Silicon is of great interest for use as the anode material in lithium-ion batteries due to its high capacity. However, certain properties of silicon, such as a large volume expansion during the lithiation process and the low diffusion rate of lithium in silicon, result in fast capacity degradation in limited charge/discharge cycles, especially at high current rate. Therefore, the use of silicon in real battery applications is limited. The idea of using porous silicon, to a large extent, addresses the above-mentioned issues simultaneously. In this review, we discuss the merits of using porous silicon for anodes through both theoretical and experimental study. Recent progress in the preparation of porous silicon through the template-assisted approach and the non-template approach have been highlighted. The battery performance in terms of capacity and cyclability of each structure is evaluated.

1. Sputter deposited LiPON thin films from powder target as electrolyte for thin film
battery applications
C.S. Nimisha a,
⁎, K. Yellareswar Rao a
, G. Venkatesh b
, G. Mohan Rao a
, N. Munichandraiah b
a
Department of Instrumentation, Indian Institute of Science, Bangalore 560012, India
b
Department of Inorganic and Physical Chemistry Indian Institute of Science, Bangalore 560012, India
a b s t r a c ta r t i c l e i n f o
Article history:
Received 6 May 2010
Received in revised form 24 December 2010
Accepted 4 January 2011
Keywords:
Powder target
Solid electrolyte
LiPON thin films
X-ray photoelectron spectroscopy
Lithium phosphorus oxynitride (LiPON) thin films as solid electrolytes were prepared by reactive radio
frequency (rf) magnetron sputtering from Li3PO4 powder compact target. High deposition rates and ease of
manufacturing powder target compared with conventional ceramic Li3PO4 targets offer flexibility in handling
and reduce the cost associated. Rf power density varied from 1.7 Wcm− 2
to 3 Wcm−2
and N2 flow from 10 to
30 sccm for a fixed substrate to target distance of 4 cm for best ionic conductivity. The surface chemical
analysis done by X-ray photoelectron spectroscopy showed incorporation of nitrogen into the film as both
triply, Nt and doubly, Nd coordinated form. With increased presence of Nt, ionic conductivity of LiPON was
found to be increasing. The electrochemical impedance spectroscopy of LiPON films confirmed an ionic
conductivity of 1.1×10− 6
Scm−1
for optimum rf power and N2 flow conditions.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
In recent years, much importance has been given to the research
and development of Li-ion batteries, which are promising candidates
for micro-power applications [1–4]. Various research groups are
involved in the development of different kinds of Li-ion batteries, in
which thin film battery (TFB), is a fast growing category. These
batteries make use of a thin solid electrolyte layer between cathode
and anode sequentially deposited on to a substrate by various
deposition processes, matching to modern semiconductor technolo-
gies. Thin films deposited by physical vapor deposition techniques
(PVD) can greatly improve reaction areas of rechargeable TFB as they
provide cleaner and intimate interface between cathode, electrolyte
and anode layers. For any lithium based battery, the electrolyte layer
permits the repeated and rapid transfer of Li+
ions between the anode
and cathode over an expected range of operating conditions. A thin
layer of solid electrolyte provides considerable savings in terms of
volume and mass of the battery compared to liquid or polymer
electrolyte.
Widely used solid electrolytes are either glassy (oxides or sulfides)
or ceramic type. Glassy or amorphous electrolytes have several
advantages compared to crystalline counterparts; such as wide range
of selection in composition, isotropic properties, no grain boundaries,
easy film formation etc. Altogether solid electrolytes exhibit higher
ionic conductivities with single ion conduction, in which only Li+
ions
are mobile while the counter anions and other cations form a rigid
network [5]. This effectively suppresses the undesirable side reactions
or decomposition of electrolyte due to anionic concentration gradient
across the electrolyte. Different solid electrolyte chemistries include
Li2S–SiS2 [6], Li2S–SiS2–Li4SiO4 [7], Li2S–SiS2–Li3PO4 [8], Li2S–P2S5 [9],
Li2O–Al2O3–TiO2–SiO2–P2O5 [10] etc. Ionic conductivities in the range
10−3
–10−4
Scm−1
have been reported from sulfur based and ceramic
electrolytes. Sulfur based electrolytes are moisture sensitive and tend
to corrode the deposition equipment making it difficult to handle.
