Orientation and morphology of chloroaluminum phthalocyanine films grown by vapor deposition: Electrical field-induced molecular alignment

Article abstract of DOI:10.1016/j.chemphys.2010.12.004

The electric field influence on the molecular orientation and the surface morphology of the chloroaluminum(III) phthalocyanine (AlClPc) films has been studied using polarization dependent Raman spectroscopy and atomic force microscopy. The experimental studies were supported by DFT quantum chemical computations of the AlClPc vibrational spectra and ¹⁵N isotopic shifts. The electric field of 1.4 kV mm^-1 applied parallel to the substrate plane during the physical vapour deposition modified the film structure noticeable. The AlClPc molecules were aligned nearly perpendicular to the substrate surface (the mean tilt angle increased to ～80° from ～20° in the films grown without the electric field). The AFM images of the AlClPc films grown in the absence of electric field revealed a predominant amount of crystallites of polyhedron shape, whereas in the case of the applied electric field the surface was more ordered and consisted of the crystallites of a smoother shape.

Full text of DOI:10.1016/j.chemphys.2010.12.004

Chemical Physics 380 (2011) 40–47
Contents lists available at ScienceDirect
Chemical Physics
journal homepage: www.elsevier.com/locate/chemphys
Orientation and morphology of chloroaluminum phthalocyanine films grown
by vapor deposition: Electrical field-induced molecular alignment
a,
⇑
b,c,
⇑
, Vladimir A. Plyashkevich , Pavel B. Cheblakov b,c,
a
Tamara V. Basova , Vitaly G. Kiselev
d
d
d
Florian Latteyer , Heiko Peisert , Thomas Chassè
a
Nikolaev Institute of Inorganic Chemistry, 3 Lavrentiev Ave., Novosibirsk 630090, Russia
Institute of Chemical Kinetics and Combustion, 3 Institutskaya Str., Novosibirsk 630090, Russia
Novosibirsk State University, 2 Pirogova Str., Novosibirsk 630090, Russia
Institute of Physical and Theoretical Chemistry, University of Tübingen, D-72074 Tubingen, Germany
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
The electric field influence on the molecular orientation and the surface morphology of the chloroalumi-
num(III) phthalocyanine (AlClPc) films has been studied using polarization dependent Raman spectros-
copy and atomic force microscopy. The experimental studies were supported by DFT quantum
Received 13 October 2010
In final form 15 December 2010
Available online 22 December 2010
15
chemical computations of the AlClPc vibrational spectra and N isotopic shifts. The electric field of
ꢀ1
1
.4 kV mm applied parallel to the substrate plane during the physical vapour deposition modified
Keywords:
the film structure noticeable. The AlClPc molecules were aligned nearly perpendicular to the substrate
surface (the mean tilt angle increased to ꢁ80° from ꢁ20° in the films grown without the electric field).
The AFM images of the AlClPc films grown in the absence of electric field revealed a predominant amount
of crystallites of polyhedron shape, whereas in the case of the applied electric field the surface was more
ordered and consisted of the crystallites of a smoother shape.
Chloroaluminum phthalocyanine
PVD under external electric field
Thin films
IR and Raman spectra
Isotopic shifts
DFT calculations
AFM
Ó 2010 Elsevier B.V. All rights reserved.
1
. Introduction
Metal phthalocyanines (MPcs) attract great attention in many
to the film properties, the external electric and magnetic fields
have recently been reported to modify the structure of the studied
MPc films [9–14]. However, the influence of electric and magnetic
fields on the growth and structure of various thin organic films still
remains relatively poorly understood.
fields of science and industry. Due to their high thermal and chem-
ical stability, MPcs are widely used as dyes and pigments [1],
photosensitizers [2], liquid crystals [3], and in the Langmuir–
Blodgett films [4]. Being stable organic semiconductors, MPcs are
also intensively applied for energy conversion in photovoltaic
and solar cells, in electrophotography, molecular electronics, dis-
play devices, nonlinear optics (e.g., [5,6] and references therein),
chemical sensors [7,8]. The structure and orientation of molecules
in the highly ordered films of MPcs are of particular importance for
electronic device applications. It is well-known that the choice of
preparation conditions might affect the growth process and molec-
ular organization of thin organic films. Significant efforts have been
made so far toward development of growth methods and, ulti-
mately, to control the molecular structure (e.g., molecular orienta-
tion, polymorphism, and morphology) of the MPc films [9,10].
Among the huge variety of possible factors that might contribute
Recent studies on
p-conjugated plain organic molecules like
2
H Pc [9], CuPc [10–12], hexa(para-n-dodecylphenyl)-hexabenzoco-
ronene [13,14] showed that the presence of electric and magnetic
fields during the film growth process could noticeably modify
the molecular arrangement in the thin films of above-mentioned
compounds. Aromatic disc shaped molecules without metal atoms
have a relatively high polarizability, and their macrocycles are ex-
pected to be aligned parallel to the electric field. At the same time,
the metal atoms in complexes lying out of ligand plane and located
perpendicular to the macrocycle (for instance, TiOPc, VOPc) might
provide a perpendicular component of permanent electric dipole
moment. This complicates an alignment of such complexes in an
external electric field. The nonplanarity of the macrocycle in the
TiOPc and VOPc compounds (e.g., the angle between benzene
and C–N rings in the TiOPc is ꢁ7°) [15] also contributes to the dipo-
lar character of this species. This renders such compounds a spe-
cific polymorphism that differs significantly from those of planar
non-polar phthalocyanines [15–17]. The external magnetic field
was found to have a noticeable influence [18] on the structure of
⇑
Corresponding authors. Address: Nikolaev Institute of Inorganic Chemistry, 3
Lavrentiev Ave., Novosibirsk 630090, Russia (T.V. Basova).
