28-07-2012, 03:40 PM
THE ELECTRICAL, OPTICAL AND STRUCTURAL STUDIES ON PHTHALOCYANINE THIN FILMS
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Introduction
Phthalocyanine and its metal complexes have been known for
many years. The metal-free phthalocyanine was first detected by Braun
and ~cherniac' as a minor product in the synthesis of o-cyanobenzamide
from phthalamide and acetic anhydride in 1907, while the first metal
complex was prepared by Diesbach et a/.' in 1927. Linstead used the
term 'Phthalocyanine' derived from the Greek term 'naphtha' (rock oil)
and 'cyanine' (dark blue) t:, describe this particular class of materials.
Since then, there have been extensive studies on the physics and
chemistry of phthalocyanines. These are aromatic hydrocarbons exhibiting
semiconducting properties and hence come under the class of organic
semiconductors.
Organic Semiconductors
Semiconductors play an important role in day today life. They are
broadly classified into two main groups as inorganic semiconductors and
organic semiconductors. Though inorganic semiconductors like
germanium and silicon are extensively used in electronic industry, they
are expected to be replaced by organic semiconductors in the near future.
The electrical conductivity of a semiconductor depends on the
mobility and charge carrier cctncentration. They are low for organic
semiconductors compared to those for inorganic semiconductors.
A comparison of the electrical conduction parameters of the organic
semiconductors and those of inorganic semiconductors is given in Table 1.2.
Molecular Structure
C. E. Dent et a/." reported the structure of the planar
phthalocyanine molecule for the first time. The metal-free phthalocyanine
(H2Pc) has the general formula C32H~8Nosr (CEH~N~)~HItZ i.s chemically
designated as 5, 10, l!i, 20 Tetraazatetrabenzporphyrin or
~etrabenzporphyrazin.'~ The molecule is planar consisting of four
isoindole molecules linked together at the corners of the pyrrole ring by
four nitrogen atoms as shown i r ~F igure 1.3.1.
Electrical Studies
Phthalocyanines are the most extensively studied materials among
the organic semiconductors. :In a series of papers ~ l e y 're~p orted that
HzPc and copper phthalocyanine (CuPc) behave as semiconductors and
proposed that the current is carried by the mobile n-electrons.
vartanyanls reported that the phthalocyanines exhibit semiconducting
behaviour and the presence of oxygen affects the electrical conductivity.
Delacote et ail6 have reported that there are three regions - ohmic,
exponential and square law dependent - in the current voltage
characteristics of CuPc thiri films in metal-insulator-metal (MIM)
configuration. Harrison and ~udewig'~h ave studied the electrical
conductivity and crystal phase changes in phthalocyanines and explained
that the intrinsic conductivity of the a and P-phases does not change due
to rearrangement of molecules. ~amann'' has reported that the electrical
properties at high fields are determined by an exponential trap
distribution. Barbe and westgatelg investigated the temperature
dependence of the space-charge-limited (SSLC) densities in HzPc single
crystals and proposed the electron trapping model. Aoyagi et a/.' made
the electrical conductivity studies in H~Pc, CuPc, ZnPc and NiPc single
crystals. Ukei et a/."
[attachment=29411]
Introduction
Phthalocyanine and its metal complexes have been known for
many years. The metal-free phthalocyanine was first detected by Braun
and ~cherniac' as a minor product in the synthesis of o-cyanobenzamide
from phthalamide and acetic anhydride in 1907, while the first metal
complex was prepared by Diesbach et a/.' in 1927. Linstead used the
term 'Phthalocyanine' derived from the Greek term 'naphtha' (rock oil)
and 'cyanine' (dark blue) t:, describe this particular class of materials.
Since then, there have been extensive studies on the physics and
chemistry of phthalocyanines. These are aromatic hydrocarbons exhibiting
semiconducting properties and hence come under the class of organic
semiconductors.
Organic Semiconductors
Semiconductors play an important role in day today life. They are
broadly classified into two main groups as inorganic semiconductors and
organic semiconductors. Though inorganic semiconductors like
germanium and silicon are extensively used in electronic industry, they
are expected to be replaced by organic semiconductors in the near future.
The electrical conductivity of a semiconductor depends on the
mobility and charge carrier cctncentration. They are low for organic
semiconductors compared to those for inorganic semiconductors.
A comparison of the electrical conduction parameters of the organic
semiconductors and those of inorganic semiconductors is given in Table 1.2.
Molecular Structure
C. E. Dent et a/." reported the structure of the planar
phthalocyanine molecule for the first time. The metal-free phthalocyanine
(H2Pc) has the general formula C32H~8Nosr (CEH~N~)~HItZ i.s chemically
designated as 5, 10, l!i, 20 Tetraazatetrabenzporphyrin or
~etrabenzporphyrazin.'~ The molecule is planar consisting of four
isoindole molecules linked together at the corners of the pyrrole ring by
four nitrogen atoms as shown i r ~F igure 1.3.1.
Electrical Studies
Phthalocyanines are the most extensively studied materials among
the organic semiconductors. :In a series of papers ~ l e y 're~p orted that
HzPc and copper phthalocyanine (CuPc) behave as semiconductors and
proposed that the current is carried by the mobile n-electrons.
vartanyanls reported that the phthalocyanines exhibit semiconducting
behaviour and the presence of oxygen affects the electrical conductivity.
Delacote et ail6 have reported that there are three regions - ohmic,
exponential and square law dependent - in the current voltage
characteristics of CuPc thiri films in metal-insulator-metal (MIM)
configuration. Harrison and ~udewig'~h ave studied the electrical
conductivity and crystal phase changes in phthalocyanines and explained
that the intrinsic conductivity of the a and P-phases does not change due
to rearrangement of molecules. ~amann'' has reported that the electrical
properties at high fields are determined by an exponential trap
distribution. Barbe and westgatelg investigated the temperature
dependence of the space-charge-limited (SSLC) densities in HzPc single
crystals and proposed the electron trapping model. Aoyagi et a/.' made
the electrical conductivity studies in H~Pc, CuPc, ZnPc and NiPc single
crystals. Ukei et a/."