The data about unadducted silver β-diketonates volatility are missing, indicating that this is not a typical properties for these compounds.
However, Lewis-base adducted silver(I) β-diketonates with phosphanes, phosphites, alkenes, alkynes etc. as auxiliary ligands have been successfully applied as CVD precursors. These complexes deonstrated improved stability and volatility. The Lewis-base-stabilized silver enolates (so far best suited as CVD precursors) are summarized in the Table :
Also the use of silver fluorinated β-diketonates including [Ag(tfac)]and [Ag(hfac)] as CVD metal sources is possible, however, most of these compounds do not sublime easily and hence, require special vaporization techniques.
Synthesis of Ag β-diketonates is similar to preparation methodology of respective copper(I) enolates. In general, starting silver(I) salt is [AgNO3].
In 1993 a new method for the synthesis of silver β-diketonates has been proposed
by Wakeshima and coworkers [[i]]. Equimolar reaction of β-diketone (HL) containing NEt3 with AgNO3 in a mixed solution of dry MeOH and MeCN yielded pure AgL (HL - acetylacetone, benzoylacetone, dibenzoylmethane, dipivaloylmethane).
Ag complexes were characterized by elemental analysis and IR spectroscopy.
[i] Wakeshima I., Ohgi H., Kijima I., Synth. React. Inorg. Met.-Org. Chem., 1993, 23(9), 1507-13.
Volatile, soluble, light-sensitive (decompose to give elemental silver on prolonged storage).
The structure of the Ag(β-diketonate)(Ph3P)2 complexes is unknown, but it may be similar in structure to the corresponding copper complexes with an oxygen-linked β-diketonate group or a three-coordinate structure bound to (R1,R2)2P-AgI having a carbon-linked β- diketone group (benzoyl and hexafluoroacetylacetone derivatives may exist in both forms).
Complexes of this class (bisphosphine) are not photosensitive, whereas as monophosphine adducts are photosensitive, presumably due to the disproportionation to the highly photosensitive silver acetylacetonate.
Silver acetylacetonate Ag(CH3COCHCOCH3) (Ag(acac)), first synthesized in 1893 [[i]], is not well characterized. The pure compound can be held for a few days with only moderate darkening. Degradation with silver is faster when the compound is stored in water, in organic solvents, or exposed to oxygen, or when heated. AgA is insoluble and water-insoluble, slightly soluble in ethanol, insoluble in benzene, ether and chloroform.
Synthesis Method [ii]: Mixing equimolar amounts of approximately 1 M AgNO3 and C5H7O2Na solutions (solvent - water, deoxygenated) immediately results in a cream-white silver compound. It was quickly filtered through a porous sintered glass filter, rinsed quickly with a small amount of deoxygenated water, and then dried under high vacuum. The yield is almost quantitative.
The compound was analyzed
by treatment with excess standard NaCl solution and titration of excess chloride with AgNO3.
[i]J.U.Nef, Ann.Chem 277, 68, (1893)
[ii] R.West, R.Riley “The infra-red spectra of metal acetylacetonates in the sodium chloride region”, J. Inorg. Nucl.Chem., 1958, Vol.5, pp.295 to 303.
The Ag(acac)(Ph3P) complex is monomeric in solution (benzene or chloroform) - like the corresponding gold complexes, but their solid IR spectra are not similar, so the structure is not similar either.
The Ag (acac) (Ph3P) IR spectrum is very similar to the Me3Pt(acac) spectrum and it is quite possible that their structure (dimers with acetylacetone coordination on both oxygen and C-3 carbon) is similar, and possibly could have increased volatility. But this hypothesis requires verification.
Silver 1,1,1-trifluoro-2,4-pentanedione Ag (tfac) was obtained analogously. [[i]]
Silver fluorinated diketonates (tfac) or hfac) form (olefin) (β-diketonate) silver-type complexes (olefin-1,5-cyclooctadiene, 1,3,5,7-cyclooctatetraene, cyclohexene, cycloheptene, cyclooctene [[ii]], but they decompose at higher temperatures.
The volatility of (Ph3P) Ag (-diketonate) (β-diketonate - acac or tfa) and (Ph3P) 2Ag (β-diketonate) (β-diketonate - ba or hfa) complexes was not noted in [iii]
[i] T.J.Wenzel, T.C.Bettes, J.E. Sadlowski, R.E.Sievers, "New Binuclear Lanthanide NMR Shift Reagents for Effective Aromatic Compounds", J.Am.Chem.Soc., 1980, 102, 5903-5904.
