Content uploaded by Szabolcs Beke
Author content
All content in this area was uploaded by Szabolcs Beke on Oct 21, 2014
Content may be subject to copyright.
1 23
Applied Physics A
Materials Science & Processing
ISSN 0947-8396
Appl. Phys. A
DOI 10.1007/s00339-012-6765-1
Highly transparent ITO thin films on
photosensitive glass: sol–gel synthesis,
structure, morphology and optical
properties
László Kőrösi, Szilvia Papp, Szabolcs
Beke, Béla Pécz, Róbert Horváth, Péter
Petrik, Emil Agócs & Imre Dékány
1 23
Your article is protected by copyright and
all rights are held exclusively by Springer-
Verlag. This e-offprint is for personal use only
and shall not be self-archived in electronic
repositories. If you wish to self-archive your
work, please use the accepted author’s
version for posting to your own website or
your institution’s repository. You may further
deposit the accepted author’s version on a
funder’s repository at a funder’s request,
provided it is not made publicly available until
12 months after publication.
Appl Phys A
DOI 10.1007/s00339-012-6765-1
Highly transparent ITO thin films on photosensitive glass: sol–gel
synthesis, structure, morphology and optical properties
László K˝
orösi ·Szilvia Papp ·Szabolcs Beke ·
Béla Pécz ·Róbert Horváth ·Péter Petrik ·Emil Agócs ·
Imre Dékány
Received: 24 August 2011 / Accepted: 22 December 2011
© Springer-Verlag 2012
Abstract Conductive and highly transparent indium tin ox-
ide (ITO) thin films were prepared on photosensitive glass
substrates by the combination of sol–gel and spin-coating
techniques. First, the substrates were coated with amor-
phous Sn-doped indium hydroxide, and these amorphous
films were then calcined at 550◦C to produce crystalline
and electrically conductive ITO layers. The resulting thin
films were characterized by means of scanning electron mi-
croscopy, UV-Vis spectroscopy, X-ray photoelectron spec-
troscopy and spectroscopic ellipsometry. The measurements
revealed that the ITO films were composed of spherical crys-
tallites around 20 nm in size with mainly cubic crystal struc-
ture. The ITO films acted as antireflection coatings increas-
ing the transparency of the coated substrates compared to
that of the bare supports. The developed ITO films with a
thickness of ∼170–330 nm were highly transparent in the
visible spectrum with sheet resistances of 4.0–13.7 k/sq.
By coating photosensitive glass with ITO films, our results
open up new perspectives in micro- and nano-technology,
Electronic supplementary material The online version of this article
(doi:10.1007/s00339-012-6765-1) contains supplementary material,
which is available to authorized users.
L. K˝
orösi ()·S. Papp ·I. Dékány
Supramolecular and Nanostructured Materials Research Group of
the Hungarian Academy of Sciences, University of Szeged, Aradi
vértanúk tere 1, 6720 Szeged, Hungary
e-mail: l.korosi@chem.u-szeged.hu
Fax: +36-62-544042
S. Beke
Department of Nanophysics, Italian Institute of Technology,
Via Morego 30, 16163 Genova, Italy
B. Pécz ·R. Horváth ·P. Petr i k ·E. Agócs
Research Institute for Technical Physics and Materials Science,
Konkoly-Thege út 29-33, 1121 Budapest, Hungary
for example in fabricating conductive and highly transpar-
ent 3D microreactors.
1 Introduction
By virtue of its excellent optical and electrical properties,
indium tin oxide (ITO) is one of the most extensively stud-
ied transparent conductive oxides [1]. ITO thin films with
high transmittance in the visible spectral range and with low
resistivity have previously been prepared by several meth-
ods, such as sputtering [2], spray pyrolysis [3], chemical
vapor deposition [4], electron-beam evaporation [5], screen
printing [6], pulsed-laser deposition [7], and the sol–gel pro-
cess [8]. The sol–gel method is a popular technique to pro-
duce high-quality thin films as it has a number of advan-
tages, such as relatively low cost, a need for only simple
equipment, and a high degree of control over the chemical
composition of the resulting metal oxides.
