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Home > Preparation, Characterization and Applications of Quantum Dots in Conducting Polymer Composites and Low Cost Devices

Preparation, Characterization and Applications of Quantum Dots in Conducting Polymer Composites and Low Cost Devices

Thesis Info

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Author

Chughtai, Ambreen Ayub

Program

PhD

Institute

Quaid-I-Azam University

City

Islamabad

Province

Islamabad.

Country

Pakistan

Thesis Completing Year

2019

Thesis Completion Status

Completed

Subject

Physics

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/12619/1/Ambreen%20ayub%20chughtai%20QAU%20isb%20physics%20year%202019.docx

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676726998170

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Owing to the growing importance of quantum dots in future materials and devices, this thesis mainly concerns with the synthesis, characterization and applications of quantum dots in conducting polymer composites and devices such as Schottky diodes and quantum dot sensitized solar cells (QDSSCs). Quantum dots (QDs) involved in these studies include II-VI semiconductors cadmium selenide (CdSe) and cadmium sulfide (CdS) and IV-VI semiconductor lead sulfide (PbS). As regards the work related to application of QDs in functional materials, CdSeQDs have been synthesized, characterized and incorporated in polyaniline (PANI). CdSe/PANI nanocomposites have been prepared with varying amounts of CdSe QDs in PANI by in-situ polymerization technique. Pure PANI, CdSeQDs and their composites have been characterized by using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and UV-VIS absorption spectroscopy. The surface morphologies have been investigated by Scanning Electron Microscopy (SEM). The electrical and dielectric properties have been studied by using 4-probe mechanism and LCR meter respectively. The DC conductivity of the nanocomposites has been studied in the temperature range from 298 to 368 K and it is increased with the temperature risedepicting the semiconducting behavior of the samples. DC conductivity is found to follow Mott’s 1D (one dimension) variable range hopping model. It is observed that AC conductivity of the samples is enhanced with the increase in temperature and the frequency dependent AC conductivity follows the universal power law. Dielectric behavior of the nanocomposites discussed as a function of frequency and temperature exhibits a rapid fall of dielectric constant with rise in frequencywhich can be described by Maxwell-Wagner capacitor model. It is observed that the dielectric constant is increased with the increasing temperature and also with the increase of QDconcentration in the nanocomposites. Two Schottky devices have also been fabricatedto study the device application ofCdSe/PANI nanocomposites. One device was fabricated employing layer-by-layer deposition of PANI and CdSe films on PEDOT-PSS/ITOcoated glass substrate {ITO (indium tin oxide)/PEDOT-PSS [poly (ethylene dioxy thiophene) poly (styrene sulphonate)]/PANI (polyaniline)/CdSe (cadmium selenide)} and the other by depositing PANI-CdSeQDs composite film on the same substrate (ITO/PEDOT-PSS/CdSe-PANI) using spin coating technique. The diode performance parameters have been compared and J-V characteristics of these devices show a rectifying contact with aluminum metal, however, with variation in performance parameters like barrier height, ideality factor and reverse saturation current density, the ITO/PEDOT-PSS/CdSe-PANI/Al (composite assembly) device exhibits better diode performance as compared to ITO/PEDOT-PSS/PANI/CdSe/Al (layer-by-layer) device.This work has been presented in Chapter 5 of this thesis. Fabrication and study of two series of low cost QDSSC devices prepared by varying successive ionic layer adsorption and reaction (SILAR) cycles: ITO/TiO2/CdS/CdSe/ZnS QDSSCs and FTO/TiO2/PbS/CdS/CdSe/ZnS QDSSCsare reported in Chapter 6 of this thesis.The structural, optical, morphological and electrical properties of these devices have been studied. Different modes of vibrations in the deposited films have been studied by RAMAN spectroscopy. X-ray Diffraction (XRD) patterns show that the particle size of the QDs increases with the number of SILAR cycles. However, the intensity peak of CdS QDs has not been observed after three SILAR cycles. UV-VIS spectroscopy measurement of the devices show enhancement in absorbance upto three SILAR cycles and saturation for further SILAR cycles. The SEM images of devices reveal capping of CdS QDs by CdSe QDs for four and higher SILAR cycles, resulting decrease in power conversion efficiency (PCE) of these devices. The J-V characteristics show that in order to achieve the best performance of QDSSC, the optimum parameters for CdS and CdSe QDs deposition are three cycles. The highest PCE of 5.0 % has been achieved after an optimization of dipping SILAR cycles. After adding 3 SILAR cycles of PbS QDs, the PCE value has been improved upto 6.43 %. Electrochemical Impedance Spectroscopy has been performed under dark conditions in order to discuss the physical mechanism of QDSSCs. Maximum values of recombination resistance (Rrec) and constant phase element (CPE) have been found for efficient devices with three SILAR cycles: ITO/TiO2/3CdS/3CdSe/3ZnS and FTO/TiO2/3PbS/3CdS/3CdSe/3ZnS QDSSCs. Lower and higher numbers of SILAR cyclesgive lower values of Rrec and CPE in all other QDSSCs. This shows that the charge carriers in QDSSCs with three SILAR cycles can be efficiently transported because of longer carrier lifetimes in these devices.
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صادق جب لکھنے بیٹھا ہے