E-mail addresses: basova@niic.nsc.ru (T.V. Basova), vitaly.kiselev@kinetics.nsc.ru
(
V.G. Kiselev).
0
301-0104/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.chemphys.2010.12.004

T.V. Basova et al. / Chemical Physics 380 (2011) 40–47
41
the VOPc films. In the absence of a magnetic field, the mean angle
between the substrate and macrocycle planes was about 24°, while
in the presence of the magnetic field perpendicular to the sub-
strate, the corresponding angle reduced significantly up to ꢁ3°
using atomic force microscopy (AFM). The study of orientation of
AlClPc molecules in the films was performed using polarization
dependent Raman spectroscopy. The assignment of all significant
bands in the Raman and IR spectra of AlClPc was made by combi-
nation of various experimental and theoretical techniques. The IR
[
19]. In a very recent paper [20] we have studied electric field ef-
fects on the molecular orientation and the surface morphology of
thin titanyl(IV)phthalocyanine (TiOPc) films by the use of polarized
Raman spectroscopy and atomic force microscopy. It was found
and Raman spectra of AlClPc, as well as isotopic shifts upon 15
N
substitution in AlClPc, were obtained experimentally. Experimen-
tal studies were supported by density functional theory (DFT) com-
putations of the vibrational spectra and isotopic shifts.
ꢀ1
that the electric field ꢁ2.5 kV mm applied parallel to the sub-
strate surface during the film deposition changes the tilt angle of
TiOPc molecules w.r.t. the surface from ꢁ60° to ꢁ90° [20].
2
. Experimental and computational details
In the present work, we considered in detail another metal
phthalocyanine complex, namely, chloroaluminum(III) phthalocya-
nine (AlClPc, Fig. 1). The structure of the AlClPc compound is similar
to those of VOPc and TiOPc. The Al atom lies out of plane of the Pc
macrocycle and the Cl atom is in extra-coordination position. In
contrast to the TiOPc and VOPc cases, the only slipped stack triclinic
2.1. Synthesis
The chloroaluminum(III) phthalocyanine (AlClPc) was prepared
from the phthalic anhydride, urea and aluminum(III) chloride in
the presence of ammonium molybdate in the 1,2,4-trichloroben-
ꢀ
crystal phase (symmetry group P1) was reported for AlClPc [21]. A
15
zene media at the temperature of 220 °C [30]. The N analogue
characterization of the AlClPc thin films by optical spectroscopy and
scanning electron microscopy [22] revealed that the substrate tem-
perature during the deposition process is a key factor responsible
for the formation of highly-structured surfaces. No significant mor-
phology changes occurred after annealing of thin films of AlClPc.
The influence of the structure of AlClPc thin films on their conduc-
tivity and charge carrier mobilities was also investigated [23–25].
Aroca and coworkers [26,27] studied AlClPc films using IR and res-
onance Raman optical spectroscopy techniques. The authors
15
of the chloroaluminum phthalocyanine (AlClPc- N) was synthe-
15
sized by the same procedure using urea containing 98% N (from
Sigma–Aldrich Chemical Company). The obtained phthalocyanines
were purified by vacuum gradient sublimation at a residual pres-
ꢀ4
sure of 10 Torr.
2.2. Preparation of thin films
Gold electrodes of 60–80 nm thickness were evaporated in high
[
26,27] assigned some characteristic vibrations of the AlClPc in
ꢀ8
ꢀ1
vacuum (2 ꢂ 10 mbar) with a deposition rate of 5 Å/min on clean
two-side polished quartz substrates. The application of the electric
field of 250 V to the electrodes with an interelectrode gap of
the region of IR spectrum 400–1600 cm . However, the assign-
ments of different bands were based on a simple comparison of
the wavenumbers and the forms of normal vibrations, and were
not supported by reliable quantum chemical calculations.
ꢀ1
1
80 lm resulted in an electric field of about 1.4 kV mm parallel
to the substrate surface (Fig. 2). The DC voltage and current mea-
surements during the thin film growth were carried out using a
DC power supply and a Keithley high-impedance electrometer.
To avoid the influence of an electrical current during the deposi-
tion, we investigated only thin films (with the thickness about
Note that similarly to the TiOPc and VOPc cases, the AlClPc mol-
ecule is a polar pseudoplanar compound with a permanent electric
dipole moment. While the dipole moment of TiOPc was found to be
less than 1.5 Debye [28], the corresponding value for the AlClPc is
more than two times higher [29]. Due to the significant polarity of
AlClPc, the effects of the external electric field on the film structure
might be especially pronounced in this case.
5
0 nm). The current measured during the thin film growth was
in the range of a few pA.
The thin films of the AlClPc were prepared via physical vapor
deposition in high vacuum (10- mbar) under strictly controlled
evaporation conditions (the evaporation rate of 5 Å/min and the
substrate temperature of 200 °C). The film thickness was con-
trolled using a quartz crystal microbalance. In such a way, the film
of nominal thickness of 50 nm was prepared after every deposition
cycle. In order to obtain the AlClPc thin film sample with both the
regions grown in the presence and in the absence of the electric
field, a particular sample geometry was used (Fig. 2).