Sol–gel-based ITO films can be prepared either by the
deposition of coating solutions [9] or from sols containing
colloids [10]. In the coating solutions, the precursors are not
hydrolyzed before the film deposition step [11]. In this case,
after film deposition, the resulting, partially hydrolyzed pre-
cursors transform to ITO upon calcination. The coating so-
lutions are frequently used to prepare ITO films, but they
contain inorganic ions of the precursors, which could be
unfavorable during calcination. Sols (or colloidal disper-
sions) containing ITO [12] or other types of nanoparticles
(e.g. indium tin hydroxide, ITH) can also be used for thin-
film preparation [10]. ITH sols are generally synthesized by
the hydrolysis of InCl3or In(NO3)3and SnCl4in aqueous
medium [13]. Since the hydrolysis and condensation of the
precursors result in colloidal particles, the undesired ions
(Cl−and NO−
3) can be removed from the media of the sol
Author's personal copy
L. K˝
orösi et al.
by washing or use of dialysis. Another advantage of the sol-
based process is that the morphology or crystal phase of the
ITO particles can be controlled via the synthesis tempera-
ture and pH. Sol–gel-based films are usually prepared on a
glass or quartz substrate by dip- or spin-coating techniques.
During film deposition, the medium of the sol evaporates
and subsequently a metal oxide/hydroxide xerogel film is
formed [10]. The as-prepared layers are often amorphous,
and heat treatment at 500–550◦C is therefore necessary to
obtain crystalline and conductive ITO films. This heat treat-
ment is an important step because it causes particle sinter-
ing, which leads to a decrease in the electrical resistance of
the ITO layers. For sol preparations, the well-known hydro-
[14] and solvothermal [15] methods can also be employed.
These synthesis methods, with the application of elevated
temperature and pressure, can produce ITO nanoparticles di-
rectly instead of ITH [16].
In a recent study [10], we presented a short survey of the
preparation of ITO films with well-controlled layer thick-
ness (∼40–1160 nm) by applying a combination of sol–gel
and dip-coating methods. The adhesive ITH sols applied al-
lowed the rapid preparation of high-quality ITO films. It was
revealed that the sheet resistance of the ITO films was signif-
icantly lower when the ITH sols contained polyvinylpyrroli-
done (PVP). In another study [17], we demonstrated a novel
concept through which to achieve embedded 3D conductive
and completely transparent structures in glass microchips
by using a combination of femtosecond laser microfabrica-
tion and a sol–gel method. The application of ITO coatings
on photosensitive glass can be a breakthrough toward the
further exploitation of microchip technology by fabricating
microchips with novel features. The idea relies on the wide-
ranging applicability and sensitivity of ITO films of value
for sensitive biochemical analysis and biological, chemi-
cal, and medical inspections based on the development of
highly functional microdevices. Photosensitive glass (under
the trade name Foturan®) has all of the unique properties of
traditional glass (e.g. transparency, hardness, chemical, etc.)
and is an excellent material with which to embed hollow mi-
crochannels and other complicated 3D structures by using
femtosecond laser direct writing [18–20]. Moreover, Fotu-
ran glass can withstand thermal treatment at 550◦C, which
is a requirement for the production of sintered, conductive
ITO films.
In the present study, we report on the preparation of sol–
gel-based ITO thin films on photosensitive glass from PVP-
containing amorphous ITH sol through use of spin-coating
method and subsequent calcination. The structural, optical
and electrical properties of the resulting ITO thin films are
reported and the effects of the aging time on the crystallinity
and crystal phase composition are discussed.