High temperature annealing requirement for ceramic electrolytes
limits their applications when multi-layered stacks made of materials
with varying thermal expansion coefficients are used. As an alterna-
tive, amorphous lithium phosphorus oxynitride (LiPON) thin films
formed by sputtering from Li3PO4 target in pure N2, with a composition
of Li3.3 PO3.9 N0.17 and a Li+
-ion conductivity of 2×10−6
Scm−1
at
25 °C [11] has been integrated as an electrolyte layer of TFB [2–4].
Although LiPON has lower ionic conductivity compared to other solid
electrolytes, stability with Li anode, better durability, ease of
integration with TFB with a matching potential window of 0–5.5 V
favor this oxinitride glassy electrolyte. A recent review on fast Li-ion
conductors by Knauth provides more insight in to the state-of-the-art
knowledge of solid electrolytes [12].
LiPON electrolyte films have been synthesized by different vapor
deposition techniques like rf magnetron sputtering [13–16], ion-beam
assisted deposition (IBAD) [17], pulsed laser deposition (PLD) [18], and
e-beam evaporation [19]. Among rf sputtering, IBAD, PLD and e-beam
evaporation, a maximum ionic conductivity of 3.3×10−6
Scm−1
has
been reported from rf sputtered LiPON films [20]. Rf sputtering is
preferred over other PVD processes due to its high repeatability for
multi-elemental compounds, formation of pin hole free films with good
contacts and high particle energy leading to dense layers. The major
Thin Solid Films 519 (2011) 3401–3406
⁎ Corresponding author. Fax: +91 8023600135.
E-mail address: nimishacs@yahoo.com (C.S. Nimisha).
0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.tsf.2011.01.087
Contents lists available at ScienceDirect
Thin Solid Films
journal homepage: www.elsevier.com/locate/tsf

2. limiting factor of rf magnetron sputtering from Li3PO4 ceramic target is
the low deposition rate (typically 2 nm/min) [20] and a non-uniform
erosion which eventually leads to non stoichiometry of the multi-
elemental target. Lee et al. [21] for rf sputtered LiPON films and Kim et al.
[22]for plasma assisted PVD of LiPONfilmshave reported higher growth
rates with an ionic conductivity in the range of 10−7
–10−9
Scm−1
.
Typically lithium phosphate targets are prepared by a series of
steps which includes calcinations of Li3PO4 powder, binder addition,
drying, sieving and ball milling followed by hot/cold press to increase
the density of the target. This disc has to be sintered for long hours to
complete the target making process. But after few depositions, β
Li3PO4 transforms to polymorphic γ Li3PO4 due to temperature
increase in the target which finally leads to cracking of the sintered
targets [23]. Considering the material loss associated and cost of
production of ceramic sintered targets, sputtering from powder target
is a straight forward and cost effective technique. This avoids cracking
of brittle targets due to low thermal conductivity. Sputtering from
powder target has been reported for multi-component films such as
YBCO, CrB–MoSx and CrB–TiC–MoSx with good repeatability [24,25].
In the present study we have combined the merits of rf sputter
deposition and a cost effective powder compact Li3PO4 target in N2
plasma. The goals of this study are to,
i. Explain the synthesis of LiPON films in N2 plasma from a
powder compact Li3PO4 target with a high deposition rate.
ii. Characterize the properties of resulting films in terms of
structure, surface morphology, N2 incorporation by elemental
composition study and Li+
-ion conductivity.
iii. Optimize the deposition conditions in terms of rf power and N2
flow during deposition.
2. Experimental details
Stoichiometric Li3PO4 powder targets were made by filling Li3PO4
powder (99.99% Sigma Aldrich ) in a 3 inch diameter Cu disk with a
trench of 3 mm depth and was packed tightly by pressing with a flat
metal plate. This powder target was fixed on to rf magnetron in a
sputter-up configuration. The schematic representation of the
deposition system with powder target arrangement is shown in Fig. 1.
