CVD of pure copper films from novel iso-ureate complexes

Article abstract of DOI:10.1039/c3dt00104k

We report the synthesis and characterisation of a new family of copper(i) metal precursors based around alkoxy-N,N′-di-alkyl-ureate ligands, and their subsequent application in the production of pure copper thin films. The molecular structure of the complexes bis-copper(i)(methoxy-N,N′-di- isopropylureate) (1) and bis-copper(i)(methoxy-N,N′-di-cyclohexylureate) (5) are described, as determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted complex 1 as a possible copper CVD precursor. Low pressure chemical vapour deposition (LP-CVD) was employed using precursor 1, to synthesise thin films of metallic copper on ruthenium substrates under an atmosphere of hydrogen (H₂). Analysis of the thin films deposited at substrate temperatures of 225 °C, 250 °C and 300 °C, respectively, by SEM and AFM reveal the films to be continuous and pin hole free, and show the presence of temperature dependent growth features on the surface of the thin films. Energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic copper.

Full text of DOI:10.1039/c3dt00104k

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CVD of pure copper films from novel iso-ureate
complexes†
Cite this: Dalton Trans., 2013, 42, 5554
Alexander M. Willcocks,a Thomas Pugh,a Jeff A. Hamilton,a Andrew L. Johnson,*a
Stephen P. Richardsb and Andrew J. Kingsleyb
We report the synthesis and characterisation of a new family of copper(I) metal precursors based around
alkoxy-N,N’-di-alkyl-ureate ligands, and their subsequent application in the production of pure copper
thin films. The molecular structure of the complexes bis-copper(I)(methoxy-N,N’-di-isopropylureate) (1)
and bis-copper(I)(methoxy-N,N’-di-cyclohexylureate)(5) are described, as determined by single crystal
X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted complex 1 as a
possible copper CVD precursor. Low pressure chemical vapour deposition (LP-CVD) was employed using
precursor 1, to synthesise thin films of metallic copper on ruthenium substrates under an atmosphere of
hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 225 °C, 250 °C and
300 °C, respectively, by SEM and AFM reveal the films to be continuous and pin hole free, and show the
presence of temperature dependent growth features on the surface of the thin films. Energy dispersive
X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all
show the films to be high purity metallic copper.
Received 11th January 2013,
Accepted 5th February 2013
DOI: 10.1039/c3dt00104k
www.rsc.org/dalton
electromigration resistance that is far superior to that of alu-
minium (though inferior to tungsten). Industrially, copper
Introduction
The production of metallic thin films by chemical vapour interconnects/seed layers are deposited onto a ruthenium ‘glue
deposition (CVD),1 or more recently atomic layer deposition layer’ which allows for better adhesion to common barrier
(ALD)2 has been an area of significant interest to those in the layers such as TiN and TaN, which are necessary to inhibit
microelectronics industry for the last three decades, mainly diffusion of copper into the underlying substrates, such as Si
due to numerous potential applications in which these and SiO2, in microelectronic devices.3
materials can be exploited.1d,e,2a,b During this time the depo-
Over the past few years a great deal of effort has been
sition of copper has continually been at the forefront of employed on research into ternary and quaternary compound
research, and the 2011 International Technology Roadmap for semiconductors; namely copper indium diselenide (CIS),
Semiconductors (ITRS) predicts that copper will remain the copper indium gallium diselenide (CIGS) and copper zinc tin
primary interconnect material throughout the next 15 years, sulfide (CZTS) have shown excellent solar cell properties.4 Thin
although there are some technical challenges still to overcome. film CIGS based solar cells have been produced with an
As the size-downscaling of microelectronics continues, the use efficiency of up to 20%.5 One of the techniques used to form
of copper as an interconnect material in integrated circuitry CIGS layers is a two-stage approach which involves the depo-
and the chip fabrication process has increased.1c,e,2b The phys- sition of a precursor layer (e.g. Cu) on a substrate followed by a
ical properties that make copper so desirable for such appli- high temperature activation step (reaction with Se or S) that
cations include its very low resistivity (significantly lower than converts the precursor layer into solar cell grade semiconduc-
aluminium and much lower than tungsten) and tor materials.6
As a result of this interest, considerable research into the
development of copper metal precursors for CVD and ALD
application has been described, and examples of potential pre-
aDepartment of Chemistry, University of Bath, Bath, BA13 3DN, UK.
E-mail: A.L.Johnson@bath.ac.uk
bSAFC-Hitech, Power Road, Bromborough, Wirral, CH62 3QF, UK
†Electronic supplementary information (ESI) available: Supporting information
cursors1d include Cu(I) organometallics,7 Cu(I) and Cu(II)
β-diketonate,8 β-ketoiminate2i,9 and β-ketoesterate10 complexes
as well as Cu(I) and Cu(II) carboxylates,11 and alkoxide com-
plexes.12 Typically precursors based around Cu(I) are quite
volatile and have low deposition temperatures, whereas Cu(II)
systems are on average rather too stable, and show low
includes the EXD spectra for Cu films grown at 250 °C and 300 °C as well as and
XPS spectra for the same films (pre- and post-A-etching). A powder X-ray diffrac-
tion spectra of the Ru substrate used throughout this study is also included.
CCDC 901461–901465. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c3dt00104k
5554 | Dalton Trans., 2013, 42, 5554–5565
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volatility, need high deposition temperatures and require redu- the delocalised {NCN} unit. Similarly, with an sp hybridised
cing carrier gases e.g. H2 to activate them. It is therefore the oxygen centre, π-bonding to the {NCN} unit imposes a planar-
desire to combine the best of these features that has directed ity with one of the two p-orbital based lone pairs, but more
new attention towards the development of Cu(I) based importantly the C–O–R angle will tend towards linearity (180°).
precursors.
Any degree of π-bonding to the {NCN} unit will be
Recently, copper(I) amidinate2c,e,f,h,j,13 and guanidinate13,14 accompanied by a reduction in C–O bond length as the
complexes have received attention as potential precursors for multiple bond character of this exocyclic bonding increases, as
the deposition of pure copper thin films, because of their rela- well as a change in the pyramidalisation of the amide nitrogen
tive air stability, thermal stability and lack of oxygen within the atoms; caused, in part, by steric interactions between the
ligands system. Closely related to formamidinate, amidinate, oxygen substituents and the substituents on the {NCN} core.
guanidinate and triazenide ligands, are O,N,N′-trisubstituted Similar arguments have been presented for metal guanidinate
iso-ureate ligand (alternatively named pseudoureas),15 which complexes elsewhere.14c
differ only by virtue that they contain an alkoxide, {OR}, substi-
Despite the fact that the addition of alcohols into carbodii-
tuent at the central carbon atom of the {NCN} moiety rather mides to form O,N,N′-trisubstituted iso-ureas (R′NC(OR)NHR′′)
than an H-atom (formamidinate), alkyl/aryl group (amidinate) have been known since the early 1900’s there is a paucity of
or an amine group i.e. {NR2} or {NHR} (guanidinate). Together data concerning the formation of metal iso-ureate complexes.
with the triazenide ligands, these systems are iso-electronic In an analogous manner to amidinate and guanidinate com-
and as such should share common structural and electronic plexes formed by the insertion of carbodiimides into M–C and
features (Fig. 1), an observation which is apparent in the case M–N bonds respectively, there are reports that describe the for-
of copper amidinate and copper guanidinate complexes.
