Applied Surface Science 315 (2014) 516–522
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Applied Surface Science
journal homepage: www.elsevier.com/locate/apsusc
Influence of different solvents on the morphology of APTMS-modified
silicon surfaces
G. Jakša a , B. Štefane b , J. Kovač a,∗
a
b
Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000 Ljubljana, Slovenia
a r t i c l e
i n f o
Article history:
Received 23 December 2013
Received in revised form 28 April 2014
Accepted 23 May 2014
Available online 2 June 2014
Keywords:
APTMS
Aminosilane, Silicon
Solvents
XPS
AFM
a b s t r a c t
In this study 3-aminopropyltrimethoxysilane (APTMS) was used for the modification of single-crystal silicon wafers (1 1 1). We deposited the self-assembled layers from a solution of APTMS in five solvents with
different polarities under various reaction conditions. The influence of the different solvents on the morphology of the modified surfaces was studied, since the possible heterogeneity may significantly influence
the application of such surfaces. The surface composition and the chemical bonding were characterized
by X-ray photoelectron spectroscopy and the morphology of the modified surfaces was investigated
using atomic force microscopy and scanning electron microscopy. Our results show that the amount of
coatings and the morphology of the modified surface strongly depend on the type of solvent. Silanization
carried out in acetonitrile and toluene leads to the formation of a rough surface with a large density of
APTMS polymerized molecules in the form of islands. The surfaces modified in N,N-dimethylformamide
were smoother, with a lower density of APTMS islands. When using acetone and ethanol as a solvent we
prepared a smooth, thin, modified surface, with a very low density of the APTMS islands. We discuss the
influence of the polarity/nature of the solvents on the morphology of the modified surfaces.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Aminosilanes are used for surface modification and adhesion
promotion. They have the ability to form a durable bond between
organic and inorganic materials. A surface modified with aminosilanes has many applications: it can be used in chromatography
[1], as a biosensor (immobilization of DNA, proteins, etc.) [2–5], in
medicine [6], for attaching metal nanoparticles [7], for the detection
of specific gases [8] and explosives [9,10], etc. The general formula for organosilanes is R Si X3 , where X is a hydrolysable group
and R is a non-hydrolyzable organic substituent with the desired
functionality. A reactive silanol group (formed by the hydrolysis of
the hydrolysable group) can condense with another silanol group
(a silanol group of the surface or a silanol group from another
organosilane molecule) and form siloxane linkages [1,11,12].
There are many studies on optimizing silanization conditions: silanization with different aminosilanes [13–15], different
aminosilane concentrations [16], the temperature of deposition [17,18], the time of silanization [16,17], the drying/curing
∗ Corresponding author. Tel.: +386 1 477 3403.
E-mail address: janez.kovac@ijs.si (J. Kovač).
http://dx.doi.org/10.1016/j.apsusc.2014.05.157
0169-4332/© 2014 Elsevier B.V. All rights reserved.
conditions [12,16,19], the wetting behaviour [20] the presence of
water [16], the type of solvent [21], etc.
The 3-aminopropyltrimethoxysilane (APTMS) used in our study
is one of the most commonly used aminosilanes. The APTMS
molecule has three methoxy groups and is capable of polymerization in the presence of water [13]. Water can be added in
solution, it may be present on the substrate surface, or it may
come from the atmosphere. The presence of water can give rise
to a number of possible surface structures: the covalent attachment of molecules, horizontal polymerization and the formation of
oligomers/polymers of silanes in solution, which can also attach to
the surface [14,15]. In general, it was believed that the aminosilanemodified silicon surface is homogeneous, but this is not always
the case. A possible heterogeneity in the surface morphology and
the chemistry may be present, and it may significantly influence
the application of modified surfaces. Therefore, the aim of our
study was to investigate the influence of different solvents on the
APTMS modification of Si wafers. In our previous study we showed
that the number of polymerized molecules and the layer thickness
depend on the number of aminosilane bonding sites [14]. Among
the published studies in this field we found only one study on SiO2
silanization with APTES molecules carried out using different solvents, performed by Vandenberg et al. [21]. They studied the water
stability of prepared aminosilane layers, but did not include a study
G. Jakša et al. / Applied Surface Science 315 (2014) 516–522
Fig. 1. Chemical structure of (3-aminopropyl)-trimethoxysilane.
of the influence on the morphology of the modified surfaces. In the
majority of published studies the authors modified the surface in
a different solvent and then they focused on a particular application property. Since the morphology of the modified surface greatly
depends on the solvent, it is important to find the right conditions
for the intended use. The most widely used solvent for silanization
is toluene [17,22,23]. However, silanization can also be performed
with bicyclohexyl [24], acetone [25], water [12] or a mixture of a
few solvents [26–28]. Because of the polar nature of the APTMS
molecule, we expected better solubility in polar solvents. In the
presence of non-polar solvents the APTMS molecules tend to form
polymer structures.
