Laser cooling in a CO2-laser optical lattice

Received: 19 June 1998     

CO2 laser-induced plasma CVD synthesis of diamond

2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron). Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H₂:CH₄ gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO₂ laser focused beam produced plasma. The deposition area was about 1 cm² and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed. Received: 15 January 1998/Accepted: 16 January 1998     

Light scattering diagnostics of silicon particle growth in CO2 laser-driven reactions

2 laser-induced pyrolysis of silane in a flow reactor, based on scattering of He-Ne laser light by a particulate in the reaction flame. The scattering and extinction measurements have been used to measure nucleation and growth kinetics of silicon powders within the reaction zone. The experience gained by this technique allowed synthesis of silicon particles with a wide size range. Received: 29 April 1998/Accepted: 30 April 1998     

Wet bone ablation with mechanically Q-switched high-repetition-rate CO2 laser

2 laser using a miniature water spray is demonstrated. An ablation threshold of 1.4 J/cm², an optimal energy density of 9–10 J/cm², and a corresponding specific ablation energy of 25–30 J/mm³ are found for pig thighbone compacta at λ=9.57 μm and a beam waist diameter of 0.5 mm. The water spray alleviates tissue carbonization even at high laser pulse repetition rates and increases ablation efficiency. Received: 9 March 1998/Revised version: 6 July 1998     

Splitting of vibrational mode of CO isotopic species in the unstable trapping site in argon matrix

FTIR spectra of the antisymmetric stretch and symmetric bending vibrational modes of isotopic species of CO₂ trapped in argon matrix are recorded at 5 K with a resolution of . A splitting of the mode is observed for the different species in the trapping site termed unstable. Considering this splitting and the width of the line observed for this unstable site, one expects this site to be larger than the stable one. A theoretical model is elaborated to interpret this splitting. Calculations performed at harmonic level of approximation for vibrational modes in a single substitutional site (S1) and a double substitutional one (S2) in a fcc distorted argon lattice to minimize the free energy of the molecule-matrix system, show the splitting to occur in the larger site. The latter result leads us to invert former attribution of the sites: the stable site is a single substitutional one, whereas the unstable site is a double substitutional one. Received: 27 January 1998 / Revised: 30 July 1998 / Accepted: 17 August 1998     

High-resolution measurements of line intensity, broadening and shift of CO around m

Fundamental spectroscopical parameters of CO₂ are reported using a high resolution, direct absorption spectrometer, based on a distributed feed-back diode laser emitting at 2 μm. Line intensity, self- and foreign broadening and shift, with N₂ and O₂ as foreign gases, have been measured with high accuracy in the combination band of CO₂, for 13 lines of the R branch, from R(22) up to R(46). Comparison with available data is made, when possible, and a generally good agreement has been found. Received: 24 April 1998 / Received in final form: 28 October 1998     

Fundamental noise sources in a high-sensitivity two-tone frequency modulation spectrometer and detection of CO2 at 1.6 μm and 2 μm

2 , and its sensitivity is 7(2)×10^-8 in a 1-Hz bandwidth. The corresponding minimum detectable concentration of CO₂ in air has been estimated to be 1 ppm · m. This opens the possibility of a detection at ppb levels at 2 μm, where a two orders of magnitude increase in the CO₂ absorption signal is demonstrated. Received: 06 April 1998/Revised version: 02 July 1998     

CO2 and C2H4 grafting to the native defects of ion-bombarded porous silica

• )₄, though it is expected to relax via formation of peroxidic bridges), and the oxygen-bridge vacancy (which in the absence of relaxation can be described as a diradical center (≡Si^•)₂– the E^′′ center). These radicals react with the residual atmosphere according to completely new pathways: the bombardment in a CO₂ atmosphere results in the formation of ester-like and carboxylate groups, stable up to 500 °C at least, inserted in the SiO₂ network at the oxygen-bridge vacancies. The bombardment in a C₂H₄ atmosphere results in more complex configurations: the oxygen-bridge vacancy reacts at room temperature with ethylene forming a Lewis adduct which, after heating at 500 °C, presumably reverts to a -CH₂-CH₂- bridge in between silicon atoms; the silicon-link vacancy likely reacts with C₂H₄ forming CH₃CHO. These conclusions, based on experimental data (mainly infrared spectroscopy), are also supported by extended quantum mechanical calculations (density-functional methods and ab initio molecular dynamics). Received: 6 March 1998/Accepted: 21 September 1998     

Na-β Alumina powder processing by a Na2CO3 precipitation method

A Na₂CO₃ precipitation method to prepare powder of Na-β-Alumina is presented. Comparisons have been made with powder of the same composition obtained by two other methods: the traditional one and a slurry-solution method. After phase characterisation by X-ray, the powders were calcined at different temperatures. The resulting products were characterised by TGA, DSC and XRD analysis. Finally, density and ionic conductivity of sintered pellets were measured. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

CO2 laser CVD of a-Si:H: in situ gas analysis and model calculations

4 and disilane Si₂H₆ induced by continuous wave CO₂ laser irradiation has been investigated under the conditions of chemical vapor deposition (CVD) of amorphous hydrogenated silicon a-Si:H. At the very position of depositing the thin film the stationary chemical composition of the processing gas is probed in situ by an effusive molecular beam which passes through a differential pumping stage into a quadrupole mass spectrometer (QMS). With SiH₄ as educt and SF₆ as a sensitizer, SiH₄ and Si₂H₆ are found in the processing gas while Si₃H₈ or higher silanes are lacking. Si₂H₆ and SF₆ lead to SiH₄, Si₂H₆, and Si₃H₈, but higher silanes are missing. The experimentally determined composition of the processing gas is semi-quantitatively reproduced by model calculations based on the assumption of stationary local equilibrium conditions and applying thermodynamic and spectroscopic data (molecular statistics). The mass balance of the processing gas entering and leaving the CVD chamber states an atomic ratio Si:H of 1:2 for the gas phase species forming the solid deposit on the reactor walls. This finding together with theoretical considerations indicates the intermediate Si₂H₄ to be the dominating gas phase species forming the a-Si:H thin films. Received: 17 July 1998/Accepted: 20 July 1998     

Si in-diffusion during the 3D islanding of Ge/Si(001) at high temperatures

Received: 7 September 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999     

Surface preparation and characterization of indium tin oxide substrates for organic electroluminescent devices

Received: 10 March 1998 / Accepted: 21 September 1998 / Published online: 24 February 1999     

KrF excimer laser ablation of thin Cr film on glass substrate

Received: 5 October 1998 / Accepted: 14 December 1998 / Published online: 24 February 1999     

The mechanism of nanostructuring upon nanosecond laser irradiation of a STM tip

Received: 20 April 1998/Accepted: 2 June 1998     

Ultrafast structural changes measured by time-resolved X-ray diffraction

Received: 17 April 1998/Accepted: 17 April 1998     

Slow positron annihilation studies of vacancy-type defects in the near-surface region of Cu and Nb before and after wear

Received: 22 June 1998 / Accepted: 9 November 1998     

Simultaneous measurements of second-harmonic generation and two-photon photoelectric emission from Au

Received: 1 October 1998 / Accepted: 30 October 1998     

Transmission characteristics of dichroic filters measured by THz time-domain spectroscopy

Received: 19 March 1998/Accepted: 23 March 1998