In the present contribution we address the electric field effect
on the molecular orientation and the surface morphology of thin
AlClPc films prepared by physical vapour deposition (PVD). Thin
films were prepared in the absence and in the presence of an elec-
tric field parallel to the substrate surface during the thin film
growth. The surface morphology of AlClPc films was investigated
7
Fig. 2. A scheme of the experimental setup: a top view of the sample. The
electrodes are yellow and the quartz substrate is blue. A DC voltage (250 V) applied
ꢀ
1
to an interelectrode gap of 180 lm results in an electric field of 1.4 kV mm . (For
interpretation of the references to colour in this figure legend, the reader is referred
Fig. 1. Structure of the polar chloro-aluminum phthalocyanine (AlClPc) molecule.
to the web version of this article.)

4
2
T.V. Basova et al. / Chemical Physics 380 (2011) 40–47
2.3. Characterization of thin films
Figs. 3 and 4, respectively. The comparison of the experimental
and calculated wavenumbers of the most intense vibrations of
AlClPc, isotopic shifts, and their assignment are given in Table 1.
The assignment of experimental bands was primarily based on
The Raman scattering spectra of the deposited films were re-
corded with a SPEX Triplemate spectrometer and a confocal Raman
spectrometer (LabRam HR 800, Horiba Jobin Yvon, Bensheim, Ger-
many) equipped with CCD spectrometric detectors and a micro-
scope attachment for backscattering experimental geometry. The
the calculated spectra and isotopic wavenumber shifts upon 15
N
substitution. In the case of ambiguity, the IR intensity data were
also used.
4
88 nm line (40 mW) of an argon ion laser was used for spectral
It is seen that the experimentally measured vibrational wave-
numbers of AlClPc molecule coincide well with DFT theoretical
predictions. The RMS difference between the calculated and exper-
excitation. The laser beam was focused onto the sample by a
microscope objective with 100-fold magnification (a numerical
aperture NA = 0.9); the diameter of an incident laser beam was
ꢀ1
ꢀ1
imental values was 20 cm for wavenumbers and about 1 cm
ꢀ1
approximately 1
lm. The spectral resolution was about 2 cm
.
for isotopic shifts. The results of calculations presented here are
in a fairly good agreement with recent computations of the similar
metal (II) phthalocyanines [34–38]. The positions of Raman and IR
bands in the spectra of AlClPc corresponding to the Pc macrocycle
vibrations are close to those determined by Jennings et al. [26] and
The polarization dependent Raman spectra were collected in both
cross (Iij) and parallel (Iii) polarization configurations w.r.t. the inci-
dent laser polarization vector.
The atomic force microscopy (AFM) measurements were per-
formed under ambient conditions in a tapping mode with a Nano-
scope IIIa (Digital Instruments; now Veeco Instruments, Plainview,
USA) scanning probe microscope. All measurements were carried
out at room temperature.
1
Aroca et al. [27]. The assignments of the A modes are also in a
good agreement with the previously reported ones [23]. The exper-
The UV–VIS spectra of the films on quartz substrates were re-
corded with a UV–VIS–NIR scanning spectrophotometer (UV–VIS-
3
101PC «Shimadzu») in the wavelength range of 400–1000 nm.
2.4. Theoretical calculations
The IR and Raman spectra of the AlClPc and of its isotope ana-
1
5
logue AlClPc- N were calculated at the B3LYP/6-311++G(2df,p) le-
vel of theory [31–32]. An ultrafine integration grid was used for
numerical solving of the Kohn–Sham equations. All calculations
were performed using Gaussian 03 suite of programs [33]. The
ꢀ1
experimental wavenumbers below 250 cm were not considered
because of the strong mixing of external (collective lattice modes)
and internal vibrations in this range. The Raman intensities were
not calculated because of the resonant nature of the Raman spectra
excited by the lasers of the visible spectral range.
3
. Results and discussion
Fig. 3. The experimental IR spectra of AlClPc (a, blue) and AlClPc-15N (a, red) and
the calculated (B3LYP/6-311++G(2df,p)) IR spectrum of AlClPc (b). (For interpreta-
tion of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
3.1. Experimental and theoretical study of vibrational spectra of AlClPc
Due to the particular sample geometry (the interelectrode dis-
tance of 180 lm, Fig. 2), to study the film structure we opted for
the experimental techniques with a high lateral resolution:
namely, the polarized Raman optical spectroscopy and the atomic
force microscopy (AFM). However, the reliable polarized Raman
measurements can be performed only provided that the accurate
assignment of the Raman and IR bands is available. Therefore, we
investigated first the vibrational spectra of the AlClPc. In order to
obtain comprehensive data and identify and assign clearly all
intensive bands, in the present study we combined the experimen-
tally measured IR and Raman spectra, quantum chemical (DFT) cal-
culations, and the data on the isotopic substitution. Such a
combination of different techniques is especially useful to interpret
the vibrations of the large conjugated phthalocyanine macrocycle
with a number of overlapping bands in the vibrational spectra.
