Morphology and optical properties of SnO₂ nanofilms
Results of surface morphology and optical density investigations and the photoluminescence phenomenon were obtained for SnO₂ thin films. Films having nanosize of their grains ~ 10-15 nm were obtained using polymeric materials. Evaluation of a dimensional quantization is fulfilled by two methods:...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2008
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| Цитувати: | Morphology and optical properties of SnO₂ nanofilms / V.A. Smyntyna, L.N. Filevskaya, V.S. Grinevich // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 2. — С. 163-166. — Бібліогр.: 11 назв. — англ. |
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irk-123456789-1188622017-06-01T03:06:58Z Morphology and optical properties of SnO₂ nanofilms Smyntyna, V.A. Filevskaya, L.N. Grinevich, V.S. Results of surface morphology and optical density investigations and the photoluminescence phenomenon were obtained for SnO₂ thin films. Films having nanosize of their grains ~ 10-15 nm were obtained using polymeric materials. Evaluation of a dimensional quantization is fulfilled by two methods: analytically using AFM data, and by means of optical density spectra; results obtained by these two methods are in a good agreement. 2008 Article Morphology and optical properties of SnO₂ nanofilms / V.A. Smyntyna, L.N. Filevskaya, V.S. Grinevich // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 2. — С. 163-166. — Бібліогр.: 11 назв. — англ. 1560-8034 PACS 61.82.Rx, 68.37.Ps http://dspace.nbuv.gov.ua/handle/123456789/118862 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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English |
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Results of surface morphology and optical density investigations and the
photoluminescence phenomenon were obtained for SnO₂ thin films. Films having
nanosize of their grains ~ 10-15 nm were obtained using polymeric materials. Evaluation
of a dimensional quantization is fulfilled by two methods: analytically using AFM data,
and by means of optical density spectra; results obtained by these two methods are in a
good agreement. |
| format |
Article |
| author |
Smyntyna, V.A. Filevskaya, L.N. Grinevich, V.S. |
| spellingShingle |
Smyntyna, V.A. Filevskaya, L.N. Grinevich, V.S. Morphology and optical properties of SnO₂ nanofilms Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Smyntyna, V.A. Filevskaya, L.N. Grinevich, V.S. |
| author_sort |
Smyntyna, V.A. |
| title |
Morphology and optical properties of SnO₂ nanofilms |
| title_short |
Morphology and optical properties of SnO₂ nanofilms |
| title_full |
Morphology and optical properties of SnO₂ nanofilms |
| title_fullStr |
Morphology and optical properties of SnO₂ nanofilms |
| title_full_unstemmed |
Morphology and optical properties of SnO₂ nanofilms |
| title_sort |
morphology and optical properties of sno₂ nanofilms |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2008 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118862 |
| citation_txt |
Morphology and optical properties of SnO₂ nanofilms / V.A. Smyntyna, L.N. Filevskaya, V.S. Grinevich // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 2. — С. 163-166. — Бібліогр.: 11 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT smyntynava morphologyandopticalpropertiesofsno2nanofilms AT filevskayaln morphologyandopticalpropertiesofsno2nanofilms AT grinevichvs morphologyandopticalpropertiesofsno2nanofilms |
| first_indexed |
2025-07-08T14:47:53Z |
| last_indexed |
2025-07-08T14:47:53Z |
| _version_ |
1837090551943397376 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 2. P. 163-166.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
163
PACS 61.82.Rx, 68.37.Ps
Morphology and optical properties of SnO2 nanofilms
V.A. Smyntyna, L.N. Filevskaya, V.S. Grinevich
I.I. Mechnikov Odessa National University,
2, Dvoryanskaya str., 65082 Odessa, Ukraine
Phone/fax 38-048-7317403, e-mail: grinevich@onu.edu.ua
Abstract. Results of surface morphology and optical density investigations and the
photoluminescence phenomenon were obtained for SnO2 thin films. Films having
nanosize of their grains ~ 10-15 nm were obtained using polymeric materials. Evaluation
of a dimensional quantization is fulfilled by two methods: analytically using AFM data,
and by means of optical density spectra; results obtained by these two methods are in a
good agreement.
Keywords: tin dioxide, surface morphology, optical properties.
Manuscript received 20.02.08; accepted for publication 15.05.08; published online 30.06.08.
