IR Transmission Measurements Research Articles

ChemInform Abstract: Synthesis, Structure, and Optical Properties of BiCuOCh (Ch: S, Se, and Te).

AbstractCrystals of the title compounds are prepared from salt fluxes and characterized by powder XRD, single crystal XRD for (VIII), and IR diffuse reflectance and transmission measurements.

Infrared transmission of Na+-doped γ-La2S3 ceramics densified by hot pressing

Na-doped γ-La2S3 powders with various Na/La ratios were synthesized by the gas–solid reaction method. Then they were sintered by hot pressing to study the effects of Na+ ions on the microstructures and optical properties of γ-La2S3 ceramics. A phase analysis indicated that the least appropriate Na+ dose to stabilize γ-La2S3 was Na/La = 1 : 20. IR transmission measurements showed that the pellet with Na/La = 1 : 20 had a higher infrared transmittance than other pellets, and the maximum transmittance reached 64.5% at 13 µm, which was near the theoretical transmittance of a γ-La2S3 crystal.

Characterization of CdZnTe Crystals Grown Using a Seeded Modified Vertical Bridgman Method

In this paper, several 60 mm diameter CdZnTe crystal ingots, containing large-size single crystals, were grown using (111) or (211) orientation seeds by the modified vertical Bridgman method. The Zn concentration distribution along the axial direction of the ingots was measured by near-infrared transmission spectroscopy at room temperature. The partition coefficient of Zn during the growth was calculated to be about 1.2. Zinc distribution uniformity measurements were carried out using photoluminescence mapping measurement at 80 K, which showed that the band gap variation in the CdZnTe wafers is less than 0.004 eV. IR microscopy showed that the diameters of the Te inclusions present in the material are in the range 6-9 mum, and the density of the inclusions is 1~3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . IR transmission measurements in the wave number region from 500 to 4000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> demonstrate that the IR transmittance of CdZnTe wafers is higher than 60%. Current-voltage measurements were performed on test structures fabricated using thermally evaporated Au contacts deposited on as-grown crystals, which revealed bulk resistivity values of 2~5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Omegamiddotcm. Typical leakage currents for the planar devices were <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">~</i> 4 nA at a field strength of 1500 Vcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The electron and hole mobility-lifetime products were evaluated using alpha particle irradiation. The obtained typical (mutau) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and (mutau) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> values for the as-grown CdZnTe were 2.3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 1.5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively.

New accessory for studies of isotopic 1H/2H exchange and biomolecular interactions using transmission infrared spectroscopy

We present here a new accessory for IR transmission measurements of 1H/2H exchange, as an ancillary tool for monitoring structural features of biomolecules in aqueous solution. This new accessory results from the combination of two dialysis membranes and a conventional liquid cell having two cylinders containing 2H2O buffer. When compared with conventional transmission measurements, carried out either after dissolving lyophilized biomolecules in 2H2O or after dialyzing the aqueous solution considered against 2H2O buffer, this accessory shows the following advantages: (1) controlled measurements over the initial steps of this isotopic exchange and absence of molecular aggregation, and (2) smaller sample amounts. This new Fourier transform IR cell can also be used to analyze ligand-biomolecule and drug-cell interactions.

Lattice vibrations of pure and doped GaSe

The Bridgman method is used to grow especially undoped and doped single crystals of GaSe. Composition and impurity content of the grown crystals were determined using X-ray fluorescence (XRF) method. X-ray diffraction, Raman scattering, photoluminescence (PL), and IR transmission measurements were performed at room temperature. The long wavelength lattice vibrations of four modifications of GaSe were described in the framework of modified one-layer linear-chain model which also takes into consideration the interaction of the selenium (Se) atom with the second nearest neighbor gallium (Ga) atom in the same layer. The existence of an eight-layer modification of GaSe is suggested and the vibrational frequencies of this modification are explained in the framework of a lattice dynamical model considered in the present work. Frequencies and the type of vibrations (gap, local, or resonance) for the impurity atoms were calculated and compared with the experimental results.

FTIR spectroscopy for the hermeticity assessment of micro-cavities

This paper presents an alternative method for the hermeticity assessment of micro-cavities. The method consists in monitoring the internal gas pressure of a cavity by Fourier Transform Infra Red (FTIR) spectroscopy, and then deducing the cavity’s leak rate from the pressure variations. In order to carry out the IR transmission measurements, nitrous oxide was chosen as bombing gas due to its excellent absorption properties for mid-IR radiations. First FTIR spectroscopy measurements performed on test vehicles have demonstrated the method feasibility on silicon-silicon micro-cavities with internal volumes of 5mm 3 or more. These test vehicles were then bombed with nitrous oxide, and standard leak rates of 3.4 × 10 −7 atm.cm 3.s −1 were assessed by FTIR spectroscopy. These leak rates have been confirmed by N 2O pressure variation monitoring for a 20 mm 3 micro-cavity.