2 Experimental details
2.1 Synthesis of ITH sols
1.1727 g of InCl3·4H2O and 0.1402 g of SnCl4·5H2Owere
dissolved in 100 ml of deionized water, and the precur-
sors were hydrolyzed at room temperature by the addi-
tion of 2.0 ml of 25% NH3solution during intensive stir-
ring. The resulting dispersion was centrifuged and the sed-
iment obtained was washed with water and subsequently
with ethanol. After the washing procedure, a stable sol
was prepared by redispersion of the sediment in 25 ml of
ethanol with the addition of PVP in a final concentration of
0.1 w/v%. This sol was designated ITH-NA.
The ITH-A sol was prepared as previously reported [10].
In this synthesis the aqueous dispersion of the as-prepared
precipitate was dialyzed against deionized water until the
conductivity had decreased below 1 µScm−1. The dialysis
was continued for a further 3 days, during which the precipi-
tate was aged. After dialysis, the dispersion was centrifuged
and the sediment obtained was washed with ethanol. Finally,
the resulting precipitate was dispersed in 50 ml of ethanol
with the addition of PVP as described above.
2.2 Preparation of ITH and ITO thin films
ITH thin films were prepared on Foturan glass substrates
(10 ×10 ×2 mm) by the spin-coating method. 50 µl of
ITH-NA or ITA-A sol was dropped onto the substrate ro-
tating with 3000 rpm and the as-prepared layer was subse-
quently dried for 30 s in the spin-coater. To prepare multi-
layer films the above deposition step was applied again with
the desired number of repetition. To obtain ITO thin films,
the deposited ITH layers were calcined for 30 min in air at
550◦C in a preheated furnace.
2.3 Characterization
Thermogravimetric (TG) investigations were carried out in
air with a TGA/SDTA 851e (Mettler Toledo) derivatograph
at a heating rate of 5◦Cmin
−1. X-ray diffraction (XRD)
patterns were collected on a Bruker D8 Advance diffrac-
tometer equipped with a Göbel mirror. The measurements
were made in θ-θconfiguration using CuKαradiation. The
operating voltage and current were 40 kV and 40 mA, re-
spectively. Transmission electron microscopy (TEM) im-
ages were obtained with a Philips CM-10 electron micro-
scope at an accelerating voltage of 100 kV. Scanning elec-
tron microscopy was performed with a Hitachi S-4700 FE-
SEM cold-field emission electron microscope operated at
5 kV. UV-Vis spectrophotometry was performed with an
Ocean Optics Chem2000-UV-VIS diode array spectropho-
tometer at wavelengths in the range 250–800 nm.
Author's personal copy
Highly transparent ITO thin films on photosensitive glass: sol–gel synthesis, structure, morphology
The X-ray photoelectron spectroscopy (XPS) was carried
out with VG ESCALAB 250 spectrometer (Thermo Fisher
Scientific K.K.) using monochromatic Al K X-ray radiation.
The X-ray gun was operated at 200 W (15 kV, 13.3 mA).
The C 1s binding energy of adventitious carbon was used as
energy reference; it was taken at 284.8 eV.
Ellipsometry measures the complex reflection ratio (ρ=
tan(Ψ )eiΔ, where Ψand Δare the ellipsometric angles),
the ratio of the reflection coefficients of light polarized par-
allel and perpendicular to the plane of incidence [21]. By
sensitively measuring phase changes of the light passing
through the deposited layers, ellipsometry has a sensitivity
of ∼0.1 nm and 0.0001 in the thickness and the in refrac-
tive index, respectively. However, as it is an indirect method,
the accuracy depends on the choice of an appropriate opti-
cal model. The ellipsometric measurements were performed
with a Woollam M-2000DI rotating compensator spectro-
scopic ellipsometer in the wavelength range 400–800 nm, at
angles of incidence ranging from 50◦to 70◦. A microspot
was used to avoid backside reflection from the transparent
substrate. The refractive index of the bare Foturan substrate
was determined by using the multiple-angle spectra with
backside roughening.
