Alain Gleizes

MOCVD of chalcogenides, pnictides, and heterometallic compounds from single-source molecule precursors

The single-source approach to processing materials as thin films by metal-organic chemical vapor deposition (MOCVD) started with pioneering works in the late 1970s and early 1980s, and has developed considerably during the late 1980s and the 1990s. The literature contains some review and feature articles dedicated to its application to various types of materials, the most recent ones appearing in the mid 1990s. The present review aims at putting together results obtained for very different materials so as to obtain a comparative view of the different approaches. Faced with the considerable amount of data accumulated over more than twenty years, the scope of this article will be deliberately and arbitrarily limited to those compounds mentioned in the title. Materials consisting of elements from the second row of the periodic table, or binary combinations including one element from the second row, will not be considered here. This article will refer to precursors that have actually been used in MOCVD processes, rather than potential MOCVD sources.

Two different (oxalato)(bipyridine)copper(II) complexes in one single crystal. Crystal structures and magnetic properties of [Cu2(bipy)2(H2O)2(C2O4)]X2·[Cu(bipy)(C2O4)](X = NO3–, BF4– or ClO4–)

Three complexes of formula [Cu2(bipy)2(H2O)2(C2O4)]X2·[Cu(bipy)(C2O4)](bipy = 2,2′-bipyridine; C2O42–= oxalate, X = NO3–1, BF4–2 or ClO4–3 have been synthesised and their crystal structures determined by single-crystal X-ray diffraction methods at room temperature. They are all isostructural and crystallize in the monoclinic system, space group C2/c, Z= 4, with a= 21.739(2), b= 10.458(1), c= 16.023(2)A, β= 95.69(1)° for 1, a= 22.740(5), b= 10.508(1), c= 16.129(2)A, β= 92.32(1)° for 2, and a= 22.819(3), b= 10.583(2), c= 16.389(2)A, β= 91.52(2)° for 3. The crystal structures of 1 and 2 were determined from Patterson and Fourier analysis and refined by full-matrix least-squares techniques, whereas that of 3 was solved by direct methods. Final values of the reliability factors R(R′) were 0.029 (0.051) for 1, 0.033 (0.046) for 2 and 0.057 (0.059) for 3 with 3290, 3526 and 1972 observed reflections respectively. Their structures consist of cationic centrosymmetric dinuclear [Cu2(bipy)2(H2O)2(C2O4)]2+ units, neutral axiosymmetric mononuclear [Cu(bipy)(C2O4)] entities and either NO3–, BF4– or ClO4– as counter ion. Each copper atom of the dinuclear species is in a square-pyramidal environment with two oxalate oxygen and two bipyridine nitrogen atoms as a base and a water molecule at the apical position. The copper atom of the mononuclear complex is in a slightly tetrahedrally distorted square comprised of two bipyridine nitrogen and two oxalate oxygen atoms. In both complexes one or two more distant atoms of the counter ion completes a (5 + 1) or a (4 + 2) copper co-ordination, respectively. The mono- and di-nuclear entities form an alternating chain via weak interactions through counter ions and copper atoms. Variable-temperature (20–300 K) magnetic susceptibility measurements revealed a strong antiferromagnetic interaction within the dinuclear unit, the singlet–triplet energy gap being –386, –378 and –376 cm–1 for 1, 2 and 3, respectively. The χMT versus T curve for all three complexes exhibits a plateau at T < 80 K which corresponds to the Curie law expected for the mononuclear complex. The magnitude of the exchange coupling in this series has been analysed in the framework of a simple orbital model.

Influence of metallic vapours on the properties of air thermal plasmas

This paper deals with properties of air thermal plasmas containing vapours of iron, silver or copper. The plasma is supposed to be in local thermodynamic equilibrium, for temperatures ranging from 2000 to 30 000 K. First, the equilibrium composition and thermodynamic properties are presented. Then, the radiative properties are calculated using the method of the net emission coefficient. Finally, the viscosity, electrical and thermal conductivities are calculated using the method of Chapman–Enskog. For all mixtures, mole fractions have been used. The results are computed for various values of pressure, plasma size and proportions of vapours. The influence of metallic vapour is important on the electrical conductivity and on the radiation, even at low concentration. All the metallic vapours present a similar behaviour except iron, which has a stronger radiation emission than the other components.

