Thermal and MS studies of silver(I) 2,2-dimethylbutyrate complexes with tertiary phosphines and their application for CVD of silver films

Article abstract of DOI:10.1016/j.poly.2006.12.028

[Ag₂(CH₃CH₂C(CH₃)₂COO)₂] (1), [Ag₂(CH₃CH₂C(CH₃)₂COO)₂(PMe₃)₂] (2) and [Ag₂(CH₃CH₂C(CH₃)₂COO)₂(PEt₃)₂] (3) were prepared and characterized by MS-EI; ¹H, ¹³C, ³¹P NMR, variable temperature IR (VT-IR) spectroscopy and thermal analysis. MS and VT-IR data analysis suggests bidentate bridging carboxylates and monodentately bonded phosphines in the solid phase. The same methods used for gas phase analysis of 1-2 proved [(CH₃CH₂C(CH₃)₂COO)Ag₂]⁺ as the main ion, which could be transported in the gas phase during the CVD process. In the case of 3, similar intensity to the latter ion revealed [Ag{P(C₂H₅)}]⁺ and it is responsible for the CVD performance of 3. Thermal analysis results revealed that decomposition of 1-3 proceed in one endothermic process, with metallic silver formation between 197 and 220 °C. In the case of 1, VT-IR studies of the gaseous decomposition products demonstrate the presence of ester molecules and CO₂, whereas for 2 the main gaseous product appeared to be acid anhydride. Therefore, 2 was not used as a silver CVD precursor. Metallic layers were produced from 3 in hot-wall CVD experiments, (between 200 and 280 °C), under a total reactor pressure of 2.0 mbar, using argon as a carrier gas. Thin films deposited on Si(1 1 1) substrate were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Silver films obtained at moderate temperature (220-250 °C) revealed a thickness below 50 nm, and were whitish colored and slightly matt.

Full text of DOI:10.1016/j.poly.2006.12.028

Polyhedron 26 (2007) 2440–2448
www.elsevier.com/locate/poly
Thermal and MS studies of silver(I) 2,2-dimethylbutyrate complexes
with tertiary phosphines and their application for CVD of silver films
*
´
I. Szymanska , P. Piszczek, R. Szcze˛sny, E. Szłyk
Nicolaus Copernicus University, Faculty of Chemistry, 87 100 Torun´, Poland
Received 24 October 2006; accepted 12 December 2006
Available online 29 December 2006
Abstract
[Ag2(CH3CH2C(CH3)2COO)2] (1), [Ag2(CH3CH2C(CH3)2COO)2(PMe3)2] (2) and [Ag2(CH3CH2C(CH3)2COO)2(PEt3)2] (3) were pre-
pared and characterized by MS-EI; 1H, 13C, 31P NMR, variable temperature IR (VT-IR) spectroscopy and thermal analysis. MS and VT-
IR data analysis suggests bidentate bridging carboxylates and monodentately bonded phosphines in the solid phase. The same methods
used for gas phase analysis of 1–2 proved [(CH3CH2C(CH3)2COO)Ag2]+ as the main ion, which could be transported in the gas phase
during the CVD process. In the case of 3, similar intensity to the latter ion revealed [Ag{P(C2H5)}]+ and it is responsible for the CVD
performance of 3. Thermal analysis results revealed that decomposition of 1–3 proceed in one endothermic process, with metallic silver
formation between 197 and 220 °C. In the case of 1, VT-IR studies of the gaseous decomposition products demonstrate the presence of
ester molecules and CO2, whereas for 2 the main gaseous product appeared to be acid anhydride. Therefore, 2 was not used as a silver
CVD precursor. Metallic layers were produced from 3 in hot-wall CVD experiments, (between 200 and 280 °C), under a total reactor
pressure of 2.0 mbar, using argon as a carrier gas. Thin films deposited on Si(111) substrate were characterized by X-ray diffraction
(XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Silver films obtained at moderate temperature
(220–250 °C) revealed a thickness below 50 nm, and were whitish colored and slightly matt.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Ag(I) complexes; Phosphine; Carboxylates; Thermal properties; MS; CVD
1. Introduction
fore, the silver precursors most often used in CVD are
organometallics or b-diketonates complexes with tertiary
phosphines (PMe3 [3,5], PEt3 [3,5]), silylated alkenes [6],
alkynes [7,8] and recently carboxylates [4,9]. Out of the
latter ones, volatile perfluorinated and aliphatic Ag(I) carb-
oxylates and their complexes with tertiary phosphines have
been reported [4,10,11]. The majority of Ag(I) carboxylates
appeared to be dimers with bridging RCOO groups [9].
