CVD synthesis

Molecular Group 3-5 compounds are currently of considerable interest for two reasons (a) they can serve as volatile low molecular weight single-source precursors for the CVD synthesis of binary and multinary group 3/5 semiconductors with remarkable optoelectronic properties (54), or (b) they are potentially useful cocatalysts for the polymerization reactions of unsaturated organic substrates (55, 56). Various strategies have been employed to synthesize well-defined aggregates. 

FIG. 26. Scanning electron micrographs (A) the template-synthesized gold tubule ensemble obtained after dissolution of the polyester template membrane (B) as per A, but after CVD synthesis of TiSj outer tubes on the Au inner tubes. These tubular microstructures contained 0.86 mg of TiS2 cm of substrate A1 surface area (C) as per B, but with a larger quantity (2.04 mg cm ) of TiSj (D) CVD TiSj film. 

For a successful CVD-synthesis of c-BN a reaction system has to be found, where c-BN is deposited and h-BN and amorphous BN formation can be prevented or where the undesirable phases can be removed by selective etching during the deposition. 

The most widely used precursors for the CVD-synthesis of TiC>2 thin films are TiCl4 and titanium isopropoxide. The chemical nature of the precursors has been shown to have a direct influence on the properties of the deposited Ti02 films, as reported by Evans and coworkers (2006). The existence of oxygen in titanium isopropoxide molecules makes it possible for an intramolecular reaction to take place. 

Figure 12 Schematic process flow-chart for the CVD synthesis of regular arrays of oriented nanotubes on a porous silicon through catalyst patterning (a) SEM image of nanotube blocks synthesized on 250 tm by 250 pm catalyst pattern. The nanotubes are 80 pm long and oriented perpendicular to the substrate, (b) SEM image of nanotube towers synthesized on 38 pm by 38 pm catalyst pattern. The nanotubes are 130 pm long, and (c) side view of the nantube towers in (b). (Reprinted with permission from S. Fan, M.G. Chapfrne, N.R. Franklin, T.W. Tombler, A.M. Cassell, and H. Dai, Science, 1999, 283, 512. 1999 AAAS)...

Figure 14 Different types of carbon nanotubes formed by irradiation (A) and CVD synthesis (B). (A) Cross-linking of SWNTs using 60 s electron irradiation (1.25 MeV with beam intensity ca. 10 Acm ) at 800 °C (a) before irradiation and (b) after irradiation. (Reprinted with permission from M. Terrones, F. Banhart, N. Grobert, J.-C. Charlier, H. Terrones, and P.M. Ajayan, Phys. Rev. Lett, 2002, 89, 075505. 2002 by the American Physical Society.) (B) Y -Jimction MWNTs synthesized using nickelocene with thiophene at 1000 °C. (Ref. 91. Reproduced by permission of American Instimte of Physics)...

Fig. 21 Reaction scheme for CVD synthesis of azomethine conjugated polymer, poly.

Solvothermal decomposition of titanium tcrt-butoxide and titanium oxy-acetylacetonate (TiO(acac)2) in toluene at 300°C yields nanocrystalline anatase. It should be noted that the lowest temperature required for the formation of crystalline titania by CVD synthesis was reported to be 400 to 450°C. ° ° ... 

Zakhidov, A., KhayruUin, L, Baughman, R. et al., CVD synthesis of carhon-hased metallic photonic crystals, Nanostruct. Mater., 12, 1089, 1999. 

THERMAL CVD SYNTHESIS OF CARBON NANOTUBES IN SWIFT HEAVY ION TRACKS OF SILICON DIOXIDE... 

The CVD-synthesis of DWNT is conducted at conditions similar to those in the preparation of other nanotubes by deposition from the gas phase. The catalyst is... 

The NbiSn phase was first determined to be superconducting at 18.0 K in 1954 by Matthias et al. [39]. NbiSn adopts the cubic [Cr.iSij structure (Fig. 2-5) with an -axis spacing of about 5.29 A. NbjSn is a nonductile material with a CTE of 9.8 ppm/K as determined using high temperature X-ray diffraction from 25 to 700 °C (Table 2-4). The CVD synthesis of Nb Sn was first realized in 1964 by G. W. Cullen et al. [40]. This was a landmark contribution as it was the first LTS superconducting material to be synthesized by CVD. Two reviews by researchers at RCA provide additional details and specialized information on Nb Sn CVD [40, 41]. 

K [75a]. NbN can be considered to be a face-centered cubic interstitial compound which adopts the B1 rocksalt structure (Fig. 2-6) with an a-axis spacing of 3.33 to 3.36 A [76] (Table 2-4). The first CVD synthesis of NbN was reported by Powell et al. in 1955 [77]. Only a limited number of papers have been reported subsequently. 

NbiSi adopts the cubic [Cr Si] A15 structure (Fig. 2-5) with an a-axis spacing from 5.16 to 5.23 A. The CVD synthesis of superconducting Nb Si films by hydrogen reduction of niobium and silicon chloride mixtures (Eq. 2.9) has been reported by two groups... 

There is one report of the CVD synthesis of superconducting V,Si films by hydrogen reduction of vanadium and silicon tetrachloride mixtures (Eq. 2.10) [84], Supercon-... 

Researchers at Advanced Technology Materials (ATM) and Los Alamos National Laboratory (LANL) have focused on the CVD synthesis of Tl-2212 thin films on MgO substrates [277]. Fluorinated MOCVD precursors were used to grow Ba-Ca-Cu-O (F) thin films which were then annealed in the presence of H2O/O2 to promote fluoride evolution. The films were placed face down between two TBCCO pellets and annealed. The resultant superconducting films exhibited average electrical properties with Tc = 108 K and 7. = 1 x in Acm at 90 K. 

While HPHT, shock wave, and CVD synthesis of diamond have been commercialized, these methods have serious limitations. None of them allows economical growth of large single crystals and the diamond quality does not satisfy the requirements for electronic or gem applications. Since the quality and size of the best natural diamonds have not yet teen reproduced in the lab, the search for a tetter method of diamond synthesis continues. Recent work demonstrates that diamond can be formed metastably under a variety of conditions. 

Current understanding of the diamond synthesis under hydrothermal conditions and quantity of diamond produced are comparable with those of CVD synthesis of diamond at the end of the 1950s or the beginning of the 1960s. Thus, we are at the beginning of the road and further research is strongly recommended. 

Cassell AM, Raymakers JA, Kong J, Dai H. Large scale CVD synthesis of single-walled carbon nanotubes. J Phys Chem B 1999 103 6484-92. 

Susi T, Nasibulin AG, Jiang H, Kauppinen EL CVD synthesis of hierarchical 3D MWCNT/carbon-fiber nanostructures. J Nanomater 2008 2008 61. 

M.S.P. Shaffer, et al., CVD synthesis of carbon nanotubes, 2012, Cambridge University Technical Services Limited (Cambridge, GB) US Patent 8173211B2. 

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