MO-CVD

As stated in the introduction, hexamethyldisilazyl can be used to coordinate electropositive elements in a very efficient way. Nevertheless, with divalent metallic elements it is often found that further organic bases are coordinated to the metal thus, in [(Me3Si)2N]2Cr(THF)2 the chromium atom is linked to two nitrogen and two oxygen atoms [9]. Such compounds tend to dissociate in the gas phase which makes them less appropriate for reactions controlled by pressure and temperature, as in MO-CVD processes. 

Thin films of Ce02 have been obtained using molecule based metal-organic chemical vapor deposition (MO-CVD). This method is attractive because of the possibility to coat complex shapes and to use lower growth temperatures. The actual application of this technique was accomplished for the first time using a newly developed Ce precursor molecule to grow Cc02 on YSZ(IOO). The method... 

O. Bernard, A.M. Huntz, M. Andrieux, W. Seiler, V. Ji, S. Poissonnet, Synthesis, structure, microstructure and mechanical characteristics of MO CVD deposited zirco-nia films, Appl. Surf. Sci. 253 (2007) 4626. 

R. Tu and T. Goto, Thermal Cycle Resistance of Yttria Stabilized Zirconia Coatings Prepared by MO-CVD, Mater. Trans., 46, 1318-1323 (2005). 

MO-CVD uses metal-organic precursors and has relatively low process temperatures. 

The gases used in the CVD reactor may be either commercially available gases in tanks, such as Ar, N2, WF, SiH, B2H, H2, and NH Hquids such as chlorides and carbonyls or soflds such as Mo carbonyl, which has a vapor pressure of 10 Pa (75 mtorr) at 20°C and decomposes at >150° C. Vapor may also come from reactive-bed sources where a flowing haUde, such as chlorine, reacts with a hot-bed material, such as chromium or tantalum, to give a gaseous species. 

The atomic structure of the transition metals is such that the J shell is only partly filled. The first transition series (3d) comprises Sc, Ti, V, Cr, Mn, Fe, Co, and Ni the second (4d), Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag the third (5d), Hf, Ta, W, Re, Os, Ir, Pt, and Au. Carbonyl derivatives of at least one type are found for all these metals. Although only a few are presently used in CVD, many are being investigated as they constitute an interesting and potentially valuable group of precursor materials. 

Although boron forms borides with many elements, only the borides of the transition metals have been investigated extensively for their CVD characteristics. Boron forms stable borides with the transition metals, and the most refractory of these and those with the greatest potential interest are the borides of the elements of Groups IVa (Ti, Zr, Hf), Va (V, Nb, Ta) and, to a lesser degree. Via (Cr, Mo, W) (see Table... 

An older process to form silicides is siliconizing which is a relatively simple CVD process used to provide oxidation and chemical resistance to refractory metals. The siliconizing reaction uses the substrate itself, (such as Mo or Ti), as the metal source. Silicon diffuses readily in... 

Crystalline films of TiB2 obtained by CVD are used at lower temperatures as protective coatings. The interaction of these films with various substrates is studied" and desirable properties of the substrate in cases when the coating is deposited according to Eq. (a) are formulated. Substances meeting the requirements in this respect are W, Ta, Mo, WC, TiC, graphite, Fe-Ni-Co-Mn alloy (Kovar) and some high-chrome steels. 

CVD of Mo(CO)is into zeoHtes has been used as first step in the preparation of samples containing well-defined oxicarbide, oxinitride and sulfide used as catalysts in different reactions [25, 35-37]. Several cycles of adsorption of Mo(CO),5 in a NaY zeolite followed by thermal treatment afforded an oxicarbide dimer species in the zeolite cages that was characterized by EXAES [36]. 

CVD starting from zerovalent complexes such as [Fe(CO)s] and [Mo(CO)6] can be attained over a quite broad temperature range (373-673 K), but the final deposits are significantly contaminated by carbon [65, 66], presumably generated by the Boudouart reaction involving two CO and affording CO2 and C. To avoid carbon deposition oxygen can be introduced into the gas phase [67], but metal oxides are produced instead. 

Imipramine (Tofranil) [Antidepressant/TCA] WARNING Close observation for suicidal thinking or unusual changes in behavior Uses Depres-sion, enuresis, panic attack, chronic pain Action TCA t CNS synaptic serotonin or norepinephrine Dose Adults. Hospitalized Initial 100 mg/24 h PO in doses T over several wk 300 mg/d max Output Maint 50-150 mg PO hs, 300 mg/24 h max Peds. Antidepressant 1.5-5 mg/kg/24 h daUy-qid Enuresis >6 y 10-25 mg PO qhs T by 10-25 mg at 1-2-wk int vals (max 50 mg for 6-12 y, 75 mg for >12 y) Rx for 2-3 mo, then tap Caution [D, /-] Contra Use w/ MAOIs, NAG, acute recovery from MI, PRG, CHF, angina, CVD, arrhythmias Disp Tabs, caps SE CV Sxs, dizziness, xerostomia, discolored urine Interactions t Effects W/ amiodarone, anticholinergics, BBs, cimetidine, diltiazem, Li, OCPs, quinidine, phenothiazines, ritonavir, verapamil, EtOH, evening primrose oil t effects OF CNS depressants, hypoglycemics, warfarin T risk of serotonin synd W/MAOIs 4-... 

Whereas the surface interaction between [Mo(CO)6] and oxide supports were extensively studied and reactivity features generally well described, in depth characterization of the final deposif was offen neglecfed in the spectroscopic studies. On the other hand, many CVD studies carried out with zerova-lent carbonyl precursors revealed that incorporation of significant amounts of carbon and oxygen takes place. Additional studies are thus needed to correlate the influence of the state of the surface of the substrate to the chemical purity of the deposited ultra-thin films or nanoparticles. Probably, and as shown in other cases, the addition of a reactive gas in the system could also improve the quality of the films. 

Chemical Vapor Deposition. Deposition of tungsten, molybdenum, and their silicides by chemical yapor deposition (CVD) is of relatively recent interest in the microelectronics industry. These materials arc useful for gates and interconnects in metal oxide semiconductors (MOS) devices. Aluminum, the widely used interconnect material, has a comparatively low melting point (600°C) and a markedly different coefficient of thermal expansion (compared to silicon), so that over a period of years researchers have been seeking an alternative for aluminum,... 

The rapid development of solid state physics and technology during the last fifteen years has resulted in intensive studies of the application of plasma to thin film preparation and crystal growth The subjects included the use of the well known sputtering technique, chemical vapour deposition ( CVD ) of the solid in the plasma, as well as the direct oxidation and nitridation of solid surfaces by the plasma. The latter process, called plasma anodization 10, has found application in the preparation of thin oxide films of metals and semiconductors. One interesting use of this technique is the fabrication of complementary MOS devices11. Thin films of oxides, nitrides and organic polymers can also be prepared by plasma CVD. 

Supported metallic Ni, Cr, Fe, Mo, Co, V, Ti, Sn, Ru, and Pd catalysts have been prepared with the help of the CVD method fundamentally using carbonyl and chloride precursors [16]. 

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

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