Fig. 1. Schematic illustration of magnetron sputtering system using Li3PO4 powder
target for LiPON deposition.
Fig. 2. Schematic layout of metal–insulator–metal (MIM) structure of Pt/LiPON/Al for
impedance measurement.
Fig. 3. XRD patterns of pure Li3PO4 powder target and LiPON film deposited.
(Deposition conditions: rf power density of 3 Wcm−2
, N2 flow of 30 sccm).
Fig. 4. (a) SEM image of LiPON film surface on Pt coated Si substrate and (b) cross-
section of Pt/LiPON/Al (MIM) structure. (Deposition conditions are, Rf power density of
3 Wcm−2
, N2 flow of 30 sccm.)
3402 C.S. Nimisha et al. / Thin Solid Films 519 (2011) 3401–3406

3. Pre-cleaned platinum deposited silicon substrates (Silicon Valley
Inc.USA) were held at a distance of 4 cm away from the target. The
substrate holder was provided with a to and fro movement above the
target for homogeneous deposition of the film over the substrate. A
base vacuum of 1×10−6
mbar was obtained with a turbo molecular
pump backed by a rotary pump. The powder compact target was pre-
sputtered for an hour to remove any hydrocarbons present and also to
sinter the top layers of target locally. Substrate temperature was not
controlled during deposition, but was observed to rise up to 110 °C
towards the end of deposition due to plasma heating. The deposition
time of 40 min was kept constant for all the depositions used in this
Fig. 5. Impedance spectra of LiPON thin films deposited from powder target at different rf power densities (a) 1.7 Wcm− 2
(b) 2.2 Wcm−2
, (c) 2.6 Wcm−2
, (d) 3 Wcm−2
from Pt/
LiPON/Al sandwich structure.
Fig. 6. Arrhenius plot of ionic conductivity of LiPON thin film vs. temperature.
(Deposition conditions: rf power density of 3 Wcm−2
, nitrogen flow of 30 sccm).
Fig. 7. XPS survey spectra of LiPON film and Li3PO4 powder used as target. (Deposition
conditions are, rf power density of 3 Wcm−2
, N2 flow of 30 sccm).
3403C.S. Nimisha et al. / Thin Solid Films 519 (2011) 3401–3406

4. study. Rf power density was varied from 1.7 Wcm−2
to 3 Wcm−2
and
N2 flow from 10 to 40 sccm in order to optimize the processing
conditions.
The crystal structure of Li3PO4 powder and films was characterized
by X-ray diffraction (XRD) using Bruker D8 Advance (Cu-Kα radiation,
λ=1.5405 A0
). A SIRION 200 field emission scanning electron
microscope (FESEM) was employed to investigate the surface
morphology and cross sectional microstructure of LiPON films. All
the samples were coated with a thin Pd/Au layer to reduce surface
charging effects.
X-ray photoelectron spectroscopy (XPS) analysis was performed
with SPECS GmbH spectrometer (Phoibos 100 MCD Energy Analyzer)
using MgKα radiation (1253.6 eV). The residual pressure inside the
analysis chamber was in 10−10
mbar range. The spectrometer was
calibrated using photoemission lines of Ag (Ag 3d3/2=367 eV with
reference to Fermi level). Peaks were recorded with constant pass
energy of 40 eV. Because of surface charge induced peak shifts, C 1s at
284.6 eV was taken as a reference energy position to correct the shift.
The N 1s peaks were resolved using a peak synthesis program in
which a non-linear background was assumed. The synthetic peaks
were defined with a combination of Gaussian and Lorentzian
distributions with a fixed FWHM of 1.8 eV.