[ii] Partenheimer W. Johnson Johnson, "The Syntheses of Some New Silver Olefin Compounds of the Type (Olefin) (-Diketonate) Silver (I)", Inorganic Chemistry, Vol.11, No.11, 1972, 2840 -2841.
[iii] Gibson D., Johnson F.G., Lewis J. “Metal α-diketone complexes. Part VI. Some -Diketone Complexes of Copper (I), Silver (I), and Gold (I) ”, Inorg. Phys. Theor., J.Chem.Soc. (A), 1970 (?), 367-369
New Ag (hfac) (PMe3) (I) and Ag (hfac) (PMe3) 2 (II) compounds were synthesized by adding the appropriate amount of PMe3 to Ag (hfac), and investigated as potential precursors for the surface-selective vapor deposition is of particular interest. [[i]]
Monocrystalline X-ray diffraction studies show that (I) has a trigonal planar structure and (II) has a distorted tetrahedral structure. These compounds are quite volatile and readily sublimates in vacuo at temperatures of 20-50 ° C.
CVD of these compounds was performed at 200-425 ° C both in vacuum (10-4 Torr) and in the presence of H2. In the second case, non-selective deposition of silver films on glass, silicon, copper, tungsten, aluminum and nickel was performed at relatively low temperature 200° C (apparently with formation of hfacH). (the H2 flow was 25 sccm; with this flow, the partial H2 pressure was 10-2 Torr in the deposition zone).
In contrast, in vacuum at 200-425 ° C temperatures, Ag is not deposited on glass, silicon, tungsten, aluminum,
nickel, cobalt and silver, while passing the precursor through the hot zone. However, on copper substrates, both compounds readily form light silver layers. Possibly, the redox transmetalation process takes place to form Ag and Cu (hfac) 2, as has been demonstrated
for Pd. Films with electron spectroscopy were found to contain less than 1% of C, O and F impurities. (Note: crystallographic data, atomic coordinates, communication distances and angles (3 pages) for both silver compounds are available in most libraries in
microfiche form and can be ordered via ACS)
[i] W.Lin, T.H.Warren, R.G. Nuzzo, G. S. Girolami, "Surface-Selective Deposition of Palladium and Silver Films from Metal-Organic Precursors: A Novel Metal-Organic Chemical Vapor Deposition Redox Transmetallation Process," J. Am. Chem. Soc., 1993, 115, 11644-11645.
Non-selective deposition of Ag films is described in [.[i],[ii], [iii]]
[i] Moshier R.W., Sievers R.E., Spendlove L.B. U.S. Patent 3,356,527, 1967.
[ii] Oehr C., Suhr H. Appl.Phys. A, 49, 691-696, 1989.
[iii] Siedle A.R., Newmark R.A., Pignolet L.H., Inorg. Chem., 1983, 22, 2281-2286
[i] Moshier R.W., Sievers R.E., Spendlove L.B. U.S. Patent 3,356,527, 1967.
[ii] Oehr C., Suhr H. Appl.Phys. A, 49, 691-696, 1989.
[iii] Siedle A.R., Newmark R.A., Pignolet L.H., Inorg. Chem., 1983, 22, 2281-2286
A new complex Ag2(hfac)2(μ-dmpm)2, where hfac-hexafluoroacetylacetonate group and dmpm - Me2PCH2PMe2, was synthesized and its spectroscopic and X-ray studies were performed. The obtained data indicate that hfac ligands have a predominantly ionic character, which may lead to low volatility of Ag (hfac) Ln complexes compared to Cu (hfac) Ln.
An interesting application
of these complex is its use as silver CVD precursor [[i]]
[i] Yuan Z., Dryden N.H., Vittal J.J., Pudderphatt R.J. "A Binuclear bis (bis (Dimethylphosphino) methane) Disilver (I) Complex with Weakly Bonded Hexafluoroacetyl Acetonate Ligands", Canadian Journal of Chemistry - Rev. Canadienne de Chimie, 1994, Vol.72, Iss.7, pp.1605-1609.
The novel Ag (hfac) (C≡N-Me)) complex was shown to be a good precursor for Ag CVD. X-ray structures revealed
the complex is monomeric with distorted trigonal planar silver (I) coordination. Thermal silver CVD can be performed at 320°C for carbon and oxygen-free films. Pure silver films can be obtained at 250
° C by thermal CVD in the presence of H2.[i]
[i] Yuan Z., Dryden N.H., Vittal J.J., Pudderphatt R.J. "Chemical Vapor Deposition of Copper or Silver from Precursors M (hfac) (C-NMe) (M = Cu, Ag, hfac = CF3COCHCOCF3)", Journal of Materials Chemistry 1995, Vol.5, Iss.2, p.303 -307.