However, for ½AgðO2CCH3ÞðPBut3Þꢀ and [Ag(O2CCH3)-
(PPh3)2] symmetrical chelating carboxylates were detected,
whereas in the case of [Ag(OOCH)(PPh3)2] monodentately
bonded formate was reported [9,12–14]. The studied, sil-
ver(I) carboxylates were thermally stable, and decompose
to metallic silver in a wide temperature range [15–17]. In
CVD experiments, knowledge about the metallated species
transported in the gas phase is fundamental for deposition
process control [18–20]. The gaseous products transported
in a CVD reactor, should include the metal ion and be
In recent years silver(I) carboxylates and their complexes
with tertiary phosphines have found application as precur-
sors for Chemical Vapor Deposition (CVD) [1–4]. The
produced silver thin layers can be applied in contacts for
ULSI microelectronic circuits, catalysis, or as a dopant in
fabrication of high-temperature superconductors and other
applications [2]. The precursors should be volatile and
decompose at relatively low temperatures in the CVD appa-
ratus. Therefore, knowledge about thermal properties of the
precursors is important for the evaporation of metallated
species and deposition on substrates. It has been noted that
the volatility of complexes is improved in the case of bulky
peripheral substituents and perfluorinated ligands. There-
*
Corresponding author. Tel.: +48 56 611 4317; fax: +48 56 654 2477.
´
E-mail address: pola@chem.uni.torun.pl (I. Szymanska).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.12.028

I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
2441
stable in the gas phase until deposition on the substrate.
Therefore, temperature variable MS and TGA-IR spectra
of the gases evolved during the decomposition processes
will be described in the presented paper. Data from the lat-
ter studies will be use for elaboration of the fragmentation
schemes. Moreover, the fragmentation schemes of coordi-
nated ligands, should provide unique knowledge about
the chemistry of silver(I) complexes in the gas phase. The
article is also intended to describe a mechanism of carbox-
ylates thermal decomposition, therefore VT-IR spectra
were measured and discussed.
solution (1:1), heated to 40 °C and stirred 1 h, followed
by silver nitrate (3.5 mmol) addition (all manipulations
were carried out in the darkness). The obtained precipi-
tate was filtered, washed with water, ethanol and dried.
Anal. Calc. for C12H22Ag2O4: C, 32.2; H, 5.0; Ag, 48.3.
Found: C, 32.0; H, 5.2; Ag, 48.7%. IR: 1555, 1477,
1405, 1366, 1357, 1290 cmꢁ1
;
1H NMR (CD3CN):
0.83 ppm (3H, t, CH3), 1.10 ppm (6H, s, CH3),
1.49 ppm (2H, q, CH2); 13C NMR (CD3CN): 10.3 ppm
(CH3), 26.9 ppm (CH3)2, 35.5 ppm (CH2), 44.7 ppm (C),
183.9 ppm (COO).
2. Experimental
2.2.2. [Ag2(CH3CH2C(CH3)2COO)2(PMe3)2] (2) and
[Ag2(CH3CH2C(CH3)2COO)2(PEt3)2] (3)
2.1. Chemicals and instrumentation
Complexes were synthesized, in dried argon, using
Schlenk techniques, in the darkness. In a general proce-
dure: 1 (4 mmol) in C2H5OH (40 cm3) was mixed with
5 cm3 of TEOF and PR3 (4 mmol) (THF solution), where
R = Me, Et. The mixture was stirred at room temperature
for 4 h, filtered and solvents evaporated on a vacuum line.
[Ag2(CH3CH2C(CH3)2COO)2(PMe3)2] (2) was obtained as
white crystals, which were recrystallized from ethanol,
whereas [Ag2(CH3CH2C(CH3)2COO)2(PEt3)2] (3) was
obtained as a green–yellow oil and was analyzed directly
after evaporation. Anal. Calc. for C18H40Ag2O4P2 (2): C,
36.1; H, 6.7; P, 10.3; Ag, 36.1. Found: C, 36.3; H, 6.9; P,
10.2; Ag, 36.4%. IR: 1550, 1472, 1399, 1359, 1286,
CH3CH2C(CH3)2COOH (97%), trimethylphosphine
(PMe3) (1 M solution in THF), triethylphosphine (PEt3)
(1 M solution in THF), triethylorthoformate (TEOF) were
purchased from Aldrich, AgNO3, NaHCO3 and C2H5OH
were purchased from POCh (Poland), and all compounds
were used as received. Ethanol was dried by standard
methods.
Thermal studies (TG, DTG, DTA) were performed on a
SDT 2960 TA analyser. Decomposition processes were
studied in a dynamic atmosphere of dry nitrogen flowing
at 40 ml minꢁ1, heating rate 2.5 °C minꢁ1, heating range
up to 400 °C and sample mass 2–5 mg. Gaseous products
of thermal decomposition were detected by a FT IR Bio-
Rad Excalibur spectrophotometer equipped with a thermal
connector for gases evolved from a SDT 2960 TA analyser.
