Infrared spectra, optical constants and semiconductor behavior of 5-(2-phenylhydrazono)-3,3-dimethylcyclohexanone thin films

Article abstract of DOI:10.1016/j.molstruc.2012.09.067

The 5-(2-phenylhydrazono)-3,3-dimethylcyclohexanone (PHDMC) is synthesized by reacting 5,5-dimethylcyclohexane-1,3-dione with 2-phenylhydrazine. Synthesized PHDMC is polycrystalline with monoclinic space group, P2 ₁/a. Miller's indices values f

Full text of DOI:10.1016/j.molstruc.2012.09.067

Journal of Molecular Structure 1036 (2013) 144–150
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Infrared spectra, optical constants and semiconductor behavior of
5-(2-phenylhydrazono)-3,3-dimethylcyclohexanone thin films
b
c
E.M. El-Menyawy a, , N.A. El-Ghamaz , H.H. Nawar
⇑
a Solid State Electronics Laboratory, Solid State Physics Department, Physics Division, National Research Center, Dokki, Cairo 12615, Egypt
b Department of Physics, Faculty of Science at New Damietta, Damietta University, 34517 New Damietta, Egypt
c Department of Chemistry, Faculty of Education, AlJabl Al Gharbi University, Libya
h i g h l i g h t s
"
"
"
"
Hydrazine derivative has been synthesized.
FTIR indicates that the thermal evaporation is suitable technique for obtaining thin films.
Optical constants of thin films are independent of their thickness.
The compound has semiconductor behavior.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2012
Received in revised form 25 August 2012
Accepted 25 September 2012
Available online 2 October 2012
The 5-(2-phenylhydrazono)-3,3-dimethylcyclohexanone (PHDMC) is synthesized by reacting 5,5-
dimethylcyclohexane-1,3-dione with 2-phenylhydrazine. Synthesized PHDMC is polycrystalline with
monoclinic space group, P21/a. Miller’s indices values for each diffraction peak in the X-ray diffraction
spectrum are calculated. Thin films of PHDMC with different thickness values (0.83–1.247 lm) are pre-
pared by thermal evaporation technique and they exhibit amorphous structure. Different vibrational
modes, observed in infrared spectra of the powder and thin films, were assigned to the molecular bonding
structure of PHDMC compound. The optical properties of PHDMC thin films are investigated by measur-
ing the optical transmittance and reflectance at the normal incidence of the light in the spectral range
200–2500 nm. The refractive and absorption indices of the films are found to be independent of the film
thickness range mentioned above. The refractive index is analyzed and the dispersion parameters are
extracted. Analysis of the absorption coefficient spectra showed that the films have two major indirect
allowed electronic transitions; the corresponding optical band gaps are estimated as 2.1 and 3.2 eV in
the framework of electronic band-to-band transition theory. The direct current electrical conductivity
measurements showed the semiconductor property of the films.
Keywords:
Organic thin films
Structural properties
Optical constants
Conductivity
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
They have been used as optical sensors [6] and have been investi-
gated for dye sensitized solar cell applications [7]. A class of hole
Promising chemical and physical properties of organic thin
films provide a route that open up avenues for a variety of indus-
trial applications. They have been used as active layers in several
electronic and optoelectronic devices such as solar cells [1], Scho-
ttky junctions [2], light emitting diodes [3] and optical data storage
[4] due to their advantages of low cost, tenability of electronic
properties via chemical synthesis and ease of device fabrication.
The titled compound belongs to the class of hydrazones. Hydra-
zones are known as one of the most important classes of organic
compounds, some of which have semiconductor properties [5].
transporting hydrazones have been studied as new optoelectronic
materials [8].
Due to the emergence of organic materials in advanced applica-
tions, there is considerable interest in the search for new optical
and semiconductor materials. Information concerning the electri-
cal and optical properties of organic thin films as well as their
structure relationship would be very important tool in determina-
tion the area of application. There are several parameters which
control the optical properties of organic layers [9,10]. The film
thickness can be considered as a key factor for designing advanced
devices. Some studies showed that the optical properties of organic
thin films are independent on film thickness, while others are
dependent. For instance, El-Nahass and Youssef [11] have reported
⇑
Corresponding author. Tel.: +20 1006021326; fax: +20 233709310.