The AlClPc is a pseudoplanar molecule of C4v point group symme-
try (Fig. 1). The geometry of the AlClPc optimized using the B3LYP/6-
3
11++G(2df,p) method is given in Supporting information (Fig. S1
and txt file). Assuming a C4v point group for the AlClPc molecule
comprised of 58 atoms, the corresponding vibrational representa-
tion reads as U = 23 A
and E modes are Raman active, and the A
The experimental and calculated IR and Raman spectra of AlClPc
1
+ 19 A
2
+ 21 B
1
+ 21 B
2 1 1 2
+ 42 E. The A , B , B
1
and E modes are IR active.
Fig. 4. The experimental Raman spectra of the AlClPc (a, blue) and of the AlClPc-15
N
(
b, red). (For interpretation of the references to colour in this figure legend, the
1
5
15
and of its N-substituted analogue (AlClPc- N) are presented in
reader is referred to the web version of this article.)

T.V. Basova et al. / Chemical Physics 380 (2011) 40–47
43
Table 1
The experimental and calculated (B3LYP/6-311++G(2df,p)) Raman and IR wavenumbers (cm 1) and isotopic shifts (cm-1) of the AlClPc and AlClPc-15N.
ꢀ
Experimental
Wavenumber
Calculated
Symmetry
Assignment
Isotopic
shift
Wavenumber
Isotopic
shift
IR Intensity,
arb. units
Raman/IR
Raman
IR
2
52
3.5
2.4
B
E
A
A
B
E
E
A
E
B
E
A
A
B
E
B
E
B
E
A
E
E
A
1
254
255
256
293
296
302
312
359
394
433
434
442
489
495
498
523
528
566
586
601
649
658
695
695
703
711
742
754
769
773
785
785
790
792
796
799
817
4.4
2.8
0.8
2.8
5.7
4.7
4.4
10.2
0.5
1.3
1.1
0.6
0.8
2.9
2.7
2.2
6.9
3.3
2.9
7.4
1.8
3.2
11.2
4.0
0.4
4.9
4.6
4.1
15.5
12.4
1.7
0.3
1.4
5.4
3.3
4.7
7.1
N
a
–Al–N
–N –Al, C
Al–N , isoindole breathing
–C –C , Al–N OOP
–C –N , C –N , C –C
Al–N –C , C –C –C
–C , N –C –N
–C ,C –N –C
, N –C –C , C
–H, C –C –C
–C , C –C –H OOP
–H OOP
a
, C
a
–N
b
–C
a
C
a
a
a
–C
b
–C
c
1
1
a
2
93
C
a
b
c
a
2
N
b
a
a
a
a
a
b
–C
c
OOP
a
a
a
b
c
C
C
a
a
–C
–N
b
c
a
a
b
, C
a
–N
b
–C
a
3
4
51
26
7.0
0.3
1
b
a
a
a
a a
, Al–Cl, Al–N OOP
Al–N
a
a
a
b
a
–C
b
–C
c
2
C
C
C
b
–C
–C
–C
c
a
b
c
4
449
28
2.0
0.9/0.9
25.4
95.4
95.4
a
b
c
b
c
4
47
1
1
b
c
Al–Cl OOP
1
1
2
C
C
C
C
a
–C
–C
–C
–N
b
–C
-C
–H, N
–C
c
, C
a
–C
b
–N
b
4
5
89
24
1.0
0.6
b
c
d
, C
d
–C
–C
d
–H, C
a
–C
b
–C
c
d
d
b
a
–C
b
518
6.8/7.2
11.4
a
b
a
, N
b
–C
a
–C
b
, C
a
–C
b
c a
–C , Al–N
macroring breathing
–C –C , N –C –N
macroring breathing, C
5
76
46
1.4
7.0
7.0
1.1
2.4
4.9
0.0
C
b
c
d
b
a
a
5
90
1
a
–N
–H
–C
a
C
C
C
b
–C
–C
–N
c
–C
–C
d
, C
b
–C
a
–N
–C
–C
–C
, benzene def.
b
, C
, C
, C
, C
c
–C
–N
–C
–C
d
6
4.0
10.7
b
c
d
, C
b
–C
b
c
a
b
a
, C
a
–N
a a
–C
6
6
7
79
87
21
1
a
b
–C
–N
a
, N
, N
a
–C
–C
a
b
b
c
–C
–C
d
B
B
B
E
1
1
2
N
b
–C
a
a
b
a
b
c
d
d
OOP
0.1
C
C
C
a
a
a
–C
–N
–N
b
–C
c
a
a
a
a
a
–C
–C
–N
–C
–C
a
, N
, C
, C
a
–C
–C
–C
a
–N
–H, C
–H, C
, N
, N
b
, C
–C
–C
–C –C
–C –N
b
–C
–H, C
–H, C
c
–H, C
c
–C
–H
d
–C –H, OOP
d d d
–H, C –C –H
4.3
6.2
0.4
298.8
a
b
c
c
d
d
–C
d
7
34
A
1
N
a
–C
–N
–N
b
b
c
c
d
d
B
E
B
E
B
B
E
2
C
C
C
C
C
a
a
, Al–N
, Al–N
a
b
a
b
7
7
49
76
757
13.1/ꢁ10
54.2
0.4
a
a
a
a
a
b
, C
c
–C
d
–C
d
2.1
2
b
–C
–C
–C
c
–H, C
c
–C
–C
–C
–C
d
–H OOP
–H, C –C
–C , C –C
–C , Al–N
a
a
b
–C
–C
b
, C
, C
, C
b
c
b
b
–C
c
7
97
1.6
4.9
1
2
b
b
a
b
c
b
c
–H, C
b
–C
b
–C
c
N
a
–C
a
–C
b
b
c
c
a
c
, C –C –H
d
0.8
15.6
2.0
C
C
C
d
–C
c
–C
c
–H, C
–H, C
c
–C
–C
d
–H, N
–H, N
a
–C
–C
a
–N
–N
b
b
783
A
E
1
1
d
c
d
a
a
OOP
a
–N
a
–C
a
, C
a
–N
b
–C
a,
C
b
–C
c
–C
d
,
macroring breath.
