensitivity of this shift was measured to be 3.7 cm(-1) nm(-1). These results illustrate how a grating substrate can be exploited in a standard infrared reflectance measurement to provide additional information about the relative thickness of adsorbed surface films.

Characterisation of YBa2Cu3O6+x films grown by the trifluoro-acetate metal organic decomposition route by infrared spectroscopy

Infrared reflectivity measurements have been performed at T=300 K on c-axis oriented YBa2Cu3O6+x films obtained by deposit of trifluoroacetate precursors on (100)-LaAlO3 single crystalline substrates. A detailed simulation of the infrared spectra acquired on the thin films based on the use of an appropriate complex dielectric function model is proposed here. It allows us to determine with a single experiment the thickness and the residual porosity of the layers. To reinforce the statement of the infrared simulations, the results have been compared with the film porosity obtained by scanning electron microscopy imaging. Moreover the local grain orientation has been checked by polarized Raman microspectroscopy. Finally, the three complementary experimental ways give consistent results that justify the present approach.

Multivariate Curve Resolution Applied to Infrared Reflection Measurements of Soil Contaminated with an Organophosphorus Analyte

Multivariate curve resolution (MCR) is a powerful technique for extracting chemical information from measured spectra of complex mixtures. A modified MCR technique that utilized both measured and second-derivative spectra to account for observed sample-to-sample variability attributable to changes in soil reflectivity was used to estimate the spectrum of dibutyl phosphate (DBP) adsorbed on two different soil types. This algorithm was applied directly to measurements of reflection spectra of soils coated with analyte without resorting to soil preparations such as grinding or dilution in potassium bromide. The results provided interpretable spectra that can be used to guide strategies for detection and classification of organic analytes adsorbed on soil. Comparisons to the neat DBP liquid spectrum showed that the recovered analyte spectra from both soils showed spectral features from methyl, methylene, hydroxyl, and P=O functional groups, but most conspicuous was the absence of the strong PO-(CH2)3CH3 stretch absorption at 1033 cm(-1). These results are consistent with those obtained previously using extended multiplicative scatter correction.

Infrared reflectance measurement for InN thin film characterization

AbstractInfrared reflectance measurements of a series of InN thin films have been performed and attempt to derive carrier concentration and other physical constants for InN thin film characterization. Fitting calculations are performed by use of the dielectric function equation based on phonon‐plasmon coupling model. Longitudinal and transverse optical phonon frequencies, plasma frequency and their damping parameters can be derived from fitting. From those results, electrical and phonon properties of InN and characterization of films are discussed. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Surface Layer Properties of Dough Liquor Components: Are They Key Parameters in Gas Retention in Bread Dough?

Gas cell stability during bread making is controlled by both surface and bulk properties. This paper is focused on studying the surface properties of the water-soluble phase of the dough, the dough liquor (with and without lipids), as well as the composition of the air/water interface. Using infrared reflection measurements, we showed that in lipid-poor liquor, proteins are the dominant species present at the air/water interface. With complete liquor (including the lipids), a mixed interface of protein and lipids is obtained. However, the presence of lipids in the surface layer did not significantly affect the surface pressure. We also added enzymes to the flour to evaluate in what way the surface-active properties of the liquor components can be affected. These results were compared to the effect of adding a surfactant [diacetyl tartaric esters of mono- and diglycerides (DATEM)]. Biobake 10804, a xylanase that increased the arabinoxylan content of the dough liquor, decreased the surface pressure and increased the dilational modulus in lipid-poor liquor. This effect was not observed with the liquor including the lipids. Lipopan 50 BG, a 1,3-specific lipase, increased the surface pressure of the liquor that included the lipids. Lipopan F BG, which converts polar lipids to their lyso form, strongly increased the surface pressure not only in the lipid-containing liquor but also in the lipid-poor liquor. DATEM, as expected, increased the surface pressure while strongly decreasing the dilational modulus. Results of these studies were used to help explain changes in loaf volume observed in a series of baking tests, using the same enzymes and additives. This led to the conclusion that the effect of surface-active components alone cannot account for the larger loaf volumes observed. Clearly, both the effect of bulk and interfacial rheological properties should be considered together when explaining gas cell stability. © Springer Science+Business Media, Inc. 2006.