The LiPON film thickness was determined from Dektak 150 stylus
profilometer. Ionic conductivity of the films was obtained from the
AC-impedance measurement of Pt/LiPON/Al sandwich structures
(Fig. 2) fabricated on Pt coated silicon substrates with a LiPON
thickness of 1 μm and Al top layer deposited by thermal evaporation
to an area of 2×2 mm. The test cells showed an open circuit voltage of
1.6 V. The AC-impedance measurements were performed at room
temperature and at higher temperature (27 °C to 130 °C) using a Bio-
Logic SA potentiostat/Galvanostat (model: VPM3) at frequencies from
1 Hz to 100 KHz.
3. Results and discussion
X-ray diffraction patterns of pure Li3PO4 powder and LiPON film
deposited on silicon wafer are shown in Fig. 3. While Li3PO4 powder
has various crystalline phases, LiPON film did not exhibit any peaks,
indicating amorphous nature of the film. This is advantageous for
battery applications since the ionic conductivity of amorphous films is
generally more isotropic and higher than that of single crystal or
textured polycrystalline films [26].
Fig. 4(a) shows the surface micrograph of as deposited LiPON film
on Pt coated silicon and the cross-sectional view of Pt/LiPON/Al
sandwich structure in Fig. 4(b). The as deposited LiPON film is smooth
without any cracks or pin holes on the surface. Also at the interface it
makes a clean contact with the top and bottom metal layers,
minimizing interfacial resistance between the layers.
Li+
-ion conductivity of LiPON films was measured by electro-
chemical impedance spectroscopy. Complex impedance of each of the
test pads was measured in 1–105
Hz frequency range at room
temperature. The impedance obtained is a characteristic of a single-
phase ionic conductor with blocking electrode configuration. The
ionic conductivity was calculated from the electrolyte resistance Rel
(which is the real part of impedance ZRe value at selected frequency in
which −Zim goes through a local minimum-Yu method) using the
relation,
σ = 1= Rel × d = A
where d is the thickness and A is the surface area of contact of LiPON
thin films [27]. There have been contradictory reports on the effect of rf
power density on ionic conductivity of LiPON film. Earlier Choi et al.
[28] reported that ionic conductivity of sputter deposited LiPON films
was inversely proportional to rf power density, whereas, studies by
Roh et al. supported a directly proportional relation of ionic
conductivity with rf power density [29]. Our experiments showed an
increased ionic conductivity with increase in rf power density in
conformity with the study of Roh et al. The bode plot representation of
ionic conductivity obtained from LiPON films deposited with different
rf powers is shown in Fig. 5(a–d). It can be seen that as the rf power
density is increased from 1.7 Wcm−2
to 3 Wcm−2
, there is an increase
in the ionic conductivity from 2.3×10−9
Scm−1
to 1.1×10−6
Scm−1
.
According to linear fit of Arrhenius equation, impedance analysis
showed an increased ionic conductivity with increase in measurement
temperature (Fig. 6). The activation energy Ea of LiPON has been
calculated using the equation,
ln σTð Þ = ln σ0Tð Þ−Ea = kT
where Ea is the activation energy, σ is ionic conductivity, T is
temperature in Kelvin and k is Boltzmann constant. Activation energy
was found to be 0.44 eV for the LiPON film deposited at optimized
conditions.
In some of the reported studies on LiPON thin films, the rate of
deposition was very low from the ceramic target and hence long hours
of deposition were employed [20,30]. But we have observed that films
of 1.2 μm thick can be deposited from powder target of Li3PO4 in N2
plasma with a deposition time of 40 min. Here the rate of deposition is
around 30 nm/min, which is 15 times higher than the sputtering rate
from ceramic Li3PO4 target. In order to remove an atom from a target
surface, energy greater than surface binding energy (Esurf) has to be
supplied. Since for the powder target, atoms are loosely confined to
surrounding atoms, the energy required to remove it from the lattice
Fig. 8. (a) Core level spectra of P 2p region showing the shift in binding energy (B.E.) of
P 2p for film and Li3PO4 powder used as target, (b) C 1s region of LiPON film and Li3PO4
powder.