In this study we used five solvents with different polarities.
We carried out the silanization in a non-polar solvent (toluene),
polar aprotic solvents (acetone, N,N-dimethylformamide and acetonitrile) and a polar protic solvent (ethanol) for various deposition
times and temperatures. Our results show that with the use of the
appropriate solvent we can significantly influence the morphology
of the modified surface and consequently its adhesion/adsorption
properties. In our previous study we showed that with APTMS
molecules the modified surface of MEMS (micro-electromechanical
systems) can be used for the detection of explosive gases [29].
For the best response of the sensor (selectivity, rapid response,
reversibility, etc.) it is essential to understand the modification
parameters.
2. Materials and methods
2.1. Materials
Silicon wafers (1 1 1 orientation, resistivity 10 cm), polished
on one side, were used as a substrate for the chemical modifications. The 3-aminopropyltrimethoxysilane (Fig. 1) was obtained
from Sigma–Aldrich and was used as received. The solvents were
purchased from Sigma–Aldrich and were of pro-analysis grade.
The solvents were dried prior to use in accordance with standard
procedures [30]. The toluene was dried using sodium and distilled afterwards. Ethanol absolute (≥99.8%) was dried using CaH2
and distilled afterwards. Acetone puriss was dried over CaSO4 and
distilled before use. Acetonitrile (HPLC grade) was dried using
CaH2 (24 h) and filtered before use over a 0.2-␮m filter. The
N,N-dimethylformamide (anhydrous) was stored, before use, over
molecular sieves (H2 O ≤ 0.005%).
2.2. Preparation/modification of the silicon wafers
The silicon wafers were cut into suitable sizes (approximately
1 cm × 1 cm) and ultrasonically cleaned for 10 min in acetone to
remove any organic contamination. After cleaning the native oxide
517
layer was reduced from the silicon with dilute HF (HF:deionized
water = 1:10) for 2 min, followed by a deionized water rinse,
streamed with nitrogen and dried in an oven at 100 ◦ C for 30 min.
The reduced silicon wafers were then immediately oxidized in
a controlled manner using an oxygen plasma (1 min, p = 50 Pa,
P = 200 W). The modification of the freshly cleaned wafers was carried out in a 3-mM solution of 3-aminopropyltrimethoxysilane
(APTMS) in an anhydrous solvent. The silanization reaction took
place in a closed Schlenk flask for a specific time (1, 2 and 6 h)
at 25 ◦ C and at higher temperature: (a) 70 ◦ C (toluene, ethanol,
acetonitrile and N,N-dimethylformamide) or (b) 50 ◦ C (acetone).
The Schlenk flask was purged with nitrogen prior to and during the silanization. After completion of the silanization step, the
wafers were rinsed with toluene (2×), a mixture of toluene and
methanol = 1:1 (2×), methanol (2×) and dried at 80 ◦ C for 15 min in
a clean oven, to remove the physisorbed APTMS molecules and any
traces of solvent from the surface. The characterization was carried
out immediately upon cooling and the data were averaged from
three independent measurements.
2.3. Surface characterization
The surface topography and surface roughness were investigated with an atomic force microscope (AFM), model Solver Pro,
produced by the NT-MDT company. An oscillating semi-contact
mode with Si tips was used for the surface imaging over the range
1 ␮m × 1 ␮m–10 ␮m × 10 ␮m. The mean surface roughness Ra was
calculated after the subtraction of the proper background from the
image.
The chemical composition of the surfaces was determined by Xray photoelectron spectroscopy (XPS). This analysis was performed
with a TFA XPS spectrometer, produced by Physical Electronics Inc.,
equipped with a monochromated Al-K␣ X-ray source (1486.6 eV,
energy resolution ∼0.6 eV), under ultra-high vacuum (10−7 Pa). The
analysis area was 0.4 mm in diameter and the signal during the XPS
analysis came from a 6-nm-thick surface layer. During the analysis, both survey and high-resolution spectra were recorded. In
the survey spectrum, the elements that were present were identified and their concentrations were calculated by dividing the
peak intensities by the relative sensitivity factors provided by the
XPS spectrometer manufacturer using a model of the homogenous distribution of the elements in a matrix [31]. Each sample
was analyzed at two different points and the average composition
was calculated. In addition to the wide-energy-range spectra, the
high-energy-resolution spectra of the characteristic peaks of the
elements Si 2p, C 1s, O 1s and N 1s were recorded over a narrow energy range. From the shape and the shift of the energy of
the XPS spectra, the chemical bonding of the surface elements was
inferred. The XPS spectra were processed with the software MultiPak. All the components were referenced according to the C C/C H
component in the C 1s core level at a binding energy of 284.8 eV.