The sheet resistance of ITO films was determined by
four-point probe measurements with a Keithley 2400 source-
meter and a cylindrical four-point probe head (Jandel Engi-
neering Ltd). The tip array was linear with a probe spacing
of 1.0 mm. The 100-micron radius tips were made of tung-
sten carbide. The spring load was 60 g per tip. The sheet
resistance (Rs) was calculated via the following relation-
ship:
Rs=π/ln 2 ×(V /I )
where Vand Iare the voltage and the current, respectively.
3 Results and discussion
3.1 Structure, morphology and surface composition
ITO thin films were prepared by a combination of conven-
tional sol–gel and spin-coating techniques. In the first part of
the procedure, indium tin hydroxide (ITH) sol was synthe-
sized, while in the second step ITH thin films were prepared
by a spin-coating. Finally, the ITH films were calcined at
550◦C. To synthesize ITH, the precursors (InCl3and SnCl4)
were hydrolyzed in aqueous medium by the addition of NH3
solution until the pH reached 9. Following the hydrolysis
of In3+and Sn4+and the condensation of the resultant hy-
droxide species, the hydrous gel obtained was subsequently
washed with water and ethanol. Before the washing proce-
dure, the precipitate was not left to age which is a significant
difference as compared with our previously reported synthe-
sis [10]. As we presented earlier, the electric resistance of
Fig. 1 (a)TGand(b) DTG curves of ITO-NA xerogel dried at 50◦C
ITO films can be decreased by the addition of PVP to the
ITH sol [10]. After the washing procedure, therefore the gel
was dispersed ultrasonically in ethanol, and PVP was added
to the sol in final concentration of 0.1 w/v%. The solid con-
tent of the sol was 3.5 w/v%. To obtain ITH xerogel powder,
the ethanol was evaporated from the sol at 50◦C. The ther-
mogravimetric (TG) curve of the ITH-NA xerogel obtained
is presented in Fig. 1, curve a. The total mass loss in the
range 25–1000◦C was 25.2%. The differential thermogravi-
metric (DTG) curve (Fig. 1, curve b) exhibited minima at
∼50, 150, 280, 350 and 480◦C. Two main processes can be
distinguished; the first (∼25–215◦C) is due to dehydration,
while the mass loss above 215◦C is assigned to the dehy-
droxylation of ITH and the decomposition of PVP. In the in-
terval 550–1000◦C, the xerogel lost its residual OH groups,
which caused only a minor mass loss (0.7%). Since total
mass loss of the xerogel without PVP was 19.9%, the PVP
content of the ITO-NA xerogel was 5.3%. It should be noted
that the total mass loss of the previously synthesized aged
ITH xerogel [10] was slightly lower, which may be due to
the higher drying temperature (80◦C) applied prior to the
TG analysis.
The XRD patterns of the ITH-NA powder both before
and after calcination are displayed in Fig. 2. The XRD pat-
tern of the sample dried at 50◦C (Fig. 2, curve a) did not con-
tain any peaks, which indicates that the ITH-NA was amor-
phous. However, the ITH-A sample was nanocrystalline,
as reported previously [10]. In contrast with ITH-NA, the
ITH-A xerogels consisted of cubic In(OH)3and orthorhom-
bic InOOH crystal phases. It should be noted that the na-
ture of the medium during the aging process is of crucial
importance for the crystal phase evolution. When the as-
prepared precipitate (hydrous gel) was subsequently washed
with ethanol, the ITH did not become crystalline even after
several months of storage. We therefore conclude that the
aging of the gel in an aqueous medium favors the formation
of nanocrystalline ITH.
Author's personal copy
L. K˝
orösi et al.