The thermal connector was heated to 200 °C. Powder
X-ray diffraction data for the thermal analysis residues
were obtained with a Philips X’PERT diffractometer using
Cu Ka radiation. Variable temperature mass spectra were
registered using a Finnigan MAT 95 spectrometer with
1
960 cmꢁ1. H NMR (CD3CN, ppm): 0.81 (3H, t, CH3),
1.03 (6H, s, CH3), 1.34 (9H, d, PCH3), 1.46 (2H, q,
CH2); 13C NMR (CD3CN, ppm): 9.7 (CH3), 14.8
P(CH3), 26.1 (CH3)2, 34.6 (CH2), 43.0 (C), 184.4 (COO);
31P NMR (CD3CN, ppm): ꢁ35.4.
Anal. Calc. for C24H52Ag2O4P2 (3): C, 42.2; H, 7.7; P,
9.1; Ag, 31.6. Found: C, 42.3; H, 7.4; P, 9.0; Ag, 31.1%.
IR: 1549, 1458, 1405, 1364, 1045, 764 cmꢁ1 1H NMR
.
(CD3CN, ppm): 0.84 (3H, t, CH3), 1.07 (6H, s, CH3),
1.18 (9H, t, PEt3), 1.47 (2H, q, CH2), 1.69 (2H, q, PEt3).
13C NMR (CD3CN, ppm): 9.19 (CH3), 10.5 P(CH2CH3),
16.9 P(CH2CH3), 26.8 (CH3)2, 35.0 (CH2), 43.6 (C), 185.8
(COO); 31P NMR (CD3CN, ppm): 28.2.
1
the EI technique (heating range 30–300 °C). H and 13C
NMR spectra in CD3CN or C6D6 were collected with a
Varian Gemini 200 MHz spectrometer using TMS as the
standard, and 85% H3PO4 for 31P NMR (80.96 MHz). IR
spectra were recorded using a Perkin–Elmer 2000 FT IR
spectrometer in the range 4000–400 cmꢁ1, in KBr discs.
Variable temperature IR (VT-IR) studies in the solid phase
were carried out with a SPECAC (Perkin–Elmer) tempera-
ture variable cell. The composition of vapors formed
during the thermolysis of the studied compounds was
determined by VT-IR spectroscopy. Spectra of vapors
transported with the carrier gas (Ar) were recorded using
the equipment as reported [21]. Silver was determined arg-
entometrically (after complex mineralization), whereas C,
H, P were determined by elemental microanalysis.
2.3. CVD experiments
The deposition experiments were carried out using hor-
izontal hot-wall CVD reactor as described [11]. Silver films
were deposited on Si(111) and steel substrates, under
2 mbar, and in the deposition temperature 200–280 °C.
The films were characterized by X-ray diffraction (XRD).
XRD data were collected with a Philips X’PERT diffrac-
tometer, in 30–80° 2H ranges, using CuKa irradiation
and sample spinning (step size – 0.1°, program. res. slit –
0.5, measuring time – 11 s per point). The silver films’ mor-
phology were studied by a scanning electron microscopy
(SEM – LEO 1460 V) and an atomic force microscopy
instrument (Veeco, Multimode, Nanoscope IIIa Controler,
Taping Mode AFM).
2.2. Synthesis
2.2.1. [Ag2(CH3CH2C(CH3)2COO)2] (1)
2,2-Dimethylbutyric acid (3.5 mmol) and potassium
nitrate (0.43 mmol) were suspended in a water–ethanol

2442
I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
Table 2
3. Results and discussion
3.1. Preparation
13C, 31P NMR spectral analysis data [ppm]
Compound
13C
31P
d COO D1
d
D2
All silver compounds were synthesized in the dark-
ness. Silver 2,2-dimethylbutyrate 1 was obtained by the
reaction of 2,2-dimethylbutyric acid and silver nitrate in
a 1:1 ratio in a water–ethanol solution. This reaction is
fast and the white product can be simply isolated. Both
silver 2,2-dimethylbutyrate complexes with phosphines
[Ag2(CH3CH2C(CH3)2COO)2(PMe3)2] (2) and [Ag2-
(CH3CH2C(CH3)2COO)2(PEt3)2] (3) were synthesized by
the direct reaction of silver carboxylate and the respec-
tive phosphine in a 1:1 ratio, using ethanol as solvent
and in dried argon. 2 was obtained as white crystals,
which were recrystallized from ethanol, whereas 3 was
a green–yellow oil.
[Ag2(CH3CH2C(CH3)2COO)2] (1)
[Ag2(CH3CH2C(CH3)2COO)2(PMe3)2] (2) 184.4
[Ag2(CH3CH2C(CH3)2COO)2(PEt3)2] (3) 185.8
184.0
0.9
1.3 ꢁ35.4 24.9
2.7 28.2 46.3
D1 = d COO(complex) – d COO(acid); d COO(acid) = 183.1 ppm.