Band-gap energy and electron effective mass of polycrystalline Zn3N2

Zn 3 N 2 polycrystalline films with n+-type conductivity have been grown by metalorganic chemical vapor deposition and rf-molecular beam epitaxy with carrier concentration in the range between 1019 and ∼1020cm−3. Oxygen contamination without an intentional doping was found to be a cause of high electron concentration, leading to a larger band-gap energy due to Burstein-Moss shift. The significant blue shift of the optical band gap Eopt with increasing carrier concentration ne obeys the relation Eopt=1.06+1.30×10−14ne2∕3. This evaluation enables the conclusion that the actual band-gap energy of Zn3N2 is 1.06eV. Electron effective mass m* for Zn3N2 has been deduced from Fourier transform infrared reflectivity measurements to be (0.29±0.05)mo.

Far- and mid-infrared anisotropy of magnetically aligned single-wall carbon nanotubes studied with synchrotron radiation

We performed polarized infrared reflectivity measurements on magnetically oriented carbon nanotubes using conventional light sources as well as synchrotron radiation. A strong anisotropy in the far-infrared spectral range was found, indicating preferred orientation of metallic tubes. Much less effect is seen in the spectral region typical of semiconducting tubes. We propose an explanation based on preferred orientation of metallic tubes, polarization-dependent dipole selection rules, and possible doping effects in these materials.

Optical phonon modes and crystal structure of NaLaF4 single crystals

Polarized Raman scattering and infrared reflectivity measurements have been used to investigate the crystal structure of Czochralski-grown NaLaF4 single crystals. The phonon symmetries, the simultaneous presence of polar modes in the infrared and Raman spectra, as well as the observation of piezoelectric resonance, helped us to identify the P6¯ group as the correct one for this crystal. This material belongs to a family of sodium lanthanide tetrafluorides (NaLnF4) crystals, whose photoluminescence efficiency is comparable to LiYF4. Therefore, NaLaF4 crystals may be important in the development of diode pumped up-conversion solid-state lasers. The number and behavior of the observed optical phonon modes were analyzed in terms of group theory predictions for the group symmetry found. A few anomalies in the phonon characteristics are discussed in terms of cationic disorder in the crystal lattice.

Seaborne measurements of near infrared water-leaving reflectance: The similarity spectrum for turbid waters

Theory and seaborne measurements are presented for the near infrared (NIR: 700‐900 nm) water-leaving reflectance in turbid waters. According to theory, the shape of the NIR spectrum is determined largely by pure water absorption and is thus almost invariant. A ‘‘similarity’’ NIR reflectance spectrum is defined by normalization at 780 nm. This spectrum is calculated from seaborne reflectance measurements and is compared with that derived from laboratory water absorption measurements. Factors influencing the shape of the similarity spectrum are analyzed theoretically and by radiative transfer simulations. These simulations show that the similarity spectrum is valid for waters ranging from moderately turbid (e.g., water-leaving reflectance at 780 nm of order 10 24 or total suspended matter concentration of order 0.3 g m 23 ) to extremely turbid (e.g., reflectance at 780 nm of order 10 21 ). Measurement uncertainties are analyzed, and the air-sea interface correction is shown to be critical for low reflectances. Applications of the NIR similarity spectrum to atmospheric correction of ocean color data and to the quality control of seaborne, airborne, and spaceborne reflectance measurements in turbid waters are outlined.

Determination of infrared optical parameters of SrTiO 3 thin films from the reflectivity spectrum

Strontium titanate thin films have been prepared at different oxygen pressures and subjected to different post-deposition annealing treatments. The films were deposited on Si substrates with a silica buffer layer. Infrared reflectance measurements were performed to determine the optical parameters, and the spectra were fitted using adequate dielectric function forms for the layers and the substrate. The as-deposited films were found to be amorphous. Their infrared spectra presented bands corresponding to highly damped vibrational modes. As the annealing time and temperature were increased, the strontium titanate layer optical parameters became closer to those corresponding to bulk SrTiO 3 and a strong increase of the silica layer thickness was observed. The silica layer growth was attributed to the gradual oxidation of the Si substrate during the annealing that induced also a blueshift of the silica Si–O asymmetric stretching frequency. This frequency shift was associated to a decrease in the silicon oxide density as the progressive layer oxidation originated a variation of its stoichiometry from SiO 1.5 towards amorphous SiO 2.

