Cadmium O‐alkylxanthates as CVD precursors of CdS: a chemical characterization

Cadmium bis(O‐alkylxanthates) are potential single‐source molecular precursors for the chemical vapor deposition (CVD) of Cd(II) sulfide thin films. In this work, a multi‐technique characterization of Cd(O‐RXan)₂ compounds [where O‐RXan is CH₃CH₂OCS₂ (O‐EtXan) or (CH₃)₂CHOCS₂ (O‐ⁱPrXan)] is performed by means of several analytical methods (extended x‐ray absorption fine structure, Raman, Fourier transform infrared and optical absorption, spectroscopics ¹H and ¹³C NMR, thermal analysis and mass spectrometry) for a thorough investigation of their structure and chemical–physical properties. The most important results concerning the chemical behavior under different experimental conditions, with particular attention to relevant properties for CVD applications, are presented and discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

A new acousto-electro-optic improved resolution deflector for high frequency operation

The two main constrains on the characteristics of the acousto-optic deflector are the acoustic sound attenuation and velocity. These two parameters will determine the resolution and the radio frequency bandwidth.Due to a double degenerated phase matching condition on a specific acousto-optic deflector configuration, the possibility of an improvement on the resolution of the acousto optic deflector becomes evident. This degenerescence is the result of the action of a D.C. electric field by the electro-optic effect. This configuration presents several advantages upon the early related works based on optical activity of selected materials and enables a wideband interaction in such a way that the number of resolvable channels is kept high. This has implications on the acousto-optic spectrometers for wideband radio astronomy research.     

Laser Doppler vibrometry based on self-mixing effect

In this paper, a simple, compact and low cost laser Doppler vibrometer is presented. It is simply composed of a laser diode (9 mm in diameter, 2 g of weight, emitting at 825 nm) and by a two-lens optical system designed to focus the laser radiation on the vibrating target. This sensor can measure target velocity. The working principle is based on the self-mixing effect that occurs in a semiconductor laser diode when the emitted radiation is back reflected toward the cavity and then re-introduced inside. The target velocity is calculated measuring the frequency of the peak of the spectrum of the signal generated by a photodiode mounted on the back facet of the laser diode. In this article, the design and the realisation of the vibrometer is reported. The self-mixing vibrometer has been calibrated in the range 0–300 mm/s, using a rotating disk covered with white paper. The effect of the angle of measurement and target distance are reported. Finally, the sensor has been compared with a commercial laser Doppler vibrometer using a vibrating surface as a target.     

Hölder regularity for non-autonomous abstract parabolic equations

This paper contains some existence and uniqueness results for the strict and classical solutionsu : [0,T] →E of the non-autonomous evolution equationu ¹(t)=Λ(t)u(t)+f(t) in a Banach spaceE under the classical Tanabe-Sobolevski assumptions. These results do not require use of the fundamental solution and give new information about the hölder-regularity of the solutions.     

Synthesis and characterization of zinc bis(O‐isopropylxanthate) as a single‐source chemical vapor deposition precursor for ZnS

The utilization of single‐source molecular precursors in chemical vapor deposition (CVD) experiments requires a deep knowledge of their chemico‐physical properties, with particular regard to thermal stability and fragmentation pattern. This study describes the synthesis and characterization of zinc bis(O‐isopropylxanthate), Zn(O‐ⁱPrXan)₂, [O‐ⁱPrXan = (CH₃)₂CHOCS₂], a single‐source precursor for the CVD of zinc(II) sulfide thin films and nanorods. Several analytical methods yielding complementary information (extended X‐ray absorption fine structure, Raman, FT‐IR, UV–Vis optical absorption, ¹H and ¹³C NMR, thermogravimetric analysis, differential scanning calorimetry as well as mass spectrometry techniques, i.e. electrospray and electron ionization, mass‐analyzed ion kinetic energy) are adopted for a comprehensive investigation of purity, structure, thermal behavior and decomposition pathways of the molecule. The most significant results are discussed critically and the properties useful for CVD applications are highlighted. Copyright © 2005 John Wiley & Sons, Ltd.     

Measurement of stress waves in polymers generated by UV laser ablation

Propagation of stress waves into polymer substrates undergoing UV laser ablation has been studied by means of laser Doppler vibrometry technique. The measurements acquired far from the ablation point demonstrate oscillations of high amplitude and low decay. For all the studied samples, realized in polystyrene and polymethylmethacrylate of two different molecular weights, ablation generates mechanical excitation of the structure, which propagates all over the bulk as vibrational modes and stress waves.     

The oxidation of cis- and trans-CHClCHCl

When Cl atoms react with CHClCHCl in the presence of O₂ at 31°C, a long-chain oxidation occurs. The products are the geometrical isomer of the starting olefin and CHClO, HCl, CO, and CCl₂O. The quantum yields of the oxygen-containing products are the same with both isomers and are Φ{CHClO} = 30, Φ{CO} = 11.7, and Φ{CCl₂O} = 1.29. The chlorine atom adds to the olefin and is followed by O₂ addition. The reaction then proceeds with k_6a/k_6b = 19 and k_7a/k₇ ～ 0.5, where k₇ ≡ k_7a + k_7b. The CCl₂H radical oxidizes to regenerate the chain carrier. O(³P) reacts with CHClCHCl at 25°C with a rate coefficient of 6.6 × 10⁸ M^?1 sec^?1 for trans-CHClCHCl and 2.8 × 10⁸ M^?1 sec^?1 for cis-CHClCHCl. The reaction channels are with k_1a/k₁ = 0.23 and 0.28, respectively, for the cis and trans compounds. Reaction (1b) occurs < 4% of the time. Reaction (1c) leads to polymer production and presumably, via redissociation, to the geometrical isomer of the starting olefin. In the presence of O₂ the same long-chain oxidation is observed as in the chlorine-atom initiated oxidation. The chain-initiating step is      

Photoelectron spectroscopy of actinide organometallic compounds I. Bis(cyclooctatetraene)actinide(IV) complexes

The He(I) photoelectron spectra of the antinocene species Th(cot)₂ and U(cot)₂ (cot = cyclooctatetraene) have been determined. The 5f metal ionization has been detected at the onset of the uranocene spectrum. The low ionization energy region of both spectra is discussed in terms of simple qualitative molecular orbital scheme.     

Pressure-induced magnetic switching and linkage isomerism in K0.4Fe4[Cr(CN)6]2.8 x 16 H2O: X-ray absorption and magnetic circular dichroism studies

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% Cr(III)-N[triple bond]C-Fe(II) linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process.     

Curing kinetics of the epoxy system diglycidyl ether of bisphenol A/isophoronediamine by Fourier transform infrared spectroscopy

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE, n = 0) and isophoronediamine (IPD), was studied by Fourier transform infrared spectroscopy (FTIR). The degree of conversions and the reaction rates at different isothermal curing temperatures were calculated from the infrared spectra using a method derived from Beer's law. This method is based on the ratio of the height of the characteristic absorbance peak to reference absorbance peak. A kinetic model proposed by Sourour and Kamal has been used to fit experimental data. Copyright © 2008 John Wiley & Sons, Ltd.