1. Introduction
Tin dioxide is one of the most stable and sensitive oxide
semiconductors applied for detecting a surrounding
atmosphere changes. At present time, it is one of the
basic materials for adsorptive-sensitive elements in gases
analysis [1]. The possibility of obtaining these materials’
thin layers with a developed structure of a nanoscale
broadens its already existing applications. It is
conditioned by the appearance of new properties caused
by quantum scale effects.
The surface state peculiarities investigations,
optical density and thin SnO2 film photoluminescence
(PL) originally registered, together with a preparation of
these films, obtained using polymeric materials are
presented in this paper.
It is known that tin dioxide surface has high
adsorptive and reaction abilities, which are defined both
by presence of free electrons in the conductance band,
bulk oxygen vacancies, and active chemisorbed oxygen
[1]. The perfect knowledge of its morphology is
necessary for the description of physical processes
taking place on it. Electrons’ and lattice ions’ energy
states define material interaction with the visible
electromagnetic radiation, which is reflected in the
absorption spectra.
The optical absorption investigation together with
other electronic characteristics allows defining the
forbidden band width of semiconductor and optical
transition types near the absorption edge. The complex
evaluation of morphology and optical peculiarities of a
material permits the detailed description of behavior
inherent to electron and ion subsystems. It was this
attitude that defined the investigations of the surface
morphology and optical properties of SnO2 films
obtained using polymer material.
2. Experimental methods and results
The technique using polymers as assisting structuring
additives is applied for the obtaining of thin films with a
developed surface and nanograins. The basics of the
method are described in [2].
For the investigation, the SnO2 films were obtained
using gel that is PVA solution in acetone with a tin
acetyl acetonate addition as the tin containing substance.
The tin dioxide layer surface morphology was
investigated by the industrial atom-force microscope
(АFМ) NanoScope IIIa (Digital Instruments, USA) –
Courtesy of V. Lashkaryov Institute of Semiconductor
Physics of the National Academy of Sciences of
Ukraine. Measurements were fulfilled using a silicon
probe with nominal radius ~10 nm (firm-producer NT-
MDT, Russia) in the regime of a periodical contact
(Tapping Mode TM). The investigated area surface was
500×500 nm2.
The investigated layers deposited on glass
substrates were optically transparent. This gave the
possibility to study optical transition in the wavelength
range 300-750 nm. The standard methods were used for
spectrophotometer СФ-46 measurements. The
luminescence excitation was done by means of 337 nm
N-laser.
The morphology studies results are summarized in
Fig. 1. Figure 1 shows a top view and vertical profile of
the layer surface. The higher points in Fig. 1 correspond
to the lightest parts of the photo, and dark parts reflect
the deepest regions.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 2. P. 163-166.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
164
a
Surface distance 14.082 nm
Horiz distance 12.695 nm
Vert distance 4.418 nm
Angle 19.189 degree
Surface distance 10.923 nm
Horiz distance 10.742 nm
Vert distance 0.034 nm
Angle 0.182 degree
Surface distance 30.256 nm
Horiz distance 29.297 nm
Vert distance 3.780 nm
Angle 7.353 degree
b
c
Fig. 1. Vertical film’s surfaces profile (a) with the indication of sizes between bench marks (b); the nuance of grey color
corresponds to the nuance of bench marks; 3-D view of SnO2 film surface(c).
As it may be seen, the film under investigation is
enough uniform and consists of approximately equal-
size nanograins. The depth affordable for the AFM
probe at the given film is ~ 10.5 nm. The average size of
a grain is 10-15 nm. Evaluating the grain size and depth
of probe penetration, it is possible to say that the film is
nanostructured and is continues for the gel used, but not
of islet type. This is also confirmed by the 3-D view of a
film surface, given in Fig. 1c.
The general view of the absorption spectra optical
density D(hν) is given in Fig. 2, as soon as the analysis
of a form of an absorption band edge needs only an
absorption coefficient spectra changes, but not its
absolute value.
As it is seen in Fig. 2, there are two main peaks
present in the optical density spectrum: in the red region
(1.69 eV) and specific for tin dioxide peak in the nearest
UV region (3.757 eV). The sharp abruption in the UV
spectrum may be caused by several reasons. It is known
[3], that tin dioxide is transparent for the nearest UV.
Besides, the glass substrate intrinsic absorption seriously
increases in the UV, which gives principal changes to
the investigated film spectrum.
