Oxidation mechanism of hydrogen-terminated Ge(1 0 0) surface

Control of the surface chemistry to prepare a robust termination on the Ge surface is crucial for the development of high-end Ge devices. In this study, oxidation of a H-terminated Ge surface was studied in air ambient and H₂O using a multiple internal reflection Fourier transform infrared spectroscopy (MIR FT-IR) technique. Ge surface treated in less diluted HF exhibited a stronger Ge-H peak intensity, and the surface was easily oxidized in the air ambient. Therefore, it is believed that the treatment of the Ge surface in highly diluted HF solution has an advantage in suppressing the oxidation of Ge in the air ambient. For the oxidation of Ge(1 0 0) surface in air ambient, the Ge surface is attacked by oxidizing agents to break Ge-H and Ge-Ge bonds, and the transition GeO_x layer is first formed, followed by a layer-by-layer GeO₂ formation with the increase in exposure time. When the H-terminated Ge surface was treated in H₂O, GeO_x was mainly formed, the thickness of the oxide layer was not changed with an increase in treatment time, and the Ge surface was maintained in a suboxide state, which exhibits a different oxidation mechanism from that in air ambient.     

Modification of rubber surface by UV surface grafting

Rubber surface is subjected to ultraviolet radiation (UV) in the presence of allylamine and radiation sensitizer benzophenone (BP). Fourier transform infrared spectral studies reveal the presence of allylamine on the surface. The presence of irregular needle shapes on the surface as observed in scanning electron micrographs also confirms the polymerized allylamine on the surface. Allylamine coatings have been further confirmed from atomic force microscopy (AFM) analysis. Thermogravimetric analysis (TGA) reveals that allylamine coating on the rubber surface lowers the thermal degradation rate. The contact angle between the water and rubber surface decreases for the modified rubber surface confirming the surface modification due to UV surface grafting.     

Systematic analysis of the Fourier transform spectrum of CH3OH between 400 and 950 cm

We have investigated a high-resolution Fourier transform (FT) absorption spectrum of the ¹³CH₃OH isotopomer of methanol from 400 to 950 cm⁻¹ with the “Ritz” program. We present the assignments of 7160 transitions, 3021 of which belong to A-symmetry, and 4139 to E-symmetry. These transitions occur between states labeled by K quantum numbers up to 14, and by torsional quantum numbers n up to 4. The “Ritz” program evaluated the energies of the 4684 involved levels with an accuracy of the order of 10⁻⁴ cm⁻¹. All of the assigned lines correspond to transitions involving torsionally excited levels within the ground small-amplitude vibrational state.     

Multispectrum analysis of the ν9 band of C2H6: Positions, intensities, self- and N2-broadened half-width coefficients

Line positions, intensities, Lorentz self- and N₂-broadened half-width coefficients have been measured for ^PQ₃, ^PQ₂, ^PQ₁, ^RQ₀, ^RQ₁, ^RQ₂, and ^RQ₃ sub-band transitions in the ν₉ fundamental band of ¹²C₂H₆. A multispectrum nonlinear least-squares fitting technique was used to fit up to 17 high-resolution (∼0.00156 cm⁻¹), room temperature absorption spectra of pure (99.99% chemical purity) natural sample of ethane and lean mixtures of the high-purity ethane diluted with N₂. A Bruker IFS 120HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL), in Richland, Washington was used to record the data. A standard Voigt line shape was assumed to fit all the data since no line mixing or other non Voigt line shapes were required to fit any of the spectra used in the analysis. Short spectral intervals (∼2-2.5 cm⁻¹) of all 17 spectra covering a specific ^PQ or ^RQ sub-band were fit simultaneously. For the first time in an ethane band, pressure-broadened half-width coefficients were determined for the torsional-split components. However, for better reliability of the retrieved coefficients for the weaker components (transitions with large intensity ratios of 4:1 or 3:1 for most K levels between the strong and weak components), constraints were used such that the half-width coefficients of both torsional-split components for a given J were identical for a specific broadening gas. No pressure-induced shift coefficients were necessary to fit the spectra to their noise level. The present study revealed for the first time the dependence of self- and N₂-broadened half-width coefficients upon the J, K quantum numbers of the transitions in ethane. A number of transitions belonging to the ν₉+ν₄−ν₄ and the ν₉+2ν₄−2ν₄ hot bands were also observed in the fitted regions and measurements were made when possible.     