صادق جب لکھنے بیٹھا ہے
حمد سے ہی آغاز کیا ہے

ساری تعریفیں اُس کی ہیں
پہلے اُس کا نام لیا ہے

روزی روٹی اُس کے ذمے
بن مانگے سب کو دیتا ہے

کیڑے پالے پتھر اندر
بھوکا کوئی نہیں سوتا ہے

ہندو مسلم فرق نہیں ہے
ہر کوئی نعمت کھاتا ہے

اک ہم ہیں نا شکرے بندے
اور وہ کرم کیے جاتا ہے

اُس کے موسم اُس کی بارش
وہ جب چاہے برساتا ہے

اُس کی فصلیں اُس کی کھیتی
دانے سے خوشا بنتا ہے

صادقؔ کیا تعریف لکھے گا
بس فعلن فعلن کرتا ہے

برما میں روہنگیا مسلمانوں کے مذہبی مسائل اور اس کے اسباب و اثرات

Buddhism is dominated by such other characteristics as sympathy, pity, and kindness. Furthermore, it forbids all kind of cruelty, violence, murder, brutality, and giving pain to any living creature. However, contrary to his teachings, the way his followers have targeted the Rohingya Muslims with violence and atrocities only shows how little they follow Gautama Buddha. Right from the independence of Burma, Buddhists,  declaring Muslims as a threat, started their genocide, which involved attacking their mosques, their homes, dishonoring Muslim women, and harassing the Muslims without any reason. This compelled Muslims to leave their homes and migrate. The recent wave of violence, starting in June 2012,  seriously affected the Muslim majority province of Arakan. Keeping in mind, Arakan is one of the fourteen Burmese provinces, where Islam have ruled since the time of Isalmic Caliphate. Unfortunately, in 1784, Burmese Prince Bodo Phia violated this garden of Islam by carrying out Muslim genocide. He banned all symbols of Islam such as pilgrimage, sacrifice,  prayers, Friday and Eid Prayers, and preaching. This study points out the religious problems and issues of Muslims believers in Arakan including its impact, causes and consequences on their lives. The analytical research Methodolgy has been adopted in this studty.

Energy Efficiency in Wireless Sensor Networks Using Collaborative Communication in Wideband Channels