The photoluminescent investigations of tin dioxide
nano-structured films make it possible to register the
visible spectrum radiation, previously not described for
amorphous and polycrystalline SnO2 layers by the
authors. The PL absence for SnO2 like in a degenerated
semiconductor was usually explained by the great
amount of non-radiating recombination centers. Thin
peaks of visible radiation (Fig. 3, curve 1) in our case are
probably connected with nano-sized grains in SnO2
films. As it may be seen, two thin bands (halfwidth
~ 0.05 eV) 577 and 642 nm are present in the radiation
spectrum.
The SnO2 layer previously prepared by the
electrosprayed pyrolysis (ESP) method was used as a
basic sample for comparison (curve 2). In this case,
peaks 577 and 642 nm are also present at its spectrum,
but their intensity is much less. The coincidence of PL
peaks’ positions may witnesses for the identical nature
of the centres in the samples obtained by different
methods. The great radiation intensities in the case of
SnO2 films, obtained using polymer materials, witnesses
for a considerable amount of radiative recombination
centers. Besides, similar structure of PL spectra is
typical for nanosize materials [4]. It was established [5]
that the layer obtained by ESP method was amorphous
in principle with metallic Sn inclusions.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 2. P. 163-166.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
165
0
0,1
0,2
0,3
0,4
0,5
0,6
1,5 2,5 3,5hv, eV
D
, r
el
. u
n.
Fig. 2. The optical density spectrum of SnO2 nano-structured
films. Films were obtained on the base of gel (the PVA
solution in acetone with tin acetyl acetonate) addition.
0
0,2
0,4
0,6
0,8
1
450 500 550 600 650 700 750 800 850
wave length,nm
I,
re
l.u
n.
1
2
Fig. 3. SnO2 radiation spectra: 1 – for the investigated samples;
2 – for the samples that were obtained using the ESP method.
3. Discussion
The surface morphology investigations results show that
tin dioxide films have enough developed surface and
consist of grains with the average size 10-15 nm. Tin
dioxide films with a structure of such type have usually
low resistivity because of a great number of amorphous
phase presence. The resistivity of our films is on the
contrary 3-6 MOhm⋅cm–2. This fact may be explained by
the existence of a complicated potential structure which
is characterized by a great amount of potential holes
presence arbitrary distributed in the film. The charge
carrier being localized in such hole is not able to take
part in a current transport. The potential holes presence
is connected, as in [6], with clusters which is typical for
amorphous solid state. The crystal type clusters presence
in the films is indirectly supported by the grain sizes of
10-15 nm, as it was established from AFM methods. The
clusters’ dimensions may vary from several to 1000
atoms [6] in amorphous semiconductors, hence, its size
may reach hundreds of nanometers.
The structural nature of the films may be illustrated
by the calculations of tin dioxide films’ parameters that
are based on the optical density spectral data. Different
literature sources give carriers effective masses data for
tin dioxide, which notably differs from each other. Our
calculation of the Bohr exciton radius (aB = εh2/µe2)
based on the data from [7] gives for tin dioxide crystal
the value ~ 2.67 nm, but from [3] it is ~ 1.28 nm. With
all that it was supposed the hole localization on the
quantum-dimensional object, therefore, aB value
practically approaches to the Bohr radius value for
electrons in SnO2 (~2.75 nm).
The dimensional quantization energy may be
evaluated according to formula [8]
( )2,
2
01
2,
01 2/71.0 rmhE he
he r
ϕ=
by means of substitution of the known values r , me, mh.
Nanocrystallites’ mean radius in our case is in
correspondence with the Atom Force Microscopy data
and gives ~ 5 nm. Substituting these values into the
dimensional quantization energy formula [8], we shall
obtain the dimensional quantization energy value heE ,
01
(for l = 0 and n = 1 levels) ~ 0.63 eV, using the values
for effective masses from [7], and using the similar
values from [3] ~ 0.31 eV. If this energy is defined from
the optical density spectra, as the difference between the
first absorption maximum energy, which corresponds to
the energy he
g EE ,
01+ and the forbidden band width
(~ 3.35 eV) that is obtained from the optical density
data, then we shall obtain the value equal to ~ 0.40 eV.