Fig. 2 XRD patterns of (a) ITH-NA and (b) ITO-NA powders. The
characteristic reflections of In2O3with cubic and rhombohedral struc-
tures are indexed
In the XRD pattern of the calcined ITH-NA at 550◦C
(hereafter designated ITO-NA), cubic (JCPDS No. 06-0416)
and rhombohedral (JCPDS No. 22-0336) In2O3can be iden-
tified (Fig. 2, curve b). Other crystal phases (e.g. SnO and
SnO2) could not be detected, indicating a homogeneous dis-
tribution of Sn4+in the In2O3host. The broadened XRD
lines revealed that the ITO-NA was nanocrystalline. Due to
this broadening, several reflections of the two crystal phases
overlapped. The predominant crystal phase was cubic; the
(104) reflection of the rhombohedral phase appeared only
as a shoulder on the wide angle side of the (222) peak. To
determine the average crystallite size, the broad peak in the
range 29–32◦was deconvoluted in accordance with the posi-
tions of (222) and (104) reflections. From the FWHM of the
(222) and (110) reflections, the average sizes (determined
via the Scherrer equation) were 19.5 and 11.6 nm for the cu-
bic and rhombohedral crystallites, respectively. The effects
of aging on the crystallinity and structure can be compared
with the aid of the XRD patterns presented in Fig. 3.From
a comparison of the line broadening it is clearly seen that
the calcined ITH-A at 550◦C (hereafter designated ITO-A)
consisted of smaller crystallites than those of ITO-NA. For
ITO-A, the sizes were 8.3 and 9.4 nm for the cubic and
rhombohedral crystallites, respectively. The XRD patterns
also revealed that the ratio of the cubic and rhombohedral
phases was influenced by the aging. For ITO-NA, the inten-
sities of the lines relating to the rhombohedral phase were
significantly lower. Consequently, the aging of ITH favors
the formation of rhombohedral ITO crystallites. However, it
should be noted that the phase evolution may also depend on
the pH during aging. Kim et al. [22] reported that lower pH
(∼8)promotes the formation of rhombohedral ITO.
TEM picture of the ITH-NA (Fig. 4a) indicated an amor-
phous structure confirming the XRD results. In contrast, in
the case of ITH-A (Fig. 4b), polymorphic particles could be
observed: round particles measuring a few nanometers were
Fig. 3 Comparison of XRD patterns of (a) ITO-NA and (b) ITO-A
powders
present together with 40–70-nm cubic and columnar parti-
cles. These findings revealed that these rectangular objects
were formed during the aging process. The ITO-NA sam-
ple (Fig. 4c) was composed of round particles with a diam-
eter of ∼8–26 nm. The estimated average particle size was
∼17 nm, although the precise particle size distribution could
not be given because of the sintering, which caused the parti-
cles to assemble into large aggregates. The electron diffrac-
tion pattern of ITO-NA (inset in Fig. 4c) confirmed the pres-
ence of both cubic and rhombohedral phases. As may be
seen from the TEM picture of ITO-A (Fig. 4d), the rect-
angular morphology remained after calcination; the cubes
and columns were still present and only a minor coarsen-
ing of the round particles could be observed. It is clear from
the TEM image of ITO-A that the large rectangular particles
were composed of primary particles 5–10 nm in size, in ac-
cordance with the value (8.3 nm) calculated via the Scherrer
equation.
ITH-NA thin films with different layer numbers were pre-
pared on photosensitive glass from ITH-NA sol by a spin-
coating technique. To obtain crystalline and conductive ITO
films, the as-deposited ITH layers were calcined at 550◦C.
No heat treatment was applied between the film deposition
steps. The surface morphology of the ITO-NA films ob-
tained is presented in Fig. 5a. The SEM picture revealed
that ITO-NA consisted of fine particles with uniform round-
shaped morphology, resulting in lower surface roughness as
compared with ITO-A (Fig. S1 in the Supplementary Ma-
terial). The SEM picture also revealed that the film was sig-
nificantly porous. The cross-sectional view (Fig. 5b) of ITO-
NA film made up of 3 layers showed a uniform thickness of
∼360 nm.