3404 C.S. Nimisha et al. / Thin Solid Films 519 (2011) 3401–3406

5. site is less compared with sintered target, which is relatively tight
packed. Thus, the higher deposition rate obtained from the powder
target compared to a ceramic target can be due to less binding energy
associated with the powder target. Also the microscopic unevenness
of top surface layer leads to higher effective surface area of powder
particles which contributes to high deposition rates.
To investigate the chemical nature of deposited films, XPS analysis
of LiPON thin films deposited from powder target was done to provide
information about elemental bonding environment. Estimated error
in the calculated chemical composition can be around 10% for multi-
elemental compounds [31]. Survey scans of Li3PO4 powder and LiPON
films done from 1100 to 10 eV clearly depict the incorporation of
Fig. 9. N 1s XPS spectra with component analysis showing triply coordinated nitrogen as Nt and doubly coordinated nitrogen as Nd of LiPON films deposited with 4 different rf
powder densities, (a) 1.7 Wcm−2
, (b) 2.2 Wcm−2
, (c) 2.6 Wcm−2
, (d) 3 Wcm− 2
.The solid symbols represent the raw data and smooth curve represents the fitted data.
Fig. 10. Ionic conductivity and Nt/Nd ratio of LiPON thin films as a function of rf power
density.
Fig. 11. Ionic conductivity and Nt/Nd ratio of LiPON thin films as a function of nitrogen
flow.
3405C.S. Nimisha et al. / Thin Solid Films 519 (2011) 3401–3406

6. nitrogen in to LiPON film, which was otherwise absent in powder
sample (Fig. 7).
Studies with XPS showed a P 2p peak shift of Li3PO4 from 134.5 to
132.8 eV for LiPON films due to nitrogen incorporation [32]. This
reduction in binding energy is attributed to the replacement of P–O
bonds by P–N bonds which change the charge distribution around
phosphorus in thin films. Core level spectra of P 2p for both film and
powder samples are shown in Fig. 8(a) for comparison. Fig. 8(b)
shows the corresponding C 1s peaks from both Li3PO4 powder and
LiPON film. Also the study of amorphous phosphorous nitrides by
Veprek et al. suggested nitrogen incorporation as doubly (–N=) and
triply coordinated (–N≤) state [33]. Our studies on LiPON films,
revealed nitrogen incorporation in to Li3PO4 as both doubly
coordinated ‘Nd’ (peak at, 399.4 eV), or triply coordinated ‘Nt’, (peak
at, 400.8 eV) manner. Resolving N 1s spectrum of LiPON films
deposited with different rf power densities, into two components
and measuring the area of Nt and Nd gives a quantitative measure of
each. Fig. 9(a–d) shows N 1s spectrum and its component analysis for
the films deposited with different rf power densities of 1.7, 2.2, 2.6
and 3 Wcm−2
. A clear trend on increase in Nt is observed with
increase in rf power.
The effect of increased Nt/Nd ratio on ionic conductivity of LiPON film
with the increase in rf power density is plotted in Fig. 10. Due to the
higher ionic radius of N3−
compared with O2−
, the nitrogen substitution
in LiPON film for oxygen in Li3PO4 induces structural distortions, which
in fact improves the ionic conductivity and stability of LiPON. The
reduction in electrostatic energy, once the P–O bond is replaced by a
more covalent P–N bond, lowers the activation energy of Li±
mobility in
the defect lattice. It was suggested that more structural distortion
induced by cross linked Nt than Nd in the LiPON films, consequently
improving ionic conductivity with increased triply coordinated nitrogen
Nt [29,34]. For an rf power density of 1.7 Wcm−2
, Nt/Nd ratio obtained
was 0.27 with an ionic conductivity of 2.3×10−9
Scm−1
. But as the rf
power density increased to 3 Wcm−2
, Nt/Nd ratio improved to 1.42 and
the ionic conductivity also increased to 1.1×10−6
Scm−1
. However
increase of rf power density beyond 3 Wcm−2
was difficult as the
powder particles of the target begin to splash to growing thin film
surface.