In our case, the mean nanocrystallites radius nearly
two times exceeds the Bohr radius value. However, as it
is shown in the work [9] the holes’ energy dimensional
quantization practically did not tell on the absorption
spectra type, and the calculation technique applied with
using the optical absorption spectra gives a reasonable
agreement with the results. As it may be seen comparing
dimensional quantization energies values obtained by
different methods, we have enough similar results. These
results permits to use the optical density investigations
data for the dimensional quantization energy definition,
heE ,
01 , for the definition of nanocrystallite mean
dimension.
The optical density spectra rebuilt in D 1/s = f (hν)
coordinates, where s = ½, 3/2, 2, 3 depend on optical
transitions types. The best linearization of optical density
dependence has place when 1/s = 1/3. This situation
corresponds to indirect electrons’ forbidden transitions
with phonons participation, which, evidently, takes place
not in the Brillouin zone centre, where k = 0, but in its
vicinity. This conclusion may be useful in the future
discussion of PL results.
The nearest UV band absorption corresponds to the
absorption edge and gives the forbidden band width
equal to 3.35 eV. The optical absorption character says
about the “density of states tales” in the forbidden band,
which defines the difference of Eg energy obtained in our
work, from that in the crystalline SnO2 forbidden band
value. At the same time, the Eg obtained here is a bit
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 2. P. 163-166.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
166
higher than the literature data for amorphous tin dioxide
films, which witnesses in favour of crystalline structure
of films’ grains. The absorption peak (1.69 eV)
corresponds to the middle part of the forbidden band
defining some density of states with the energy Eg / 2,
which is typical for amorphous or degenerated
semiconductor [6]. Such spectrum type confirms the
clusters existence supposition for the films discussed.
Metallic Sn has 579 nm band in its spectrum, which is
typical for single charged atoms [10]. Single charged
oxygen atoms have series of spectral bands for the
region of 645 nm [10]. Metal clusters’ presence in SnO2
films was also registered by authors [5, 11] together with
the clusters’ contribution to SnO2 adsorptive activity. All
these facts comparison supports the assumption of the
correspondence between PL band 577 nm in both films’
types and the radiation centres which are connected with
tin atoms or with clusters of these atoms.
Grains’ nanosizes define a considerable potential
hole density with a discrete level distribution. This
assumption is supported by our PL results. If a PL
spectra is rebuilt in coordinates ±[ln (I0 / I)]1/2 ~ E, then
they shall be perfectly described by a linear dependence
and by the Gauss function. This result permits to
consider PL peaks to be of intercenter type. As it follows
from our previous discussion, lattice vibrations play a
noticeable role in tin dioxide electronic processes. Thus,
the joint evaluation of optical absorption and PL results
permits to connect 1.69 eV absorption peak with a
1.91 eV peak of PL. Both the energies difference and the
radiation energy exceeding over the absorption energy
may be interpreted as the anti-Stokes mechanism of PL
in which 0.22 eV phonon takes part. Developing this
idea, the intercentres PL at 1.91 eV may also be of anti-
Stokes type. These conclusions are supported also by
optical density spectra analysis, in connection with
which lattice vibrations take also their part in the optical
transitions near the forbidden band edge, as these
transitions are not direct.
4. Conclusions
The main results of the presented work may be
given as follows
− the SnO2 films were obtained using the
polymeric substance and have nano-sized grains;
− it was established that the principal surface
morphology peculiarity is developed film surface having
grains of 10-15 nm sizes;
− optical investigations showed that absorption
and photoluminescence spectra give evidences of the
cluster structure inherent to the films;
− the film optical density and PL joint analysis
witnesses for phonons role in a overdistribution of
absorpted electromagnetic energy;
− evaluation of a dimensional quantization is
fulfilled by two methods: analytically using AFM data,
and by means of optical density spectra; results obtained
by these two methods are in a good agreement.
The film surface morphology investigations make it
possible to foresee the surface electric potential
distribution. Thus, regions of charge nonuniformity may
be shown. Such regions’ presence perfectly influences
charges exchange processes. Especially it becomes
important when film surfaces interact with different
chemically active molecules, i.e. the film electronic
subsystem interaction with the electron gas systems.
Acknowledgements.
Authors are thankful to our colleague Oksana Lytvin,
from the V. Lashkaryov Institute of Semiconductor
Physics, National Academy of Sciences of Ukraine,
Kyiv, for her support in AFM investigations.
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