The polymerization mechanism of a modified Pechini process was investigated by 87Sr nuclear magnetic resonance spectroscopy for the mixed solution of strontium nitrate, citric acid, and ethylene glycol. The C-ratio (the ratio of citric acid to metal ions in the polymer complex) is suggested to have a strong influence on the quality of the derived film. An analysis of the chemical shift variation, as a function of C-ratio, indicates the presence in the solution of two species: solvated strontium ions and strontium ions bound to the polymer complex, with a stoichiometry of 1:7. A polymeric precursor model based on this stoichiometry is proposed. Through a relaxation rate study of the strontium sites, it was found that the polymerization mechanism is predominantly bimolecular within the concentration region being studied. The equilibrium rate constant for the polymerization was calculated to be 104 s−1. A kinetic study of the fast cation exchange between the two identified strontium sites indicates that the inhomogeneity of the polymeric network leads to film cracking during pyrolysis.

Ferroelectric and other high dielectric constant metal oxides currently are sought-after for a variety of applications in the electronics industry. To meet the demand of preparation of these interesting materials in a manner compatible with traditional silicon-based fabrication procedures, chemical vapor deposition routes are desired for film growth. Compounds displaying high vapor phase stability are necessary as precursors for these applications. Additionally, in general, it is preferred to utilize compounds in a liquid state, due to the more rapid re-establishment of equilibrium at a liquid-vapor interface, compared to that present at a solid-vapor interface. This combination of desired molecular properties, in turn, presents a great challenge to the coordination chemist. Several of the metals of interest for these uses reside in groups 2–5. Common design features are emerging for the ligands best suited for attachment to these metals for subsequent utilization in the deposition of metal oxides. In order to achieve coordinative saturation of the relatively high ionic radii exhibited by most of these elements, multidentate, monoanionic ligands are relied upon. In the past, most often, homoleptic ligand sets have been employed, thereby reducing the chance for ligand scrambling to occur during the growth process. Such disproportionation processes have been credited, in previous work, with the observation of a temporal decay in vapor pressure of heteroleptic compounds. In some interesting new developments, it has been found that heteroleptic compounds possess sufficient vapor phase integrity to permit their evaluation as CVD precursors. These, and related, results are presented herein.

New strontium (host lattice constituent) and cerium (doping element) precursor sources have been developed and evaluated for deposition of blue color emitting SrS:Ce thin films by ALE (Atomic Layer Epitaxy). In the case of strontium, the monomeric derivative [Sr(hfac)2]*triglyme has been synthesized and structurally characterized, whereas, for cerium, the utilization of its homoleptic tris amide derivative Ce{N[Si(CH3)3]2}3 has led to a blue color emitting SrS:Ce. In a further effort, emission characteristics of SrS:Ce doped with the β-diketonate-related Ce(tmhd)4 derivative have been weighed against data obtained employing the cerium tris amide composition.

Compounds of the general formula M(SR)2 (M = Zn, Cd; R = i-Pr, t-Bu, Bz) have been prepared and explored as potential unimolecular starting materials for the preparation of binary group 12 metal sulfides. These new compounds have been characterized by IR spectroscopy and thermogravimetric analysis. Chemical derivatization of these insoluble metal-bis(thiolate) compounds by complexation with N-CH3 -imidazole renders them more soluble. These adducts were investigated by elemental analysis. Thermolytic decompositions of both the parent and derivatized compounds have been carried out both in the solid state and by heating a suspension of the appropriate metal-bis(thiolate) compound in an inert high boiling hydrocarbon medium. The thermolysis products have been studied by GC/MS (liquids) and x-ray powder diffraction (XRPD), scanning electron microscopy (SEM), and particle size determination (solids).

The synthesis, characterization and decomposition of several indium thiolates containing the bulky substituted aryl ligand 2,4,6-i-Pr 3C6H2 (Ar′) or the internally chelating ligands 2-CH3O,5-CH3C6H3 (Ar″) and o-C6H4CH2N(CH3)2 (Ar"‘) are described. Two synthetic methods have been utilized: metathesis reactions between lithium thiolates and the appropriate metal halides and the addition of elemental metal to diaryl disulfides. The thermal decomposition of each indium precursor results in the formation of 1n2S3, based on thermogravimetric data. The homoleptic compound In(SAr′)3 can be isolated as a yellow oil. This liquid precursor has been derivatized by the reversible formation of acetonitrile and tetrahydrofuran adducts. Although, the molecule exists as a monomer in both adducts, the coordination number of the metal and he orientation of the ligands are markedly different. The internally chelating In(SAr″)3 and In(SAr.″′)3 adopt contrasting dimeric and monomeric structures respectively.