XPS measurements on the ITO-NA film yielded the high-
resolution spectra of In 3d,Sn3dand O 1sregions depicted
in Fig. 6. Both the In 3dand the Sn 3dspectra were sym-
metric, indicating a single chemical state and the O–In–O
Author's personal copy
Highly transparent ITO thin films on photosensitive glass: sol–gel synthesis, structure, morphology
Fig. 4 TEM images of (a) ITH-NA, (b) ITH-A, (c) ITO-NA and (d) ITO-A samples. The inset in (c) shows the corresponding electron diffraction
pattern
and O–Sn–O chemical environments. The In 3d5/2and Sn
3d5/2peaks were located at 444.3 and 486.6 eV, respec-
tively. These binding energies reveal In and Sn oxidation
states of 3+and 4+, respectively [16,23]. Table 1lists the
binding energies of In, Sn and O components in various ITO
samples prepared by different synthesis methods.
Our XPS results are in good agreement with those re-
ported for ITO films elsewhere [24,25]. Quantitative analy-
sis using the atomic sensitivity factors (ASF) of In (ASF =
4.51) and Sn (ASF =4.89) resulted in an In:Sn atomic ratio
of 8.73, a value slightly lower than the estimated theoret-
ical atomic ratio In:Sn =10. While the In 3dand Sn 3d
spectra are symmetrical, reflecting one chemical state, the
O1sspectrum has a shoulder on the high binding energy
side at 531.6 eV, due to surface OH groups. Similar asym-
metric O 1sspectra were observed for other OH-containing
metal oxides (SnO2and TiO2)[23,26]. The main compo-
nent of the O 1sspectrum is at ∼530 eV, which corresponds
to the lattice oxygen. The atomic ratio (In+Sn):O was found
to be 0.664.
3.2 Optical and electrical properties
The UV-Vis transmittance spectra of ITO-NA films are pre-
sented in Fig. 7a. It is clearly seen that in the visible wave-
length range the uncoated photosensitive glass has a lower
transmittance (T)than that of the ITO-NA-coated substrate
(Fig. 7a, inset). This phenomenon is due to the ITO layers
on the substrate acting as an antireflection coating. After de-
position of an ITO-NA monolayer, Tincreased from 91.6
to 95% throughout the whole visible wavelength range. In
the UV range, Tdecreased slightly with increasing number
Author's personal copy
L. K˝
orösi et al.
Fig. 5 SEM images of (a) surface morphology and (b) cross-sectional view of ITO-NA thin film made up of 3 layers on Foturan glass
Fig. 6 High-resolution XP
spectra of In 3d,Sn3dand O 1s
regions for ITO-NA thin film
calcined at 550◦C
Tabl e 1 Binding energy values
of In, Sn and O in ITO samples
prepared by different synthesis
method
Method Binding energy (eV) Ref.
In 3d5/2Sn 3d5/2O1s
Sol–gel 444.3 486.9 530.6 532.0 [24]
444.3 486.6 529.9 531.6 In this work
Solvothermal 444.1 486.1 529.6 530.7 [16]
Thermal evap.-ox. 444.4 486.0 529.9 532.4 [25]
of layers. The Tspectra of the ITO-NA multilayers exhib-
ited interference fringes, and hence the Tvalues depended
on the wavelength of the incident light. It should be noted
that the ITH-NA layers also exhibited higher transparency
than that of the uncoated substrate (Fig. S2 in the Supple-
mentary Material). The Tvalues of all ITO-A-coated Fotu-
ran glasses also exceeded the Tof the uncoated substrate
(Fig. 7b, inset). For ITO-A films, the transparency increased
with increasing layer number in the whole UV-Vis range.
The highest Twas ∼96% after three deposited ITO-A lay-
ers.
