Pressure-broadening in the THz frequency region: The 1.113 THz line of water

It is well established that water plays a fundamental role in various atmospheric phenomena and that the accuracy of its collisional broadening parameters has a crucial influence on reduction of remote sensing data. Nevertheless, in this field the experimental data are still scarce and consequently the estimates reported in spectroscopic databases are not always reliable and/or accurate. In the view of filling this gap, the self-, N₂- and O₂-broadening parameters of the J=1_1,1←0_0,0 rotational transition of water (1.113 THz) have been determined at room temperature. The experimental investigation has also been supported by theoretical calculations.     

Experimental determination of air-broadening parameters of pure rotational transitions of HNO3: intercomparison of measurements by using different techniques

We report on the air-broadening of the 44_d, 25 ← 44_d, 26, 43_d, 25 ← 43_d, 26, 25_d, 25 ← 24_d, 24, 27_d, 25 ← 27_d, 26, 26_1, 25 ← 26_0, 26, 15_13, 3 ← 14_13, 2, and 27_d, 27 ← 26_d, 26 transitions of HNO₃ at room temperature, which are useful for measurements of nitric acid in the Earth’s atmosphere by microwave limb sounders. In fact, the lines selection was essentially made on the basis of the spectral range requirements of MASTER, a limb sounding instrument managed by ESA. It is well established that the collisional-broadening parameters have a crucial influence on reduction of remote sensing data, but it is also well known that systematic errors make the evaluation of pressure-broadening parameters accuracy difficult. To this purpose, the investigation has been carried out in two different laboratories employing different techniques: the intercomparison allowed us to check the accuracy of the retrieved parameters as well as to estimate the extent of systematic errors affecting them.     

Luminescence and EPR studies of Eu doped BaAl12O19 blue light emitting phosphors

Europium doped BaAl₁₂O₁₉ powder phosphors have been synthesized by combustion process within few minutes. The phosphors have been characterized by XRD, SEM, FT-IR, EPR and PL techniques. The EPR spectrum exhibits an intense resonance signal at g=1.96 characteristic of Eu²⁺ ions. In addition to this two weak resonance signals have been observed at g=2.28 and g=4.86. The population of the spin levels (N) for the resonance signal at g=1.96 is calculated as a function of temperature. By post-treating the phosphor at 1350 °C under a reducing atmosphere, it is observed that the population of spin levels has been increased five times. The excitation spectrum shows a peak at 326 nm with a shoulder at 290 nm. Upon excitation at 326 nm, the emission spectrum exhibits a well defined broad band with maximum at 444 nm emitting a blue light corresponding to 4f⁶5d→4f⁷ transition. The luminescence intensity also has been enhanced to 60% by post-treating the phosphor at 1350 °C under a reducing atmosphere.     

Multilayered metal oxide thin film gas sensors obtained by conventional and RF plasma-assisted laser ablation

Multilayered thin films of In₂O₃ and SnO₂ have been deposited by conventional and RF plasma-assisted reactive pulsed laser ablation, with the aim to evaluate their behaviour as toxic gas sensors. The depositions have been carried out by a frequency doubled Nd-YAG laser (λ = 532 nm, τ = 7 ns) on Si(1 0 0) substrates, in O₂ atmosphere. The thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical resistance measurements. A comparison of the electrical response of the simple (indium oxide, tin oxide) and multilayered oxides to toxic gas (nitric oxide, NO) has been performed. The influence on the structural and electrical properties of the deposition parameters, such as substrate temperature and RF power is reported.     

Experimental study of H2O spectroscopic parameters in the near-IR (6940-7440 cm) for gas sensing applications at elevated temperature

Tunable diode laser (TDL) absorption sensors of water vapor are attractive for temperature, gas composition, velocity, pressure, and mass flux measurements in a variety of practical applications including hydrocarbon-fueled combustion systems. Optimized design of these sensors requires a complete catalog of the assigned transitions with accurate spectroscopic data; our particular interest has been in the 2ν₁, 2ν₃, and ν₁+ν₃ bands in the near-IR where telecommunications diode lasers are available. In support of this need, fully resolved absorption spectra of H₂O vapor in the spectral range of 6940-7440 cm⁻¹ (1344-1441 nm) have been measured as a function of temperature (296-1000 K) and pressure (1-800 Torr), and quantitative spectroscopic parameters inferred from these spectra compared to published data from Toth, HITRAN 2000 and HITRAN 2004. The peak absorbances were measured for more than 100 strong transitions at 296 and 828 K, and linestrengths determined for 47 strong lines in this region. In addition to reference linestrengths S(296 K), the air-broadening coefficients γ_air(296 K) and temperature exponents n were inferred for strong transitions in five narrow regions, near 7185.60, 7203.89, 7405.11, 7426.14 and 7435.62 cm⁻¹ that had been targeted as attractive for future diagnostics applications. Most of the measured results, determined within an accuracy of 5%, are found to be in better agreement with HITRAN 2004 than with earlier editions of this database. Large discrepancies (>10%) between measurements and HITRAN 2004 database are identified for some of the probed transitions. These new spectroscopic data for H₂O provide a useful test of the sensor design capabilities of HITRAN 2004 for combustion and other applications at elevated temperatures.     