mation of iso-ureate complexes by the insertion of carbodii-
For guanidinate and iso-ureate ligands the possibility exists mides into Mg–OMe,16 Ti–OiPr,17 Sn–OMe18 and Pb–OMe19
of significant lone-pair interaction and delocalisation of elec- bonds (Scheme 1), although characterising data for these pro-
tron density from the {NR2} or {OR} substituents into the ducts is limited.16
{NCN} core. Any such delocalisation has a substantive effect
There are also several comprehensively characterised
on the orientation of either the {NR2} or {OR} moiety, as examples of adducts formed between carbodiimides and metal
shown in Fig. 1. In the case of the iso-ureate ligands the alkoxide complexes, hinting at a reduced reactivity of the alk-
oxygen atom of the {OR} group can be either considered as oxides towards insertion compared to metal amide
sp3, sp2 or sp hybridised: for an sp3 hybridisation there is no complexes.20
exocyclic π-bonding as both lone pairs of electrons are orien-
While several coordination complexes and adducts of iso-
tated away from the delocalized {NCN} unit. For a sp2 hybri- ureas are known, examples are limited.21 Similarly, reactions
dised oxygen atom the C–O–R angle of the iso-ureate should between O,N,N′-trisubstituted iso-ureas with metal alkyl or
ideally approach 120°. For delocalisation of electron density to amide complexes are also limited, and restricted to examples
occur the p-orbital based lone pair needs to be coplanar with involving cyclic-iso-ureas (alternatively named amino-oxazo-
lines).22 However, copper iso-ureate complexes have appeared
in the patent literature.23
The dearth of fully characterised iso-ureate complexes,
coupled with the range of derivatives that are potentially
available through substitution at the terminal nitrogen
atoms and the {OR} group, which allow the tunability
of important features such as volatility, stability and reactivity,
makes such complexes an appealing area of study. We
report here the synthesis and characterisation of a new family
of copper metal precursors based around the novel iso-ureate
ligands and the subsequent utility of these new precursors
in the production of pure, continuous, copper thin films
deposited onto ruthenium substrates at a range of substrate
temperatures by low pressure chemical vapour deposition
(LP-CVD).
Fig. 1 General structure of formamidinate, amidinate, guanidinate, iso-ureate
and triazenide anions. Comparative resonance forms of the guanidinate and iso-
ureate; showing the effect of orientation, and lone pair interaction (A, B, E and
F) with the π-delocalised {NCN} core, on the steric interactions and N-orbital pro-
jections (C, D, G and F) within the ligand.
Scheme 1 The general insertion of metal alkoxides into carbodiimides.
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1
The H NMR spectrum of complex 5 consists of four multi-
plets for the cyclohexyl protons (δ = 1.21, 1.50, 1.64, 1.93 ppm)
and a singlet for the {OMe} protons (δ = 3.39 ppm). Corres-
pondingly the 13C NMR spectrum contains the six resonances
attributed to the cyclohexyl group, the methoxy group and the
central NCN carbon at δ = 26.7, 27.0, 39.7, 55.9, 60.0 and
168.2 ppm respectively. In all cases the solution state NMR
studies are consistent with the formation of dimeric complexes
of the general formula [Cu2(L)2] (L = iso-urea).
Single crystal X-ray quality crystals of all the complexes
described in this paper were grown from hexane solution at
−28 °C. All the iso-ureate complexes described in this study
are dimeric and show common gross structural features. The
molecular structures of the complexes 1 and 5, discussed
below, are shown in Fig. 2 and are taken as demonstrators of
common structural features in both the isopropyl and cyclo-
hexyl substituted iso-ureates. Selected bond lengths and
angles are shown in Fig. 2. Complexes 2–4 are isostructural to
complex 1, with the only significant differences in the mole-
cular structures focused on the relative orientation of the
{OR} moiety. The molecular structures of complexes 2–4 along
with bond lengths and bond angles are provided in the ESI†
for this paper. Crystal data and collection parameters for
complexes 1–5 are shown in Experimental section of this
paper (Table 4).
For both 1 and 5, the copper metal atoms are bridged by
two iso-ureate ligands in a μ,η1,η1-fashion. Unlike structurally
related copper(I) guanidinate complexes, which in the solid
state show significant twisting of the {Cu2(N2C)2} core at the
Cu–Cu axis,14a,c the iso-ureate complexes 1–5 show no such
disruption. Both {Cu2(N2C)2} cores are planar [RMS deviation
of the fitted atoms: 0.0119 Å (for 1) and 0.0068 Å (for 5)]. It is
also noteworthy that unlike the comparable guanidinate com-
plexes, where a change in the N-substituent from iso-propyl to
cyclohexyl results in a significant twisting of the core. No such
observation is made for the iso-ureate complexes 1 and 5, as
can be seen from the least-squares overlay of the two com-
plexes (Fig. 3).
In both complexes the geometries about the two-coordinate
metal atoms approach linearity [for 1: N(1)–Cu(1)–N(3) =
176.04(9)° and N(2)–Cu(1)–N(4) = 175.11(9)°; for 5: N(1)–Cu(1)–
N(2A) = 175.83(10)°], with the deviation presumably the result
of inter-nuclear Cu⋯Cu repulsion. In both complexes, the
metal–metal distances [Cu(1)–Cu(2): 2.4653(4) Å and Cu(1)–
Cu(1A): 2.4624(7) Å respectively], which are comparable to
related di-copper amidinate, guanidinate, and triazenide com-
plexes, are significantly shorter than the sum of the Van der
Waals radii of Cu (1.40 Å), suggesting the possible presence of
d10–d10 metallophilic interaction, although this is a matter of
some debate in the literature.24 The Cu–N bond distances in
1–5 are within the expected ranges for terminal Cu(I)–N
bonds.2c,f,13,14c,23,24 Similarly the N–C bond lengths within the
iso-ureate ligands are also comparable to those observed in
related systems.
Scheme 2 Synthesis of the copper(I) iso-ureate complexes 1–5.
Results and discussion
Synthesis and molecular structures
Of the iso-ureas used in this study (Scheme 2) only the
methoxy-N,N′-di-isopropylurea, is commercially available. The
potassium salt of t-butoxy N,N′-di-isopropylurea can be
efficiently formed in situ by the reaction of potassium tert-but-
oxide with N,N′-diisopropylcarbodiimide. The remaining urea
ligands were synthesised by the CuCl catalysed (∼0.075 mol%
CuCl per mmol of carbodiimide) reaction of carbodiimide
with equimolar amounts, or greater, of primary, secondary, or
tertiary alcohols without solvents at room temperature in a
slightly exothermic reaction. Subsequent filtration of the reac-
tion mixture and addition to a THF solution of Lithium hexa-
methyldisilylamide (LiHMDS) affords the desired lithium iso-
ureate in situ.
All Cu(I) iso-ureate compounds shown in Scheme 2, were
synthesised by reaction of anhydrous CuCl with the corres-
ponding lithium iso-ureate in THF at ambient temperature to
afford the final products. All of the products were soluble in
hexane, and extraction followed by recrystallisations at −28 °C
afforded pure products as colourless or pale yellow crystalline
solids (yield 58–74%). In all case products were characterised
by 1H, 13C{1H} NMR spectroscopy, elemental analysis and
single crystal X-ray diffraction.
The 1H NMR spectra of the complexes 1–4, all contain a
doublet between δ = 1.11–1.14 ppm and a septet between δ =
3.67–3.80 ppm, which correspond to the methyl and methine
protons of the isopropyl groups, respectively. Additional
signals were observed for the {OMe}, {OEt}, {OiPr} and {OtBu}
groups in the expected coupling patterns and intensity ratios.