For the ellipsometric measurements, the wavelength
range of high T(400–800 nm, see Fig. 7) was used because
this allows application of a simple polynomial dispersion
Author's personal copy
Highly transparent ITO thin films on photosensitive glass: sol–gel synthesis, structure, morphology
Fig. 7 UV-Vis transmittance spectra of (a) ITO-NA and (b) ITO-A thin films composed of different numbers of layers on Foturan glass
function for the refractive index [27] (in a broader range,
complex oscillator models must be used [28]). The spec-
tra could be fitted by using a linearly graded depth profile
of the refractive index in the range 3–8% (graded models
have also been described for RF sputtered ITO films [27]).
Figure 8shows the better fit with the graded model relative
to non-graded one. We note that the application of a sur-
face nano-roughness model did not improve the fit, which
indicates that the thin films were of high surface quality,
in agreement with the above SEM results. For the ITO-NA
samples, the inset in Fig. 8demonstrates a linear increase
of total thickness (from 166 to 330 nm) as a function of the
number of layers. For the ITO-A samples, the thickness var-
ied from 26 to 72 nm. The lower film thickness of ITO-A is
due to the lower concentration of the ITH-A sol. The refrac-
tive indices at the He–Ne laser wavelength of 633 nm were
in the range 1.3–1.4 and 1.1–1.3 for the ITO-NA and ITO-A
samples, respectively. This is lower than the published val-
ues for evaporated and sputtered ITO films (in the range
1.7–2.0 [28,29]), which is in agreement with the porous
structure revealed by SEM (Fig. 5).
The measured sheet resistance (Rs)ofITO-NAfilmsde-
creased significantly with increasing layer number. For film
thickness of 166, 254 and 328 nm, Rswas 13.72 ±0.04,
5.96 ±0.05 and 4.02 ±0.02 k/sq, respectively, i.e. lower
than the values measured earlier [10] for ITO-A at similar
layer thickness. The differences may be due to the lower
surface roughness and better particle-to-particle contacts in
ITO-NA films.
4 Conclusions
ITO thin films were successfully prepared on photosensi-
tive glass substrates by the combination of sol–gel and spin-
coating techniques. For film deposition, an amorphous ITH
Fig. 8 Measured (symbols)andfitted(lines) ellipsometric spectra of
a bilayer of ITO-NA on Foturan glass. Solid and dashed lines indi-
cate graded and non-graded models, respectively. The inset shows total
thickness as a function of layer number
sol in ethanol medium was used. Whereas the as-deposited
films were amorphous, nanocrystalline ITO was formed af-
ter calcination at 550◦C. These ITO nanoparticles displayed
spherical morphology and high crystallinity. It was estab-
lished that the aging process in aqueous medium promotes
the crystallization of ITH and favors the formation of large
(40–70 nm) particles with rectangular morphology. With-
out the application of aging, a lower surface roughness is
achieved and the resulting ITO film on photosensitive glass
acts as an antireflection coating. After deposition of an ITO
monolayer, the transmittance in the visible wavelength range
increased from 91.6 to 95%. As the thickness increased from
Author's personal copy
L. K˝
orösi et al.
166 to 328 nm, the sheet resistance decreased from 13.7 to
4.0 k/sq.
We believe that the developed ITO films, especially their
successful processing on photosensitive glass, can find ap-
plications in diverse areas of micro- and nano-technology,
such as the development of conductive and highly transpar-
ent 3D structures for microreactor applications.
Acknowledgement The authors thank Dr. Aiko Nakao (Cooperative
Support Team, Riken—Advanced Science Institute, Wako, Saitama,
Japan) for the assistance on XPS measurements. The authors also
thank the Hungarian National Scientific Fund (OTKA) K81842 and
PD 73084 for the financial support.