D2 = d ꢁ d PR3; d(PMe3) = ꢁ60.3 ppm; d(PEt3) = ꢁ18.1 ppm.
inductive effect imposed by the fluorine atoms. However,
the coordination shifts of the COO carbon in perfluori-
nated carboxylates (ꢂ1 ppm) were similar to the value cal-
culated for 1, which reveal comparable silver–carboxylate
interactions for fluorinated and non-fluorinated silver
salts. In the case of complexes 2 and 3, the carbonyl carbon
exhibited weak singlets at 184.4 and 185.8 ppm, respec-
tively. For [Ag2(PPh3)2(l-RCOO)2], R – aliphatic chain
and [Ag(PPh3)(RCOO)], R – silylated radical, COO sing-
lets were detected in the range 180.8–187.7 ppm [28,29].
However, in the case of sil0ver complexes with perfluori-
nated carboxylates [Ag2ðPR3Þ2(l-RCOO)2] (R0 = Me, Et),
resonances of COO were observed upfield (161.3–
163.2 ppm) [30,34]. The coordination shifts for 2 of 1.3
and 3 of 2.7 ppm were close to the values calculated for
the compounds ½Ag2ðPR03ÞðRCOOÞꢀ. Therefore, the bridg-
ing mode of the silver–carboxylate linkage in ½Ag2ðPR03Þ-
ðRCOOÞꢀ salts can be similar for aliphatic, silylated and
perfluorinated carboxylates. Single 31P resonances appeared
at ꢁ35.4 2 and 28.2 ppm 3 – Table 2. The values of chemical
and coordination shifts for 2 are close to those observed
for perfluorinated carboxylate complexes [Ag2(PMe3)2-
(l-RCOO)2]. However, for 3 only the coordination shift is
similar to the value registered for [Ag2(PEt3)2(l-RCOO)2],
but the signal was detected at higher fields (13.5–13.1 ppm)
[30,34].
3.2. IR and NMR spectra
Table 1 demonstrates characteristic absorption bands in
the IR spectra, which can be assigned to the stretching
modes of the COO group. Carboxylates can coordinate
in many modes such as: unidentate, chelating or bridging
bidentate [22–24]. The carboxylate coordination can be
proposed by analysis of the parameter DmCOO = masym ꢁ msym
,
calculated for studied compounds and identical sodium salts.
In the case of silver 2,2-dimethylbutyrate the COO bands
were detected at: masym = 1548 cmꢁ1, msym = 1405 cmꢁ1. For
complexes 2 and 3 DmCOO was 153 cmꢁ1 and 159 cmꢁ1
,
respectively, which suggest similar coordination as for 1.
The calculated D parameters for the discussed compounds
are bigger than those for the appropriate sodium salts. This
fact suggests a bridging coordination mode of the carboxylic
group and a polymeric structure [9,25]. Absorption bands of
phosphines derived from P–C stretching vibrations are
shifted for 2 by 32 cmꢁ1 and for 3 by 19 cmꢁ1 in comparison
to the free phosphines, which confirms the coordination of
the ligands [26,27].
3.3. Analysis of variable temperature IR spectra
The 13C and 31P NMR spectral chemical shifts of 1–3
are listed in Table 2. One might expect that the 13C signal
of the COO carbon should give the most significant changes
upon coordination. However, the 13C NMR spectra of 1–3
revealed the COO carbon line at 184.0–185.8 ppm, with a
coordination shift (0.9–2.7 ppm) downfield in comparison
to the free acid spectra. In the case of perfluorinated silver
carboxylates, this signal was observed at higher field
(159.1–165.7 ppm) [32]. The observed chemical shifts sug-
gest an opposite effect on the COO carbon due to the
An application of 1–3 as CVD precursors requires deter-
mination of their thermal stability and composition of the
vapors formed during their thermolysis. Therefore variable
temperature IR (VT-IR) studies have been carried out and
the results are presented in Figs. 1–4. IR spectra of 1–3,
registered between 20 and 250 °C, revealed differences in
the mechanism of their thermal decomposition (Fig. 1).
In the case of 1 and 2, the thermolysis proceeds with com-
plete decomposition of these compounds. Bands registered
at 1676, 1608 cmꢁ1 1 and 1680, 1598 cmꢁ1 2, at 250 °C,
Table 1
Selected IR band (cmꢁ1) of the studied compounds
Compound
mas(COO)
ms(COO)
Dm(COO)
m(P–C)
[Ag2(CH3CH2C(CH3)2COO)2] (1)
[Ag2(CH3CH2C(CH3)2COO)2(PMe3)2] (2)
[Ag2(CH3CH2C(CH3)2COO)2(PEt3)2] (3)
1548
1549
1553
1405
1396
1394
143
153
159
740
689
DmCOO(sodium salt) = 119 cmꢁ1
.