8
30
52
12
0
A
850
15.3
4.4
C
C
C
C
a
–N
a
–C
–C
–H, C
–H, C
a
, C
a
–N
b
–C
a
, N
a
–C
a
–N ,
b
b
b
b
–C
–C
–C
c
d
, macroring breath.
8
67
03
E
894
894
920
976
978
979
980
0
0
14.0
15.9
0
0
0
0
0.0
c
c
–C
–C
d
–H
–H
B
E
B
B
E
A
E
B
B
E
1
c
c
d
9
14.4
16.0
54.5
N
a
–C
–N
a
–N
–C
b
, C
, N
a
–N , isoindole def.
b
–C
a
9
1
2
C
C
C
C
C
C
C
C
C
C
C
a
b
a
a
–Al–N , isoindole def.
a
b
b
b
–C
–C
–C
c
–H, C
–H, C
–H,C –C –H OOP
c d
c
–C
–C
d
–H
d d
–H, C –C –H
9
47
0
0
2.3
0
c
c
c
d
1
1006
1006
1028
1028
1029
1064
1093
1098
1129
1142
1154
1166
1189
1189
1208
1220
1225
1319
1329
1338
1355
1371
1374
c
c
c
c
–C
–C
–C
–C
d
d
d
d
–H, C
–H, C
–H, C
–H, C
d
d
d
–C
–C
–C
d
d
d
–H
–H
–H, C
1
0.2
0.2
0.2
0.2
15.2
18.4
4.9
4.1
1.8
6.5
2.5
1.4
1.7
8.1
6.5
5.9
1.4
1.2
10.0
13.6
2.0
6.3
2
c
–C
d
–C
d
12.7
0.2
c
–C
–C
d
–C
–C
d
1
004
036
0
A
1
b
–C
c
–H, C
c
d
d
, C
d
–C
d
–H
B
E
E
B
E
A
B
E
1
a
a
–N
–N
–C
b
–C
–C
–C
a
, isoindole def.
, isoindole def.
1
1064
081
14.2/ꢁ15
4.5
236.6
b
a
1
5.1
N
b
a
b
, C
a
–N
a
1
C
C
C
C
C
C
C
C
C
C
C
C
C
C
b
–C
c
–C
c
–C
c
–C
c
–C
c
–H, C
–H, C
–H, C
–H, C
–H, C
d
–C
d
–C
d
–C
d
–C
d
–C
d
d
d
d
d
a a
–H, C –N
–H, benzene breath.
1
1
1
1
1
104
132
186
210
306
1121
1.6/1.8
164.2
0.6
b
b
b
b
1
–H, C
–H, C
–H
a
a
–N
–N
a
–C
–C
a
3.0
1.5
0
2
a
a
1168
34.5
0.4
A
1
d
–C
–N
–N
–N
d
–H, C
c
–C
, isoindole breath., C
, isoindole def., C –C
–H
d
–H
B
E
B
E
B
B
E
E
2
a
a
a
a
–C
–C
a
d
–C
–H
d d c
–H, C –C –H
5.1
0.2
a
a
a
b
c
1
, C
b
–C
c
1289
1335
1.0/1.5
43.9
b
b
c
–C –H, C
c
–C –H, C
c
–C
–C
d
–H, C
–H, C
a
a
–C
–C
b
–C
–C
b
1
2
c
d
b
b
a
a
–N
–N
a
a
–C
–C
a
, pyrrole def., C
a
–C
–C
, benzene def.
b
27.0
259.3
1.8
a
, C
a
–N
b
, N
a
–C
a
b
b
–C
b
, C
b
c
–C , C
c
–C
d
1
335
4.1/4.8
A
1
macroring def.