References
1. C.G. Granqvist, A. Hultåker, Thin Solid Films 411, 1 (2002)
2. C. Guillén, J. Herrero, J. Appl. Phys. 101, 073514 (2007)
3. T. Ogi, F. Iskandar, Y. Itoh, K. Okuyama, J. Nanopart. Res. 8, 343
(2006)
4. K. Maki, N. Komiya, A. Suzuki, Thin Solid Films 445, 224 (2003)
5. J. George, C.S. Menon, Surf. Coat. Technol. 132, 45 (2000)
6. H. Mbarek, M. Saadoun, B. Bessais, Mater. Sci. Eng. C 26, 500
(2006)
7. J.H. Kim, K.A. Jeon, G.H. Kim, S.Y. Lee, Appl. Surf. Sci. 252,
4834 (2006)
8. S.R. Ramanan, Thin Solid Films 389, 207 (2001)
9. A.C. Dippel, T. Schneller, P. Gerber, R. Waser, Thin Solid Films
515, 3797 (2007)
10. L. K˝
orösi, S. Papp, I. Dékány, Thin Solid Films 519, 3113 (2011)
11. Y. Djaoued, V.H. Phong, S. Badilescu, P.V. Ashrit, F.E. Girouard,
V.V. Truong, Thin Solid Films 293, 108 (1997)
12. C. Goebbert, R. Nonninger, M.A. Aegerter, H. Schmidt, Thin
Solid Films 351, 79 (1999)
13. T. Kanbara, M. Nagasaka, T. Yamamoto, Chem. Mater. 2, 643
(1990)
14. A. Solieman, S. Alamri, M. Aegerter, J. Nanopart. Res. 12, 2381
(2010)
15. E. Hammarberg, A. Prodi-Schwab, C. Feldmann, Thin Solid Films
516, 7437 (2008)
16. J. Ba, D.F. Rohlfing, A. Feldhoff, T. Brezesinski, I. Djerdj,
M. Wark, M. Niederberger, Chem. Mater. 18, 2848 (2006)
17. S. Beke, L. K˝
orösi, K. Sugioka, K. Midorikawa, I. Dékány, Appl.
Phys. A 102, 265 (2011)
18. Y. Cheng, K. Sugioka, K. Midorikawa, M. Masuda, K. Toyoda,
M. Kawachi, K. Shihoyama, Opt. Lett. 28, 1144 (2003)
19. M. Masuda, K. Sugioka, Y. Cheng, N. Aoki, M. Kawachi, K. Shi-
hoyama, K. Toyoda, H. Helvajian, K. Midorikawa, Appl. Phys. A
76, 857 (2003)
20. Y. Cheng, H.L. Tsai, K. Sugioka, K. Midorikawa, Appl. Phys. A
85, 11–14 (2006)
21. M. Fried, T. Lohner, P. Petrik, in H.S. Nalwa (ed.) Handbook of
Surfaces and Interfaces of Materials (Academic Press, San Diego,
2001)
22. B.C. Kim, J.Y. Kim, D.D. Lee, J.O. Lim, J.S. Huh, Sens. Actuator
B89, 180 (2003)
23. L. K˝
orösi, S. Papp, S. Beke, A. Oszkó, I. Dékány, Microporous
Mesoporous Mater. 134, 79 (2010)
24. M.K. Jeon, M. Kang, Mater. Lett. 62, 676 (2008)
25. X.S. Peng, G.W. Meng, X.F. Wang, Y.W. Wang, J. Zhang, X. Liu,
L.D. Zhang, Chem. Mater. 14, 4490 (2002)
26. L. K˝
orösi, A. Oszkó, G. Galbács, A. Richardt, V. Zöllmer,
I. Dékány, Appl. Catal. B 77, 175 (2007)
27. R.A. Synowicki, Thin Solid Films 394, 313 (1998)
28. M. Losurdo, M. Giangregorio, P. Capezzuto, G. Bruno, R.
De Rosa, F. Roca, C. Summonte, J. Pla, R. Rizzoli, J. Vac. Sci.
Technol. A 20, 37 (2002)
29. J.A. Dobrowolski, L. Li, J.N. Hilfiker, Appl. Opt. 38, 4891 (1999)
Author's personal copy