E-mail address: emad_elmenyawy@yahoo.com (E.M. El-Menyawy).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.09.067

E.M. El-Menyawy et al. / Journal of Molecular Structure 1036 (2013) 144–150
145
that the refractive and absorption indices of asymmetrically substi-
tuted indium phthalocyanine chloride thin films are independent
of thickness range 105–350 nm, while Yakuphanoglu et al. [12]
pointed out that the optical constants of Cr(III) complex having
2-pyridine carbaldehye thiosemicarbazone films are governed by
their thickness (33–500 nm). On the other hand, electrical conduc-
tivity and its temperature dependence can be used to determine
the nature of materials and to characterize the conduction process
under application of an electrical field [13].
In this work, 5-(2-phenylhydrazono)-3,3-dimethylcyclohexa-
none (PHDMC) is synthesized. PHDMC thin films are prepared by
using thermal evaporation technique. The X-ray diffraction and
Fourier transforms infrared spectra are studied in both powder
and thin film forms. The optical properties of thin films are inves-
tigated in terms of the spectrophotometric measurements of the
transmittance and reflectance. The refractive and absorption indi-
ces and their related parameters are determined and analyzed.
The electrical conductivity of the films is measured on planar
samples.
grade KBr, whereas the measurements of thin films were achieved
for films deposited on rectangular KBr single crystal substrates.
X-ray diffraction patterns of PHDMC in powder form and in thin
film form of thickness 1.247 lm (deposited onto quartz substrates)
were recorded on X-ray diffractometer (Philips X0 pert) with
0
Ni-filtered Cu Ka-radiation (k = 1.5418 ÅA) in the range of diffraction
angle (4–55°). The applied voltage and the tube current were 40 kV
and 30 mA, respectively.
The transmittance of PHDMC thin films was measured at the
normal incidence of the light in the spectral range 200–2500 nm
by using a double beam spectrophotometer (JASCO model V-570
UV–VIS–NIR). The spectrophotometer was also provided with a
reflectance unite in order to measure the reflectance in the same
spectral range. The films in this experiment were deposited onto
optical flat quartz substrates. The structural and optical measure-
ments have been performed on the samples at room temperature
(300 K).
Direct current electrical resistance, R, of PHDMC thin films was
measured on planar samples by using high impedance electrome-
ter (Keithley 617). The conductivity of the organic material was
calculated from the sample dimensions through the relation;
r
DC = L/Rwd, where L is the distance between the two electrodes,
2. Experimental procedures and optical constants
determination
w is the width of the film and d is the film thickness. The ohmic
electrodes were made from gold. The gold electrodes were depos-
ited on the two ends of the film by using high vacuum coating unit
mentioned above.
2.1. Synthesis of organic compound
Chemical reagents were commercially available and used with-
out further purification. A solution of 5,5-dimethylcyclohexane-
1,3-dione (0.01 mol) was stirred with 2-phenylhydrazine
(0.01 mol) in a cold water for an hour. The product was collected
by filtration and re-crystallized from acetone to give 5-(2-phen-
ylhydrazono)-3,3-dimethylcyclohexanone (PHDMC) as red crystals
in yield 85%, melting point, m.p. 164–166 °C. The molecular struc-
ture of PHDMC compound is shown in Scheme 1.
2.3. Optical constants determination
The absolute values of total measured transmittance, T, and
reflectance, R, after introducing corrections resulting from the
absorbance and reflectance of the substrate are calculated by [15]:
Ift
T ¼ ð1 ꢁ RqÞ;
ð1Þ
Iq
and
2.2. Thin film preparation and measurements
Ifr
Im
2
R ¼ Rm½ð1 ꢁ RqÞ þ 1ꢂ ꢁ T2Rq;
ð2Þ
A high vacuum coating unit (Edwards Model E 306 A, England)
was used to prepare PHDMC thin films with different thickness
values onto different substrates maintained at room temperature.
The vacuum chamber was pumped down to about 5 ꢀ 10ꢁ4 Pa.
The films were vacuum deposited from the powder by using a
quartz crucible source heated gradually by a molybdenum boat.
The film thickness and deposition rate were monitored and con-
trolled during deposition by using a quartz crystal thickness mon-
where Ift, Iq, Ifr, Im are the intensities of light passing through film-
substrate system, reference quartz substrate, light reflected from
the sample and light reflected from the reference aluminum mirror,
respectively. Rq and Rm are the reflectance of reference quartz sub-
strate and the reflectance of the mirror, respectively.