Terahertz absorption spectrum of D2O vapor

The absorption spectrum of D₂O vapor from 0.2 to 2.0 THz (6.7-67 cm⁻¹) which is associated with rotational modes was measured at one atmosphere using terahertz time-domain spectroscopy (THz-TDS). The linewidth and collisional dephasing times were measured for 26 pure rotational transitions in the ground vibrational state (0 0 0). The temperature dependence of the linewidth (Δν) behaves as Δν ∼ T^−3/4 and the linewidth decrease with increasing temperature is attributed to the 1/r⁶ force of interaction between colliding D₂O molecules.     

Trace complex-molecule detection using near-IR diode lasers

The goal of the present paper was to develop an experimental technique to detect trace concentrations of complex molecules in the atmosphere using near-IR diode lasers. Ethanol and propane were chosen as model species. New optical, hardware, instrument-operation-mode and data-processing approaches for detection of trace complex molecules were developed. Different physical processes limiting the sensitivity of trace molecule detection were considered and solutions were developed to reduce the influence of these mechanisms on instrument operation. An absorption sensitivity of α_min=2.5×10^-5 for 4.5 ms measurement time was achieved, which is comparable with the sensitivity of “small” molecule detection. The first results utilizing this technique for in-field monitoring of trace complex molecules are presented. Received: 25 April 2002 / Revised version: 29 May 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +7-095/135-8281, E-mail: anber@nsc.gpi.ru     

A heuristic approach to automated molecular line assignment

A first investigation on the feasibility of automated molecular line assignment is presented. Dense rovibrational molecular spectra are normally assigned by strongly interactive computer methods, ranging from commercial spreadsheets to dedicated programs, like Loomis-Wood or Ritz. While a general-purpose, fully automated assignment procedure seems to be out of reach for the near future, we show that a thorough investigation of the problem can lead to new, more efficient and less interactive methods, at least in reasonably favorable conditions. Interesting suggestions are provided by some modern “heuristic” problem-solving algorithms, which mimic natural processes. As a first step, we have developed a “transgenic-evolutionary” algorithm, which has successfully assigned artificial spectra of up to almost 3500 lines. We discuss also its performance on an experimental, but “filtered,” methanol spectrum. Possible future improvements and developments of this method, as well as its limits, are discussed.     

Crystallization of D2O thin films on Ru(0 0 1) surfaces

The phase conversion of amorphous solid water (ASW) to crystalline ice (CI) has been investigated in the very thin (∼10 monolayers) film regime on a Ru(0 0 1) surface. We analyze the converted CI fraction with the Avrami model, and recognize that one-dimensional CI growth occurs, which can be contrasted to the three-dimensional CI growth generally established in the thick (≥50 monolayers) film regime. We evaluate activation energy for the ASW crystallization to be about 1.0 eV. We suggest that the ASW crystallization is not influenced by the substrate even near the substrate-ice interface.     

Computer study of acetylene and ethane adsorption by disperse water medium

Adsorption of acetylene and ethane molecules by water clusters has been investigated by the molecular dynamics method at T=233 K. With the help of determination of statistical weights the cluster systems are created. In the frequency range of 0?ω?1000 cm⁻¹ the integral absorption coefficient of IR-radiation increases after the adsorption of acetylene or ethane molecules by the ultra disperse water system. The dissipation power of IR-radiation by cluster systems increases if C₂H₂ molecules are adsorbed, and it reduces in the case of C₂H₆ molecules' adsorption.     

Influence of particle surface properties on the dielectric behavior of silica/epoxy nanocomposites

Silica/epoxy composites have been widely used in functional electric device applications. Silica nanoparticles, both unmodified and modified with the coupling agent KH-550, were used to prepare epoxy composites. Dielectric measurements showed that nanocomposites exhibit a higher dielectric constant than the control sample, and had more obvious dielectric relaxation characteristics. Results showed that particle surface properties have a profound effect on the dielectric behavior of the nanocomposites. These characteristics are attributed to the local ununiformity of the microstructure caused by the large interface area and the interaction between the filler and the matrix. This phenomenon is explained in terms of prolonging chemical chains created during the curing process. The mechanism is discussed with measurements of X-ray diffraction (XRD) and Fourier transform infrared (FTIR).     