I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
2443
Fig. 1. Variable temperature IR spectra of 1–3, registered at 20 and 250 °C.
suggest formation of a different type of Ag–OOCR linkage
in the solid residue than at room temperature. Calculated
Dm parameters exhibit the increase from 208 to 252 cmꢁ1
for 1 and from 239 to 291 cmꢁ1 for 2, in comparison to
spectra registered at 20 °C (Table 1). The latter suggests
decomposition of the polymeric structure of 1 and 2, where
carboxylate ligands form syn–syn bidendate bridges, and
the formation of another type of Ag(I) interaction with
the carboxylate ligands [22,23].
The differences in the decomposition pathway of 1 and 2
are also observed on the plot of integral intensity of
mas(COO) bands versus temperature (Fig. 2). The relatively
high thermal stability of 1 can be noted between 40 and
180 °C. However, the presence of a weak band at
1676 cmꢁ1 suggests decomposition process onset at 60 °C.
Above 180 °C a rapid increase of this band’s intensity is
observed, while the mas(COO) = 1548 cmꢁ1 band reveals
the opposite effect. The latter can be related to complete
decomposition of 1 with the evolution of carboxylic acid.
Between 180 and 230 °C (Fig. 3) the main components of
the gas phase of 1 are: CO2 (2359, 667 cmꢁ1), ester species
(mC@O = 1767, dOCO = 1116 cmꢁ1), and fragments contain-
ing carboxylate acid groups (mOH = 3520, mC@O
=
1716 cmꢁ1). Bands that could be assigned to volatile sil-
ver–carboxylate species were not found, which confirms
the postulated decomposition pathway by DTA/TGA
studies. The latter is in favor of decomposition of 1 leaving
silver containing species in the solid phase.
For 2, the dependence of the integral intensity of mas-
(COO) bands versus temperature changes stepwise, exhibit-
ing the first step at 60 °C, with the second one at 160 °C
(Fig. 2b). Simultaneously CH3 librational modes (rocking
and/or wagging) at 959 cmꢁ1 and m(P–C) (738 cmꢁ1) bands
Fig. 2. Temperature dependence of the integral intensity of bands
assigned to mas(COO) and m(CO), observed between 1480 and 1800 cmꢁ1
in spectra of 1 (a) and 2 (b).
,

2444
I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
Fig. 3. VT-IR spectra of vapors formed during the thermal decomposition of 2.
Fig. 4. The dependence of the frequency of mas(COO) motions vs. temperature (a), and changes of the vapor composition during the thermal
decomposition of 3 (b).

I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
2445
revealed intensity decrease. Hence, the phase transition at
lower temperatures can be attributed to phosphine detach-
ment from 2. The same as for 1, the main decomposition
product appears to be Ag(I) carboxylate intermediates.
However, their complete decomposition processes was
observed above 160 °C, (bands at 1680 and 1549 cmꢁ1),
which indicate low thermal stability of these species.
Analysis of vapors spectra, registered in the range 160
and 200 °C, revealed phosphine bands: d(CH2) 1430–
observed (Fig. 4b). Species containing ester groups (1741,
1758, and 1176 cmꢁ1) and aliphatic ethers (group of bands
between 1024 and 1146 cmꢁ1) were the main volatile com-
ponents at lower temperatures. Above 160 °C, the compo-
sition of the vapors changes and bands at 763, 1031, 1243
and 1460 cmꢁ1 indicate the presence of Ag–phosphine
derivatives as the main volatile decomposition products.
When compared to the room-temperature spectrum of 3
the bands assigned to Ag–PEt3 groups are almost identical
(766, 1046, 1250 and 1459 cmꢁ1). Simultaneously, absorp-
tion bands derived from volatile species containing Ag–
OOCR fragments were not observed. In the temperature
range 160–260 °C, only bands from acid anhydride (1745,
1441 cmꢁ1
, d , d(CH3) 939–
sym(CH3) 1282–1311 cmꢁ1
948 cmꢁ1 and masym(P–C) 703–716 cmꢁ1. The latter is in
favor of phosphine species (PCH2, PCH3), which are pre-
dominant in the vapors of 2. Besides that, weak bands
observed in the range 1698–1808 cmꢁ1, (registered at
180 °C), can be assigned to a volatile acid anhydride
(1808, 1746 cmꢁ1) and aliphatic carboxylate (1698 cmꢁ1).
Comparison VT-IR and MS data confirms the proposed
decomposition mechanism of 2. According to MS data
(Table 3), the complete decomposition of 2, proceeds
between 80 and 260 °C, with volatile species formation.
The main constituents are: [PH(CH3)]+, [P(CH3)2]+ and
[P(CH3)3]+ fragments, whereas only trace quantities of
[AgP(CH3)3]+ were noticed. Carboxylate silver bonded
fragments (e.g. [Ag2(OOCC(CH3)2CH2CH3)]+) were not
observed in the vapors. This can be explained by the low
stability of species containing the above fragments and
their rapid decomposition.
1808 cmꢁ1) and ester derivatives (1153, 1720–1750 cmꢁ1
were noticed.