Mixing rules for thermal plasma properties in mixtures of argon, air and metallic vapours

Modelling of electric arcs and thermal plasmas in mixtures of gases and vapours needs prior knowledge of rather large data banks corresponding to thermodynamic functions, transport coefficients and radiation properties. For a given pressure these data are functions of temperature and gas proportions in the mixture. In order to reduce the memory or because some properties of the mixtures are not known, some mixing laws can be useful. These mixing rules allow estimation of the properties of the mixtures when only the corresponding properties of the pure gases or vapours are known. In this paper we study several mixing rules for mixtures of argon or air with metallic vapours. Simple laws such as linear interpolations are compared with relations deduced from physical consideration and some general behaviour is given in conclusion: mixing rules for electrical conductivity, viscosity and net emission coefficient are good. For other properties the use of a mixing law may produce rather large errors.

Lanthanide(III)-copper(II) squarates: synthesis, crystal structure, magnetism and thermal behaviour of [La2Cu(C4O4)4(H2O)16]·2H2O and [Gd2Cu(C4O4)4(H2O)12]2H2O

Abstract [La2Cu(C4O4)4(H2O)16]2H2O and [Gd2Cu(C4O4)4(H2O)12]·2H2O were obtained as single crystals from a mixture of squaric acid and metal chlorides in water. The structures, determined from X-ray diffraction data, are made of heterobimetallic layers in which hydrated Ln(III) and Cu(II) cations are related by squarate anions, according to a scheme which depends on the lanthanoid. Both compounds were submitted to thermal gravimetric and differential analyses in an oxygenated atmosphere, yielding Ln2CuO4 oxides as final decomposition products. The magnetic study of [Gd2Cu(C4O4)4(H2O)12]· 2H2O showed no significant spin coupling between Gd(III) and Cu(II).

Barium-copper(II) oxocarbon compounds: synthesis, crystal structures and thermal behaviours of [Ba(H2O)5][Cu(C2O4)2(H2O)] and [Ba(C4O4)0.5(H2O)2]2[Cu(C4O4)2(H2O2]

[Ba(H2O5][Cu(C2O4)2(H2O)] and [Ba(C4O4)0.5(H2O)2]2[Cu(C4O4)2(H2O)2] were obtained as single crystals in water. The structures were determined from X-ray diffraction data. [Ba(H2O)5][Cu(C2O4)2(H2O)]: triclinic, space group P1, a=9.209(2), b=10.938(1), c=6.547(1) A, α=100.83(1), β=99.65(2), γ=85.45(2)°, Z=2; [Ba(C4O4)0.5(H2O)2]2[Cu(C4O4) 2(H2O)2]: triclinic, space group P1, a=7.752(1), b=10.445(2), c=7.420(1) A, α=99.24(1), β=113.20(1), γ=109.87(1)°, Z=1. They are made of cationic layers separated by anions [Cu(C2O4)2(H2O)]2− and [Cu(C4O4)2(H2O)2]2−, respectively. Both compounds were submitted to thermal gravimetric and differential analyses in an oxygenated atmosphere, up to 950 °C. Final decomposition products were (i) BaCuO2 with small amounts of BaCO3 and CuO for [Ba(H2O)5][Cu(C2O4)2(H2O)], and (ii) an equimolecular mixture of BaCuO2 and BaCO3 for [Ba(C4O4)0.5(H2O)2]2[Cu(C4O4)2(H2O)2].

Complex formation between oxalate and (2,2′:6′,2″-terpyridyl)copper(II) in dimethyl sulphoxide solution. Synthesis and crystal structures of mono- and di-nuclear complexes