The synthesis and characterization of thermally stable, volatile, group 2 element-containing complexes is an important prerequisite for the subsequent use of these compounds in chemical vapor deposition (CVD) of superconducting metal oxides (SMO) and other electronic materials, e.g., YBa2Cu3O7-δ. and CaGa2S4:Ce. The utilization of group 2 metal ethoxide compounds {[M(OEt)2(EtOH)4]n (where M = Ca, Sr or Ba)) as precursors to additional complexes is discussed. For example, the compounds [M(tmhd)(OEt)(EtOH)]n (Htmhd = 2,2,6,6- tetramethylheptane-3,5-dione) may be obtained by reacting one equivalent of Htmhd with the metal bis(ethoxide), and these also may be reacted further with functionalized alcohols, or a second β–diketone, to form heteroleptic compounds. Additionally, the preparation and characterization of some Lewis base adducted complexes have been examined with an emphasis on the role that water plays in their isolation.

Zinc selenide doped with nitrogen deposited by organometallic vapor phase epitaxy (OMVPE) is one example which leads to a material that produces a blue emission. However, the effective incorporation of the nitrogen dopant into the zinc selenide lattice has not yet resulted in the demanded efficiency. One potential solution involves the design of a precursor introducing the nitrogen dopant bonded to zinc that survives the thermal decomposition process. Several new zinc bis(amide) compounds with the general formula Zn[N(R)(R′)]2 have been synthesized. Investigations into the thermal decomposition mechanisms of these compounds have provided insight into the potential usefulness of the designed precursor in the preparation of ZnSe:N.

The homoleptic compound erbium{tris[bis (trimethylsilyl)]amide} displays high doping ability for incorporation of the rare earth element into epitaxially grown semiconducting host materials for fabrication of temperature-independent, monochromatic solid state optoelectronic devices. Electronic characteristics derived from erbium doped semiconducting films have been obtained. Several more volatile and lower melting representatives of this class of compounds have been synthesized, characterized by various analytical techniques and examined for their suitability to incorporate optically-active erbium centers into a semiconducting environment.

MOCVD, one preferred technique of the present electronics industry, has not yet emerged as the thin film method of choice for group 2 element containing materials due to the demonstrable shortcomings of the available source compounds. Most specifically, the challenge presented by the group 2 element charge/ionic radius ratio must be overcome to meet the vapor pressure requirements for CVD. To date, development of group 2 precursors suitable for MOCVD has focused mainly on the use of substituted acetylacetonate (acac) complexes. Earlier, several series of somewhat volatile precursors were developed by the use of acetylacetonate complexes containing fluorinated sidegroups. These precursors, while elegantly designed for the thermal deposition of BaF2, are not ideal for the preparation of oxide thin films. This arises from their propensity to initially form MF2, which must be reacted further in situ, or in a post-deposition treatment to yield the ultimately sought metal oxide. It is of interest, therefore, to develop stable, volatile precursors lacking fluorinated ligands.

The roles which ligand size and stability play in influencing solid-state thermolyses products and phases are developed for a group of metal thiolate compounds. The exploration includes Pb(SR)2 [R = t-Bu, i-Bu, s-Bu], Cd(SR*)2 [ R* = i-Pr, I-Bu, Bz], ClHgSR** [ R** = i- Pr, neo-Pent, Bz] and In(SR***)3 [R*** = 2,4,6-(i-Pr)3C6H2, 2-CH3O-5-CH3C6H3, o- C6H4CH2N(CH3)2]. In several examples, the precursors have been characterized by single crystal X-ray diffraction. In most cases, solid-state decomposition products have been identified by XRPD, and volatile decomposition products have been identified by GC/MS. All precursors have been studied by TGA.

Examples of chemical control in CVD of metallic and ceramic films are highlighted. Specific attention is paid to the complexity of precursor design. The effect of reactor environment on growth chemistry is investigated. Examples where reducing or oxidizing atmospheres provide a high level of control over deposit composition are outlined. The system examined centers on yttrium and yttria. These materials are, in general, desired less for their optical or electronic properties and more for their structural properties. Thus, the rigid purity demands of the microelectronics industry are somewhat relaxed. Nevertheless, critical attention must be paid to the issues of vapor pressure and decomposition profile. Where sufficient data is available to justify it, some explaination of the issues relevent to vapor pressure is presented.

Coordination compounds of alkaline-earth metals with simple monodentate ligands were mentioned in the literature as early as 1820, when Faraday reported ‘metal-ammonias’.[1] The number of heavy alkaline earth element coordination compounds remained limited for many years, however, as it was thought to be unlikely for the large earth alkaline cations to form such complexes. In 1967 Pedersen discovered that cyclic oligoethers (crown ethers) can serve as suitable ligands for divalent alkaline earth cations.[2] His findings were extended a few years later by Lehn who found that macrobicyclic multidentate ligands (cryptands) are efficient ligands for alkaline earth cations.[3] In each of these examples, the primary mode of metal-ligand interaction is electrostatic in origin. These examples demonstrate the lack of well-defined covalent bonding for Ca, Sr and Ba compounds. In the 25 years which have passed since Pedersen's seminal discovery, a large number of coordination compounds containing alkaline earth metals have been synthesized. In recent years, the emphasis has shifted towards the preparation of group 2 element-containing compounds which potentially can be used as precursors in the preparation of metal oxides by chemical vapor deposition [4–8]. In light of the general agreement that no “perfect” barium source presently exists for OMVPE purposes, this article will focus on general themes in group 2 element chemistry and, where relevant, correlate those themes within an integrated approach to design of new compounds of greater potential utilization for the preparation of electronic materials in thin film form.