Deuterium separation by multiphoton dissociation of dichlorofluoromethane

Absorption and dissociation probabilities of CHCl₂F and CDCl₂F were investigated by a pulsed CO₂ laser in the wavenumber region of largest selectivity for deuterium. The absorption of CHCl₂F, which is a difference band, can largely be suppressed by cooling. At 200 K and at 920 cm^–1 absorption selectivities up to 4000 were found by extrapolation. In the presence of buffer gas, CDCl₂F can be multiphoton excited nearly like a linear absorber (harmonic oscillator). This is interpreted by a nearly resonant collisional relaxation v₇ to v₂ and by the smallness of the cross anharmonicity x₂₇. The dissociation selectivityS was 24,000 at natural abundance. Such large values were measured by a chromatographic method.S depends only onp _D, the partial pressure of the deuterated species. This dependence is approximately ln Sp _D ^–1 . It can be rationalized by considering only the average energy transferred to the nonresonant molecules by collisions with CDCl₂F. The above functional shape is related to an Arrhenius type law. Comparison with trifluoromethane for D separation shows that CHCl₂F has primarily two advantages: its rapid H-D exchange with water and the less stringent requirements of laser energy and pulse length.A preliminary account of this work has appeared in Quantum Electr.2, 13 (1985) (in Chinese)     

Near-infrared cavity enhanced absorption spectroscopy of hot water and OH in an oven and in flames

A compact diode laser operating around 1.5 μm was used to measure cavity enhanced absorption spectra of hot water molecules and OH radicals in radiative environments under atmospheric conditions. Spectra of air were measured in an oven at temperatures ranging from 300 K to 1500 K. These spectra contained rovibrational lines from water and OH. The water spectra were compared to simulations from the HITRAN and HITEMP databases. Furthermore, spectra were recorded in the flame of a flat methane/air burner and in an oxyacetylene flame produced by a welding torch. The results show that cavity enhanced absorption spectroscopy provides a sensitive method for rapid monitoring of species in radiative environments. Received: 22 February 2001 / Revised version: 23 April 2001 / Published online: 7 June 2001     

On the accurate determination of pressure- induced line shifts in the 2ν<Subscript>3</Subscript> band of H<Subscript>2</Subscript>O at 1320 nm

A simple technique is demonstrated for the accurate determination of pressure-induced line shifts of water in air. High- and low-pressure water samples are simultaneously probed on selected overtone transitions at 1.32 μm using a current-modulated distributed-feedback diode laser and harmonic detection. The resultant profiles yield an average line shift of -293±30 MHz/atm for the 3,3,0 (002)2,2,1 (000)transition at 227251 GHz and -134±7 MHz/atm for the 3,2,1 (002)2,1,2 (000) transition at 227027 GHz. Comparisons are made between first- and second-harmonic detection, and wavelength- and frequency-modulation regimes. The effect of modulation broadening on the returned line shifts is quantified. Received: 12 August 2002 / Revised version: 21 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +44-01865/275410, E-mail: gus.hancock@chemistry.ox.ac.uk     

Frequency measurement of I2 lines in the NIR using Ca and CH4 optical frequency standards

2 lines have been carried out using difference-frequency mixing of the emission of CH₄ and Ca frequency standards at 88 THz (or 3.4 μm) and 456 THz (or 657 nm), respectively. A power of ≈10 pW for the mixing product at 815 nm was obtained using a critically phase-matched KTP crystal and input powers of the order of mW. The relative uncertainty of the measurement was a few times 10^-11, limited by the frequency instability of the laser source locked to I₂. Received: 3 December 1997/Revised version: 16 February 1998     

Local field corrections for light absorption by fullerenes

Semi-empirical atom-atom potential energy calculations based on pairwise additive interactions are performed and, after applying the Born-Oppenheimer approximation to separate high frequency vibrational modes from low frequency orientational and translational modes, the infrared vibrational spectra of CO₂ and N₂O monomers trapped in an argon matrix at a temperature of 5 K are determined. It is shown that only a double substitutional site in argon can accommodate N₂O, whereas CO₂ is trapped in two distinct sites, of single and double substitutional types. The model shows that splitting of the degenerate mode occurs for both molecules in the double site. In the ground electronic state, the vibrational frequency shifts due to the matrix and the vibrational transition moments for low-lying levels are determined using the contact transformation method, as used for gas phase calculations. Calculated energy levels compare well with observed ones and the theory also predicts some unobserved levels. Moreover, calculations show no significant changes in the dipole moments of both CO₂ and N₂O trapped molecules. Received 22 March 2000 and Received in final form 10 May 2000     

Structure and conformational analysis of CFC-113 by density functional theory calculations and FTIR spectroscopy

Altitude-resolved volume mixing ratio profiles of CFC-113 have recently become available on a global scale with the Atmospheric Chemistry Experiment (ACE) satellite mission. However, the accuracy of the retrieval is currently limited by the uncertainties on the spectroscopic parameters of CFC-113. This paper reports on the geometrical structure, harmonic frequencies and intensities in the mid-infrared region of the two conformers of CFC-113 and the evaluation of whether theoretical calculations reproduce measurements. The calculations are performed using density functional theory at the B3LYP/6-311+G(3df) level. The molecular geometry parameters, the enthalpy difference and the potential barrier between conformers are calculated. The harmonic frequency of the normal modes of vibration are presented and accurately compared to experimental data. Overtones and combination bands are assigned in the 1200-2500 cm⁻¹ region.     

