Characterization of pure and dopant tio2 thin films for gas sensors applications

مقدم أطروحة جامعية

Yahya, Khalid Z.

مشرف أطروحة جامعية

al-Haddad, Rad M. S.
Haydar, Adawiya Jumah

الجامعة

الجامعة التكنولوجية

الكلية

-

القسم الأكاديمي

قسم هندسة الليزر و الإلكترونيات البصرية

دولة الجامعة

العراق

الدرجة العلمية

دكتوراه

تاريخ الدرجة العلمية

2010

الملخص الإنجليزي

Titanium dioxide (TiO2) has been extensively studied and demonstrated to be suitable to detect toxic gases such as CO and NOx that affect the quality of life, Therefore TiO2 thin films are good candidates in the gas sensor industry .In addition noble metal dopants to the titanium dioxide materials make them sensitive to CO gas.

In this work, a double frequency Q-switching Nd : YAG laser beam (λ = 532nm, repetition rate 6 Hz and the pulse duration 10ns)has been used, to deposit TiO2 thin films pure and doped with (Ag, Pt, Pd and Ni ) at various doping percentages (1wt.

%, 2 wt.

% and 3 wt.

%) on glass and Si (111) substrates to be activated by visible light irradiation as well as ultraviolet irradiation.

Basic material characterization has been carried out.

Many growth parameters have been considered to specify the optimum condition, namely substrate temperature (200-500˚C), oxygen pressure (10-5 x 10-2 mbar) and laser fluency energy density (0.8, 1.2 and 1.8) J / cm2.

The structure properties of TiO2 pure and doped with noble metal were investigated by means of x-ray diffraction.

As a result, it has been found that film structure and properties strongly depended on substrate temperature and doping concentration.

X-ray diffraction (XRD) showed that at substrate temperatures higher than 300 °C the structure of the deposited thin films changed from amorphous to crystalline corresponding to the tetragonal TiO2 anatine phase, and at substrate temperature Ts = 500°C produced both rutile and anatine phases.

It has been found that 3 % wt (Ag, Pt, Pd and Ni) doped TiO2 thin film was the most sensitive element to CO gas.

The surface morphology of the deposits materials have been studied by using scanning electron (SEM) and atomic force microscopes (AFM).

The grain size of the nanoparticles observed at the surface depended on the substrate temperature, where 500°C was the best temperature and partial pressure of oxygen 5 × 10-1 mbar was the best pressure during the growth process.

TiO2 doped with Pt metal has the smallest grain size 1nm), 1RMS roughness increased with increasing substrate temperature (Ts) which are (11.2nm) for thin films deposited at (500) ºC and the samples are very rough with RMS value of (28 nm) for TiO2 thin films doped with 3 % UV-VIS transmittance measurements have shown that our films are highly transparent in the visible wavelength region, with an average transmittance of 90 % which makes them suitable for sensor applications Dopants such as Ag and Pt shifted the absorption edge of TiO2 into the visible region .The optical band gap of the films has been found to be 3.2 eV for indirect transition and 3.6 eV for direct transition at 400˚C.

The refractive index (n) and extinction coefficient (K) decreased as the substrate temperature increased In addition the photoluminescence spectrum analyses of all the thin films showed that there were two kinds of luminescence transitions involved when the thin film was excited with energy higher than the band gap value (3.2 eV) .

The intensity of two peaks, a lied in the UV spectrum (375 nm) and B lied in the visible spectrum (525 nm) the sensitivity toward CO gas has been measured under 50 ppm concentrations.

TiO2 doped with noble metal has sensitivity higher than pure TiO2 whereas TiO2 doped with Pt metal deposited on Si (111) has maximum sensitivity to CO gas with value of (23 %) with best annealing operation temperature at 250°C, and resistance decreased reached (109 Ω) with increasing doping concentration due to increase in the sensing current reached (10 nA) of the TiO2 films.

التخصصات الرئيسية

الفيزياء

الموضوعات

• الأجسام الصلبة

• APA
• MLA
• AMA

لغة النص

الإنجليزية

نوع البيانات

رسائل جامعية

رقم السجل

BIM-305334