Different computational methods [16–19] have been used to get
the refractive index, n, and absorption index, k, of thin films depos-
ited onto thick non-absorbing substrates. They comprise computer
software intended to solve equations relating that constants with
spectrophotometric measurements of T and R measured at normal
incidence of light. For calculating n and k of films, a modification
bidifference search technique of Bennett and Booty [16] has been
used in this work. A computer program is used to minimize simul-
taneously the difference between the calculated values and the
experimental ones of both transmittance and reflectance as:
itor (Model TM-350 MAXTEK, Inc., USA). The deposition rate was
0
controlled at 3.5–4 ÅA/s. A mechanical shutter, fixed near to the
evaporation source, was used to avoid any probable contamination
of the substrates in the initial stage of evaporation and to control
roughly the thickness of films. After vacuum breaking, the film
thickness was determined from spectral transmittance curve using
the interference fringes [14].
Fourier transforms infrared spectra were recorded on ATI Matt-
son (infinity series FTIR) infrared spectrophotometer in spectral
range 400–4000 cmꢁ1. The measurements were carried out for
the as-synthesized PHDMC powder mixed with vacuum dried
2
2
ðD
TÞ ¼ jTcal ꢁ Tj ꢃ 0
ð3Þ
and
2
2
ð RÞ ¼ jRcal ꢁ Rj ꢃ 0
D
ð4Þ
where T and R are the experimentally determined values calculated
from Eqs. (1) and (2), respectively. Tcal and Rcal are the calculated
values using Murmann’s exact equations [20]. The experimental er-
rors are taken into account as follows: 2.2% for film thickness mea-
surements, 1% for T and R calculations, 3% for refractive index and
2.5% for absorption index computations [21].
Scheme 1. Molecular structure of PHDMC compound.

146
E.M. El-Menyawy et al. / Journal of Molecular Structure 1036 (2013) 144–150
Table 1
3. Results and discussion
Crystallographic data for PHDMC compound.
0
3.1. X-ray diffraction
Peak no.
2hobs (ꢀ)
2hcal (ꢀ)
(hkl)
dobs (AÅ)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
10.82843
8.586035
6.951989
6.968023
5.428059
5.204754
4.892065
4.404671
4.32799
4.105357
3.923641
3.738321
3.632276
3.532684
3.40704
8.190
8.221
011
120
The X-ray diffraction spectra of PHDMC in both as-synthesized
powder and as-deposited thin film (1.247 lm) are shown in Fig. 1.
ꢁ
10.350
12.280
12.790
16.510
17.240
18.380
20.500
20.880
22.070
23.150
24.370
25.130
25.890
26.920
28.030
29.120
30.540
32.283
33.510
34.400
35.442
36.613
38.485
39.578
40.787
42.698
10.374
12.239
12.923
16.484
17.171
18.421
20.481
20.895
22.024
23.127
24.382
25.143
25.918
26.915
28.027
29.119
30.528
32.305
33.493
34.410
35.448
36.654
38.491
39.594
40.807
42.688
211
ꢁ
PHDMC powder spectra exhibit different peaks with different
intensities indicating polycrystalline nature. Films deposited at
room temperature show an amorphous structure without any
characteristics of the crystallinity judged from XRD measurements.
The amorphous nature of as-deposited PHDMC films is primarily
attributed to the low adatom mobility due to the low film deposi-
tion temperature, where the adatoms on the growing film surface
are not activated enough to find the crystalline lattice sites.
The diffraction peaks in powder spectra are indexed and the lat-
tice parameters are determined with the aid of CRYSFIRE computer
program [22]. The values of interplanar spacing, d, and Miller indi-
ces, hkl, for each diffraction peak before and after refinement are
determined by using CHEKCELL program [23]. The values of d
and corresponding hkl for PHDMC are listed in Table 1. The results
show that PHDMC has a monoclinic crystal structure with space
group P21/a. The lattice parameters are estimated as:
220
022
122
ꢁ
410
ꢁ
331
013
ꢁ
103
ꢁ
340
223
ꢁ
133
ꢁ
323
512
ꢁ
3.282417
3.16972
333
ꢁ
243
ꢁ
3.035595
2.888023
2.79395
2.730223
2.660005
2.586275
2.478606
2.420947
2.361191
2.274523
261
361
414
353
731
462
325
415
a = 19.932 Å, b = 18.869 Å, c = 13.095 Å,
a = c = 90° and b = 91.5°.
