An-Najah National University Physics Symposium Department of Physics May 2007

بسم الله الرحمن الرحيم قَالَ رَبِّ اشْرَحْ لِي صَدْرِي {25} وَيَسِّرْ لِي أَمْرِي {26} وَاحْلُلْ عُقْدَةً مِّن لِّسَانِي {27} يَفْقَهُوا قَوْلِي {28} ( سورة طه )

Electrode material effect on ac conductivity, capacitance and loss tangent of the organic zinc phthalocyanine, ZnPc, semiconducting thin films

Prof. A. M. Saleh 1, Mr. A. O. Abu-Hilal 1, 2, Prof. R. D. Gould 2, and Prof. M. I. Abu Taha 1 1- Al-Quds University 2- Keele University, UK

Properties Of Phthalocyanine: * Planer aromatic organic compounds, they exist in three forms  -,  - and  -forms. * They exhibit semiconducting properties. (A prototype of organic semiconductors).

* Conductivity depends on amount of gas absorbed. (gas sensor) * They are thermally stable and having very intense color. Therefore they are used: 1- As pigments or dyes in textile industry 2- As catalysts in petroleum products, and 3- In Lubricating greases

* A good system to study its electrical, mechanical, structural, optical and magnetic properties. * Many Medical Applications * Many Technological and Industrial applications

The Crystal Structure

Experimental * Phthalocyanine, Pc, thin films were thermally evaporated, under high vacuum, at low evaporation rates. * Films were sandwiched between two Al or Au electrodes, Au-Pc-Au or Al-Pc-Al structure.

Film thickness was measured using a computerized Planer Surfometer stylus instrument. Film temperature was measured by a chromel-alumel thermocouple attached to a digital thermometer.

A.C. parameters (conductivity, capacitance and loss tangent) were measured by a Hewlett - Packard 4276 LCZ meter. D.C. parameters were measured by a stabilized power supply and a Keithley picometer.

Measurements: 1:- Structural Analysis: * Dependence of structure on deposition rates. * Dependence of structure on film thickness.

2:- D. C. Parameters * I-V characteristics at room temperature. I-V Characteristics as a function of temperature.

3:- A. C. Parameters Conductivity as a function of temperature and frequency. Capacitance as a function of temperature and frequency. Loss tangent as a function of temperature and frequency

A. C. Conductivity σ (ω) was measured in the temperature range 140 to 430 K and frequency range kHz σ (ω) α ω s, s ≤ 1 suggesting a dominant hopping conduction process at Low T. At high T, a band conduction process was observed for both Al and Au Electrodes

A: Al-electrode B: Au-electrode

To check the anomaly in σ (ω) ( No thermal hysterises was found after recycling)

2: Capacitance measurements C versus d (film thickness) C versus T and f

C Versus f

C versus T

Loss tangent as a function of f and T The loss tangent [ tan δ ] is a measure of the energy loss in the medium

Loss tangent versus f

tan δ versus T

Theoretical

Equivalent circuit model This equivalent circuit model assumes that the dielectric medium could be satisfactorily represented by an inherent capacitive element C, unaffected by both the frequency and temperature, in parallel with a discrete resistive element R due to the dielectric film.

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