Metal alkoxide precursors volatile

Solution Deposition of Thin Films. Chemical methods of preparation may also be used for the fabrication of ceramic thin films (qv). MetaHo-organic precursors, notably metal alkoxides (see Alkoxides, metal) and metal carboxylates, are most frequently used for film preparation by sol-gel or metallo-organic decomposition (MOD) solution deposition processes (see Sol-GEL technology). These methods involve dissolution of the precursors in a mutual solvent control of solution characteristics such as viscosity and concentration, film deposition by spin-casting or dip-coating, and heat treatment to remove volatile organic species and induce crystaHhation of the as-deposited amorphous film into the desired stmcture. 

The volatile metal-containing precursors which satisfy the ALD criteria fall into four main categories (i) halides, (ii) y0-diketonate complexes, (iii) alkoxides, and (iv) true organometallics, viz. metal alkyls and cyclopentadienyl-type compounds (Fig. 3). Also amido complexes have recently gained attention as possible ALD precursors. Occasionally other compounds have been used as ALD precursors for thin films, for instance, metal nitrates, carboxy-lates and isocyanates [17,18]. 

It may thus be concluded that application of metal alkoxides for preparation of PZT-based thin films in many aspects may be nowadays considered to be a routine technique widely used in many laboratories. The research work is presently mostly focused on electrical and microstructural aspects of these films rather than on chemical routes of their preparation. Irrespective of the technique for the precursor preparation, when 10% excess of Pb is introduced (to prevent loss of lead due to the PbO volatility) the ferroelectric perovskite PZT films are obtained after annealing at about 700°C, demonstrating nonlinear properties of the level acceptable for most of the desired applications. Their typical microstructure is presented in Fig. 10.3. 

Group 2 metal alkoxide compounds are potentially suitable as CVD precursors, especially because hydrolysis and subsequent thermally induced dehydration are likely to lead to complete removal of the supporting ligands. There are examples of Group 2 metal alkoxide compounds that are claimed to have suitable volatility for CVD, but to our knowledge these have not been used successfully. However, Group 2 metal alkoxide compounds have found widespread application in solution routes to metal oxide materials, an area that has been reviewed.1... 

Although metal alkoxides proved to be excellent precursors for the preparation of ceramics by the sol-gel process, their applications in the MOCVD technique are not as widespread, in spite of the attractive features of their volatility and tendency to decompose to the metal oxides. Both of these desirable prerequisites appear to be enhanced, as discussed earlier, by choosing more ramified alkoxide groups. Despite these attractive features, the MOCVD applications of metal alkoxides appear to be limited by (a) their commercial nonavailability, (b) handling difficulties arising from their ready hydrolyzability, and (c) the lack of a clear understanding of their decomposition pathways, which could lead to improvement(s) in the purity of the deposited material. 

The syntheses, physical properties, and molecular structures of alkoxides and aryloxides have been discussed in CCC (1987).161 The alkoxides of scandium and yttrium were reviewed in CCC (1987).1 There have been more recent developments in this area and the impetus for this chemistry has been the developments in materials research. Metal alkoxides and /3-diketonates can be used as precursors for oxide and nonoxide thin films.162 The stable M—O bond and the volatility of the metal alkoxides are important features of this area of chemistry. This has lead to more research in this area particularly in synthesis, NMR, and X-ray crystallography. 

Several rare earth element oxides are components of high 7 superconducting materials. Their preparation is discussed elsewhere in this book (see Chapter 2). In general, rare earth metal oxides can be obtained by the chemical vapor deposition of the appropriate metal /S-diketonates or carboxylates [96]. Volatile metal alkoxides also should be potentially useful precursors for the preparation of rare earth oxides by CVD. Although several volatile rare earth element alkoxides have been reported in recent years [97-101], detailed information concerning their decomposition behavior is not available at this time. 

Volatile metal alkoxides are increasingly being used as precursors for CVD because they are readily converted by thermolysis to pure metal oxides. The first systematic study in this direction was reported by Bradley and Faktor, who investigated the formation of Zr02 from Zr(OBu )4 in a stoichiometric reaction (Equation (4)). 

Sirio, C Poncelet, O., Hubert-Pfaizgraf, L. G., Daran, J. C., and Vaissermann, J., Reactions between copper p-diketonates and metal alkoxides as a route to soluble and volatile copper(II) oxide precursors Synthesis and molecular structure of Cu4( J-3,n -0C2H40iPr)4(acac)4 and (acac)Cu(p-OSiMe3)2Al(OSiMe3)2, Polyhedron, 11, 177 (1992). 

The combination of the greater acidity and the typically lower volatility of phenols over alcohols allows metal alkoxides to be used as precursor for the synthesis of corresponding aryloxide derivatives (Eq. 6.43 ). 

The catalytic activity is a manifestation of the chemical lability of metal alkoxides especially their reactivity with hydroxyl-containing molecules. The volatility and solubility in common organic solvents of certain metal alkoxides has made them attractive precursors for depositing pure metal oxides by chemical vapour deposition (MOCVD) or by the sol-gel process. The requirement for heterometal oxides as useful materials in the electronics industry has stimulated research in this field in recent years and led to renewed interest in the preparation and characterization of alkoxides of some of the p-block elements which had previously been neglected. In particular, the discovery of the high Tc copper oxide-based superconducting heterometal oxides has made a tremendous impact on this field. 

The redox reactions do not in fact belong to the common approaches in preparation of precursors for the sol-gel technology. The only example worth noting here is the oxidation of low-valent chromium derivatives (dibenzene-chromium, Cr(OR)s) by the t-butylperoxide, providing access to chromium(lV) alkoxides— highly soluble and volatile compoimds (Krauss, 1967). On the other hand, the redox reactions are in many cases responsible for the transformation of metal alkoxides in solutions leading to formation of... 

Saita and Maenosono have reported the synthesis of FePt NPs using iron(ni) ethoxide [Fe(OEt)3] and platinum(II) acetylacetonate [Pt(acac)2] as precursors without any reducing agent. Fe(OEt)3 is a brown powder at room temperature (nonvolatile) and is a highly reactive late transition metal alkoxide [248]. In addition, decomposition products of Fe(OEt)3 are less toxic. For these reasons, the use of Fe(OEt)3 as a precursor is suitable for industrialization. An amount of 1 mmol of Fe(OEt)3, 0.5 mmol of Pt(acac)2, 17 mL of octyl ether, 1.6 mL of oleic acid, and 1.7 mL of oleylamine were placed in a three-necked flask at ambient air. The color of the resulting mixture was brown. The molar ratio of Fe to Pt in the mother reaction solution was adjusted to 2. The flask was then evacuated to remove oxygen and volatile components from the reaction solution. After evacuation, the flask was... 

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