Similarly, the 13C NMR spectra of the complexes show reson-
ances between δ = 27.2–28.0 ppm for the methyl carbons, and
between δ = 46.5–47.8 ppm for the methine carbons. The
spectra for 1–4 also contain a common resonance between δ =
165.31–167.692 ppm, which is attributed to the central carbon
atom of the {NCN} moiety. Resonances are also observed for
the {OMe} (δ = 59.6 ppm), {OEt} (δ = 15.2, 67.9 ppm), {OiPr} (δ
= 22.3, 73.8 ppm) and {OtBu} (δ = 30.0, 80.5 ppm) moieties in
the 13C{1H} NMR spectra.
As noted earlier, the relative orientation of the {OR} substi-
tuent can give some indication, along with {N2C–OR} bond
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Fig. 2 Diagram showing the molecular structures of the complexes 1 and 5 (50% probability ellipsoids). Hydrogen atoms have been omitted for clarity. Symmetry
transformations used to generate equivalent atoms in 5: 2 − X, 1 − Y, −Z. Selected bond lengths (Å) and angles (°) for 1: Cu(1)–Cu(2) 2.4653(4), Cu(1)–N(1) 1.877(2),
Cu(1)–N(3) 1.872(2), Cu(2)–N(2) 1.878(2), Cu(2)–N(4) 1.879(2), C(1)–N(1) 1.321(3), C(1)–N(2) 1.324(3), C(11)–N(3) 1.325(3), C(11)–N(4) 1.322(3), C(1)–O(1) 1.384(3),
C(11)–O(2) 1.382(3), O(1)–C(2) 1.447(3), O(2)–C(12) 1.447(3); N(1)–Cu(1)–N(3) 176.04(9), N(2)–Cu(2)–N(4) 175.11(9), N(1)–C(1)–N(2) 124.0(2), N(3)–C(11)–N(4)
123.8(2), C(1)–O(1)–C(2) 112.54(18), C(11)–O(2)–C(12) 112.23(19). Selected bond lengths (Å) and angles (°) for 5: Cu(1)–Cu(1A) 2.4624(7), Cu(1)–N(1) 1.873(2),
Cu(1)–N(2A) 1.874(2), C(1)–N(1) 1.321(4), C(1)–N(2) 1.321(4), C(1)–O(1) 1.380(3); N(1)–Cu(1)–N(2A) 175.83(10), N(1)–C(1)–N(2) 122.8(3), C(1)–O(1)–C(2) 112.9(2).
C–NR2 multiple bond character is typically ascribed. We must
assume the apparent lack of C–O multiple bond character is a
result of the increased electronegativity of oxygen compared to
nitrogen in related guanidinate systems.
Thermal profile of complexes and use as deposition precursor
Thermogravimetric analysis (TGA) was performed on com-
pounds 1–5 with all of the complexes leaving residues of
between 23–31% of the original mass. Fig. 4 shows the TGA
data for complex 1–5. In the case complexes 1 and 2 the
residual mass percentages observed (1: 25.8% and 2: 24.4%)
are all less than the expected residual mass % for the for-
mation of pure copper (28.8% and 27.1% respectively), indicat-
ing that while some material has been lost due to sublimation,
the majority of the product undergoes decomposition. Conver-
sely, for complexes 3–5 the residual mass percentages observed
(3: 26.0%, 4: 28.13% and 5: 24.2%) are higher than those
expected for pure copper (25.6%, 24.2% and 21.1% respect-
ively) suggesting carbon and/or oxygen incorporation into the
residue. Of the complexes investigated compound 1 provided
the sharpest decomposition profile. Once mass loss begins, it
is relatively sharp for all but compound 5, which has a temp-
erature range of >150 °C, from the onset of mass loss
(∼195 °C) to formation of a stable residue (∼346 °C). The
{OtBu} derivative 4, shows a stepwise decomposition profile,
with a slight plateau at 180 °C corresponding to a mass loss of
40%, which is potentially due to the loss of one iso-urea ligand
Fig. 3 Least-squares overlay of the two complexes 1 and 5 (1 in red; 5 in
green). RMS error of displacement over the two core {Cu2(N2C)2} fragments is
1.24 Å.
length, of π-delocalisation into the {NCN} core of the iso-
ureate ligand. The bond angle belonging to the {OR} substitu-
ents in complexes 1–5 are indicative of sp2 hybridisation at the
oxygen center. For delocalisation to occur within these iso-
ureate ligands the {Cu2(N2C)2} plane and that plane defined by
the central C-atom of the iso-urea ligand and the {OMe} group
should be coplanar (Fig. 1); in 1 and 5 these planes are
approaching
a perpendicular arrangement [1: 72.17°, 5:
86.29°]. This observation along with C–O bond lengths [1:
1.384(3) Å and 1.382(3) Å, 5: 1.380(3) Å] suggest single bond
character to the {RO–CN2} bond in the iso-ureate ligands. This
observation is in contrast to guanidinate systems, where
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Table 1 The general physical parameters for the low pressure CVD of
complex 1
Substrate temperature (°C)
Operating pressure (Torr)
Carrier gas
225 250 300
∼30 ∼30 ∼30
H2
H2
H2
Carrier flow rate (L min−1
)
0.3 0.3 0.3
0.3 0.3 0.3
Bubbler flow rate (L min−1
)
Temp of precursor bubbler and carrier gas lines (°C) 100 100 100
Deposition duration (min) 60 60 60
attempt to emulate industrially relevant substrates, where
ruthenium is used as an adhesion layer for copper thin film
deposition.3 The deposition of copper metal was investigated
at three different substrate temperatures; 225 °C, 250 °C and
300 °C respectively.
Fig. 4 The TGA data for complexes 1–5. Experiments were run under N2
(50 ml min−1) at a ramp rate of 20 °C min−1
.
during the first step in the TGA decomposition profile. Such
observations are consistent with the proposed thermolysis
mechanisms proposed by Barry and co-workers for related
copper(I) guanidinate systems.14b
All of the complexes, apart from 1, decompose to give a
stable residue that is a slightly higher value than that which
corresponds to pure copper, indicating some contamination in
the residue from ligand incorporation. Combined with a
melting point of 96 °C, lower than typical temperatures used
for vaporisation, complex 1 was deemed a suitable candidate
for assessment as a Cu deposition precursor.
In all of the deposition runs the precursor and the carrier
gas lines were externally heated to 100 °C, and the pressure
during deposition was maintained at 30 Torr. H2 gas was used
as the carrier gas at flow rates of 0.3 L min−1. Table 1 shows
the general physical parameters used throughout the depo-
sition experiments.
Fig. 5 shows the top and cross-sectional SEM images of the
thin film deposited at 225 °C (Fig. 5A and B) and 250 °C
(Fig. 5D and E), respectively, alongside the AFM images
(Fig. 5C: 225 °C and Fig. 5F: 250 °C). Both films appear con-
tinuous and pin-hole free with submicron morphology consist-
ing of particles, uniform in both size and shape (approx.
0.1 μm in dimension). Analysis of the AFM images show the
films deposited at 250 °C to be marginally rougher (225 °C:
Rms = 0.1107 μm, Ra = 0.0767 μm, 250 °C: Rms = 0.1278 μm,
Ra = 0.0931 μm). At both temperatures the deposited surfaces
Copper deposition and thin film analysis
Copper films were deposited using the iso-ureate complex 1 at
low pressure in a hot-walled Electro-gas CVD apparatus. Films
were deposited onto ruthenium coated silicon wafers, in an
Fig. 5 SEM and AFM images of the thin films deposited from the copper precursor 1 at 225 °C (A–C) and 250 °C (D–C) respectively.