Structural and spectroelectrochemical (UV–vis and IR) studies of nanocrystalline sol–gel derived TiO2 films

Abstract Nanocrystalline TiO 2 films with a high surface roughness were prepared by the sol–gel route from titanium (IV) iso-propoxide and brij 56 surfactant. XRD and TEM showed that the films consisted predominantly of anatase nanoparticles embedded in an amorphous phase. Addition of the surfactant significantly increased the intensity of the surface hydroxyl modes between 3600 and 3750 cm −1 in IR spectra. Spectroelectrochemical measurements of the films in 0.1 M LiOH electrolyte revealed optical modulation beyond 70%T. Slow-scan cyclovoltammetry showed that bleaching occurred in two steps, suggested to correspond to anatase and amorphous phase. The changes that occur during intercalation and deintercalation were followed by ex-situ IR transmission measurements in the regions of Ti–O, carbonate and surface hydroxyl bands.

Free carrier absorption in heavily doped silicon layers

The standard parametrization of free carrier absorption in silicon predicting a linear dependence of the absorption on carrier concentration is revised, finding that due to several simplifications, it is only applicable up to carrier densities of about 3×1016 cm−3. A parametrization applicable for both p- and n-type silicon and for doping densities as high as 1021 cm−3 is introduced. Using this parametrization, considerably better agreement between the emitter sheet resistance of diffused layers measured by IR transmission and electrical measurements is found, proving the applicability of the enhanced model even for heavily doped layers. Additionally, parameters for the dependence of the refractive index of silicon on doping concentration are given.

Growth of In doped CdZnTe by vertical Bridgman method and the effect of In on the crystal properties

An Indium (In) doped Cd 0.9Zn 0.1Te (CdZnTe:In) ingot was grown by vertical Bridgman method. The distribution of In in the ingot was analyzed. It was evaluated that the segregation coefficient of In in CdZnTe during the growth was 1.3, which caused a higher In concentration in the initial part of CdZnTe:In ingot and a lower In concentration in the final part. In was also enriched at the grain boundaries but homogeneously distributed inside the grains in the as-grown crystal. Photoluminescence spectra indicated that In had two states existing in the CdZnTe:In ingot. One was interstitial neutral In and the other was substitutional ion In +. The two states led to the two donor levels at 0.12 and 0.04 eV in CdZnTe:In band construction, respectively. IR transmission measurements exhibited that CdZnTe:In was almost opaque to IR emission when the wavenumber was larger than 1000 cm −1, then was 24% transparent when the wavenumber was decreased to lower than 1000 cm −1. This phenomenon also confirmed the existence of the donor level of 0.12 eV demonstrated by the PL spectra. Resistivity measurements revealed that CdZnTe:In obtained three orders higher resistivity than CdZnTe. It meant that doping of In into CdZnTe could improve the crystal properties.

Polytypic Transition of n-Hexatriacontane during Solution Crystallization

The crystallization process of n-hexatriacontane (n-C36H74) was investigated by means of micro-FTIR spectroscopy. From the results of in-situ oblique IR transmission measurements, it was confirmed that single crystals of the M011 modification exhibited a polytypic transformation during solution growth. At the initial stage of the crystallization, single crystals appeared as the single-layered polytype (Mon). The overgrowth of the double-layered polytype (Orth II) took place subsequently on the (001) face of the single crystal. After that, the single crystal gradually transformed into a single crystal of the Orth II type through a solution-mediated phase transition. It was suggested that the transformation from Mon to Orth II was caused by a drop in the supersaturation of the solution.

Characteristics of doped indium in Cd0.9Zn0.1Te grown by the Bridgman method

The Cd1−xZnxTe crystal is one of the key materials for room temperature x-ray and gamma-ray detectors. By the vertical Bridgman method (VBM) several indium (In) doped Cd0.9Zn0.1Te (Cd0.9Zn0.1Te: In) ingots have been grown. The characteristics of In in these ingots have been studied. It is found that the segregation coefficient of In in Cd0.9Zn0.1Te is 1.3. In is enriched at the grain boundary but homogeneously distributed inside the grains in the as-grown crystals. IR transmission measurements reveal that Cd0.9Zn0.1Te: In is almost opaque to IR emission when the wave number is larger than 1000 cm−1, then is 24% transparent when the wave number is decreased to lower than this value. This phenomenon indicates that some In atoms are interstitial impurities and act as neutral donors. These In atoms bring out a donor level of 0.12 eV below the bottom of conduction band for Cd0.9Zn0.1Te: In. Resistivity measurements reveal that the resistivity is highly increased after doping of In into Cd0.9Zn0.1Te, and the In concentration is positive to raise the resistivity of Cd0.9Zn0.1Te: In.