Quantum cascade laser spectroscopy of N2O in the 7.9 μm region for the in situ monitoring of the atmosphere

A quantum cascade laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to precisely study nitrous oxide (N₂O) line parameters near 7.9 μm. The spectral region ranging from 1275 to 1280 cm^-1, which is suitable for the in situ measurement of N₂O in the atmosphere from balloon-borne measurements, was studied using a commercial laser from Alpes Lasers. Five lines of the ν₁ band of N₂O have been studied. The results of intensity measurements, air-broadening coefficients and their variation with temperature from −58 °C up to ambient temperature are compared with previous determinations and available databases. These results demonstrate that these parameters for N₂O are quite well known in the literature. Parameters obtained in this work are given with a very high precision.     

Study of the switching phenomena of TlGaS2 single crystals

Single crystals of TlGaS₂ were prepared by a special modified Bridgman technique and used to investigate the switching phenomena. The particular interest shown in switching studies of p-type TlGaS₂ compound is associated with the possibility of its uses as an effective switching and memory elements in electronic devices. The switching effect observed in such crystal shows a memory character. Using a crystal holder and cryostat we measured the switching phenomenon at different ambient conditions such as temperature, light illumination as well as sample thickness. Pronounced parameters for switching for sample of thickness 0.17 cm were determined from the experimental data such as threshold voltage V_th = 400 V, threshold current I_th = 37 μA, holding voltage V_h = 350 V, holding current I_h = 42.3 × 10⁻⁴ A, threshold power P_th = 1.48 × 10⁻² W, threshold field E_th = 196.429 V/cm as well as the ratio between the resistance in the off state R_OFF to the resistance in the conducting state R_ON as 130.253. The factors affecting these parameters have also been investigated.     

Study on contamination of projection optics surface for extreme ultraviolet lithography

Ru-capped Mo/Si multilayer mirrors were irradiated by EUV in a vacuum atmosphere with ethanol or decane gas, and their reflectivity changes by contamination were investigated by changing the amount of introduced gas. The reflectivity hardly decreased by EUV irradiation in the ethanol-introduced atmosphere. On the other hand, the reflectivity decreased by about 5% in the decane-introduced atmosphere at a decane pressure of P_Decane = 1.3 × 10⁻⁴ Pa, an EUV power of about 200 mW/mm², and an EUV dose of 150 J/mm². EUV irradiation to the Ru-capped multilayer mirrors was also performed in the presence of water vapor and decane. The surface oxidation by EUV irradiation with a water vapor pressure of PH₂O=1.3×10⁻⁵ Pa was controlled by the introduction of decane at a pressure of P_Decane = 7.0 × 10⁻⁷ to 1.3 × 10⁻⁶ Pa.     

Ground state rotational spectrum of nitrogen trifluoride: The K = 3 splittings of NF3 and NF3

The ground state rotational spectrum of the ¹⁴NF₃ and ¹⁵NF₃ isotopic species of nitrogen fluoride has been observed in the ∼450-810 GHz frequency range. This investigation allowed us to improve the rotational parameters for both isotopologues. In particular, for the first time the K = 3 line splitting parameter and the sextic centrifugal distortion constants have been determined for ¹⁵NF₃.     

CW-cavity ring down spectroscopy of the ozone molecule in the 6220-6400 cm region

The absorption spectrum of ozone,¹⁶O₃, has been recorded in the 6220-6400 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 3 × 10⁻¹⁰ cm⁻¹). 1836 rovibrational transitions have been assigned to the 2ν₂ + 5ν₃, 5ν₁ + ν₃ and 2ν₁ +  2ν₂ + 3ν₃ A-type bands centred at 6305, 6355 and 6387 cm⁻¹, respectively. In addition, 99 lines of the very weak ν₁ + 2ν₂ +  4ν₃ and 4ν₁ + 3ν₂ B-type bands are identified. The modeling of the observed spectrum in the effective Hamiltonian approach was particularly laborious and complex as several rovibrational interactions of both Coriolis and anaharmonic type were found to be of importance, in particular for the (124) vibrational state. Nevertheless, it has finally been possible to fit the 990 experimentally determined energy levels with an rms deviation of 8.29 × 10⁻³ cm⁻¹ and to derive the transition moment parameters allowing a satisfactory reproduction of the observed intensities. As the differences in positions between the final calculations and observations are still larger than the experimental accuracy, we provide the list of all energy levels derived from the observation, in addition to their differences with the calculated ones. These experimental energy levels, with the transition moment parameters were used to generate a line-list of 2451 transitions, reproducing the observed spectrum. This list is given as Supplementary Material.     