3.2. Fourier transforms infrared
ꢁ
634
921
Fourier transforms infrared, FTIR, transmittance spectra of
PHDMC compound in both powder and thin film (150 nm) forms
are demonstrated in Fig. 2. The results show several absorption
bands; the important IR characteristic absorption bands, along
with their proposed assignments, are summarized in Table 2. The
spectrum of PHDMC powder shows two absorption signals at
3246 and 3214 cmꢁ1 which are due to asymmetric and symmetric
NAH stretching vibrations, respectively. The two bands of weak
intensity at 3088 and 3022 cmꢁ1 are corresponding to asymmetric
and symmetric stretching vibrations of the aromatic CAH bonds,
respectively. The vibrations at 2964 cmꢁ1 can be attributed to the
asymmetric stretching vibration of aliphatic CAH bonds, whereas
the 2922 cmꢁ1 vibration may arises from the resonance of CH3.
The vibration at 1602 cmꢁ1 is due to the conjugation of the aro-
matic ring. The band observed at 1546 cmꢁ1 reflects the presence
of C@N bond. Generally, the functionality in the molecular system
made by FTIR spectra (Fig. 1 and Table 1) agrees well with the pro-
posed chemical structure of PHDMC compound given in Scheme 1.
On the other hand, the broad band observed around high energies
(at 3437 cmꢁ1 for powder and at 3442 cmꢁ1 for thin film) is due to
100
90
80
70
60
(b)
(a)
50
100
90
80
70
60
50
8
6
9
2
5
7
11 13
12
4000 3600 3200 2800 2400 2000 1600 1200 800 400
3
10
4
-1
Wavenumber (cm )
14
18
16
17
21
20
19
15
24
22
23
26
1
27
(a)
(b)
25
Fig. 2. FTIR spectra for PHDMC: (a) powder and (b) thin film.
AOH group vibrations which can be assigned to hydroxyl group of
water; probably water vapors are absorbed from the air atmo-
sphere by potassium bromide and/or the organic material itself.
The symmetric absorption bands in powder and thin films indicate
5
10
15
20
25
30
2θo
35
40
45
50
55
Fig. 1. XRD patterns for PHDMC (a) powder and (b) thin film.

E.M. El-Menyawy et al. / Journal of Molecular Structure 1036 (2013) 144–150
147
Table 2
Assignment of the important bonds in PHDMC compound.
2.6
2.4
2.2
2.0
1.8
1.6
Wavenumber (cmꢁ1
Powder
)
Assignment
Thin film
3437
3246
3214
3088
3022
2964
2922
1602
1546
1493
1372
1228
1151
758
3442
3234
3210
3089
3025
2968
2921
1603
1543
1495
1370
1226
1150
757
m
m
m
m
m
(OH)
(NH) as
(NH) s
(CH) as (Ar)
(CH) s (Ar)
as (CAH) aliphatic
(CH3)
m
C@C (Ar)
C@N
d as(CH3)
d s(CH3)
m(CAN)
(CH3) wagging
(CH3) rocking
200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
693
501
695
498
c
(CH) (Ar)
λ (nm)
CAC in plane bending
Fig. 4. Refractive index dispersion curve for PHDMC thin films.
that the thermal evaporation technique is a suitable one for obtain-
ing undissociated PHDMC films. Obviously, the intensity of absorp-
tion bands in powder form is stronger than that of thin film form
which can be ascribed to the abundance of the material used.
0.20
3.3. Optical constants of thin films
0.15
0.10
0.05
0.00
Fig. 3 illustrates the optical transmittance and reflectance of
PHDMC thin films as a function of light wavelength, k. At
k P 600 nm, the total sum of the transmittance and the reflectance
nearly equals to unity, indicating an optical transparent region. At
k < 600 nm, the total sum of the transmittance and the reflectance
is less than unity implying optical absorption region. The films
have two transmittance edges centered at about 345 and
515 nm. The oscillations observed in transmittance and reflectance
spectra arise from the interference effect due to reflectance from
the top surface of the film and reflectance at the interface between
the film and substrate. The systematic oscillating behavior indi-
cates that the films are homogenous and have flat surface [9].