Composite Ag and YSZ (Y2O3-stabilized ZrO2) films were fabricated by co-deposition of MOCVD on metal and ceramic, using aerosol delivery of a solution of Ag(hfac) (C4H8OS) 2 and Zr (tfac) 4, Y (hfac) 3 precursors in toluene, the layers were grown usingn Ag volume of 0.007 to 0.60. The film morphology and impedance varied at room temperature depending on the amount of Ag. For films with a volume fraction Ag greater than 0.30, the resistivity is compared to that of typical granular composite films. When the Ag volume fractions were less than 0.10, the impedance was significantly lower than generally reported. Percolation behavior of the films was analyzed and possible explanations for the results of the resistivity tests were discussed. [24]
Composite Ag and YSZ (Y2O3-stabilized ZrO2) films were fabricated by co-deposition of MOCVD on metal and ceramic, using aerosol delivery of a solution of Ag(hfac) (C4H8OS) 2 and Zr (tfac) 4, Y (hfac) 3 precursors in toluene, the layers were grown usingn Ag volume of 0.007 to 0.60. The film morphology and impedance varied at room temperature depending on the amount of Ag. For films with a volume fraction Ag greater than 0.30, the resistivity is compared to that of typical granular composite films. When the Ag volume fractions were less than 0.10, the impedance was significantly lower than generally reported. Percolation behavior of the films was analyzed and possible explanations for the results of the resistivity tests were discussed. [24]
Two new silver hexafluoroacetylacetonate adducts [Ag(hfac)(bipy)] (1), and [Ag(hfac)(tmeda)] (2), were synthesized and chsracterised. Both silver compounds were characterized by single-crystal XRD, indicating that 1 exists as a dimeric species [Ag(hfac)(bipy)]2 , and 2 as polymeric chains [Ag(hfac)(tmeda)]x
Both complexes were applied for the MOCVD deposition of thin films of metallic Ag on glass substrates. The grown layers were analyzed by XRD, XPS and AFM, revealing
a high crystallinity and fairly good quality with negligible C and O contamination (when using the [Ag(hfac)(tmeda)] adduct as precursor.[[i]]
[i]L. Zanotto, F. Benetollo, M. Natali, G. Rossetto, P. Zanella, S. Kaciulis, A. Mezzi
Chemical Vapor Deposition, Volume 10, Issue 4, pages 207–213, August, 2004
http://onlinelibrary.wiley.com/doi/10.1002/cvde.200306290/abstract
Silver 2,2,6,6-tetramethylheptanedionate Ag (thd), or Ag (dpm) is a potential silver CVD precursror.
Ag(thd) synthesis:
To 1 g of AgNO3 solution in 100 ml of distilled water a suspension of 1.2 g of Na (thd) in 100 ml of methanol
was added. The solution turned brown immediately and a light brown precipitate formed. After stirring the solution for another 5 minutes, the solid was filtered off and dried under vacuum over P4O10 for 24 hours. The product has to be protected from light.
[[i]]
[i] T.J. Wenzel, R.E. Sievers, "Nuclear Magnetic Resonance Studies of Terpenes with Chiral and Achiral Lanthanide (III) -Silver (I) Binuclear Shift Reagents", J.Am.Chem.Soc., Vol.104, No.2 , 1982, 382-389.
Ag(fod) synthesis:
A solution of 9.6 g H (fod) in 5 ml methanol was neutralized with 8.1 ml 4M aqueous NaOH and this solution was added to a stirred solution of 5.5 g silver nitrate in 75 ml water. The white precipitate was filtered off and dried in vacuo over P4O10. [8]
Ag(fod)(PR3) complexes (fod - 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octandionate, R - CH3, C2H5) (and for comparison Ag (hfac) PR3 ) were synthesized either
by substitution of the olefin from Ag (hfac) (alkene) compounds with phosphines PR3 or by direct reaction with silver (I) oxide, PR3 and the corresponding β-diketone . Ag (fod) PEt3 melts at 26-28 ° C and can thus be used as a liquid CVD precursor
above this temperature. In contrast to several other silver (I) hfac complexes, these phosphine derivatives are monomeric as shown by X-ray structure study of Ag (hfac) PMe3 and volatile. All complexes were shown to be excellent precursors to thermal CVD of
silver films at temperatures of 250-350 ° C. The resulting films examined by XPS and EDX were composed of silver with a small amount of carbon impurities. Pure silver films were obtained by CVD from Ag (fod) PR3 at 300 ° C using wet hydrogen as a gas
carrier. The SEM image of a film grown from Ag (hfac) PMe3 at 350 ° C shows an uneven surface with an average grain size of 1-2 µm. Smoother films with a grain size of 0.1-0.25 µm are formed by CVD from Ag (fod) PR3 with H2 gas carrier. [[i]]
[i] Yuan Z., Dryden N.H., Vittal J.J., Pudderphatt R.J. “Chemical Vapor Deposition of Silver”, Chemistry of Materials, 1995, Vol.7, Iss.9, pp.1696-1702.