(
continued on next page)

4
4
T.V. Basova et al. / Chemical Physics 380 (2011) 40–47
Table 1 (continued)
Experimental
Wavenumber
Calculated
Symmetry
Assignment
Isotopic
shift
Wavenumber
Isotopic
shift
IR Intensity,
arb. units
Raman/IR
Raman
IR
B
A
E
2
1381
1434
1453
1464
1480
1489
1505
1515
1522
1551
1569
1603
1624
1625
1627
1645
1647
0.1
8.2
2.1
0.6
0.1
4.8
3.3
0.8
8.7
8.4
2.2
20.8
0.2
1.6
0.2
0.2
0.2
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
b
–C
–N
–C
–C
–Cb,
–N
–C
–C
c
,
C
, C
a
–C
–N
–H, C –C
– H, C –C
–C –H
, N –C –C
–H, C –C –H, C
, C –Cd, –C –H
–C –C
b
–Cb,
–C
–H, C
–H, C
C
c
–Cd,
–C
–C
–C
C
b
–C
c
1
1
403
472
6.6
2.1
1
8.3
88.9
0
a
a
a
b
a
,
C
d
d
1425
b
c
d
d
b
b
A
1
c
d
b
c
b
b
0.5
B
B
E
B
E
E
2
b
C
b
c
1
a
b
a
a
b
, C
c
–C
d
–H
1474
1516
1560
ꢁ5
20.1
c
d
d
d
b
–C
c
1
a
a
a
a
a
b
c
C
c
d
2.0
51.7
0
–N
–N
b
, C
, C
a
a
–C
–C
b
, C
, C
a
b
c
, C
–N
b c
–C –H
7.2
ꢁ1
ꢁ17
0
b
b
b
–C
–N
b
, C
,
a
a
1
1
538
526
A
1
b b b a
–C , C –C , C
–N
b
b
B
E
B
A
E
2
0.7
b
b
b
b
b
–C
–C
–C
–C
–C
b
b
b
, C
, C
, C
d
–C
d
–C
d
–C
d
d
d
1
592
608
2
, C
, C
b
–C
–C
c
1
0.3
14.1
d
d
–H
1
1610
0/0
c
, C
, C
c
–C
–C
d
0.1
B
1
c
c
d
imental data along with the theoretical simulations allow for
assignment of not only totally symmetric A vibrations but also
the B , B , and E modes in the Raman spectrum of AlClPc (Table 1).
1
1
2
3.2. Analysis of the molecular orientation in the thin films by
polarization dependent Raman spectroscopy
After the detailed assignment of all bands in the vibrational
spectra of the AlClPc, we were able to scrutinize the structure of
the thin films of the title compound using the polarized Raman
spectroscopy. The principles of its application for the study of the
molecular film orientation are described elsewhere [20,39–40].
Here we present very briefly only the basic ideas of this technique.
The intensity of Raman bands can be expressed as a function of
the molecular orientation in the crystal and of the polarization
geometry [41]:
2
I / je~
ꢃ R ꢃ e~
j ;
ð1Þ
i
s
where I is the reflected Raman intensity, e~
and e~
are the unit polar-
0
0
0
i
s
Fig. 5. The orientation of the coordinate axes of the AlClPc molecule (x , y , z ; red
color) with respect to the substrate surface coordinate system (x, y, z; black color).
(For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
ization vectors of the electric field of the incident and of the scat-
tered laser beam, respectively, and R stands for the Raman
scattering tensor of a particular vibrational mode. The detailed anal-
ysis of the Raman tensors for the C4v symmetry group and the deter-
mination of the molecular orientation are also given elsewhere [20].
If the molecules in a sample are rotated w.r.t. a chosen coordi-
nate system, the corresponding Raman tensors can be obtained by
rotation of the initial tensors by the appropriate angles. In the par-
ticular case of the AlClPc molecule, the designation of the molecu-
lar axes is presented in Fig. 5. Note that the molecular z-axis
should be represented by their average values (the
c angle ranges
from = 0 to /2, see Eqs. (2) and (3)). The final expressions for
c
c = p
I and I read as:
ii
ii
ij
ij
Z
p
2
p
2
p
2
2
I
I
¼
¼
ꢃ
ꢃ
f ð
a
; b;
; b;
c
Þd
c
;
;
ð2Þ
ð3Þ
ii
0
Z
p
coincides with the C
of the AlClPc molecule around x- and y-axes by the angles
4
-axis of the C4v point group. Upon rotation
and
2
2
f ð
a
c
Þd
c
a
ij
0
b, respectively, the resulting molecular orientation exhibits an
inclination angle of the molecular plane (pseudoplanar macrocy-
cle) with respect to the substrate plane (Fig. 5). This inclination an-
gle coincides with the respective Eulerian angle h, and it can be
where fii
(
a, b,
c
) and fij(a
, b,
c
) are the Raman tensor components (ii)
and (ij) of a particular Raman mode obtained by rotation around the
x-, y-, and z-axes by the angles , b, and , respectively. Since the
expressions for f( , b, ) and, consequently, for = Iii/Iij are rather
complex, they are omitted here for the sake of brevity. Thus, the
and b angles can be derived from (2) and (3) using the experimen-
a
c
easily represented as a function of
a
and b (e.g., in the case of
a
c
q
b = 0, one simply obtains h = ). The depolarization ratio
a
q
= Iii/Iij
a
for each symmetry type of vibrations can be deduced considering
the Raman tensor components obtained upon rotation around
the x-, y-, and z-axes by the angles a, b and c, respectively. The mol-
tally measured depolarization ratios
(Table 2).
1 1 2
q for the A , B , B and E modes
ecules in a film sample are usually disordered w.r.t. the z-axis (see
below), therefore, the elements of corresponding Raman tensors
Typical Raman spectra in parallel and cross polarization config-
uration of the thin AlClPc films grown in absence and in the pres-

T.V. Basova et al. / Chemical Physics 380 (2011) 40–47
45
Table 2
The experimental depolarization ratios
1 2
q=Iii/Iij for the A , E and B modes obtained
from polarization dependent Raman spectra of the AlClPc films grown in the absence
and in the presence of the electric field.