Phonon and free-charge-carrier properties ofZn1−xMnxSeepilayers grown by molecular-beam epitaxy

Far infrared and mid infrared (FIR-MIR) reflectivity measurements have been carried out on two different series of undoped and chlorine-doped ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$ epilayers grown by molecular-beam epitaxy. The FIR reflection studies performed upon the series of undoped ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$ samples suggest an intermediate-mode behavior for the optical phonon modes in the composition range $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.43)$. In addition to the known ZnSe-like and MnSe-like phonon resonances a ``weak-mode'' feature is found below the MnSe-like phonon band. The frequency of this feature shows a temperature and Mn dependent redshift. We suggest that this feature originates from the alloy disorder present in the samples. The shape of the reststrahlen band is found to change significantly with layer thickness. This is discussed in some detail for pure ZnSe epilayers. To extract some information about the electron effective mass, we performed room-temperature plasma edge measurements on chlorine-doped $n$-type ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$ epilayers $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.13)$. Via Drude-Lorentz-type multioscillator fits to our data, we extracted the optical electron effective mass $({m}_{\mathrm{op}}^{*})$ in a series of doped Zn(Mn)Se:Cl samples with different Mn contents and free-electron concentrations. Our results indicate that ${m}_{\mathrm{op}}^{*}$ in ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$ is lower than that for ZnSe. In $n$-type chlorine-doped ZnSe samples with different free-electron concentrations, ${m}_{\mathrm{op}}^{*}$ varied from $0.133\phantom{\rule{0.3em}{0ex}}{m}_{0}$ to $0.152\phantom{\rule{0.3em}{0ex}}{m}_{0}$, while in ${\mathrm{Zn}}_{0.87}{\mathrm{Mn}}_{0.13}\mathrm{Se}:\mathrm{Cl}$ samples, we found a variation from $0.095\phantom{\rule{0.3em}{0ex}}{m}_{0}$ to $0.115\phantom{\rule{0.3em}{0ex}}{m}_{0}$ within about $\ifmmode\pm\else\textpm\fi{}9%$ experimental accuracy. From theoretical calculations, we determined the extrapolated room-temperature band-edge electron mass in ZnSe and ${\mathrm{Zn}}_{0.87}{\mathrm{Mn}}_{0.13}\mathrm{Se}$ to be about $0.132\phantom{\rule{0.3em}{0ex}}{m}_{0}$ and $0.093\phantom{\rule{0.3em}{0ex}}{m}_{0}$, respectively. Additionally, from electrical Hall effect measurements on ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}:\mathrm{Cl}$ epilayers, we found a drastic reduction in the free-electron concentration with increasing Mn content. The incorporation of Mn increases the resistivity and decreases the mobility of the free charge carriers in the samples.

Morphological transformation and kinetic analysis in the aluminum-mediated a-Si:H crystallization

We analyzed the amorphous–crystalline morphological transformation of a-Si:H films caused by applying an annealing treatment to the Al/a-Si:H system at low temperature (250 °C) during several hours. Optical micrographs show the growth of Si nuclei formed on the amorphous matrix and also a t 2 dependence of the average area of these crystalline grains, which suggest a bidimensional growth. Also was investigated the growth kinetics in the μc-Si:H films considering the annealing time dependence of the crystalline fraction. The application of the Avrami equation showed a good description of the experimental results during this morphological and structural transformation. The low growth velocity measured V g = 7.2 × 10 −3 μm/min is a direct consequence of the low annealing temperature applied (250 °C), which reduces the silicon diffusion across the interface Al/a-Si:H. Infrared reflectance measurements show a relative diminishing of the intensity for Si–H wagging mode with annealing time, suggesting effusion of hydrogen to the surface of the μc-Si:H films.