Optical,spectral and thermal properties of organic nonlinear optical single crystal: 2,3-Dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate

The potential organic nonlinear optical single crystal of 2,3-dimethoxy-10-oxostrychnidinium hydrogen oxalate dihydrate has been grown by slow evaporation solution growth technique (SEST) using ethanol–water solution at room temperature. The powder X-ray diffraction study reveals that the crystal belongs to orthorhombic system with non-centrosymmetric space group P2₁2₁2₁ and the cell parameters are a = 7.61 Å, b = 10.73 Å, c = 29.49 Å, V = 2410.75 Å³. The functional groups of the synthesized compound have been identified by FT-Raman and FTIR analyses. Photoluminescence spectroscopy study is determined to explore its efficacy towards device fabrications. Birefringence measurement has been carried out in order to analyze the optical homogeneity of the grown crystal. The optical constants such as reflectance (R) and extinction coefficient (K) have been determined from the transmittance data. The relative second harmonic efficiency of the compound is found to be 4 times greater than that of KDP. DTA-DSC measurements indicate that the crystal is thermally stable up to 174 °C.     

High-resolution FTIR spectrum and analysis of the ν2+ν4 combination band of SF6

The spectroscopic knowledge of sulfur hexafluoride, which is necessary for a correct remote sensing and monitoring of this species in the Earth’s atmosphere, is still very partial. In particular, the hot bands in the strongly absorbing ν₃ region (near 948 cm⁻¹) have not been analyzed yet. Their study implies the analysis of many vibrational levels and thus the spectroscopy of various fundamental, harmonic, and combination bands. The present work is a new contribution to this topic, concerning the ν₂+ν₄ combination band. The FTIR spectrum of this region has been recorded at room temperature with a resolution of 0.002 cm ⁻¹. The data have been analyzed thanks to the HTDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html) developed in Dijon for XY₆ octahedral molecules. Seven hundred and fifty-nine lines could be assigned up to J=112, and the standard deviation is 0.0022 cm⁻¹. The distance between the two vibrational sublevels with respective symmetry F_1u and F_2u is 0.348 cm⁻¹.     

Rotational spectrum and structure of asymmetric dinitrogen trioxide, N2O3

The rotational spectra of the ground vibrational state and the ν₉ = 1 torsional state have been reinvestigated and accurate spectroscopic constants have been determined. The torsional frequency, ν₉ = 70(15) cm⁻¹, has been determined by relative intensity measurements. The assignment of the infrared spectrum has been slightly revised and an accurate harmonic force field has been calculated. The equilibrium structure has been determined using different, complementary methods: experimental, semi-experimental and ab initio, leading to r(NN) = 1.870(2) Å, in particular.     

Solid solutions on the base of bismuth vanadate: Preparation, structure, phase transitions, dielectric and transport properties

Ceramic solid solutions (Bi_1-yLa_y)₄(V_1-xMe_x)₂O_11-y with x, y < 0.2, Me-Zr, Ga, Fe, Cu, have been prepared by the solid state reaction method. Crystal structure parameters, phase transitions, dielectric and transport properties of ceramic samples have been studied. Concentration and temperature stability regions of monoclinic α-, orthorhombic β- and tetragonal γ- or γ’- polymorph modifications have been determined.Annealing of samples, containing large amount of Cu and/or La dopants, at 973 K in the reducing atmosphere resulted in their decomposition, though compositions containing low content of La, Ga or Zr dopants, remained pretty stable.     

Studies of the phosphorescence of polycrystalline hafnia

Persistent phosphorescence induced by ultraviolet light in polycrystalline HfO₂ and enhancement of the phosphorescence by sintering are investigated. The phosphorescence afterglow emission is in the 1.8-3.2 eV spectral range, with a peak at 2.53 eV. The afterglow intensity is significantly increased by sintering in either inert atmosphere or air. The afterglow light sum measured at room temperature for samples sintered at 1500 °C is more than an order of magnitude higher than that before sintering. In the temperature range −50 to 200 °C, three thermoluminescence (TL) peaks are observed near −10, 30, and 100 °C. The relative contribution of the low-temperature TL peak to the total TL intensity decreases after sintering, and this effect is more pronounced upon sintering in inert atmosphere. Conversely, the contribution of the TL peak near 100 °C increases after sintering. The enhancement of the afterglow by sintering is associated with the observed increase in the intensity of TL peaks at and above room temperature and attributed to an increase in the number of deep charge traps. The room-temperature afterglow time decay has a form consistent with the second-order mechanism, ∝(t₀+t)⁻ⁿ, and the best-fit values of both fitting parameters t₀ and n tend to increase with the sintering temperature.     

