Thin-film preparation compounds

Aylett, B. J., and Tannahill, A. A., Chemical Vapour Deposition of Metal Silicides from Organometallic Compounds with Silicon-Metal Bonds, SIRA Int. Seminar on Thin Film Preparation and Processing Technolgy, Brighton, UK (March 1985)... 

In addition to metal alkyls and cyclopentadienyl compounds other types of true organometallic precursors have also been applied in ALD depositions. For example, ( 6115)361 [162,163] and (C6H5)4Pb [164] have been used for the preparation of bismuth- and lead-containing oxide thin films. These compounds are nof exfremely reactive and therefore ozone is needed to obtain completely oxidised films [162,163]. H2O2 as a second precursor does not oxidise (C6H5)3Bi completely, since metallic bismuth was observed in the deposited films [162]. 

Chemical vapor transport is used to synthesize thin films of materials on a substrate. The film can be the same composition as the substrate or different. In order to proceed with chemical vapor transport, the constituent elements of the compound to be deposited as a thin film must be brought into the vapor phase. Given that many of the thin films of commercial importance involve elements with little or no practical vapor pressure, a lot of attention has been focused on preparing volatile compounds that contain the elements needed in thin-film preparations. Most chemical supply companies carry these compounds as stock items. The major classes of compounds include metal alkyl, metal carbonyl, metal alkoxide, metal 3-diketonates, and organometallics. Examples of each are given in Table 3.1. 

Intermetallic compounds, even those of the transuranium elements, can be prepared by vapor transport and deposition of thin films. The compound AUCm was recently formed in this way on the submilligram scale. ... 

Interest in barium yttrium alkoxides stems from metal organic vapor deposition experiments for the preparation of superconducting thin films. The compound [Y4Ba20(0Et)8(dmp)6] (where dmp = B C CHC Bu1) has been prepared by the reaction of Y50(0Pr1)13 with Ba(OEt)2 (PPOH) in the presence of dmpH.167 The structure contains seven-coordinate yttrium atoms with... 

Sampling methods used for IR analysis of clathrate hydrate compounds, which are largely composed of highly absorbing water molecules, were limited to mulls, thin films prepared by vapor co-deposition methods (the resulting amorphous deposit is warmed in a vacuum to the crystallization temperature" ), or adamantane pellets... 

Figure 27.11 SEM surface images of Ca-modifled PbTi03 thin films prepared from solutions containing (a) a short carbon chain carboxylate compound of calcium (calcium acetate) and (b) a long carbon chain compound of calcium (calcium acetylacetonate). (c) IR analysis of the powder resulting after...

Thin films of metals, alloys and compounds of a few micrometres diickness, which play an important part in microelectronics, can be prepared by die condensation of atomic species on an inert substrate from a gaseous phase. The source of die atoms is, in die simplest circumstances, a sample of die collision-free evaporated beam originating from an elemental substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect die crystallographic form of die condensate. If diis surface is at room teiiiperamre, a polycrystalline film is usually formed. As die temperature of die surface is increased die deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while odier properties such as surface morphology and dislocation sttiicmre can be established by electron microscopy. 

Fabrication techniques, especially the preparation of thin films of functional materials, have made major progress in recent years. Thin-film solid electrolytes in the range of several nanometers up to several micrometers have been prepared successfully. The most important reason for the development of thin-film electrolytes is the reduction in the ionic resistance, but there is also the advantage of the formation of amorphous materials with stoichiometries which cannot be achieved by conventional techniques of forming crystalline compounds. It has often been observed that thin-film electrolytes produced by vacuum evaporation or sputtering provide a struc-... 

Direct-current sputtering is not generally applicable for the preparation of thin-film solid electrolytes since these compounds are electronic insulators. The target surface would be charged with the same polarity as that of the ions in the plasma, and the sputtering plasma would rapidly break down. 

Several patents dealing with the use of volatile metal amidinate complexes in MOCVD or ALD processes have appeared in the literature.The use of volatile amidinato complexes of Al, Ga, and In in the chemical vapor deposition of the respective nitrides has been reported. For example, [PhC(NPh)2]2GaMe was prepared in 68% yield from GaMes and N,N -diphenylbenzamidine in toluene. Various samples of this and related complexes could be heated to 600 °C in N2 to give GaN. A series of homoleptic metal amidinates of the general type [MIRCfNROilnl (R = Me, Bu R = Pr, BuO has been prepared for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. The types of products are summarized in Scheme 226. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. 

Recent considerations of metal UPD on semiconductor surfaces suggest that light-assisted processes gain much significance in the relevant technology. The use of photoinduced UPD as an approach for the preparation of compounds and composite semiconductors either in thin films (layered structures) or in particulate suspensions is a challenging issue that will be outlined promptly. 

To date, most small molecule-based OLEDs are prepared by vapor deposition of the metal-organic light-emitting molecules. Such molecules must, therefore, be thermally stable, highly fluorescent (in the solid state), form thin films on vacuum deposition, and be capable of transporting electrons. These properties limit the number of metal coordination compounds that can be used in OLED fabrication. 

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