All complexes [Ag(fod)(PR3)] (R = Me, Et) were shown to be excellent precursors to thermal CVD of silver films at temperatures of 250-350 ° C. The resulting films examined by XPS and EDX were composed of silver with a small amount of carbon impurities. Pure silver films were obtained by CVD from Ag (fod) PR3 at 300 ° C using wet hydrogen as a gas carrier. The SEM image of a film grown from Ag (hfac) PMe3 at 350 ° C without reactive carrier gas shows an uneven surface with an average grain size of 1-2 µm and contained 5-10% carbon impurities. The presence of impurities (C but also F, O, P is some cases) were explained by the higher temperatures (370 – 380 °C) needed for the deposition process (due to non-selective decomposition).
Smoother films with a grain size of 0.1-0.25 µm were formed by CVD from Ag(fod)(PR3) with H2 carrier gas. [i]]
The main decomposition products of Ag(fod)(PR3) were fodH and PMe3/ PEt3 - both in the presence or absence of H2 as carrier gas. No disproportionation of silver(I) precursors was observed as for analogous copper(I) species, because Ag(II) as less common oxidation state for silver than Cu(II) for copper.
Silver films grown from Ag(fod)[(PEt3)] on glass substrates using H2/H2O mixtures as carrier gas grown at different substrate temperatures (320 °C (left) and 230 °C (right)) without annealing were studied by SEM (Fig.)
The temperature-dependent decomposition reaction paths of [(Ag(fod)(PEt3)] were suggested by Puddephatt et al .
Article [[ii]] describes a novel ultra-high vacuum device that increases the volatility of low vapor pressure precursors used in CVD processes while reducing their dissociation. Reflection-absorption IR spectroscopy (RAIRS) and mass spectrometry have demonstrated the efficiency of this device in transferring, for example, Ag(fod)PMe3 onto polished and polyurethane Al disks.
The paper [[iii]] investigated the surface chemistry of this precursor in its reaction with unmodified and modified plasma or oxygenated polyurethane. The increase in the concentration of silver produced by CVD is proportional to the increase in oxygen content incorporated into the polymer surface.
Further studies [[iv]] by RAIRS, XPS, and Atomic Force Microscopy (AFM) indicate that specific interactions between Ag (fod) PMe3 and the carbonyl groups of polyurethane occur, leading to full replacement of trimethylphosphine by long-term maintenance of the polyurethane with silver complex. The storage of adsorbed (fod) Ag-polyurethane complex in formaldehyde vapor leads to additional silver deposition and Hfod formation and desorption from the polyurethane surface. The AFM shows that silver is in the form of clusters.
These studies indicate that silver CVD can be performed on soft organic polymer substrates at room temperature.
The use of Ag(fod)(PMe3) as MOCVD precursor was reported for the growth of Ag layers on glass, Si and Cu substrates at 250-350°C
temperature, 50 mTorr pressure, with carrier gas (H2 or H2/H2O) or without carrier. Ag(fod)(PMe3) was evaporated at 50-100°C temperatures; growth rate 30 nm/min was achieved.
[i] Yuan Z., Dryden N.H., Vittal J.J., Pudderphatt R.J. “Chemical Vapor Deposition of Silver”, Chemistry of Materials, 1995, Vol.7, Iss.9, pp.1696-1702.
[ii] Serghinimonim S., Coatsworth L.L., Norton P.R., Puddephatt R.J. "New Doser for Chemical Vapor Deposition of Low Vapor Pressure Solid Precursors", Review of Scientific Instruments, 1996, Vol.67, Iss.10, pp.3672-3674.
[iii] Serghinimonim S., Norton P.R., Puddephatt R.J. "Chemical Vapor Deposition of Silver on Plasma Modified Polyurethane Surfaces", Journal of Physical Chemistry B 1997, Vol.101, Iss.39, p. 7808-7813.
[iv] Serghinimonim S, Norton PR, Puddephatt RJ, Pollard KD, Rasmussen JR, "Adsorption of a Silver Chemical Vapor Deposition Precursor Polyurethane and Reduction of Adsorbate to Silver Using Formaldehyde", Journal of Physical Chemistry B 1998, Vol.102, Iss.8, p. 1450-1458.