The morphology of the modified surfaces was analyzed with a
scanning electron microscope (SEM). The SEM analysis was carried
out with a FE-SEM Zeiss ULTRA plus scanning electron microscope.
The microscopy was performed with a 5-kV accelerating voltage
using a standard Everhart–Thornley SE detector.
3. Results
The modified surfaces with APTMS molecules were characterized using the AFM, SEM and XPS techniques to determine the
morphology, roughness, surface composition and chemical bonding of the APTMS film.
Fig. 2 shows the topography of the APTMS coatings obtained
after 3 h of silanization at 25 ◦ C from five different solvents. From
518
G. Jakša et al. / Applied Surface Science 315 (2014) 516–522
Fig. 2. AFM images (2 ␮m × 2 ␮m) of Si wafer (a) and APTMS molecules on Si wafer after 3 h of deposition at 25 ◦ C from: ethanol (b), acetone (c), N,N-dimethylformamide
(d), toluene (e) and acetonitrile (f).
the AFM images of the modified surfaces we can observe differences
in the topography. The surfaces modified with various solvents
contain different numbers of bright spots, which are polymerized
aminosilane molecules in the form of islands. In our previous study
we showed that the polymerization process took place already in
solution and not directly on the surface [14]. The smaller islands
are from 1 to 2 nm in height and around 20 nm in width. The bigger
islands, as a result of increased polymerization, are from 4 to 10 nm
Table 1
Mean surface roughness (Ra ), density of APTMS islands, from XPS calculated total thickness (nm) of Si-oxide + silane layer and thickness of silane layer on modified Si surfaces
after 3 h of deposition at 25 ◦ C in different solvents: ethanol, acetone, N,N-dimethylformamide (DMF), toluene and acetonitrile.
Ra [nm]
Number of islands [␮m2 ]
Thickness [nm] (SiO2 + silane)
Thickness [nm] (silane layer)
Si wafer
Ethanol
Acetone
DMF
Toluene
Acetonitrile
0.09
–
1.4 ± 0.2
–
0.16
27 ± 3
1.8 ± 0.2
0.4 ± 0.2
0.15
23 ± 3
2.3 ± 0.2
0.9 ± 0.2
0.14
24 ± 3
2.2 ± 0.2
0.8 ± 0.2
0.29
63 ± 6
2.6 ± 0.2
1.2 ± 0.2
0.43
110 ± 10
3.2 ± 0.2
1.8 ± 0.2
G. Jakša et al. / Applied Surface Science 315 (2014) 516–522
519
Table 3
Nitrogen concentration (atomic %) on APTMS surfaces modified from different solvents at different times and temperatures. Higher temperatures are related to 50 ◦ C
in the case of acetone and 70 ◦ C in the case of ethanol, N,N-dimethylformamide
(DMF), toluene and acetonitrile.
Fig. 3. Scanning electron microscopy images of Si-oxide surfaces modified with
APTMS molecules. (a) 3 h of deposition from acetone at 25 ◦ C and (b) 3 h of deposition
from toluene at 25 ◦ C.
in height and around 50 nm in width. The mean surface roughness and the density of the islands are given in Table 1, for all five
solvents.
We performed SEM analyses to understand the surface morphology of a larger area of the samples (50 ␮m and more). The SEM
images of the modified surfaces after 3 h of deposition from acetone
and toluene at 25 ◦ C are shown in Fig. 3.