The crystal and molecular structures of two new complexes [{Cu(terpy)(H2O)}2(ox)][{Cu(terpy)}2(ox)][ClO4]4·2H2O 1 and [Cu(terpy)(H2O)(ox)]·4H2O 2(terpy = 2,2′:6′,2″-terpyridine and ox = oxalate) have been determined by X-ray diffraction. Crystals of 1 are monoclinic, space group P21/c, with Z= 2, a= 13.443(2), b= 23.183(4), c= 12.394(1)A and β= 116.29(1)°, whereas those of 2 are triclinic, space group P, with Z= 2, a= 10.192(2), b= 12.319(2), c= 8.397(3)A, α= 86.65(3), β= 96.80(3) and γ= 106.14(1)°. The structure of 1 contains two different centrosymmetrical copper(II) dinuclear dicationic units, unco-ordinated perchlorate groups and lattice water. In both dinuclear units the terpyridyl group is terminal and the oxalate acts as an asymmetrical bis(chelating) bridge. However, the copper atom is five-co-ordinate in one dinuclear unit and six-co-ordinate in the other. The structure of 2 consists of neutral mononuclear [Cu(terpy)(H2O)(ox)] entities and unco-ordinated water molecules. The copper atom is in a six-co-ordinate, teragonally elongated, octahedral environment. The stability constants of the oxalato complexes of [Cu(terpy)]2+[equations (i)–(iii)][Cu(terpy)]2++ ox2–+ H+[graphic omitted][Cu(terpy)(Hox)]+(i) 2[Cu(terpy)]2++ ox2–[graphic omitted] [{Cu(terpy)}2(ox)]2+(ii)[Cu(terpy)]2++ ox2–[graphic omitted][Cu(terpy)(ox)](iii) were determined by potentiometry in dimethyl sulphoxide solution: log β111= 12.397(4), log β210= 10.621(6) and log β110= 7.394(2)(25 °C, 0.1 mol dm–3[NBu4][ClO4]). The co-ordination modes of oxalate in the CuIIL–ox2– system (L being tri- or bi-dentate N-donor ligands) are discussed in the light of available thermodynamic and structural parameters.

Improvements of radiative transfer calculation for SF6 thermal plasmas

We present a comparison between an exact calculation of radiative transfer in SF6 thermal plasma based on a fine description of the spectrum with 300 000 spectral points for each temperature value, for simplified conditions (1D and 2D geometries with imposed symmetrical temperature profiles and local thermodynamic equilibrium) and two kinds of approximated calculations. The first is the classical net emission coefficient largely used in arc modelling. The second one is based on a very simplified spectral description with only seven intervals assuming a grey body condition within each interval and using the Planck and the Rosseland averaging for deducing the mean absorption coefficient (MAC). At high temperature the use of the Rosseland averaging is not satisfactory. The other two approximated methods (net emission and the Planck averaging) are acceptable but the radiative flux is in general not very accurate. The radiative transfer calculation can be improved following three ways: a better knowledge of the basic processes and in particular of the absorption coefficients for diatomic and polyatomic molecules, the use of different definitions of MACs (Planck averaging at high temperature and mean natural value at low temperature) and a careful choice of the spectral intervals.

A [MnIII2O(MeCO2)2(H2O)2(bipy)2]2+(bipy = 2,2′-bipyridine) unit with accessible co-ordination sites. Contribution to the modelling of the photosynthetic oxygen evolving centre

A new MnIII binuclear system with an oxo-bis(acetato) bridge and water co-ordinated to the Mn ions has been synthesized, crystallographically characterized, and its antiferromagnetic coupling measured (singlet–triplet gap 6·8 cm–1).

Heterobimetallic d—f Metal Complexes as Potential Single‐Source Precursors for MOCVD: Structure and Thermodynamic Study of the Sublimation of [Ni(salen)Ln(hfa)3], Ln = Y, Gd

Heterobimetallic [Ni(salen)Ln(hfa)3] species [H2salen and Hhfa being N,N′-ethylenebis(salicylideneimine) and hexa-fluoroacetylacetone respectively], where Ni(salen) acts as a neutral chelating ligand towards LnIII, form a series of isostructural compounds for Ln = YIII and any lanthanideIII cation from La to Yb. They are also isostructural with some of the [Cu(salen)Ln(hfa)3] compounds. They sublime without decomposition under vacuum which makes them potential single-source precursors in MOCVD. Sublimation, thermal behaviour, pressure and composition of the vapour phase versus temperature have been studied for the yttrium derivative, by means of thermal analyses, and mass spectrometry using a Knudsen cell. The dissociation process [Ni(salen)Y(hfa)3] = Ni(salen) + Y(hfa)3 has been thermodynamically investigated. Information on the solid-state intermolecular interactions in relation with volatility was obtained through the crystal structure determination of the gadolinium derivative. A comparative structural study of [Ni(salen)Gd(hfa)3] and [Cu(saloph)Y(hfa)3], [H2saloph is N,N′-o-phenylenebis(salicylideneimine)], allows to under-stand why the latter is less volatile than the former despite similar molecular and solid-state structures.