Other than the rf power density, nitrogen flow rate is an important
process parameter that governs ionic conductivity of LiPON films [18].
We have selected four different flow rates of 10, 20, 30 and 40 sccm of
nitrogen to fine tune the conductivity obtained with rf power density of
3 Wcm−2
. The dependence of ionic conductivity on N2 flow rate and Nt /
Nd ratio obtained from XPS analysis is shown in Fig. 11. Initially ionic
conductivity increases from 7.2×10−9
Scm−1
to 1.1×10−6
Scm−1
for
a flow rate increase of 10 to 30 sccm. But for 40 sccm of N2, the
deposition rate itself reduces due to increased scattering of sputtered
species and conductivity reduces to 4.7×10−7
Scm−1
. With the
increase in the nitrogen flow, the incorporation of nitrogen into the
lithium phosphate matrix in the film as well as the source also increases.
Further addition of nitrogen into the source results in a reduction in the
sputtering rate. It was observed that the deposition rate was increased
from15 nm/min to 30 nm/min as the nitrogen flow increased from 10 to
30 sccm.At a flow rate of 40 sccm, the deposition rate reduced to 20 nm/
min and this effect was seen in the incorporation of nitrogen in the film.
It has been also confirmed by XPS studies that a film deposited with
40 sccm of nitrogen flow has lesser Nt/Nd ratio. The maximum obtained
ionic conductivity from this study is 1.1×10−6
Scm−1
, which is low
compared to the best reported ionic conductivity (3.3×10−6
Scm−1
of
LiPON films by Hu et al. [20]). However, LiPON films with an ionic
conductivity of 4.5×10−7
Scm−1
has already been demonstrated as
solid electrolyte of a LiCoO2/LiPON/Li TFB with a discharge capacity of
59 μAh cm−2
μm−1
and good capacity retention [35].
4. Conclusions
In this study we have shown that, sputtering from powder target
can be useful for certain compounds like Li3PO4 in which breaking of
ceramic target and material loss are severe problems. The ionic
conductivity of LiPON films formed was in relative good agreement
with previously reported values with a higher deposition rate. The
effects of rf power change and N2 flow during deposition are studied
in detail. It is seen that with increase in rf power density, ionic
conductivity is increased and for increased nitrogen flow, there is an
increased ionic conductivity for 10 to 30 sccm but reduces for higher
N2 flow of 40 sccm. Amorphous nature of the films during deposition
process has been ensured and verified through XRD. Incorporation of
triply coordinated nitrogen enhances the ionic conductivity which has
been confirmed by XPS and AC impedance analysis. A maximum ionic
conductivity of 1.1×10−6
Scm−1
was obtained for an Nt/Nd ratio of
1.42 for 3 Wcm−2
and N2 flow of 30 sccm.
Acknowledgement
The authors acknowledge DRDO, Govt. of India for funding this
work.
References
[1] J.W. Schultze, T. Osaka, M. Datta (Eds.), Electrochemical Microsystem Technol-
ogies, CRC Press, 2002.
[2] B.J. Neudecker, N.J. Dudney, J.B. Bates, J. Electrochem. Soc. 147 (2000) 517.
[3] H.J. Ji, S.H. Kang, H.J. Lee, P.H. Kim, S.B. Cho, Proc. IME. G J. Aero. Eng. 223 (2009)
107.
[4] W.Y. Liu, Z.W. Fu, Q.Z. Qin, J. Electrochem. Soc. 155 (2008) A8.
[5] T. Minami, Solid State Ionics for Batteries, Springer-Verlag, Tokyo, 2005.
[6] H. Morimoto, H. Yamashita, M. Tatsumisago, T. Minami, J. Am. Ceram. Soc. 82
(1999) 1352.
[7] H. Morimoto, H. Yamashita, M. Tatsumisago, T. Minami, J. Ceram. Soc. Jpn., Int. Ed.
108 (2000) 128.
[8] M. Tatsumisago, H. Yamashita, A. Hayashi, H. Morimoto, T. Minami, J. Non-Cryst.