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Table 2 PXRD peaks observed in films deposited on hexagonal Ru using 1 as
precursor at 225 °C, 250 °C and 300 °C respectively
Element/compound (hkl) 2θ
d (Å)
System PDF number
Si
(211) 32.961 2.715 Cubic
(111) 36.403 2.466 Hex
(100) 38.461 2.338 Hex
(002) 42.222 2.138 Hex
(101) 44.036 2.054 Hex
(111) 43.339 2.083 Cubic
(200) 50.508 1.805 Cubic
72-1426
78-2076
06-0663
06-0663
06-0663
89-2838
89-2838
Cu2O
Ru
Ru
Ru
Cu
Cu
are significantly rougher than desired for the microelectronics
industry, although it is well documented that chemically
deposited copper thin films are invariably irregular. It is also
worth noting that the film roughness is in the same order of
magnitude as film thickness (Fig. 5) and as such deposition
run time will have a significant effect on roughness as would
the possible future use of catalytic surfactants such as ethyl-
iodide.25 Because of the relative non-uniformity of the thick-
ness across the sample, relative deposition rates could not be
determined accurately.
Powder X-ray diffraction analysis of the films deposited
onto ruthenium at 225 °C and 250 °C showed that they consist
primarily of poly-crystalline copper metal, oriented in the (111)
direction, together with some in the (200) direction (see Fig. 5
and Table 2). At a substrate deposition temperature of 300 °C
the thin films produced were shown by SEM imaging to be sig-
nificantly more uneven in appearance, with what appear to be
nano-filaments emerging from the underlying crystalline
copper (Fig. 7A and B). The uneven appearance of the films is
Fig. 6 An overlay of the X-ray diffraction patterns derived from copper films
deposited on hexagonal Ru using 1 as precursor at 225 °C, 250 °C and 300 °C
respectively.
reinforced by the clear presence of substrate (i.e. Ru) in the
PXRD pattern (Fig. 6) which is much harder to discern in the
more continuous films grown at 225 °C and 250 °C respect-
ively. Because of the much greater roughness of the surfaces of
these films AFM images could not be obtained. In contrast
films deposited onto ruthenium substrates at 300 °C appear
from SEM images (Fig. 7) to be much more granular and
uneven in their distribution with what appear to be ‘flagella-
like’ nano-filament structures protruding from the larger par-
ticles (∼0.2 μm), which are not observed in any of the films
grown at lower temperatures. Samples of the copper filaments
where examined independently of the underlying thin film,
and shown by EDX to be pure copper (additional peaks of
Ni/C/O in the EDX spectra come from the supporting grid).
Fig. 7 SEM images of copper films grown on ruthenium substrate at 300 °C using complex 1 as a precursor (A and B). TEM images of copper filaments scratched
off the underlying copper film (C). An EDX spectrum of the copper filaments (D). An electron diffraction pattern from the copper filaments showing them to be
cubic copper metal (E).
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Table 3 Atomic % elements in copper thin films deposited at 225 °C, 250 °C
and 330 °C pre- and post-Ar etching (600 s)
225 °C
(pre)
225 °C
(post)
250 °C
(pre)
250 °C
(post)
300 °C
(pre)
300 °C
(post)
Cu
C
O
54.11
37.16
8.73
96.88
—
0.37
11.31
62.58
26.11
81.78
8.58
9.64
4.96
65.89
29.87
80.12
10.96
8.93
form of Cu2O. EDX spectroscopy also showed the presence of
underlying substrate peaks (Fig. 6).
Atomic % analysis of the copper thin films was determined
using XPS data at sputter etching times of 0 and 600 seconds
for the films deposited at 225 °C, 250 °C and 300 °C respect-
ively. Table 3 shows the relative atomic % contributions of Cu,
C and O as determined by integration of the Cu 2p (931 eV),
C 1s (284 eV) and O 1s (532 eV) binding energy peaks using
the linear method both pre- and post-etched. XPS analysis of
the untreated surface show peaks at binding energies of
284 eV and 532 eV which can be attributed to adsorbed carbon
Fig. 8 SEM images of a copper film grown on ruthenium before (A) and after
(B) thermal treatment (300 °C) under H2 for 1 h.
and oxygen containing organic species. After 600
s of
Ar-etching these peaks are significantly reduced, as can be
seen in Fig. 9, which shows the XPS spectra (both pre and
post-etching) for the copper thin film deposited at 225 °C.
XPS analysis shows the atomic % of copper in films depos-
ited at 225 °C (post-etching) to be 96.88 atomic %. XPS ana-
lysis also detects 2.75 atomic % of Ru metal, which is
attributed to the underlying ruthenium substrate: if the under-
lying ruthenium is negated the atomic % of Cu and O rises to
99.62% and 0.38% respectively. The atomic % oxygen detected
by XPS analysis in thin films deposited at 225 °C are within
the levels associated with background levels for this very sensi-
tive method of analysis.
The atomic % of oxygen recorded in the thin films depos-
ited at 250 °C and 300 °C are higher than expected, suggestive
of the possible incorporation of oxygen within the thin film
from the thermal decomposition of ligands.
The observed high purity of these copper metal thin films
is quite significant, as typical oxygen containing precursors are
prone to the incorporation of oxygen into the deposited thin
films.
Fig. 7e shows the electron diffraction pattern obtained from
an examination of the filament structures, most likely to be
looking along the (111) plane of the crystal (a distinction from
the (002) plane could not be made), and highlights the highly
crystalline nature of the filament structures.
It was therefore assumed that the nano-filament like struc-
tures, observed only on copper films deposited at 300 °C, are a
result of either a thermally induced extrusion of copper from
the underlying crystalline mass, or a result of thermally acti-
vated growth mechanism. In an attempt to test these hypo-
theses films grown at 225 °C, which appear as continuous
films, were held at 300 °C under a flow of H2 gas (0.6 L min−1
)
at 50 Torr for 1 h. During this time, while copper filament
growth was not observed, the rise in temperature of the sub-
strate did induce significant surface mobility of the copper
metal and subsequent growth of copper islands.
Successive deposition runs holding the substrate tempera-
ture at 300 °C using fresh precursor resulted in the formation
of copper films with identical features.
The resistivity of films deposited at a substrate temperature
of 225 °C measured using a 4-point probe was found to be
9.63 mΩ cm, approaching that of bulk copper (cf. 1.67 mΩ cm
for bulk copper). Despite the high purity observed by XPS the
higher than expected resistivity is likely to be a consequence of
a number of factors, including film thinness, surface oxidation
and relative unevenness of the film.
SEM images of the film before and after thermal treatment
(Fig. 8) show the formation of islands of copper and exposure
of the underlying ruthenium substrates, an observation which
is consistent with our PXRD results from direct film growth.
Attempts to grow copper films on ruthenium substrates below
200 °C using complex 1 as a precursor proved to be challen-
ging, primarily because of slow deposition rates.
It is therefore reasonable to assume that above 200 °C
either the activation barrier to decomposition of 1 is overcome
resulting in decomposition just above the wafer causing a
copper seed layer to be deposited, or the thermal barrier to
surface reaction is overcome.