We investigated the surface composition and the chemical
bonding at the modified surfaces using the XPS technique. Due to
the small size of the polymerized islands present on the surface
we did not expect that the XPS technique would directly reveal
this type of heterogeneity, since only a laterally averaged composition can be obtained from the XPS. The acquired XPS spectra
of the uncoated oxidized silicon wafer showed peaks of carbon,
oxygen and silicon. The carbon signal on the oxidized wafer is
Ethanol
Acetone
DMF
Toluene
Acetonitrile
25 ◦ C
N (at.%) at 1 h
N (at.%) at 3 h
N (at.%) at 6 h
1.6
1.8
2.2
2.1
2.3
2.3
1.3
2.1
3.3
3.0
3.6
4.8
2.1
7.3
11.5
Higher T
N (at.%) at 1 h
N (at.%) at 3 h
N (at.%) at 6 h
1.8
1.7
1.7
1.8
2.2
2.4
2.6
4.3
4.0
4.5
9.3
9.7
10.4
10.9
11.1
related to the carbon from the contamination layer. The XPS spectra of the modified Si wafers contain, in addition to carbon, oxygen
and silicon related peaks, also nitrogen peak, which is related to
the amino group from the APTMS molecules. From the intensities of these peaks we calculated the C, O, Si and N concentrations
(Table 2) in the model of homogeneous elemental distribution. As
it is expected that the layered structure is formed on modified surfaces, the results for the concentration have limited accuracy and
can only be used for a relative comparison among the different
samples.
Since the nitrogen signal is the most relevant information of the
APTMS molecules present on the surface, we represent in Table 3
the concentration of N on the modified surfaces for various solvents
after different silanization times and for two different temperatures.
We also studied high-energy-resolution XPS spectra of the
modified surfaces. The C 1s signal is composed of three different
components. These components are related to different types of
carbon-atom bonds on the APTMS molecule. The component at a
binding energy of 284.8 eV corresponds to C C and/or C H bonds;
the component at binding energies of 286.3 eV corresponds to C O
bonds; and the component at 287.9 eV is related to O C O and C O
bonds. Due to the APTMS polymerization and the different types of
interaction between the APTMS molecules and the oxidized silicon
wafer [14], the high-energy-resolution N 1s spectra are composed
of two different components: the component at a binding energy
of 399.2 eV corresponds to NH2 bonds and the component at a
binding energy of 401.0 eV corresponds to NH3 + type of bonds.
The representative C 1s and N 1s spectra are also given in Ref. [14].
Typical high-energy-resolution Si 2p XPS spectra obtained after
the silanization are shown in Fig. 4 a, where different components
can be recognized. At binding energies of 99.3 eV (Si 2p3/2 ) and
99.9 eV (Si 2p1/2 ) is the signal from the bulk silicon wafer beneath
the oxide layer. The silicon signal from the Si oxide layer and the
aminosilanes is located at higher binding energies. The signal at
102.2 eV corresponds to the aminosilane on the silicon oxide and
the signal at 103.0 eV corresponds to the silicon oxide. Fig. 4b
shows the Si 2p spectra, one above the other (reference sample and
Table 2
Surface composition (atomic %) on the Si wafer after silanization from different solvents. 3 h of deposition at 25 ◦ C and 3 h of deposition at 50 ◦ C (acetone) and 70 ◦ C (ethanol,
N,N-dimethylformamide (DMF), toluene and acetonitrile) (higher T).
Temp
Element
Si wafer
Ethanol
Acetone
DMF
Toluene
Acetonitrile
25 ◦ C
C
O
Si
N
10.8
49.6
39.6
–
25.9
38.9
33.4
1.8
17.0
46.6
34.1
2.3
17.4
45.8
34.7
2.1
35.8
34.8
25.8
3.6
43.8
27.2
21.7
7.3
Higher T
C
O
Si
N
10.8
49.6
39.6
–
23.1
39.1
36.1
1.7
21.2
46.5
30.1
2.2
34.7
32.7
28.3
4.3
53.5
21.3
15.9
9.3
57.8
18.6
12.7
10.9
520
G. Jakša et al. / Applied Surface Science 315 (2014) 516–522
a 1000
900
b
SiO2 silane
Si 2p
Si-bulk
Si 2p
APTMS, acetonitrile
Si-bulk
(2p3/2, 2p1/2)
Intensity (a.u.)
700
600
500
SiO2
400
300
silane
on SiO2
Normalized Intensity
800
APTMS, toluene
APTMS, DMF
APTMS, acetone
APTMS, ethanol
200
Oxidized Si
100
0110
108
106
104
102
100
98
96
94
Binding Energy (eV)
110
108
106
104
102
100
98
96
94
Binding Energy (eV)
Fig. 4. Typical high-energy-resolution Si 2p spectra (a), and stack plot of Si 2p spectra obtained after 3 h of silanization from different solvents at higher temperatures (b)
(50 ◦ C in the case of acetone and 70 ◦ C in the case of ethanol, N,N-dimethylformamide (DMF), toluene and acetonitrile).
modified surfaces in different solvents, 3 h deposition time at elevated temperatures).