Symmetry Raman shift
Depolarization ratio q = Iii/Iij
ꢀ
1
(cm )
Without electric
field
In the presence of electric
field
A
1
590
17
14
17
13
12
4
5
4
5
5
6
8
1
1
79
30
403
538
Mean
E
14.6
2.6
1.8
2.4
2.7
2
4.6
1.1
1
1.5
1.3
1
489
7
1
1
1
49
036
104
210
Mean
2.3
2
2
1.2
1
1
B
2
776
592
1
Mean
2
1
ence of an electric field are shown in Fig. 6a and b, respectively. The
vibrational bands were labeled in accordance with their assign-
ment to the A , E, and B modes (Table 2). The Raman spectrum
1 2
of the AlClPc film grown at 200 °C in the absence of the electric
field (Fig. 6a) exhibits considerable polarization dependence. In
the parallel polarized (ii) Raman spectrum (Fig. 6a), the intensities
ꢀ1
of the A
strong, whereas in the cross-polarized (ij) Raman spectrum
Fig. 6a) their intensity is weak. Consequently, the observed val-
ues for the AlClPc films grown in the absence of the electric field
Table 2) are very high (more than 15) for the A modes, while
the E modes show a mean depolarization ratio of about 2. In con-
trast, the above-mentioned A modes located at 590, 680, 830,
403 and 1536 cm do not exhibit such distinctive polarization
dependence in the Raman spectra of AlClPc films grown in the
presence of electric field (Fig. 6b). The mean values of 4.6, 1.2,
and 1 were found for the A , E and B modes, respectively (Table 2).
1
bands at 590, 680, 830, 1403 and 1536 cm are very
(
q
(
1
1
ꢀ
1
1
q
Fig. 6. Typical polarization dependent Raman spectra of a thin AlClPc film grown at
1
2
200 °C in the absence (a) and in the presence of an electric field (b). The parallel and
The AFM data (see below) do not suggest any preferential island
shape or preferential growth directions. At the same time, the ob-
served experimental depolarization ratios may be readily ex-
plained assuming that the phthalocyanine molecules are
disordered relative to the azimuthal orientation (z-axis) and are ro-
the cross polarized Raman spectra are labeled Iii and Iij, respectively.
thin films. Note that the same behaviour was observed for TiOPc
films grown under similar experimental conditions [20]. Both the
TiOPc and AlClPc compounds have a high permanent electric di-
pole moment: the value ꢁ1.4 Debye was reported for the former
species [28] and our B3LYP calculations yield the value of ꢁ3.7 De-
bye for the latter one. It is therefore tempting to attribute the ob-
served orientation effects entirely to the interaction of the dipole
with the electric field. However, if one estimates the energy a di-
tated around their x and y-axes by particular
2) and (3)), respectively. We have therefore adopted this model
for the further analysis.
In the case of the film grown in the absence of the electric field,
the angles
a and b angles (Eqs
(
a
and b were calculated to be ꢁ20–30° and ꢁ5–10°,
respectively. These values agree well with the previously reported
structures of the AlClPc films deposited onto various substrates un-
der similar conditions [23–25]. For instance, the slow (less than
five monolayers per hour) film deposition of trivalent metal Pcs
~
~
pole d attained in the electric field E as dꢃE (in our case,
ꢀ1
E = 1.4 kV mm ) and then compares it with the thermal energy
(in our experiments T ꢁ 470 K), the following ratio reads as
dꢃE
ꢀ3
(
AlClPc, GaClPc, and InClPc) onto the SnS
2
substrate was studied
ꢁ 3 ꢂ 10 . It is seen that the ‘‘pure’’ (external electric field)-
kT
using the surface electron diffraction [25]. The Pc rings were found
to align predominantly parallel to the substrate plane [25]. The
similar parallel orientation was observed in the triclinic AlClPc
films on KCl (0 0 1) substrates [23].
The most fascinating results were obtained for the films grown
in the presence of the electric field. The orientation of the AlClPc
macrocycles changed drastically: while the b angle was again
(permanent dipole of a single molecule) interactions cannot pro-
vide the discussed alignment. The observed ordering of AlClPc mol-
ecules in the films appears to be a result of a subtle trade-off
between the electric field effects and the substrate-molecule or
even molecule–molecule interactions (as mentioned before, the
film thickness was ꢁ50 nm). Additional studies are indeed re-
quired to clarify the role of other factors that influence the align-
ment of molecules.
ꢁ
5–10°, the
a
angle was equal to ꢁ75–80° suggesting a nearly per-
pendicular orientation of the AlClPc molecules to the substrate sur-
face. It is therefore seen that the external electric field has a
pronounced influence on the molecular orientation in the AlClPc
However, our results undoubtedly show that even for the rela-
tively small interaction energies introduced by the applied station-
ary electric field, the AlClPc molecules tend to realign during the

4
6
T.V. Basova et al. / Chemical Physics 380 (2011) 40–47
growth process. The tilt angle, here essentially described by the an-
gle
presence of the electric field. Indeed, more work is required to clar-
strate temperature leads to formation of highly-structured thin
films. The annealing of these films did not affect the orientation
of molecules and degree of crystallinity [24].
a
, increases significantly (from ꢁ20–30° to ꢁ75–80°) in the
ify the detailed mechanism of the field-induced alignment.
Finally, to get more insight into the crystalline phase of the
AlClPc films obtained, we used the UV–VIS optical spectroscopy.
The UV–VIS absorption spectrum of the AlClPc film deposited sep-
arately at the same experimental conditions on quartz substrate at
3.3. Study of the surface morphology
2
00 °C without the electric field is presented in Fig. 8. It is well-
As was discussed before, the electric field modified noticeably
known that the Q-band in the UV-spectra of thin films becomes
broader than the corresponding band in the spectra of individual
molecule [42]. The origin of this change is the Davydov splitting
of the bands corresponding to the allowed transitions [43] induced
by the intermolecular interactions.