EDX spectra of all the films (ESI†) show the presence of
copper as well as small amounts of oxygen (less than 3% by
EDX). PXRD analysis suggests that oxygen is present in the
Conclusions
A new group of five copper(I) iso-ureate complexes have been
synthesised and structurally characterised and shown to
possess bimetallic structures in which the two iso-ureate
ligands bridge a {Cu2} core, such that each copper atom
5560 | Dalton Trans., 2013, 42, 5554–5565
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Table 4 Crystal data and structure refinement for compounds 1–5
Compound
1
2
3
4
5
Chemical formula
Formula mass
Crystal system
a/Å
b/Å
C
16H34Cu2N4O2
C18H38Cu2N4O2
469.60
Monoclinic
6.9630(2)
16.1930(5)
10.4080(3)
90.00
101.5790(10)
90.00
1149.64(6)
0.20 × 0.15 × 0.10
150(2)
C20H42Cu2N4O2
497.66
Monoclinic
14.26300(10)
10.37000(10)
18.3100(2)
90.00
110.89
90.00
2530.17(4)
0.20 × 0.20 × 0.15
150(2)
C22H46Cu2N4O2
525.71
Orthorhombic
11.0610(2)
12.9330(2)
18.2690(2)
90.00
90.00
90.00
2613.42(6)
0.20 × 0.15 × 0.13
150(2)
C28H50Cu2N4O2
601.80
Monoclinic
10.2090(4)
11.2920(4)
13.1660(6)
90.00
108.123(2)
90.00
1442.48(10)
0.10 × 0.08 × 0.03
150(2)
441.55
Triclinic
10.4470(2)
11.9090(2)
18.1380(3)
108.5190(10)
99.5910(10)
91.2370(10)
2103.14(6)
0.13 × 0.10 × 0.08
150(2)
c/Å
α/°
β/°
γ/°
Unit cell volume/Å3
Crystal size/mm3
Temperature/K
ˉ
P1
Space group
P21/c
P21/c
Pcab
P21/c
No. of formula units per unit cell, Z
Theta range for data collection
Absorption coefficient, μ/mm−1
No. of reflections measured
No. of independent reflections
Completeness
4
2
4
4
2
8.52 to 25.00°
2.037
21 281
7077
95.5%
0.0509
0.0356
0.0888
0.0472
0.0956
1.076
3.21 to 27.56°
1.867
21 623
2633
99.3%
0.0499
0.0320
0.0727
0.0448
3.09 to 30.52°
1.701
52 560
7717
99.8%
0.0462
0.0291
0.0695
0.0407
3.65 to 28.28°
1.651
40 255
3244
99.8%
0.0528
0.0266
0.0635
0.0380
7.88 to 25.00°
1.505
10 591
2449
96.5%
0.0598
0.0373
0.0767
0.0584
Rint
Final R1 values (I > 2σ(I))
Final wR(F2) values (I > 2σ(I))
Final R1 values (all data)
Final wR(F2) values (all data)
Goodness of fit on F2
CCDC numbers
0.0788
1.076
901462
0.0751
1.030
901463
0.0687
1.076
901464
0.0855
1.015
901465
901461
especially attractive due its relatively low melting point, vola-
tility and thermal reactivity.
Deposition was performed at three substrate temperatures
(225 °C, 250 °C and 300 °C) under an atmosphere of hydrogen
gas. Quite significantly, at all deposition temperatures, and
especially at the lower deposition temperature of 225 °C inves-
tigated, crystalline pure copper metal was deposited, as evi-
denced by the analysis (PXRD, EDX and XPS). Removal of
surface bound organic matter by Ar-etching reveals a high
atomic percentage of copper metal (97–99 atomic %) at all
deposition temperatures. At both 250 °C and 300 °C the
atomic
% of carbon is higher than expected, again
suggesting possible carbon incorporation within the thin film
from the thermal decomposition of the ligand systems. XPS
spectra for films deposited at 250 °C and 300 °C are included
in the ESI.†
Given the structural similarity between these new iso-
ureate complexes and the structurally similar copper(I) amidi-
nate and copper(I) guanidinate precursors described by
Gordon et al.2a,c,e,f,h,j and Barry et al.13,14 we may assume that
comparable decomposition pathways are available to the pre-
cursors. At substrate temperatures below 200 °C deposition is
arrested, presumably because thermal activation of the precur-
sor above or at the surface is not achieved. At all deposition
temperatures the growing copper thin films appears to prefer
the cubic (111) orientation.
Fig. 9 XPS spectra of the copper thin films deposited using the precursor, 1, at
Copper films deposited at a substrate temperature of 300 °C
were observed to be less regular/continuous than those depos-
ited at 225 °C and 250 °C respectively: SEM images showing
225 °C, pre-etching with Ar (A) and post etching with Ar (B).
possesses a linear two coordinate geometry. Amongst them the the presence of copper nano-filaments, which through experi-
Cu(I) methoxy-N,N′-di-isopropyl-ureate (1) was found to be mentation were determined to be caused by high-temperature
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growth mechanism, rather than an extrusion of the nano-fila- resulting clear pale green solution was allowed to stir for
ments from the underlying copper films at elevated substrate 18 hours, by which time the colour had changed to dark blue.
temperatures.
Unreacted copper(I) chloride was removed by cannula fil-
tration, and the filtrate combined with a solution of lithium
bis(trimethylsilyl)amide (1.67 g, 10 mmol) in THF (10 ml). The
reaction mixture was allowed to stir for 10 minutes. In the
absence of light the solution was added to a slurry of copper(I)
chloride (0.99 g, 10.0 mmol) in THF (10 ml) at −78 °C and
allowed to warm to room temperature. After stirring for
2 hours, the volatiles were removed under reduced pressure
and dry hexane (20 ml) was added to the resultant residue.
The hexane solution was left to stir for 15 minutes and the
volatiles then removed under reduced pressure. This process
was repeated on two further occasions to remove any residual
THF and ethanol. Further hexane (20 ml) was added and the
slurry was filtered through Celite® to remove any insoluble
materials. Additional hexane (20 ml) was added, and the slurry
was filtered through Celite® to remove any insoluble materials.
Concentration of the solution in vacuo, followed by storage at
−28 °C affords 2 as pale yellow crystals (1.48 g, 63%). Anal.
Calc. for C18H38Cu2N4O2: C, 46.04, H, 8.16, N, 11.93, found: C,
45.43, H, 8.46, N, 11.5%. M.p. = 113.5 °C. 1H NMR (CDCl3,
Experimental
All manipulations were carried out under an atmosphere of
dry dinitrogen or argon using standard Schlenk and glove-box
techniques. Hexane, and THF were dried using an Innovative
Technology, Inc. Solvent Purification System (SPS) system and
degassed under dinitrogen or argon prior to use. The starting
materials, di-isopropylcarbodiimide, di-cyclohexylcarbodii-
mide, CuCl, lithium bis(trimethylsilyl)amide, lithium hexam-
ethyldisilylamide and potassium tert-butoxide where
purchased from Aldrich Chemicals. Solution H and 13C NMR
1
experiments were performed at ambient temperature using a
Bruker Avance-300. H and 13C NMR chemical shifts are refer-
1
enced internally to residual non-deuterated solvent reson-
ances. All chemical shifts are reported in δ (ppm) and
coupling constants in Hz. Elemental analyses were performed
externally London Metropolitan University Microanalysis
Service. Thermogravimetric analyses (TGA) were performed at
SAFC Hitech using a Shimadzu TGA-51 Thermogravimetric
Analyzer, while SEM-EDX analysis of the films was undertaken
on a JEOL JSM-6480LV scanning electron microscope, FE-SEM
analysis was undertaken on a JEOL 6301F microscope.
3
300.22 MHz) δ: 1.14 (d, 24H, NCH(CH3)2, J = 6.32 Hz), 1.35 (t,
3
3
12H, OCH2CH3, J = 7.10 Hz), 3.67 (sept, 4H, NCH(CH3)2, J =
6.32 Hz), 3.89 (q, 4H, OCH2CH3, 3J = 7.10 Hz). 13C{1H} NMR
(CDCl3, 75.49 MHz) δ: 15.2 (OCH2CH3), 27.3 (NCH(CH3)2), 46.6
(NCH(CH3)2), 67.9 (OCH2CH3), 166.9 (NCN).