From the XPS data we also estimated the thickness of the silane
layer. In the Si 2p spectra we estimated the relative thickness of
the silicon oxide layer and the silane layer, comparing the intensities of the bulk Si components and the total Si O components
at 102–103 eV, which represents the Si atoms involved at the SiO2
interface and the Si atoms from the silane overlayer. For the thickness calculation we used equation d = L cos()ln(1 + R/Ro ), where L
is the attenuation length of the electrons in the Si-oxide overlayer
(3.485 nm), is the angle of emission of the electrons (15◦ , 45◦ ,
75◦ ), R is the measured ratio of the oxide- and substrate-measured
intensities and Ro is the parameter 0.9329, as was proposed in Ref.
[32]. The thickness of 1.4 ± 0.2 nm obtained on the uncoated wafer
is related to the Si-oxide layer formed after the oxygen plasma
treatment of the Si wafers. For silane-coated samples with different solvents we first calculated the total thickness of the silane and
oxide layers and in the second step we subtracted from the total
thickness the thickness of the initial silicon oxide layer. In this way
we estimated the thickness of the pure silane layers, which is given
in Table 1.
4. Discussion
The AFM, XPS and SEM results show significant differences in the
morphology and the composition of the APTMS-modified Si surface
with respect to the solvent used for the modification. Therefore,
we divided all five studied solvents with different polarities into
two groups. Ethanol, acetone and N,N-dimethylformamide solvents
lead to the formation of a relatively smooth, homogenous APTMS
film with a low density of islands. In contrast, toluene and acetonitrile form a rough layer, with a large number of polymerized
islands.
4.1. Solvents forming smooth APTMS films
AFM images of the modified surfaces obtained from acetone,
N,N-dimethylformamide and ethanol are shown in Fig. 2b–d. We
observed a slightly increased mean surface roughness compared to
the reference Si wafer (Table 1). The surfaces are relatively uniform
with a low density of islands (23–27 islands/␮m2 ). In ethanol and
acetone applying longer deposition times and elevated temperatures (70 ◦ C for ethanol and 50 ◦ C for acetone, 6 h of deposition),
similar modified surfaces were formed. The surfaces were slightly
rougher (Ra ∼ 0.3 nm) but the islands remain approximately the
same size, so there is no further polymerization observed. The
AFM images of the surface modified in N,N-dimethylformamide,
for longer deposition times and at elevated temperatures, show a
slightly rougher surface (Ra ∼ 0.5 nm) compared to the ethanol and
acetone and a denser distribution of islands.
SEM images of the modified surfaces (3 h at 25 ◦ C) with ethanol
and N,N-dimethylformamide were very similar to those with the
acetone (Fig. 3a). The surfaces were relatively flat and no large,
polymerized APTMS islands were found.
The XPS results (Table 2) of the surface composition show an
increased concentration of C and N, which confirms the successful
APTMS bonding to the silicon surface after the silanization process for all three solvents. At this point it should be noted that
for longer deposition times the concentration of nitrogen on the
surface does not increase significantly. Aminosilane layers are not
so thick and the polymerization of the APTMS molecules is lower,
compared to acetonitrile and toluene (higher N concentrations,
rougher surface, increased polymerization). Similar behaviour was
observed at higher temperatures. During higher temperature deposition, the nitrogen concentration slightly increased with time in
the case of acetone and N,N-dimethylformamide, but it remained
constant in the case of ethanol (Table 3). This observation can be
explained in terms of the solvents nature/polarity. Ethanol is a
polar protic solvent with OH groups. This solvent can solvolyze
the Si O Si bonds (like hydrolysis in the case of water). In the
case of higher concentrations of ethanol, the solvolysis of the
Si O Si linkages is much faster than the competitive condensation reaction (from 2 × ( Si OH) to Si O Si bonds), which leads
to the lower polymerization. It is known that in water (also a
polar protic solvent) aminosilane layers spontaneously hydrolysed to a mono-layer [13,21]. This observation suggests that a
similar process is taking place in ethanol as a solvent and that
the estimated thickness of the formed APTMS film is about one
mono-layer. The other four solvents are different in terms of
structure/nature and could not solvolyse the molecules in this
way.
From high-energy-resolution Si 2p XPS spectra (Fig. 4b) we estimated that the APTMS coatings prepared from acetone, ethanol and
N,N-dimethylformamide are relatively thin since a signal from the
Si bulk at 99.9 eV is still present in the XPS spectra. We assume this
from the fact that the XPS sampling depth is around 6 nm.
