تحضير وتوصيف أغشية كبريتيد الرصاص المطعمة بالكادميوم والكروم بطريقة الترسيب بالليزر النبضي لتطبيقات المتحسس الغازي

Preparation and characterization of PbS films doped by Cd and Cr via pulsed laser deposition for gas sensor applications

Abstract

In this work, cadmium-chromium-doped(X=2,4,6)Wt% lead sulfide PbS thin films were deposited on a glass substrate at room temperature by means of a pulsed laser deposition (PLD) technique. The effect of laser energy and different doping ratios on the structural and optical properties of PbS films were studied using Nd:YAG laser with different laser energies from (200 – 350) mJ in increments of 50 mJ per step. The number of laser pulses was fixedly set to 100 pulses per sample.
The structures of (PbS, PbS:Cd and PbS:Cr) powder and thin films were studied using X-ray diffraction technique. X-ray study showed that the structure is polycrystalline and monoclinic with a preferred orientation plane (200) and that the crystal size increases with increasing laser energy and increases at different doping ratio .
Atomic force microscopic measurements (AFM) confirmed that the films grown by PLD technique have good crystalline and homogeneous surface. The average particle diameter for all prepared films is less than 100 nm ,so it is in the range of nanomaterial’s.
The optical measurements were studied using UV-ViS- spectrophotometer. The results showed that the (PbS, PbS:Cd and PbS:Cr) thin films have direct allowed energy gap transition and the absorbance of films increases with the increasing of laser energy and increases at different doping ratio . Also, the optical constants such as the refractive index(n), absorption coefficient (α), extinction coefficient(k) and dielectric constant real and imaginary parts(εr,εi) have been calculated. The energy gap increases with increases of laser energy and increases at different doping ratio (1.5 – 2.8) eV by doping with cadmium and (1.6 -1.8) eV by doping with Chrome.
The gas sensor measurements showed that the best sensor for NO2 gas was for the sample with a percentage of 5% PbS:Cd X = 4% with a sensitivity of 137% at 523 K and the sensitivity of the sample was decreased for PbS and for NH3 gas at an energy of 250 mJ at 523 K to 19%.