HgCdTe composition determination using spectroscopic ellipsometry during molecular beam epitaxy growth of near-infrared avalanche photodiode device structures

The application of spectroscopic ellipsometry (SE) for real-time composition determination during molecular beam epitaxy (MBE) growth of Hg1-xCdxTe alloys with x > 0.5 is reported. Techniques previously developed for SE determination of composition in long-wavelength infrared (LWIR) HgCdTe have been successfully extended to near-infrared HgCdTe avalanche photodiode (APD) device structures with x values in the range of 0.6-0.8. Ellipsometric data collected over a spectral range of 1.7-5 eV were used to measure depth profiles of HgCdTe alloy composition through the use of an optical model of the growth surface. The optical model used a dielectric-function database collected through the growth of a set of HgCdTe calibration samples with x ranging from 0.6 to 0.8. The sensitivity of this SE method of composition determination is estimated to be Δx ∼ 0.0002 at x = 0.6, which is sufficiently low to sense composition changes arising from flux variations of less than 0.1%. Errors in composition determination because of Hg-fiux variations appear to be inconsequential, while substrate-temperature fluctuations have been observed to alter the derived composition at a rate of -0.0004/°C. By comparing the composition inferred from SE and postgrowth 300 K IR transmission measurements on a set of APD device structures, the run-to-run precision of the SE-derived composition (at x = 0.6) is estimated to be ±0.0012, which is equivalent to the precision achieved with the same instrumentation during the growth of mid-wavelength infrared (MWIR) HgCdTe alloys in the same MBE system.

Vertical profiles of aerosol volume from high-spectral-resolution infrared transmission measurements I Methodology

The wavelength-dependent aerosol extinction in the 800-1250-cm(-1) region has been derived from ATMOS (atmospheric trace molecule spectroscopy) high-spectral-resolution IR transmission measurements. Using models of aerosol and cloud extinction, we have performed weighted nonlinear least-squares fitting to determine the aerosol-volume columns and vertical profiles of stratospheric sulfate aerosol and cirrus cloud volume. Modeled extinction by use of cold-temperature aerosol optical constants for a 70-80% sulfuric-acid-water solution shows good agreement with the measurements, and the derived aerosol volumes for a 1992 occultation are consistent with data from other experiments after the eruption of Mt. Pinatubo. The retrieved sulfuric acid aerosol-volume profiles are insensitive to the aerosol-size distribution and somewhat sensitive to the set of optical constants used. Data from the nonspherical cirrus extinction model agree well with a 1994 mid-latitude measurement indicating the presence of cirrus clouds at the tropopause.

Carbon nitride thin films and nanopowders produced by CO2laser pyrolysis

Nanocrystalline CNx particles and thin films were produced in a flow reactor system by the CO2 laser pyrolysis of sensitised NH3–N2O–C2 H2reactant gas mixtures. Depending on the substrate nature (silicon or quartz) the SEM and TED analysis of the CNx thin films revealed specific nucleation and growth morphologies of crystallites, resembling the β-C3 N4 phase. In the case of C3 N4 nanopowder synthesis, the relative concentration of the sensitisers (SF6 /C2 H4 ) was varied to minimise SF6 decomposition. The majority of the data obtained from powder analysis (XRD, XPS, and ir transmission measurements) suggests the presence of CN bonded phases and the formation of α-and β-C3 N4 structures.

MBE growth of HgCdTe avalanche photodiode structures for low-noise 1.55 μm photodetection

Molecular-beam epitaxy (MBE) has been utilized to fabricate HgCdTe heterostructure separate absorption and multiplication avalanche photodiodes (SAM-APD) sensitive to infrared radiation in the 1.1–1.6 μm spectral range, as an alternative technology to existing III–V APD detectors. Device structures were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The composition of the HgCdTe alloy layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1–1.6 μm spectral range and low excess-noise avalanche multiplication. The Hg 1− x Cd x Te alloy composition in the gain region of the device, x=0.73, was selected to achieve equality between the bandgap energy and spin–orbit splitting to resonantly enhance the impact ionization of holes in the split-off valence band. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin–orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on the processed wafers. Avalanche gains in the range of 30–40 at reverse bias of 85–90 V and array-median dark current density below 2×10 −4 A/cm 2 at 40 V reverse bias have been demonstrated.