)
According to the VT-IR results it can be concluded that
1 and 2 are not suitable precursors for CVD of silver, due
to their low thermal stability in the temperature range 20–
250 °C. In contrast, the formation of volatile and stable sil-
ver–phosphine intermediates between 160 and 260 °C dur-
ing the decomposition of 3 suggests its potential usability
as a Ag CVD precursor, as was confirmed by CVD exper-
iments (vide infra).
3.4. Mass spectra analysis
Variable temperature mass spectra were studied to
detect the metallated species, which can be transported in
the gas phase during precursor heating in a CVD process.
EI-MS spectra of 1, 2 and 3 were recorded in the range
30–300 °C and the results are listed in Table 3. The follow-
ing most intensive organic ions: [CH3CH2CH2]+,
[CH3CH2C@CH2]+ and [CH3CH2C(CH3)2]+, as well as
[COO]+ and [COOH]+, were detected in the studied tem-
In comparison to 1 and 2, the thermolysis pathway of 3
is different (Fig. 1). The dependence between frequency of
m
asym(COO) bands and temperature (Fig. 4a) suggests that
the decomposition pathway of 3 proceed in two stages,
with the first step near 80 °C and second one at 160 °C.
Moreover, significant differences in the vapors composition
in the temperature ranges 60–140 °C and 160–260 °C were
Table 3
Mass spectra analysis data
Fragmentation ion
m/z
Compound/Temperature/Int. (%)
1
2
3
197 (°C)
86 (°C)
107 (°C)
256 (°C)
116 (°C)
182 (°C)
245 (°C)
[CH3CH2CH2]+
[COO]+
43
44
45
47
55
56
61
70
71
100
23.3
7.9
xxx
31.0
6.8
xxx
9.0
63.8
xxx
xxx
2.0
xxx
xxx
9.5
xxx
38.3
15.1
21.4
71.6
23.9
4.8
12.2
100
1.1
13.6
14.8
46.1
12.7
4.2
8.0
100
1.1
100
40.8
9.4
56.6
12.4
17.7
xxx
25.4
7.7
xxx
5.3
30.0
xxx
55.6
100
24.2
16.7
xxx
36.8
8.7
xxx
9.1
50.0
xxx
30.5
93.8
22.1
5.9
xxx
33.2
5.9
xxx
11.1
65.3
xxx
[COOH]+
[(CH3)HP]+
[CH3CH2C@CH2]+
[CH3CH2CHCH2]+
[(CH3)2P]+
60.0
10.2
[CH3CH2C(CH3)@CH2]+
[CH3CH2C(CH3)2]+
[(CH3)3P]+
15.3
79.6
7.3
83.6
xxx
6.5
44.9
xxx
76
90
[(C2H5)2HP]+
[Ag]+
xxx
4.1
xxx
107
118
183
216
225
331
[(C2H5)3P]+
xxx
2.6
xxx
3.5
27.3
xxx
14.9
xxx
[AgP(CH3)3]+
[Ag2]+
xxx
7.2
10.6
xxx
81.8
[AgP(C2H5)3]+
[(CH3CH2C(CH3)2COO)Ag2]+
xxx
xxx
77.3
4.5
57.9
56.7
xxx, unable to observe.

2446
I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
perature range. Moreover, analysis of the spectra revealed
the presence of certain metallated species formed in the
strictly defined temperature ranges. The spectrum of 1 (at
197 °C) exhibited [(CH3CH2C(CH3)2COO)Ag2]+ (R.I. =
38%) as the most intensive signal. Similar disilver species
were observed in MS spectra of perfluorinated and ali-
phatic non-fluorinated silver carboxylates [20,31]. The lat-
ter silver(I) salts form dimers or aggregates of these
dimers in the solid phase with bridging carboxylates, and
likewise the same can be suggested for 1. The observed sil-
ver bonded species can be formed by detachment of
RCOOÅ at the temperature characteristic for the studied
precursor (e.g. 197 °C for 1). In the next stage, the
[(CH3CH2C(CH3)2COO)Ag2]+ fragment decomposes to
Agþ2 and organic ions, which is evident from the character-
istic line pattern for Agþ2 [3 lines, R.I. = 1:1.860:0.865, nat-
ural isotopic abundance of 107Ag (51.4%) and 109Ag
(48.6%)].
In the case of 2 between 30 and 120 °C the following
phosphorous containing species [(CH3)2P]+ (R.I. = 100%
at 86 °C and 107 °C), [(CH3)3P]+ (R.I. = 84% at 86 °C;
R.I. = 45% at 107 °C), [(CH3)2HP]+ (R.I. = 24% at
86 °C; R.I. = 13% at 107 °C) and [Ag(PCH3)]+ (R.I. =
2.6% at 86 °C; R.I. = 3.5% at 107 °C) were detected. These
phosphorous embodied fragments are in favor of trimethyl-
phosphine detachment and complex decomposition in the
30–120 °C range. At higher temperatures (160–240 °C),
the desirable metallated ions [(CH3CH2C(CH3)2COO)Ag2]+
(R.I. = 82% at 220 °C), [Ag2]+ (R.I. = 11% at 220 °C) and
[Ag]+ (R.I. = 4% at 220 °C) appeared (Fig. 5). Fragments
detected in the spectrum of 2 (30–300 °C) suggest detach-
ment and fragmentation of trimethylphosphine followed
by RC–COO bond dissociation (absence of RCOO and
RCO ions) [31]. The latter causes silver bonded species for-
mation, which decompose in the last stage to Agþ2 and Ag+
(Fig. 5).