The optical properties of different materials can be fully charac-
terized by the complex dielectric constant or the complex refrac-
tive index, nꢄ, where nꢄ = n + ik. In general, the real part, n, is
related to the dispersion, while the imaginary part, k, provides a
measure of dissipation rate of the electromagnetic wave in the
dielectric medium. The values of refractive and absorption indices
200
300
400
(nm)
500
600
λ
Fig. 5. Absorption index spectrum of PHDMC thin films.
for PHDMC thin films are computed using the absolute values of
transmittance and reflectance as mentioned in Section 2.3. The re-
sults of calculations show that n and k are independent of film
thickness range 0.83–1.247 lm; therefore, the results depicted in
Figs. 4 and 5 represent the average values of n and k for the above
mentioned thickness range at wavelength range 200–2500 nm. The
independency of the optical constant (n and k) on film thickness is
in accordance with the literature for different organic films [24–
27]. For the tested films, the films are of amorphous structure
and thickness values are large enough as optical properties are
independent on their thickness.
The refractive index behavior of PHDMC films in spectral range
200–600 nm represents the anomalous dispersion which can be
explained by the multi-oscillator model [28], in which the refrac-
tive index shows two peaks with maxima at the wavelength values
of 315 and 465 nm and one shoulder at the wavelength value of
245 nm. In general, an optical medium can have many characteris-
tic resonant frequencies (multi-oscillators). The resonances can be
attributed to the lattice vibrations in the infrared region and to the
oscillations of the bound electrons of the atoms in the ultraviolet
and visible regions. In a medium with many electronic oscillators
of different frequencies, the total polarization is proportional to
the dielectric constant and consequently anomalous dispersion of
the refractive index arises in the absorbing region due to electronic
1.0
T
0.8
0.6
0.4
0,830 μm
0.961 μm
1.247 μm
0.2
R
0.0
200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
λ
(nm)
Fig. 3. Transmittance and reflectance spectra for PHDMC thin films.

148
E.M. El-Menyawy et al. / Journal of Molecular Structure 1036 (2013) 144–150
6x105
0.46
0.44
0.42
0.40
0.38
0.36
0.34
0.32
0.30
0.28
0.26
5x105
4x105
3x105
α
2x105
1x105
0
2
3
4
h
5
6
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
ν (eV)
(hν
)2 (eV)2
Fig. 7. Spectral dependence of absorption coefficient,
a
, on h
m
for PHDMC thin films.
Fig. 6. The variation of (n2ꢁ1)ꢁ1 with square photon energy for PHDMC thin films.
transitions between any two atomic states [29]. In non-absorbing
region and as a result of polarization, the dipoles oscillate nearly
with the same frequency (single oscillator). In the wavelength
range 600–2500 nm, the refractive index decreases with increasing
wavelength showing a normal dispersion. The normal dispersion
behavior is analyzed on the basis of the single oscillator model
modified by Wemple and DiDomenico [30]. According to this mod-
el, the refractive index is expressed as
1600
1400
1200
1000
800
EdEo
ν
n2 ¼ 1 þ
;
ð5Þ
600
2
E2o ꢁ ðh
Þ
m
α
400
200
0
where Ed and Eo are the dispersion and oscillator energies, respec-
tively, and h is the incident photon energy. The parameter Ed is a
m
measure of the intensity of electronic inter-band transitions and it
does not depend significantly on the band gap or the density of
the valence electrons; however, Eo can be considered as the average
value of the single oscillator energy. An experimental verification of
the above equation can be obtained by plotting (n2ꢁ1)ꢁ1 versus
square photon energy for PHDMC films as represented in Fig. 6.
The values of the dispersion parameters Ed and Eo as well as the
dielectric constants at high frequency, e1 ¼ n21, are calculated as
25.75 eV, 9.01 eV and 3.86 eV, respectively.
1.5
2.0
2.5
3.0
h
3.5
(eV)
4.0
4.5
5.0
ν
1/2
Fig. 8. Relation between (
a
h
m)
and hm for PHDMC thin films.
dependence of the absorption coefficient on the photon energy
can be expressed as [31]
The absorption index spectra of PHDMC films (Fig. 5) exhibit
four absorption peaks in ultraviolet region (210, 240, 280 and
314 nm) and one peak in the visible region (435 nm). The absorp-
tion peaks are attributed to the electronic transitions across
orbitals. At wavelengths greater than 600 nm, there is no absorp-
m
ahm
¼ Bðh
m
ꢁ EgÞ
ð7Þ
where m = 1/2 and 3/2 for direct allowed and forbidden transitions,
respectively; m = 2 and 3 for indirect allowed and forbidden transi-
tions, respectively, hm is photon energy, Eg is the optical band gap
p–
pꢄ
tion at all.