It previously has been difficult to probe the localized coordination environment of aluminum atoms in amorphous alumina samples by solid state NMR spectroscopy. Such an in situ technique has benefits in probing the structure of the material and monitoring the evolution of the microstructural development during thermal processing. The recent developments of more sophisticated NMR techniques by Pines, et al., specifically devised for treatment of problems unique to the solid state spectroscopy of quadrupolar nuclei, have permitted a glimpse into these Materials. As a result of applying these experimental techniques to new materials systems, a better understanding of the solid state structure of amorphous aluminas derived from polymer pyrolysis has emerged. Correlations between the onset and completion of crystallization and the localized structure may now be possible.

In earlier work, the effective utilization of Zn {N\Si(CH3)3]2}2 as a site-selective dopant for the production of p-type ZnSe by OMVPE was demonstrated. Several new zinc-bis(dialkylamides) of the general form (R)(R′)NZnN(R″)(R‴) now have been prepared. They have been characterized by 1H- and 13C-NMR, GC/MS and elemental analysis. Vapor pressures and gas phase decompositior profiles have been examined. Correlations of vapor pressure and structure are discussed for this series of compounds. A mechanism for the site-selectivity observed in the incorporation of nitrogen is proposed.

Rare earth elements are important as dopants in the preparation of semiconductors, particularly for temperature-independent optical devices. The compound Er{N\Si(CH3)3]2}3 has been demonstrated to be a suitable source compound for erbium doping of semiconducting materials. Further investigations of this and related compounds have been carried out. New compounds have been characterized by 1H NMR, FTIR, TGA and elemental analysis techniques. Vapor pressures and decomposition profiles have been examined for these compounds.

Tetrakis(iso-propyl)diarsine was synthesized by the reaction of (i-Pr)2AsLi with (i-Pr)2AsI. The lithium salt of the secondary arsine was produced following deprotonation of (i-Pr)2AsH, obtained by reduction of (i-Pr)2AsI, which was prepared by the thermolysis of (i-Pr)3Asl2. The X-ray crystal structure of \(i-Pr)3AsI]\I] has been determined on the product of the reaction of (i-Pr)3As and 12. Compounds of the general form E=As(i-Pr)3 (E = O, S, Se) have been prepared.

Much interest in the area of ferroelectric thin films has been generated by the recent developments in unique property observation for these materials. As deposition methods move toward potential commercialization, the importance of chemically and thermally stable at use temperature, high vapor pressure and purity, readily available and economically competitive sources for the requisite group 2 elements will emerge. This presentation entails an initial overview of the presently utilized compounds, their advantages and disadvantages. New group 2 CVD precursors have been developed based both on inter- and intramolecular stabilization of cyclopentadienides, alkoxides and β-diketonates. Recent results on the coordination environment around the central metal atom have offered insight into the next generation of polydentate, monoanionic ligand design. Specific details are discussed for the metal complexes of “scorpion-tail” β-diketoethers. Results of comparison studies between these new precursors and earlier compounds are presented as a model for designing future sources.

Metal thiolates of the general formula M(SR)2 (M = Pb, Zn, Cd) and Cl-Hg-SR (R = alkyl) have been prepared and characterized by spectroscopic techniques, TGA and, in selected cases, single crystal X-ray diffraction. The metal bis(thiolate) compounds can be converted into the related metal sulfides by thermolyses. The solid state materials have been characterized by XRPD, SEM and, in selected cases, by particle size determination. The volatile pyrolytic co-products have been isolated and characterized by GC/MS. The decomposition pathways of mercury chlorothiolates are more complicated and depend on the nature of the organic group present in Cl-Hg-SR.

The overall objective of this research is to develop source materials for doping AIGaAs. We compared Er(C5H5)3 to Er{N[Si(CH3)3]2)3 for purity, decomposition kinetics and doping of germanium films deposited from Ge(CH3)4 in a hydrogen atmosphere. Cyclopentadienyl erbium left large amounts of carbon both in pure metal films, and in the germanium film, at low pressure and temperatures to 850°C. Bis-(tri-methylsilyl) erbium amide decomposed cleanly without carbon, nitrogen or silicon in the deposited film.

Films of YBa2CU3O7-δ have been grown on 1” LaAlO3 by OMVPE utilizing M(tmhd)n (M = Ba, Cu: n = 2; M = Y: n = 3; tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato) as the source materials in a cold wall, vertical rotating disk reactor. The resultant films were characterized by SEM, XRD, Tc, Jc, and surface profilometry measurements. Relative to laser ablated thin films, the surface morphology was determined to be virtually featureless. In-situ depositions at substrate temperatures of <700°C, employing nitrous oxide as the oxidizing reagent, produced annular irregularities in the electronic properties of these films. The highest quality was observed near the film's center, with a marked decay evident toward the exterior 7 mm perimeter of the coated wafer.