The comparison of the UV-absorption spectrum of the AlClPc
film (Fig. 8) with those reported in the literature [22–24] indicates
clearly the presence of the triclinic phase of AlClPc in the film
deposited in the absence of the electric field. A wide absorption
Q-band in the region 600–800 nm with a maximum at about
the structure of the AlClPc thin films. Apart from this, the electric
field has also been found to affect the surface morphology of the
films studied.
The topographic AFM image of the AlClPc film deposited in the
absence of the electric field is presented in Fig. 7a. The sample con-
sists of a mixture of disordered crystallites of polyhedron shape
and small areas containing a phthalocyanine admixture without
any preferred shape of crystallites. These crystallites mostly tend
to be oriented parallel to the substrate surface. The rms roughness
of these AlClPc films is about 2.2 nm (Fig. 7a).
7
60 nm is typical of triclinic AlClPc films [20–23,42]. The structure
On the contrary, the image of the AlClPc film grown in the pres-
ence of the electric field (Fig. 7b) exhibits a surface morphology
comprised of bigger crystallites of smoother shape. This region
looks more ordered and the phthalocyanine crystallites are located
closer to each other. The rms roughness of this part of AlClPc sam-
ple is about 1.7 nm (Fig. 7b).
and the phase composition of the AlClPc films have already been
studied by a variety of experimental techniques (UV–VIS and IR
optical spectroscopy, X-ray diffraction, DSC, transmission and
scanning electron microscopy) [21–22,29,44–47]. It has been
shown that the triclinic AlClPc films could be obtained at a sub-
strate temperature 150–300 °C [22]. The AlClPc deposition at the
substrate temperatures below 150 °C led to formation of the films
with an admixture of amorphous phase [22,44–45] It was also
found that the temperature of the transition to monoclinic phase
is higher (300–325 °C) than that corresponding to a similar poly-
morphic transition reported for the phthalocyanines of divalent
metals [48]. Aroca et al. [27] described a formation of AlClPc films
containing predominantly monoclinic phase on glass and on NaCl
substrates. The films were rather thick (ꢁ200 nm) and were depos-
ited at a high growth speed (0.5 nm/s). The formation of the mono-
clinic phase was suggested on the basis of the observed Davydov
splitting in polarized Raman spectra. It is also worth mentioning
that the Davydov splitting was not observed in the polarized Ra-
man spectra of the AlClPc films deposited at the experimental con-
ditions described in this work. This fact also confirms a triclinic
structure of the investigated films.
As mentioned before, the films of the AlClPc with the nominal
thickness about 50 nm were deposited at a substrate temperature
2
00 °C. It is worth mentioning that the deposition at a higher sub-
Fig. 8. The electronic absorption spectra of the thin film of AlClPc grown on a quartz
Fig. 7. The topographic AFM image (3
film thickness 50 nm) grown at 200 °C: (a) without the electric field; (b) in the
presence of the electric field (1.4 kV mm ).
l
m ꢂ 3
l
m) of a thin AlClPc film (a nominal
substrate at 200 °C (a, black curve) and of the AlClPc solution (1 lM) in
dichlorobenzene (b, red curve). (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
ꢀ
1

T.V. Basova et al. / Chemical Physics 380 (2011) 40–47
47
[
[
5] J. Simon, J.-J. Andre, in: J.M. Lehn, C.W. Rees (Eds.), Molecular Semiconductors,
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. Conclusion
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pared by organic molecular beam deposition at 200 °C in the ab-
sence and in the presence of the stationary electric field
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ꢀ1
ꢁ
1.4 kV mm during the film growth.
[
The polarization dependent Raman spectroscopy and the atom-
(
ic force microscopy were used for comparative analysis of the
deposited films. The AlClPc molecules in the films grown in the
presence of the electric field are tilted with respect to the substrate
plane by ꢁ80° (their macrocycles are almost perpendicular to the
substrate plane), whereas in the films grown without the electric
field the AlClPc molecules are aligned nearly parallel (the average
tilt angle is ꢁ20°) to the substrate surface. Furthermore, the AFM
images of thin AlClPc films grown in absence of the electric field
show a predominant amount of crystallites of polyhedron shape,
while in the case of the applied electric field the surface is more or-
dered and consists of the crystallites of a smoother shape. The UV–
VIS absorption spectroscopy confirmed the presence of the triclinic
phase of AlClPc in the film deposited in the absence of the electric
field.
(
[
[
[
[
[
[
[
1
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1
Finally, the use of electric field during the growth of the films of
polar organic molecules can provide a promising opportunity of
controlling the morphology and/or molecular orientation in thin
molecular films. We believe our results presented here constitute
a useful step toward this ultimate goal.
[
2
[
7
[
[
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Acknowledgments
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1989) 2272.
The authors thank W. Neu for technical support. The funding by
DAAD scholarship A/08/78369 and by the grant DFG PE 546/4-1
are gratefully acknowledged. This work was also supported by
the Siberian Supercomputer Center. V.G.K. appreciates the support
of this work by the Russian Federal Agency of Education (project
NK-187P(6), contract # P1475) and SB RAS (Lavrentiev grant
programme).
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