Solids 274 (2000) 30.
[9] F. Mizuno, A. Hayashi, K. Tadanaga, M. Tatsumisago, Solid State Ionics 177 (2006) 2721.
[10] J. Fu, J. Am. Ceram. Soc. 80 (1997) 1901.
[11] J.B. Bates, N.J. Dudney, G.R. Gruzalski, R.A. Zuhr, A. Choudhury, C.F. Luck, Solid
State Ionics 53–56 (1992) 647.
[12] P. Knauth, Solid State Ionics 180 (2009) 911.
[13] Y. Hamon, A. Douard, F. Sabary, C. Marcel, P. Vinatier, B. Pecquenard, A. Levasseur,
Solid State Ionics 177 (2006) 257.
[14] N.J. Dudney, J.B. Bates, R.A. Zuhr, C.F. Luck, Solid State Ionics 53–56 (1992) 655.
[15] W.C. West, J.F. Whitacre, J.R. Lim, J. Power Sources 126 (2004) 134.
[16] J. Schwenzel, V. Thangadurai, W. Weppner, J. Power Sources 154 (2006) 232.
[17] F. Vereda, R.B. Goldner, T.E. Haas, P. Zerigian, Electrochem. Solid-State Lett. 5
(2002) A239.
[18] S. Zhao, Z. Fu, Q. Qin, Thin Solid Films 415 (2002) 108.
[19] W.Y. Liu, Z.W. Fu, C.L. Li, Q.Z. Qin, Electrochem. Solid-State Lett. 7 (2004) J36.
[20] Z. Hu, D. Li, K. Xie, Bull. Mater. Sci. 31 (2008) 681.
[21] J.M. Lee, S.H. Kim, Y. Tak, J.M. Yoon, J. Power Sources 163 (2006) 173.
[22] Y.G. Kim, H.N.G. Wadley, J. Vac. Sci. Technol., A 26–1 (2008) 174.
[23] B. Wang, B.C. Chakoumakos, B.C. Sales, B.S. Kwak, J.B. Bates, J. Solid State Chem.
115 (1995) 313.
[24] W.G. Luo, A.L. Ding, K.S. Chan, G.G. Siu, A. Cheng, E.C.M. Young, J. Supercond. 5
(1992) 239.
[25] M. Audronis, P.J. Kelly, R.D. Arnell, A. Leyland, A. Matthews, Surf. Coat. Technol.
200 (2005) 1616.
[26] P.G. Bruce, Solid State Electrochemistry, Cambridge University Press, 1997.
[27] X. Yu, J.B. Bates, G.E. Jellison Jr., F.X. Hart, J. Electrochem. Soc. 144 (1997) 524.
[28] C.H. Choi, W.I. Cho, B.W. Cho, H.S. Kim, Y.S. Yoon, Y.S. Taka, Electrochem. Solid-
State Lett. 5 (2002) A14.
[29] N.S. Roh, S.D. Lee, H.S. Kwon, Scr. Mater. 42 (2000) 43.
[30] N.J. Dudney, J.B. Bates, J.D. Robertson, J. Vac. Sci. Technol., A 11 (1993) 377.
[31] D. Brigs, M.P. Seah (Eds.), Practical Surface Analysis by Auger and X-ray
Photoelectron Spectroscopy, Mir, Moscow, 1987.
[32] B.K. Brow, C.G. Pantano, J. Am. Ceram. Soc. 69 (1986) 314.
[33] S. Veprek, S. Iqbal, J. Brunner, M. Scharli, Philos. Mag. 43 (1981) 527.
[34] J.B. Bates, N.J. Dudney, G.R. Gruzalski, R.A. Zuhr, A. Choudhury, C.F. Luck, J.D.
Robertson, J. Power Sources 43–44 (1993) 103.
[35] N. Kuwata, N. Iwagami, Y. Matsuda, Y. Tanji, J. Kawamura, ECS Trans. 16 /26
(2009) 53.
3406 C.S. Nimisha et al. / Thin Solid Films 519 (2011) 3401–3406