and B is a parameter depending on transition probability. The vari-
ation of absorption coefficient with incident photon energy was
plotted for both the direct and indirect transitions. The plot of
The absorption coefficient,
well-known equation:
a, of the films is calculated from the
(ahm) m shown in Fig. 8 is found to have the best straight
1/2 versus h
2
c
x
a
¼
k
ð6Þ
line fit which supports the interpretation of indirect allowed transi-
tion rather than the other types of transitions. The values of Eg are
where
x
is the angular frequency and c is the velocity of light. The
obtained by extrapolating the straight lines to (ahm)
1/2 = 0. The opti-
absorption coefficient as a function of photon energy for PHDMC
thin films is depicted in Fig. 7. The films show high absorption coef-
ficient value, as it is in the order of 105 cmꢁ1. The absorption coef-
ficient curve includes two major absorption edges indicating the
presence of two main optical transitions occurring in such films.
Analysis of the absorption coefficient spectra near the threshold
energy is a standard method for determining the type of electronic
inter-band transition and evaluating the optical band gap of
different crystalline and amorphous non-metallic materials. The
cal band gaps of PHDMC thin films are estimated as 2.1 and 3.2 eV
for the onset and the fundamental absorption edges, respectively.
The observed indirect allowed transition is in accordance with
amorphous structure of the films [32].
From Fig. 7, it can be seen that the absorption coefficient shows
a tail before reaching zero value. Fig. 9 demonstrates the semi-
logarithmic plot of the absorption coefficient versus the photon
energy. The relationship is linear verifying the Urbach’s empirical
equation [33]

E.M. El-Menyawy et al. / Journal of Molecular Structure 1036 (2013) 144–150
149
where
DE1 and DE2 are the activation energy at low and relatively
11.5
11.0
10.5
10.0
9.5
high temperatures, respectively, r1 and r1 are constants, kB is the
Boltzmann’s constant and T is the absolute temperature. According
to Eq. (9), as the temperature is increased, more charge carriers
overcome the activation energy barrier and participate in the elec-
trical conduction. The values of
and 0.95 eV, respectively. The magnitude of
D
E1 and
D
E2 are estimated as 0.16
E2 is nearly half the
D
optical band gap that obtained at the onset of the absorption
(2.1 eV). This indicates that the conduction in this region is due to
intrinsic process [35]. Referring to the activation energy estimated
at lower temperatures (E1), the conduction in this region can be as-
cribed to the extrinsic process [35], in which the activation energy
is needed to excite the carriers from the corresponding trap levels to
the conduction band.
9.0
8.5
8.0
7.5
7.0
2.05 2.10 2.15 2.20 2.25 2.30 2.35 2.40 2.45 2.50
4. Summary and conclusions
hν (eV)
Fig. 9. Urbach’s relation for PHDMC thin films.
5-(2-Phenylhydrazono)-3,3-dimethylcyclohexanone (PHDMC)
powder is chemically synthesized in polycrystalline structure with
monoclinic space group, P21/a. The lattice parameters are deter-
mined as: a = 19.932 Å, b = 18.869 Å, c = 13.095 Å,
a = c = 90° and
-2.5
b = 91.5°. Thermally evaporated PHDMC thin films exhibited amor-
phous structure. Fourier transforms infrared indicated that the
thermal evaporation is a suitable technique for obtaining PHDMC
thin films. The refractive and absorption indices of the films are
-3.0
-3.5
-4.0
-4.5
-5.0
-5.5
-6.0
-6.5
found to be independent of film thickness range 0.83–1.247 lm.
The dispersion of the refractive index follows the single oscillator
model, from which the dispersion energy, oscillator energy and
dielectric constant at high frequency are estimated as 25.75 eV,
9.01 eV and 3.86, respectively. The films exhibit absorption coeffi-
cient in the order of 105 cmꢁ1, with two indirect allowed transi-
tions and the corresponding optical band gaps are determined as
2.1 and 3.2 eV. From the electrical conductivity measurements, it
has shown that the compound under investigation is an organic
semiconductor with calculated electronic parameters such as room
temperature conductivity and activation energy.
2.2
2.4
2.6
2.8
103/T (K-1)
3.0
3.2
3.4
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ꢀ
ꢁ
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ð9Þ

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