مناقشة رسالة دكتوراه

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مناقشة رسالة دكتوراة

جرت في قسم العلوم التطبيقية ، الجامعة التكنولوجية مناقشة طالبة الدكتوراه (انتصار محمد خضير) عن رسالته الموسومة (Compare Between Doping and Deposition Gold (Au) Nanoparticles with Porous Silicon for Gas Sensing (CO2 Gas) Application) وذلك يوم الاربعاء 29/11/2017 وعلى قاعة المرحوم أ.د عبد المطلب ابراهيم الشيخ
 
     abstract
 
In this work, porous silicon (PS) layer is prepared by electrochemical etching (ECE) approach using p-type silicon (100) orientation, with resistivity 1.5-5Ω.cm. The etching solution consists of HF and ethanol, at different current densities 5, 15 and 25 mA/cm2, and etching time of 15min. The different properties of the samples have been studied. Those include Morphology properties studied by AFM, the structural by X-ray diffraction and chemical properties achieved by Fourier Transform Infrared (FTIR) spectroscopy. X-ray diffraction (XRD) investigation is appeared broad a diffraction peak when the size of crystal becomes inside nanometer range where the width peak depends on size. Reflectivity for bulk and PS is investigated for PS sample of PS layer prepared at 15 mA/cm2, etching time 15 min and HFc 20%. The PL for the sample is determined in air and different organic chemical vapor like Ethanol, n-Hexane and Trichloroethylene and CO2 gas.
Gold nanoparticles (AuNPs) have been prepared by laser ablation technique of gold target submerged in double distilled deionized water (DDDW) at different laser energies 160, 300, 460 and 600 mJ at 500 pulses number of pulse, using Nd:YAG laser at 1046 nm .Then AuNPs deposited on PS were prepared at 15 mA/cm2, with etching time 15 min and HFc 20%, by drop casting (5 drop).The influence of gold colloid on PS characteristics has been investigated. The variation of the surfaces' roughness and morphology after noble metal modification was exhibited by AFM, while, FTIR characterization techniques confirmed the presence of Si-Au bond .The photoluminescence (PL) spectroscopy revealed that the intensity strongly depends on AuNPs deposition and effected by organic vapor chemical and CO2 gas where the PL intensity decreased (PL quenching) when exposed to this organic vapor and gas.
AuNPs were formed by applying the seed-growth .The size of nanoparticle depends on the amount of seed added to solution growth. Solutions of gold suspension would be characterised via UV-Vis spectrophotometer, after that using solution by adding to HF concentration of using to prepare PS by electrochemical etching. The influence of AuNPs on PS characteristics has been investigated. The morphology characteristics for samples investigated by AFM and the study of structural properties by using XRD was also carried out, while,
FTIR characterization techniques proved Si-Au bond. The PL spectroscopy revealed that the intensity strongly depended on AuNPs prepared by chemical reduction with different amount of seed and effected by chemical organic vapor and CO2 gas. PL is decreased PL quenching when exposed to this organic vapor and gas.
PL quenching in the presence of organic vapor was found by decreasing radiative recombination of exciton that happen under the effect of the dielectric constant of the medium, and in CO2 PL is quenched because of the formation COˉ ion. The absorption of CO2 increase the concentration of holes at surface. The injection of hole into valance band of porous silicon cause nonradiative decay of the excitation responsible for the extent of PS PL.
Sensitivity of samples PS and AuNPs/PS, prepared by laser ablation and chemical method for CO2 gas study by the effect of the gas on electrical properties curve I-V found the current increased when exposed to gas because of the increase of the hole. The sensitivity of samples contained AuNPs is higher than samples of PS alone.
Electrical measurements of the samples were done and found that the AuNPs enhanced electrical properties of this sample where the conductivity is increased, current increased by increasing voltage because of schottky junction between AuNPs and PS layer by increasing the voltage of the resistance junction decreased thus current increased.

 

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