Synthesis of complex 1
Synthesis of complex 3
Under an inert atmosphere (Ar), N,N′-diisopropylmethylisourea
(0.91 ml, 5.00 mmol) in 20 ml of cold THF (−78 °C) was added
a Schlenk containing lithium bis(trimethylsilyl)amide (0.837 g,
5.00 mmol) and copper(I) chloride (0.495 g, 5.00 mmol). An
immediate color change was observed, and the reaction was
allowed to warm slowly to room temperature with constant stir-
ring. After 1 hour the volatiles were removed under reduced
pressure and dry hexane (20 ml) was added to the resultant
residue. The hexane solution was left to stir for 15 minutes
and the volatiles then removed under reduced pressure. This
process was repeated on two further occasions to remove any
residual THF. Further hexane (20 ml) was added and the slurry
was filtered through Celite® to remove any insoluble materials.
Concentration of the solution in vacuo, followed by storage at
−28 °C affords 1 as colorless crystals (0.81 g, 74%). Anal. Calc.
for C16H34Cu2N4O2: C, 43.62; H, 7.79; N, 12.73, found: C,
43.85; H, 7.53; N, 12.71%. M.p. = 95.6 °C. 1H NMR (CDCl3,
300.22 MHz) δ: 1.14 (d, 24H, NCH(CH3)2, 3J = 6.32 Hz), 3.68
(sept, 4H, NCH(CH3)2, 3J = 6.32 Hz), 3.70 (s, 6H, OCH3). 13C
{1H} NMR (CDCl3, 75.49 MHz) δ: 27.2 (NCH(CH3)2), 46.5
(NCH(CH3)2), 59.8 (OCH3) 167.6 (NCN).
Complex 3 was synthesised in an analogous fashion to
complex 2 using, isopropanol (0.89 ml, 11.6 mmol) to afford 3
as colorless crystals (1.74 g, 70%). Anal. Calc. for
C20H42Cu2N4O2: C, 48.27, H, 8.51, N, 11.26, found: C, 47.26, H,
8.18, N, 10.82%. M.p.
=
119.2 °C. 1H NMR (CDCl3,
3
300.22 MHz) δ: 1.12 (d, 24H, NCH(CH3)2), J = 6.48 Hz), 1.13
(d, 12H, OCH(CH3)2), 3J = 6.48 Hz), 3.68 (sept, 4H, NCH(CH3)2,
3J = 6.48 Hz), 4.28 (sept, 2H, OCH(CH3)2), 3J = 6.48 Hz).
13C{1H} NMR (CDCl3, 75.49 MHz) δ: 22.6 (OCH(CH3)2), 27.4
(NCH(CH3)2), 47.2 (NCH(CH3)2), 73.8 (OCH(CH3)2), 165.3
(NCN).
Synthesis of complex 4
Under an inert atmosphere (Ar), potassium tert-butoxide
(1.23 g, 11.0 mmol) was placed into a dry Schlenk followed by
THF (10 ml). To this solution, N,N′-diisopropylcarbodiimide
(1.55 ml, 10.0 mmol) was added via syringe and the reaction
mixture left to stir for 2 hours. In the absence of light this
solution was then added to a slurry of copper(I) chloride
(0.99 g, 10.0 mmol) in THF and left to stir for 2 hours. The
volatiles were removed under reduced pressure and dry hexane
(20 ml) was added to the resultant residue. The hexane sol-
ution was left to stir for 15 minutes and the volatiles then
Synthesis of complex 2
Under an inert atmosphere (Ar), N,N′-diisopropylcarbodiimide removed under reduced pressure. This process was repeated
(1.55 ml, 10.0 mmol) and copper(I) chloride (0.005 g, on two further occasions to remove any residual THF. Further
0.05 mmol) were placed into a dry Schlenk tube. Anhydrous hexane (20 ml) was added and the slurry was filtered through
ethanol (6 ml, 103 mmol) was added by syringe and the Celite® to remove any insoluble materials. Concentration of
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the solution in vacuo, followed by storage at −28 °C affords 4
AFM analysis was performed using a Digital Instruments
as colorless crystals (1.81 g, 69%). Anal. Calc. for Nanoscope IIIa, with TAP300 tips in contact mode (tip radius
C22H46Cu2N4O2: C, 50.26, H, 8.82, N, 10.66, found: C, 50.37, H, <10 nm).
8.74, N, 11.04%. M.p.
=
121.3 °C. 1H NMR (CDCl3,
Powder XRD of the films was performed on a Bruker D8
300.22 MHz) δ: 1.11 (d, 24H, NCH(CH3)2, 3J = 6.32 Hz), 1.46 (s, Advance powder diffractometer, using a Cu anode X-ray source
18H, OC(CH3)3), 3.80 (sept, 4H, NCH(CH3)2, J = 6.32 Hz). 13C (Kα wavelength = 1.5406 Å) at the University of Bath.
3
{1H} NMR (CDCl3, 75.49 MHz) δ: 28.0 (NCH(CH3)2), 30.0 (OC
Single crystal X-ray crystallography
(CH3)3), 47.8 (NCH(CH3)2), 80.5 (OC(CH3)3), 165.7 (NCN).
Experimental details relating to the single-crystal X-ray crystal-
lographic studies are summarised in Table 4. For all struc-
Synthesis of complex 5
Complex 5 was synthesised in an analogous fashion to
complex 2 using, methanol (8 ml, 200 mmol) and dicyclohexyl-
carbodiimide (2.06 g, 10.0 mmol), to afford 5 as colourless
crystals (3.48 g, 58%). Anal. Calc. for C28H50Cu2N4O2: C, 55.88,
H, 8.37, N, 9.31, found: C, 56.19, H, 8.39, N, 9.03%. M.p. = dec.
137 °C, 1H NMR (C6D6, 300.22 MHz) δ: 1.21 (m, 8H, CH2), 1.50
(m, 16H, (CH2)), 1.64 (m, 16H, (CH2)), 1.93, (m, 4, CH), 3.39 (s,
6H, O(CH3). 13C{1H} NMR (C6D6, 75.49 MHz) δ: 26.7 (CH2),
27.0 ((CH2)2), 39.7 ((CH2)2), 56.0 (N(CH)), 60.0 (OCH3), 168.2
(NCN).
tures, data were collected on
a Nonius Kappa CCD
diffractometer at 150(2) using Mo-Kα radiation (λ
K
=
0.71073 Å). Structure solution and refinements were performed
using SHELX8626 and SHELX9727 software, respectively. Cor-
rections for absorption were made in all cases. Data were pro-
cessed using the Nonius Software.28 Structure solution,29
followed by full-matrix least squares refinement27b was per-
formed using the WINGX-1.80 suite of programs throughout.30
For all complexes, hydrogen atoms were included at calculated
positions.
The molecular structure of complex 3 presents disorder in
one of the isopropoxide (OiPr) groups (atoms C27–C29 and
C27A–C29A along with their associated hydrogen atoms)
which was modeled anisotropically over two positions using
an occupancy free variable.
Crystals of the complex 1 and 5 were both weakly diffract-
ing, with substantial intensity loss at higher 2 theta angle.
Hence a data completeness greater than 95.5% and 96.5%
respectively (max 2θ = 25.0°) could not be met. CCDC reference
numbers 901461–901465.