Size-selected, supported clusters: the interaction of carbon monoxide with nickel clusters

We report on the size-dependent chemical reactivity of nickel clusters with up to 30 atoms. Monodispersed Ni₃₀ clusters show a higher reactivity for CO dissociation than Ni₁₁ and Ni₂₀. Under our experimental conditions the smallest nickel clusters (Ni_x, x<4) produce nickelcarbonyl complexes. These results demonstrate that such small clusters are unique for catalytic reactions not only due to their high surface-to-volume ratio but also essentially because of the distinctive properties of different cluster sizes. In addition thermal desorption spectroscopy of CO shows that on average four molecules are weakly adsorbed per Ni₁₁ at saturation coverage. Using an isotopic mixture of ¹²CO and ¹³CO, infrared spectroscopy reveals the existence of a vibrational coupling interaction between the four COs. A semi-classical model of interacting dipoles is applied to correlate the observed vibrational frequency shifts with the arrangement of the COs on the cluster. This simple analysis favors a three-dimensional structure for the deposited clusters. Received: 23 March 1998/Accepted: 25 August 1998     

High-accuracy frequency atlas of 13C2H2 in the 1.5 μm region

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to Doppler-free transitions of the ν₁ + ν₃ and ν₁ + ν₂ + ν₄ + ν₅ combination bands of ¹³C₂H₂. The Allan deviation σ/f for a laser locked to line P(10) of the former band follows a slope of 1.6 × 10⁻¹²τ^−1/2, reaching a minimum of 5.7 × 10⁻¹⁴ at τ = 4000 s. The absolute frequencies of 61 lines of the ν₁ + ν₃ band and 43 lines of the ν₁ + ν₂ + ν₄ + ν₅ band, covering the spectral region 1520 nm to 1552 nm, have been measured by use of a combined frequency chain and femtosecond comb, together with a passive optical frequency comb generator. The mean uncertainties for the line frequencies within each band are 1.4 kHz for the ν₁ + ν₃ band and 1.9 kHz for the ν₁ + ν₂ + ν₄ + ν₅ band, representing improvements on the precision of previously published data by factors of 100 and 10⁴, respectively. Improved values of the rotational constant B″ and centrifugal distortion coefficients D″, H″ and L″ of the vibrational ground state are presented.This article is published with the permission of the Controller of HMSO and the Queen’s Printer of Scotland     

A theoretical spectroscopic study of single ammonia molecules adsorbed on the surface of fcc-type argon clusters. Surface effects on the ν 2 vibration-inversion mode

Ammonia monomers have been adsorbed on argon clusters at low temperature K by Rohmund and Huisken [#!frfh97!#] using the pick-up technique. They measured the spectrum of the NH₃ molecules in the region of the umbrella mode. Two broad bands centered around 970 and 1000 cm^-1 with finer details were observed. The authors attempted to interpret the obtained spectrum on the basis of the free rotation motions of the molecules. In this paper semi-empirical atom-atom potential energy calculations are performed for the ammonia monomer adsorbed on a rigid face-centered-cubic (fcc)-type surface of the argon cluster. In the equilibrium position of the rigid molecule on the cluster surface the orientational potential energy surface exhibits two quasi-equivalent minima separated by a potential barrier of about 100 cm^-1. The symmetry of the molecular vibration-inversion double-well potential is destroyed; the inversion motion is then forbidden in the ground state. On the basis of the two adsorption orientations, the vibrational frequency shifts are calculated and the obtained infrared bar-spectrum agrees with the experimental one. Received 6 April 1999 and Received in final form 19 July 1999     

CO2-broadening coefficients in the ν4 + ν5 band of acetylene

The CO₂-broadening coefficients of 24 P- and R-branch transitions in the ν₄ + ν₅ band of acetylene were measured at room temperature using a diode-laser spectrometer. These lines with J values up to 26, were located in the spectral range 1270 to 1400 cm⁻¹. The collisional broadening coefficients were retrieved by fitting the experimental profiles to the Voigt, Rautian, and Galatry lineshape models. Two experimental values for the narrowing coefficient were determined from the spectra and compared with the theoretical narrowing coefficient. The calculations of these broadenings were also performed in the frame of a semiclassical formalism involving a simple intermolecular potential with an adjustable parameter. The theoretical results are in good agreement with the experimental results and reproduce well the J dependence of the broadening coefficients.