Submillimeter spectrum of methyl bromide (CH3Br)

Methyl bromide is a ubiquitous component of the atmosphere, but has yet to be remotely detected in the upper atmosphere. Due to the strong ozone depletion capability of the activated bromine species, the total atmospheric bromine load needs to be carefully monitored. Combined analysis of precise measurements and cataloging of the rotational spectrum of methyl bromide may enable its concentration to be monitored with future remote sensing instrumentation. In an effort to extend and improve previous work for this molecule, the spectrum of CH₃Br has been measured at JPL. Using an isotopically enriched ¹³CH₃Br (90%) sample, spectra have been recorded from 750 to 1200 GHz. Quantum number assignments cover the CH₃⁷⁹Br, CH₃⁸¹Br, ¹³CH₃⁷⁹Br and ¹³CH₃⁸¹Br isotopologues with J < 66 and K < 17 for the ground and ν₃ vibrational states. The dataset for the ¹²C isotopologues is more precise than previous THz measurements resulting in reductions of rotational and distortion parameter uncertainties by factors of 2-15. Parameters of the ν₃ state of the ¹²C isotopologues are improved by 2-105. The spectra of the ¹³C isotopologues are the first reported beyond J = 2.     

Study of vibration-rotation levels in formamide with high resolution FTIR spectroscopy: The ν12, 2ν12, ν11, and ν9 bands

The far infrared and infrared spectra of formamide (HCONH₂) have been recorded at high resolution (0.00125 cm⁻¹) in the region of 90-1060 cm⁻¹. Over 20,000 transitions from the out-of-plane NH₂ wagging motion (n₁₂ = 1 ← 0 fundamental, n₁₂ = 2 ← 0 overtone, n₁₂ = 2 ← 1 difference bands), torsion (n₁₁ = 1 ← 0 bands), and out-of-phase NCO/NH₂ bend (n₉ = 1 ← 0 bands) have been assigned. Molecular parameters have been obtained for the ground state and the unperturbed n₁₂ = 1 state. The least-squares fit calculations were completed with the microwave data available in the literature. The complicated resonance system between the n₁₂ = 2, n₁₁ = 1, and n₉ = 1 states has been investigated carefully. Thus, we have been able to verify almost all resonances (avoided crossing) existing in the region J, K investigated. In the coupled Hamiltonian used for the fit, all Watson’s reduced parameters, including the octic ones and 16 Coriolis coupling parameters were taken into account. The rms deviation obtained from the fit was 0.000247 cm⁻¹.     

Extension of the range of resonator scanning spectrometer into submillimeter band and some perspectives of its further developments

Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′_{ka′, kc′}-J_{ka, kc} = 5_1,5-4_2,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 3_1,3-2_2,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given.     

X-ray photoemission and X-ray absorption studies of Hf-silicate dielectric layers

Photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) measurements have been performed on HfSi_xO_y and HfSi_xO_yN_z dielectric layers, which are potential candidates as high-k transistor gate dielectrics. The hafnium silicate layers, 3-4 nm thick, were formed by codepositing HfO₂ and SiO₂ (50%:50%) by MOCVD at 485 °C on a silicon substrate following an IMEC clean. Annealing the HfSi_xO_y layer in a nitrogen atmosphere at 1000 °C resulted in an increase in the Si⁴⁺ chemical shift from 3.5 to 3.9 eV with respect to the Si⁰ peak. Annealing the hafnium silicate layer in a NH₃ atmosphere at 800 °C resulted in the incorporation of 10% nitrogen and the decrease in the chemical shift between the Si⁴⁺ and the Si⁰ to 3.3 eV. The results suggest that the inclusion of nitrogen in the silicate layer restricts the tendency of the HfO₂ and the SiO₂ to segregate into separate phases during the annealing step. Synchrotron radiation valence band photoemission studies determined that the valence band offsets were of the order of 3 eV. X-ray absorption measurements show that the band gap of these layers is 4.6 eV and that the magnitude of the conduction band offset is as little as 0.5 eV.     

CO2 sensing properties of semiconducting copper oxide and spinel ferrite nanocomposite thin film

A new active layer for CO₂ sensing based on semiconducting CuO-Cu_xFe_3−xO₄ (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO₂ target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite-spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130-475 °C) and frequencies (0.5-250 kHz). The results showed a high response of 50% (Rair/RCO₂=1.9) at 250 °C and 700 Hz for a CO₂ concentration of 5000 ppm.