Materials chemistry
TGA analysis of the complexes was performed at SAFC Hitech,
Bromborough, UK, using a Shimadzu TGA-51 Thermogravi-
metric Analyser. Data points were collected every second at a
ramp rate of 20 °C min−1 in a flowing (50 ml min−1) N2
stream. Thin films were deposited using a modified cold-
walled CVD system (Electro-gas Systems Ltd, UK). The system
consisted of a tubular quartz reactor containing a silicon
carbide coated graphite susceptor. The temperature of the sus-
ceptor was monitored using a k-type thermocouple coupled
with a proportional–integral–derivative controller (PID control-
ler), and heated with a water cooled IR lamp mounted exter-
nally beneath the reaction tube. The pressure of the system
was maintained at ∼30 Torr throughout the deposition run,
with the reactor lines and precursor, held in a bubbler, at
90 °C. The vapour generated was delivered to the reaction zone
using a high purity Hydrogen (99.998%) carrier gas (300 ml
min−1) metered from a mass flow controller. Films were depos-
ited onto CVD coated ruthenium on silicon wafers at a suscep-
tor temperature of 300 °C. The total deposition time was
60 min.
X-ray photoelectron spectroscopy (XPS) measurements were
performed on a Kratos Axis Ultra-DLD photoelectron spec-
trometer, utilising monochromatic Al Kα radiation (photon
energy 1486.6 eV), at the University of Cardiff. Spectra were
calibrated to the Cu(2p) peak. Samples were sputtered for a
pre-determined set time over a 4 mm square area using 4 kV
argon ions from a minibeam I ion source. Spectra were col-
lected at pass energies of 80 and 160 eV for high resolution
and survey scans respectively, with the 100 μm aperture in
place to focus on the center of the etch pit.
Notes and references
1 (a) J. R. Creighton and J. E. Parmeter, Crit. Rev. Solid State
Mater. Sci., 1993, 18, 175–238; (b) M. J. Hampden-Smith
and T. Kodas, Polyhedron, 1995, 14, 699–732;
(c) J. A. T. Norman, J. Phys. IV, 2001, 11, Pr3-497–Pr3-503;
(d) J. Rickerby and J. H. G. Steinke, Chem. Rev., 2002, 102,
1525–1549; (e) B. Luo and W. L. Gladfelter, Chem. Vap.
Deposition, 2009, 320–356; (f) A. Grodzicki, I. Lakomska,
P. Piszczek, I. Szymanska and E. Szlyk, Coord. Chem. Rev.,
2005, 249, 2232–2258.
2 (a) B. S. Lim, A. Rahtu and R. G. Gordon, Nat. Mater., 2003,
2, 749–754; (b) A. U. Mane and S. A. Shivashankar, Mater.
Sci. Semicond. Process., 2004, 7, 343–347; (c) Z. Li,
S. T. Barry and R. G. Gordon, Inorg. Chem., 2005, 44, 1728–
1735; (d) K.-H. Park and W. J. Marshall, J. Am. Chem. Soc.,
2005, 127, 9330–9331; (e) Z. Li and R. G. Gordon, Chem.
Vap. Deposition, 2006, 12, 435–441; (f) Z. Li, A. Rahtu and
R. G. Gordon, J. Electrochem. Soc., 2006, 153, C787–C794;
(g) K.-H. Park, Z. Bradley Alexander, S. Thompson Jeffery
and J. Marshall Will, Inorg. Chem., 2006, 45, 8480–8482;
(h) Q. Ma, H.-S. Guo, R. G. Gordon and F. Zaera, Chem.
Mater., 2010, 22, 352–359; (i) B. Vidjayacoumar,
D. J. H. Emslie, S. B. Clendenning, J. M. Blackwell,
FE-SEM analysis of the films was undertaken on a JEOL
6301F. EDX analysis was performed using a JEOL 6480 LV SEM
microscope. TEM analysis was undertaken on a JEOL 1200EX,
using nickel grids, at the University of Bath.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 5554–5565 | 5563

View Article Online
Paper
J. F. Britten and A. Rheingold, Chem. Mater., 2010, 22,
Dalton Transactions
J. Mater. Res., 1999, 14, 975–979; (l) B. A. Kim and
H. H. Lee, Chem. Vap. Deposition, 2001, 7, 242–245.
9 (a) H. K. Shin, M. J. Hampdensmith, T. T. Kodas and
A. L. Rheingold, J. Chem. Soc., Chem. Commun., 1992,
217–219; (b) M. Becht, T. Gerfin and K. H. Dahmen, Helv.
Chim. Acta, 1994, 77, 1288–1298.
4844–4853; ( j) Q. Ma, H. Guo, R. G. Gordon and F. Zaera,
Chem. Mater., 2011, 23, 3325–3334; (k) G. Dey and
S. D. Elliott, J. Phys. Chem. A, 2012, 116, 8893–8901;
(l) J. Huo, R. Solanki and J. McAndrew, J. Mater. Res., 2002,
17, 2394–2398.
3 (a) O. K. Kwon, J. H. Kim, H. S. Park and S. W. Kang, J. Elec- 10 H. Guillon, S. Daniele, L. G. Hubert-Pfalzgraf and
trochem. Soc., 2004, 151, G109–G112; (b) O. K. Kwon, C. Bavoux, Inorg. Chim. Acta, 2000, 304, 99–107.
S. H. Kwon, H. S. Park and S. W. Kang, J. Electrochem. Soc., 11 (a) A. Jakob, T. Ruffer, P. Ecorchard, B. Walfort, K. Korbitz,
2004, 151, C753–C756.
S. Fruhauf, S. E. Schulz, T. Gessner and H. Lang, Z. Anorg.
Allg. Chem., 2010, 636, 1931–1940; (b) R. Mothes, T. Ruffer,
Y. Z. Shen, A. Jakob, B. Walfort, H. Petzold, S. E. Schulz,
R. Ecke, T. Gessner and H. Lang, Dalton Trans., 2010, 39,
11235–11247; (c) W. B. Szymanska, P. Piszczek and E. Szlyk,
Polyhedron, 2009, 28, 721–728; (d) J. L. Han, Y. Z. Shen,
C. X. Li, Y. Z. Li and Y. Pan, Inorg. Chim. Acta, 2005, 358,
4417–4422; (e) A. Jakob, H. Schmidt, B. Walfort,
G. Rheinwald, S. Fruhauf, S. Schulz, T. Gessner and
H. Lang, Z. Anorg. Allg. Chem., 2005, 631, 1079–1086.
4 (a) K. Ramasamy, M. A. Malik and P. O’Brien, Chem. Sci.,
2011, 2, 1170–1172; (b) A. L. Abdelhady, M. A. Malik and
P. O’Brien, J. Mater. Chem., 2012, 22, 3781–3785;
(c) K. Ramasamy, M. A. Malik and P. O’Brien, Chem.
Commun., 2012, 48, 5703–5714.
5 P. Jackson, D. Hariskos, E. Lotter, S. Paetel, R. Wuerz,
R. Menner, W. Wischmann and M. Powalla, Prog. Photo-
voltaics, 2011, 19, 894–897.
6 (a) C. Y. Cummings, G. Zoppi, I. Forbes, P. J. Dale,
J. J. Scragg, L. M. Peter, G. Kociok-Kohn and F. Marken, 12 (a) Y. Chi, P. F. Hsu, C. S. Liu, W. L. Ching, T. Y. Chou,
J. Electroanal. Chem., 2010, 645, 16–21; (b) G. Zoppi,
I. Forbes, R. W. Miles, P. J. Dale, J. J. Scragg and
L. M. Peter, Prog. Photovoltaics, 2009, 17, 315–319;
(c) J. J. Scragg, P. J. Dale and L. M. Peter, Thin Solid Films,
A. J. Carty, S. M. Peng, G. H. Lee and S. H. Chuang,
J. Mater. Chem., 2002, 12, 3541–3550; (b) M. Veith,
N. Lecerf, S. Mathur, H. Shen and S. Hufner, Chem. Mater.,
1999, 11, 3103–3112.