In the case of 3, below 200 °C, phosphorous containing
metallated fragments [AgP(C2H5)3]+ (R.I. = 77% at 116 °C;
R.I. = 15% at 182 °C) were registered, which suggest a
stronger Ag–P bond in comparison to the trimethylphos-
phine complex 2. Phosphine bonded fragments are less
desirable in CVD of metals, due to possible increase of film
contamination with P. The [Ag2]+ signals revealed similar
intensity (R.I. = 10%) for both complexes, whereas [Ag]+
appeared only for 2. The above demonstrate that the most
stable volatile silver coordinating fragment for 1–3 is the
[(CH3CH2C(CH3)2COO)Ag2]+ ion.
In the case of complex 2 abundance of [(CH3CH2C-
(CH3)2COO)Ag2]+ ion was twofold higher than for 3,
which corresponds to the detachment of the PR3 from 2
in the first stage. For 3 the lower relative intensity of
[(CH3CH2C(CH3)2COO)Ag2]+ can be related to the pres-
ence of the stable phosphine (PEt3) bonded silver(I) ions.
The formation of [AgP(C2H5)3]+ and other similar ions
can be explained by higher stability of the Ag–P bond,
coming from the stronger r-electron donor character of
PEt3 than PMe3.
Above results demonstrate that compounds 1, 2 and 3 can
be used for the deposition of silver layers using the CVD
method, due to formation of the volatile metallated species
(e.g. [(CH3CH2C(CH3)2COO)Ag2]+, [AgP(C2H5)3]+).
3.5. Results of thermal analysis (TGA/DTG/DTA)
Thermal properties of the studied compounds are also
important for the assessment of their future usage in
CVD of silver layers. The temperature of decomposition
process onset and temperature of silver formation are
two factors which determine CVD procedure parameters.
The results of thermal analysis are listed in Table 4 [10].
Salt 1 decomposes in one endothermic process (onset =
125 °C, maximum rate of reaction = 198 °C). The mass loss
on the TG curve corresponds to detachment of carboxylate
and the final residue is metallic silver formed at
Tf = 208 °C. The observed silver formation temperature
is below 250 °C, which makes 1 a promising precursor
for hot-wall CVD of silver layers. When comparing 1 to
perfluorinated silver(I) carboxylates it is evident that they
decompose at higher temperatures (e.g. CF3(CF2)2COOAg;
Tf = 470 °C) [32]. The latter suggests that perfluorinated
ligands revealed improved volatility, but they are more
thermally stable then branched non-fluorinated carboxy-
lates. In the case of 2 and 3 one endotherm was also
observed on the DTA, with onset temperatures of 164 °C
and 170 °C, respectively. The onset temperatures are
almost in the range of instrument accuracy; hence one
may presume that decomposition starts with the partial dis-
sociation of the carboxylate residue, which has further evi-
dence in the MS spectra of 1–3. Analysis of the TG curves
indicates mass losses which correspond to the detachment
of carboxylate residue and phosphine in the same endo-
thermic reaction. The maximum reaction rates (DTG) were
detected at 205 °C and 250 °C, respectively, which confirms
Fig. 5. Fragmentation scheme for [Ag2(CH3CH2C(CH3)2COO)2(PMe3)2]
(2).

I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
2447
Table 4
Thermal analysis results
Compound
Heat effect on DTA
Temperature (°C)
Residue (%)
Calc.
Tinit
Tmax
Tf
Found
[Ag2(CH3CH2C(CH3)2COO)2] (1)
[Ag2(CH3CH2C(CH3)2COO)2(PMe3)2](2)
[Ag2(CH3CH2C(CH3)2COO)2(PEt3)2] (3)
Endo
Endo
Endo
125
50
60
197
205
250
208
206
290
48.4
36.1
31.6
52.9
35.5
32.8
Tinit, initial temperature; Tmax, maximum temperature; Tf, final temperature.
MS observations that PEt3 forms a stronger Ag–P r-donor,
p-acceptor bond than PMe3. A similar phenomenon was
observed for [Au(RCOO)(PR3)] and [Ag(RCOO)(PR3)]
complexes with the studied phosphines and perfluorinated
carboxylates [30,34]. The decomposition reaction was com-
pleted at: Tf 2 = 206 °C, Tf 3 = 290 °C. In both cases,
metallic silver was confirmed by TG calculations and
detected by XRD studies of the residue in the crucible.
