Aerosol CVD

Direct metering of liquids/solids, followed by immediate vaporization in a vessel, also can be used. For metering of liquids (either neat, or as solutions of solids), flowmeters and various dispensing pumps are available (Figs. l-2a,b and 1-3, Tables 1-1 and 1-2). The final vaporization takes place in, for instance, a hot box - a vessel containing objects held at high temperature. This process should be differentiated from aerosol CVD (see Sect. 1.3.1.5). For some compositions, direct solid feed systems have been proven as a delivery mode (Fig. 1-4, Table 1-3). 

In spray pyrolysis, a solution of metal complexes is sprayed directly or via aerosol formation onto the substrate. Complicated reactions between precursors and molecules of the solution occur finally before forming the deposit. It is difficult to separate the work on spray pyrolysis from CVD, because the borderline between aerosol CVD and spray pyrolysis is not well defined and, therefore, the latter was included in this report. 

Silver(I) /3-diketonate derivatives have received significant attention due to the ease with which they can be converted to the elemental metal by thermal decomposition techniques such as metal organic chemical vapor deposition (MOCVD).59 The larger cationic radius of silver(I) with respect to copper(I) has caused problems in achieving both good volatility and adequate stability of silver(I) complexes for the use in CVD apparatus. These problems have been overcome with the new techniques such as super critical fluid transport CVD (SFTCVD), aerosol-assisted CVD (AACVD), and spray pyrolysis, where the requirements for volatile precursors are less stringent. 

AgL(hfac)] (L = SMe2, SEt2, SPr2, SBu2, 1,4-oxathiane).811 The use of aerosol vaporization methods has allowed efficient CVD from complexes [Ag(hfac)(SR2)].819... 

Films at NASA GRC were deposited using homemade spray or aerosol-assisted chemical vapor deposition (AACVD) reactors to exploit the lower deposition temperature enabled by the simpler decomposition chemistry for the SSPs.6 9 AACVD is a simple and inexpensive process that offers the advantage of a uniform, large-area deposition, just like metal organic CVD (MOCVD), while also offering the low-temperature solution reservoir typical of spray pyrolysis methods. 

In the absence of suitable volatile precursors, aerosol-assisted CVD (AACVD) has been used, whereby a precursor solution is atomized and the micron-sized particles deposited onto a heated substrate to grow into thin films [98], LSM thin layers (4 to 5 4m) have been deposited in this way [99-100],... 

The deposition of particles on macroscopic surface is the primary goal in CVD processes, bnt rednces the efficiency of vapor phase particle synthesis. Particles can deposit by Brownian motion, bnt in high-temperature reactors, thermophoretic deposition often dominates. Thermophoresis is the migration of small aerosol particles as a resnlt of a temperatnre gradient. It causes particles carried in a hot gas to deposit on a cool surface. Eor small particles, Kn 1, a dimensionless group can be created to describe thermophoresis, Th ... 

Evaporative decomposition erf solutions and spary pyrolysis have been found to be useful in the preparation of submicrometer oxide and non-oxide particles, including high temperature superconducting ceramics [819, 820], Allowing uniform aerosol droplets (titanium ethoxide in ethanol, for example) to react with a vapor (water, for example) to produce spherical colloidal particles with controllable sizes and size distributions [821-825] is an alternative vapor phase approach. Chemical vapor deposition techniques (CVD) have also been extended to the formation of ceramic particles [825]. 

Other CVD Processes. CVD also finds extensive use in the production of protective coatings (44,45) and in the manufacture of optical fibers (46-48). Whereas the important question in the deposition of protective coatings is analogous to that in microelectronics (i.e., the deposition of a coherent, uniform film), the fabrication of optical fibers by CVD is fundamentally different. This process involves gas-phase nucleation and transport of the aerosol particles to the fiber surface by thermophoresis (49, 50). Heating the deposited particle layer consolidates it into the fiber structure. Often, a thermal plasma is used to enhance the thermophoretic transport of the particles to the fiber walls (48, 51). The gas-phase nucleation is detrimental to other CVD processes in which thin, uniform solid films are desired. 

Metal sulfide films were also deposited by aerosol-assisted (AA)CVD, as exemplified by the results for Ca(SOCMe)2(15-crown-5) described here. 

Aerosol delivery of the precursors was chosen because it was expected that although the species were monomeric, their volatility was likely to be low based on the TGA results described earlier, and that the crown ether might dissociate on heating for extended periods. The compound Ca(SOCMe)2(15-crown-5) was dissolved in ethanol and delivered in a nitrogen gas stream to a cold-wall atmospheric pressure CVD reactor where the substrate temperature was varied between 300 and 400°C. Analysis of films deposited at 310°C revealed that crystalline CaS was deposited, approximately 100 nm thick, with a deposition rate of 10 nm/min. The X-ray powder pattern indicates that CaS was formed with preferential (200) orientation (see Fig. 63). The SEM data showed that the films comprised cubic crystallites with dimensions consistent with the linewidth of the peaks observed by X-ray diffraction. The bulk composition corresponded to CaS as determined by AES. 

Cn(hfac)2 (7b) °. The qnality of the copper fihns deposited on the SAM diffusion barrier was high regarding pnrity and nniformity, comparable to that of films deposited on Si(lOO) and traditional diffnsion barriers (TiN). Copper selenide binary phases can be grown from Cn(acac)2 (7a) and trioctylphosphine selenide. Depending on the techniques applied, tetragonal Cn2Se (aerosol-assisted CVD) or cnbic Cn2 xSe nanoparticles capped with hexadecylamine (liqnid deposition) are prodnced. ... 

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