Wireless Sensor Network (WSN) consists of a large number of tiny sensor nodes capable of being deployed in a range of environments in random or regular fashion. These networks are getting attention of the research community due their broad application domain. They can be applied in many fields like health care, homes, military, environment monitoring or in any commercial environment. Due to resource constrained nature of the nodes, these networks need energy efficient solutions. Since a network operation is many times more expensive than local operation, therefore very efficient and highly adaptable communication systems need to be developed for these networks in order to increase a node’s life time. To avoid resource limitation and achieve energy efficiency collaborative communication combines the power of multiple sensor nodes to transmit the same data at the same time to a base station. This research focuses on energy efficiency in Body Area Networks, sensor networks with multipath and wideband channels. All these models are investigated in the presence of Rayleigh Fading Additive White Gaussian Noise (AWGN). The received signals from collaborative nodes at the base station are considered to be out-of-phase (imperfect phase synchronization). The ultimate goal is to investigate the effect of collaborative communication on energy efficiency, channel capacity gain, received power, BER in Wireless Sensor Networks using narrow-band, multipath and wideband channels. A synchronization process is designed to reduce the phase and frequency synchronization errors among the transmitter (Collaborative) nodes and the receiver (base station). A theoretical model for unsynchronized phase using collaborative communication in the presence of Additive White Gaussian Noise (AWGN) and Rayleigh fading is proposed, analyzed and simulated. The performance of collaborative communication system is evaluated by investigating several figures of merits including “received power”, “BER”, “energy efficiency” and “channel capacity”. The theoretical findings of collaborative communication system are verified using Monte Carlo simulation by considering the parameters of “off-the-shelf” products i.e. “CC2420” and “AT86RF212”. Theoretical analysis of the derived models for received power gain, BER, energy efficiency and capacity gain show that an increase in the number of collaborative nodes also increases the gain in received power and capacity of the system whereas inversely effect BER. Simulation results for phase error intervals f?0:1 0:1g; f?0:2 0:2g; f?0:3 0:3g and f?0:4 0:4g in case of BAN show a 0:475N2 to 0:8N2 gain in received power whereas to achieve a BER of 10?3, the required transmited power decreases from 12:5dB to 10dB with an increase Anwar Ghani: 70-FBAS/PHDCS/F11 Page viii of 153 in the number of nodes from 5 to 11 over the phase error interval f?0:2 0:2g. This required power to achieve the desired BER raises 15dB to 12:5dB in case of phase error f?0:4 0:4g. In multipath communication the gain in received power improves from 0:49N2 to 0:83N2 whereas required power for BER of 10?3 in case of f?0:1 0:1g decreases from 10dB to 7:5dB and for f?0:3 0:3g the decrease is from 12dB to 9dB. In case of wideband communication the gain in received power ranges from 0:51N2 to 0:93N2 and the required power for BER of 10?3 for single node is 7:5dB and for nodes from 5 to 11 it is 3dB to 2dB. For trade-off-analysis of energy saving and transmission distances performed for off-the-shelf devices “CC2420” and “AT86RF212”, shows in all scenarios “CC2420” stabilizes before “AT86RF212”. On the basis of these results it can be concluded that collaborative communication is energy efficient and suitaWireless Sensor Network (WSN) consists of a large number of tiny sensor nodes capable of being deployed in a range of environments in random or regular fashion. These networks are getting attention of the research community due their broad application domain. They can be applied in many fields like health care, homes, military, environment monitoring or in any commercial environment. Due to resource constrained nature of the nodes, these networks need energy efficient solutions. Since a network operation is many times more expensive than local operation, therefore very efficient and highly adaptable communication systems need to be developed for these networks in order to increase a node’s life time. To avoid resource limitation and achieve energy efficiency collaborative communication combines the power of multiple sensor nodes to transmit the same data at the same time to a base station. This research focuses on energy efficiency in Body Area Networks, sensor networks with multipath and wideband channels. All these models are investigated in the presence of Rayleigh Fading Additive White Gaussian Noise (AWGN). The received signals from collaborative nodes at the base station are considered to be out-of-phase (imperfect phase synchronization). The ultimate goal is to investigate the effect of collaborative communication on energy efficiency, channel capacity gain, received power, BER in Wireless Sensor Networks using narrow-band, multipath and wideband channels. A synchronization process is designed to reduce the phase and frequency synchronization errors among the transmitter (Collaborative) nodes and the receiver (base station). A theoretical model for unsynchronized phase using collaborative communication in the presence of Additive White Gaussian Noise (AWGN) and Rayleigh fading is proposed, analyzed and simulated. The performance of collaborative communication system is evaluated by investigating several figures of merits including “received power”, “BER”, “energy efficiency” and “channel capacity”. The theoretical findings of collaborative communication system are verified using Monte Carlo simulation by considering the parameters of “off-the-shelf” products i.e. “CC2420” and “AT86RF212”. Theoretical analysis of the derived models for received power gain, BER, energy efficiency and capacity gain show that an increase in the number of collaborative nodes also increases the gain in received power and capacity of the system whereas inversely effect BER. Simulation results for phase error intervals f?0:1 0:1g; f?0:2 0:2g; f?0:3 0:3g and f?0:4 0:4g in case of BAN show a 0:475N2 to 0:8N2 gain in received power whereas to achieve a BER of 10?3, the required transmited power decreases from 12:5dB to 10dB with an increase Anwar Ghani: 70-FBAS/PHDCS/F11 Page viii of 153 in the number of nodes from 5 to 11 over the phase error interval f?0:2 0:2g. This required power to achieve the desired BER raises 15dB to 12:5dB in case of phase error f?0:4 0:4g. In multipath communication the gain in received power improves from 0:49N2 to 0:83N2 whereas required power for BER of 10?3 in case of f?0:1 0:1g decreases from 10dB to 7:5dB and for f?0:3 0:3g the decrease is from 12dB to 9dB. In case of wideband communication the gain in received power ranges from 0:51N2 to 0:93N2 and the required power for BER of 10?3 for single node is 7:5dB and for nodes from 5 to 11 it is 3dB to 2dB. For trade-off-analysis of energy saving and transmission distances performed for off-the-shelf devices “CC2420” and “AT86RF212”, shows in all scenarios “CC2420” stabilizes before “AT86RF212”. On the basis of these results it can be concluded that collaborative communication is energy efficient and suitable for resource limited networks like WSN.ble for resource limited networks like WSN.