Far IR transmission measurements on triglycine sulphate (TGS), at 5K

New measurements with a special cryostat, and a high resolution grid interferometer show that TGS exhibits Far Infrared (FIR) oscillations at θ = 5K with much smaller damping coefficients (δ = δv/v), than previously described (Gerbaux, X. and Hadni, A. (1991). Int. J. Infared and Millim. Waves, 12, 981). The values of δ are smaller than 10−4 for several lines. The lowest frequency and strongest line, located at 37.3 cm−1 can be used to predict a low temperature peak in pyroelectric response at 15.4 K, which has been observed at 16K (Mangin, J. and Hadni, A. (1983). Phys. Rev. B, 27, 7730). The low damping coefficient of the line seems to rule out an explanation in terms of anharmonicity, and strongly favors one with a second-order dipole moment which has been shown to give the same temperature behaviour (Szigeti, B. (1975). Phys. Rev. Let., 35, 1532). With Lorentz oscillators of such low damping coefficients, it is possible to fit the spectra of crystal plates with thicknesses extending from a few micrometers to several millimeters. This shows that they are homogeneous, and any evidence of a surface layer different from the bulk has not been found at low temperatures.

Influence of the surface treatment of the substrate in the LCVD of CN x films

Carbon nitride (CN x films have been prepared by UV (at 248 nm) laser-induced chemical vapor deposition using different materials (alumina, laser-activated alumina, pre-deposited Ti layers on alumina, sapphire and quartz) as deposition substrates. A mixture of ethylene, nitrous oxide and ammonia was chosen as the gas-phase precursor. The changes induced in the gas-phase composition by the irradiation in different experimental conditions were determined by IR transmission measurements. The film composition and morphology were studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron diffraction (TED). The degree of chemical content modification, especially its dependence on the nature of the substrate, is described for the first time. Depending on the substrate nature, the specific nucleation and growth morphology of crystallites were observed. The electron diffraction data agree well with experimental results obtained in previous works and theoretical data referring to crystalline α- and β-C 3N 4 phases.

Influence of process parameters on CN X films obtained by laser-CVD at two wavelengths

The carbon nitride (CN x ) films have been prepared by infrared (IR; at 10.6 μm) and ultraviolet (at 248 nm) laser induced chemical vapour deposition (CVD) using different ethylene/nitrous oxide/ammonia mixtures. The partial concentration of ammonia in mixtures was varied in order to obtain a higher nitrogen incorporation in the deposited films. The changes induced in the gas-phase composition by the laser radiation in different experimental conditions were determined by IR transmission measurements. The film composition was studied by X-ray photoelectron spectroscopy. The modification of the film chemical composition, specifically the dependence of the N C ratio, on the irradiation wavelength and on the reactants composition is described for the first time.

Preparation of carbon nitride fine powder by laser induced gas-phase reactions

We present the possibility of carbon nitride fine powder synthesis by sensitized laser pyrolysis of acethylene/nitrous oxide/ammonia mixtures. The powders were analyzed using X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and IR transmission measurements. It was found that nitrogen was incorporated in powders and that in the carbon-nitrogen phases formed, the presence of the triple bonded C≡N was not detected. The majority of X-ray diffraction data suggests the presence of a mixture of the predicted α- and β-C3N4 structure, with an α-C3N4-like form being prevalent. The powders were found to be slightly contaminated by SF6 sensitizer products. Our results suggest that by improving the experimental parameters this contamination might be reduced and that the laser pyrolysis method offers possibilities for production of CxNy materials, with controlled composition.

Microstructure of c-BN Films Deposited by IBAD: IR and Hrem Analyses

ABSTRACTThe in-depth distribution of phases in c-BN films deposited by Ion Beam Assisted Deposition (IBAD) at two different ion energy values (300 and 600 eV) was investigated using the quantitative IR transmission measurements and the HREM technique. Whatever the value of the studied ion energies, the characteristic layered morphology of c-BN film is observed including the interfacial sp2 zone between the substrate and the c-BN volume. In the case of 600 eV ion energy, this interfacial zone is less well-defined in comparison with 300 eV ion energy and the corresponding thickness is more important. Furthermore, the h-BN phase is more diluted within the c-BN film volume showing that the purest phase concentration of c-BN is found for the lowest ion energy, i.e. 300 eV.