G. Jakša et al. / Applied Surface Science 315 (2014) 516–522
4.2. Solvents forming rough APTMS films
Using toluene and acetonitrile as the media for the silanization
leads to the formation of a rough layer with a large number of
polymerized islands (Fig. 2). The obtained surfaces were rougher
(Table 1) with higher density of islands compared to the Si
wafer and the modified surface from acetone, ethanol and N,Ndimethylformamide (Fig. 2a–d). By using toluene and acetonitrile
for longer deposition times (6 h, AFM results not shown here)
we observed an increased density of islands and rougher surfaces
(Ra ∼ 0.6 nm) compared to the 3 h deposition time. Modification
using both mentioned solvents at elevated temperature (70 ◦ C, 6 h)
produces an even denser distribution of islands (Ra ∼ 1.5 nm). Some
of the formed islands also measure around 500 nm in diameter.
SEM analyses confirmed that modification with toluene (Fig. 3b)
and acetonitrile under the same preparation conditions (3 h at
25 ◦ C) leads to the formation of strongly polymerized surfaces. At
longer deposition times (6 h) and at higher deposition temperatures (70 ◦ C) we observed further polymerization of the molecules
on the surface. The distribution of polymerized APTMS molecules
is dense and some islands are around 1 ␮m wide.
The XPS results are in agreement with the morphology analyses
showing higher atomic concentrations of carbon and nitrogen on
the investigated surfaces. A modified silicon surface using toluene
and acetonitrile solvents with APTMS contains more carbon and
nitrogen than a surface modified with the acetone, ethanol and
N,N-dimethylformamide solvents (Table 2). For longer silanization
times the amount of nitrogen on the surface strongly increased
(Table 3). This is related to the increased coverage of the APTMS
coating and more aminosilanes on the surface. Together with the
results of the AFM and SEM imaging we concluded that most of the
aminosilanes are in the form of polymerized islands. The deposition
carried out at higher temperatures (70 ◦ C) leads to even stronger
polymerization and thicker coatings compared to that at 25 ◦ C. In
the case of toluene and acetonitrile the nitrogen concentration is
higher (two times higher at 25 ◦ C and five times higher at 70 ◦ C)
compared to the ethanol.
The thickness of the APTMS coating is reflected in the shape of
the Si 2p XPS spectra (Fig. 4b). In the case of the toluene the signal
from the Si bulk at 99 eV is greatly reduced and has almost disappeared. The signal from the Si bulk completely disappeared when
using acetonitrile as a solvent. This confirms the thick aminosilane
coatings on the oxidized Si wafer for the silanization carried out in
acetonitrile and toluene.
5. Conclusions
In this study we prepared self-assembled APTMS films on silicon
oxide surfaces from five different solvents under various reaction
conditions. Using the analytical techniques XPS, AFM and SEM we
investigated the surface composition, the chemical bonding, the
morphology and the roughness of the SiO2 surface before and after
silanization. Our results show that the composition and the morphology of the surfaces modified in various solvents were not the
same in the morphology. Our results show that ethanol and acetone
as solvents form thin APTMS coatings with a low density of islands
containing the polymerized molecules, even for longer deposition
times and higher deposition temperatures. The thickness of the
aminosilane layer on that modified surface is about one monolayer,
probably due to a spontaneous solvolysis. The APTMS coatings
prepared using the N,N-dimethylformamide solvent are slightly
thicker, particularly for prolonged deposition times and higher
deposition temperatures. The deposition of APTMS from acetonitrile and toluene leads to the formation of thick coatings with a
high density of islands containing polymerized APTMS molecules.
Acetonitrile as a solvent produces a slightly thicker coating than
521
toluene. We concluded that the modification of the silicon surface
by APTMS aminosilane molecules strongly depends on the type of
solvent. In the case of deposition in ethanol (polar protic solvent),
spontaneous solvolysis of the polymerized molecules is present
and a primarily smooth and thin modified surface is obtained. The
choice of solvent should be optimized for the particular application
of the modified silicon surfaces, since in some cases a monolayer
is desired, but in the other cases a polymerized morphology on the
surface can be beneficial.
Acknowledgements
The authors would like to thank Tatjana Filipič and Prof. Dr.
Marjan Marinšek for help during the XPS, AFM and SEM measurements. The work was supported by the Slovenian Research Agency
(programme P2-0082, projects J2-4287 and J7-5497).
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