2009, 517, 2481–2484; (d) J. J. Scragg, P. J. Dale and 13 T. J. J. Whitehorne, J. P. Coyle, A. Mahmood,
L. M. Peter, Electrochem. Commun., 2008, 10, 639–642;
(e) M. C. Artaud-Gillet, S. Duchemin, R. Odedra, G. Orsal,
W. H. Monillas, G. P. A. Yap and S. T. Barry, Eur. J. Inorg.
Chem., 2011, 3240–3247.
N. Rega, S. Rushworth and S. Siebentritt, J. Cryst. Growth, 14 (a) J. P. Coyle, W. H. Monillas, G. P. A. Yap and S. T. Barry,
2003, 252, 626–627; (f) M. C. Artaud-Gillet, S. Duchemin,
R. Odedra, G. Orsal, N. Rega, S. Rushworth and
S. Siebentritt, J. Cryst. Growth, 2003, 248, 163–168.
7 (a) D. W. Macomber and M. D. Rausch, J. Am. Chem. Soc.,
1983, 105, 5325–5329; (b) D. B. Beach, W. F. Kane,
F. K. Legoues and C. J. Knors, Mater. Res. Soc. Symp. Proc.,
Inorg. Chem., 2008, 47, 683–689; (b) J. P. Coyle,
P. A. Johnson, G. A. DiLabio, S. T. Barry and J. Muller,
Inorg. Chem., 2010, 49, 2844–2850; (c) A. M. Willcocks,
T. P. Robinson, C. Roche, T. Pugh, S. P. Richards,
A. J. Kingsley, J. P. Lowe and A. L. Johnson, Inorg. Chem.,
2012, 51, 246–257.
1990, 181, 73–77; (c) D. B. Beach, F. K. Legoues and 15 L. J. Mathias, Org. Prep. Proced. Int., 1980, 12,
C. K. Hu, Chem. Mater., 1990, 2, 216–219; 309–326.
(d) M. J. Hampdensmith, T. T. Kodas, M. Paffett, J. D. Farr 16 N. Matsumura, T. Ohba and H. Inoue, Bull. Chem. Soc. Jpn.,
and H. K. Shin, Chem. Mater., 1990, 2, 636–639. 1982, 55, 3949–3950.
8 (a) K. M. Chi, H. K. Shin, M. J. Hampdensmith, 17 H.-Z. Tang, D. Boyle Paul and M. Novak Bruce, J. Am. Chem.
E. N. Duesler and T. T. Kodas, Polyhedron, 1991, 10, Soc., 2005, 127, 2136–2142.
2293–2299; (b) K. M. Chi, H. K. Shin, M. J. Hampdensmith, 18 (a) A. J. Bloodworth, A. G. Davies and S. C. Vasishtha,
T. T. Kodas and E. N. Duesler, Inorg. Chem., 1991, 30,
4293–4294; (c) H. K. Shin, K. M. Chi, M. J. Hampdensmith,
T. T. Kodas, J. D. Farr and M. Paffett, Adv. Mater., 1991, 3,
246–248; (d) H. K. Shin, M. J. Hampdensmith,
J. Chem. Soc. C, 1967, 1309–1313; (b) A. G. Davies, (M and
T Chemicals Inc.), Application: US 1964-406571, 1967;
(c) I. Shibata, H. Yamasaki, A. Baba and H. Matsuda, J. Org.
Chem., 1992, 57, 6909–6914.
E. N. Duesler and T. T. Kodas, Polyhedron, 1991, 10, 19 (a) A. G. Davies and R. J. Puddephatt, J. Organomet. Chem.,
645–647; (e) T. H. Baum and C. E. Larson, Chem. Mater.,
1992, 4, 365–369; (f) R. Kumar, F. R. Fronczek,
1966, 5, 590–592; (b) A. G. Davies and R. J. Puddephatt,
J. Chem. Soc. C, 1967, 2663–2668.
A. W. Maverick, W. G. Lai and G. L. Griffin, Chem. Mater., 20 (a) T. A. Budzichowski, M. H. Chisholm, K. Folting,
1992, 4, 577–582; (g) T. Kruck and C. Terfloth, Chem. Ber.,
1993, 126, 1101–1106; (h) H. Y. Yoen, Y. B. Park and
S. W. Rhee, J. Mater. Sci.: Mater. Electron., 1997, 8, 189–194;
(i) J. H. Son, M. Y. Park and S. W. Rhee, Thin Solid Films,
1998, 335, 229–236; ( j) S. W. Kang, S. H. Han and
S. W. Rhee, Thin Solid Films, 1999, 350, 10–13;
(k) M. Y. Park, J. H. Son, S. W. Kang and S. W. Rhee,
J. C. Huffman, W. E. Streib and D. B. Tiedtke, Polyhedron,
1998, 17, 857–867; (b) Y. Cao, Z. Du, W. B. Li, J. M. Li,
Y. Zhang, F. Xu and Q. Shen, Inorg. Chem., 2011, 50,
3729–3737; (c) Z. Du, Y. Zhang, Y. M. Yao and Q. Shen,
Dalton Trans., 2011, 40, 7639–7644; (d) Z. Du, H. Zhou,
H. S. Yao, Y. Zhang, Y. M. Yao and Q. Shen, Chem.
Commun., 2011, 47, 3595–3597.
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View Article Online
Dalton Transactions
Paper
21 (a) M. Bortoluzzi, G. Paolucci, F. Sartor and V. Bertolasi, 24 A. L. Johnson, A. M. Willcocks and S. P. Richards, Inorg.
Polyhedron, 2012, 37, 66–76; (b) B. M. Bycroft and Chem., 2009, 48, 8613–8622.
J. D. Cotton, J. Chem. Soc., Dalton Trans., 1973, 1867–1870; 25 E. S. Hwang and J. Lee, Chem. Mater., 2000, 12,
(c) J. Vicente, J. A. Abad, M.-J. Lopez-Saez and P. G. Jones, 2076–2081.
Organometallics, 2006, 25, 1851–1853; (d) J. Vicente, 26 G. M. Sheldrick, SHELX-86, Computer Program for Crystal
J.-A. Abad, M.-J. Lopez-Saez, P. G. Jones and D. Bautista,
Structure Determination, University Of Göttingen, Germany,
Chem.–Eur. J., 2010, 16, 661–676; (e) F. W. B. Einstein and
1986.
J. S. Field, Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. 27 (a) G. M. Sheldrick, SHELX-97, Computer Program for Crystal
Chem., 1979, 35, 1696–1698; (f) Y. J. Park, N. S. Sickerman,
J. W. Ziller and A. S. Borovik, Chem. Commun., 2010, 46,
2584–2586.
Structure Refinement, University of Göttingen, Germany,
1997; (b) G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam.
Crystallogr., 2008, 64, 112–122.
22 (a) I. Westmoreland, I. J. Munslow, A. J. Clarke, G. Clarkson 28 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276,
and P. Scott, Organometallics, 2004, 23, 5066–5074; 307–326.
(b) A. L. Gott, S. R. Coles, A. J. Clarke, G. J. Clarkson and 29 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano,
P. Scott, Organometallics, 2007, 26, 136–142.
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni,
G. Polidori and R. Spagna, J. Appl. Crystallogr., 1999, 32,
115–119.
23 T. Chen, C. Xu, T. H. Baum, B. C. Hendrix, T. Cameron,
J. F. Roeder and M. Stender, (Advanced Technology
Materials, Inc., USA), Application: WO 2007142700, 2007.
30 L. J. Farrugia, J. Appl. Crystallogr., 2012, 45, 849–854.
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