The observed diffractogram lines (0.2352, 0.2026, 0.1179,
0.1444, 0.1233 nm) correspond to metallic silver (Powder
Diffraction File) [33]. Temperatures of silver formation
are accept for CVD purposes with the heating device work-
ing below 300 °C.
Considering decomposition mechanism of 2 and 3, one
can propose simultaneous or very close in time, consecutive
carboxylate residue and phosphine detaching reactions. In
comparison to the reported silver perfluorinated carboxy-
lates complexes with PPh3 (Tf = 219–340 °C), the studied
complexes exhibited significantly lower temperatures of sil-
ver formation [34]. The latter makes them much more
promising CVD precursors of metallic silver than ana-
logues with heavier (aromatic) phosphines.
Deposition rates of the films were calculated from the
change of films weights determined on a microbalance.
Tendency for rate increase between 200 and 250 °C (from
0.3 to 0.8 nm minꢁ1), was observed, whereas above 250 °C
the opposite trend was noted. The changes of the deposi-
tion parameters seems to be a consequence of: (a) the sig-
nificant decrease of deposition efficiency, caused by the
partial decomposition of silver species transported in the
vapors, (b) deposition of metallic films on other parts of
the CVD reactor (not only on substrate surfaces). XRD
studies exhibit characteristic peaks of polycrystalline cubic
metallic silver (38.4, 44.6, 64.7, 77.9 [deg], assigned to
(111), (200), (220), (311) lines) as reported by JCPDS
(International Centre for Diffraction Data) without pref-
erential orientation.
The SEM and AFM micrographs of the films produced
from 3 are presented in Fig. 6. It can be noted that at
vaporization temperatures below 220 °C and deposition
temperatures below 250 °C, films deposited on Si(111) sub-
strates were composed of the separated Ag grains with
diameters of 30–60 nm. Further heating resulted in coales-
cence of silver grains and the increase of their size (diame-
ter 60–280 nm), as well as packing density (Fig. 6a). SEM
and AFM studies of Ag films, deposited from 3 on steel
substrates, under similar conditions, turned out to be very
thin and dispersed, with an average grain size between 50
and 90 nm (Fig. 6b).
Analysis of the IR spectra of the gases evolved during
the thermal decomposition of 1 suggest the presence of acid
(m(OH) = 3577 cmꢁ1, C–H stretching at 2967 cmꢁ1, m(C@O)
=
1752 cmꢁ1
,
m
(C–O) = 1258 cmꢁ1
,
d )
(O–C@O) = 668 cmꢁ1
which was also detected in the gaseous products of the sil-
ver acetate thermal decomposition reaction [17].
TGA/IR studies of the gas phase from decomposition
reactions of 2 and 3 revealed the characteristic absorption
4. Conclusions
bands for acid anhydride (ma(COO) = 1816 cmꢁ1, ms(COO)
=
Analysis of variable temperature MS and IR data
revealed that thermolysis of 1 and 2 proceed with complete
decomposition of these compounds in the temperature
range 20–250 °C. However, volatile silver containing spe-
cies were not detected in the gas phase during the decompo-
sition processes, resulting in exclusion of 1 and 2 from
further thermally induced CVD experiments. Formation
of volatile and stable silver–phosphine intermediates dur-
ing decomposition of 3 suggested its usage as a precursor
in CVD methods. However, partial decomposition of a sil-
ver bonded species during transport in the gas phase of 3
seems to be the main disadvantage in the application of this
complex in metallization processes. Performed CVD exper-
iments using 3 as a precursor proved deposition of thin sil-
ver films on Si(111) and steel substrates. In general
procedures, nanometric silver films (thicknesses below
50 nm), at moderate temperature (220–250 °C) can be pro-
duced from 3.
1759 cmꢁ1) (Fig. 1). Moreover, bands typical for the phos-
phines were observed.
3.6. Results of CVD experiments
Silver films were deposited using precursor 3 and hot-
wall CVD equipment. The substrates were Si(111) and
steel plates, at a deposition temperature between 200
and 280 °C, under 2.0 mbar of the total reactor vaccum,
in argon atmosphere. The vaporization temperature was
fixed at 170 °C for CVD experiments resulting in an effi-
ciency of 75–83%. The fabricated silver films revealed
thickness below 50 nm, and were whitish colored and
slightly matt. Variation of the deposition temperature
and the amount of precursor used in the CVD experi-
ments (100–300 mg) appeared to be the main parameters
which have an impact on the thickness of the silver layers.

2448
I. Szyman´ska et al. / Polyhedron 26 (2007) 2440–2448
Fig. 6. SEM and AFM micrographs of silver films deposited on (a) Si(111) and (b) steel surfaces (TV = 170 °C, TD = 240 °C, p = 2 mbar, Ar).
[15] N.F. Uvarov, L.P. Burleva, M.B. Mizen, D.R. Whitcomb, C. Zou,
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