Department of Physics
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Item Fabrication and Characterization of Self Assembled Molecular Monolayers Based Electronic Devices(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) KIRAN IQBAL KHAN; CIIT/FA19-RPH-006/LHR; Dr. Abdul Sattar; LHR TP 7266Efficient, miniaturized, lightweight, and cost-effective electronic devices are the need of the moment. The main goal of electronic researchers is to increase the performance of FETs, which are the building blocks of microelectronics, but the issue of trade-off between mobility and ION/IOFF is still prevalent in currently used FETs, which decreases its performance. To overcome this, SWCNTs were used as an active region, and Self Assembled Monolayer (SAM) was used as a gate dielectric. Three different SAMs of differing dielectric constant (Octanethiol (OT), Dodecanethiol (DDT), Benzyl Mercaptan (BMT)) were employed as a gate dielectric in SWCNT-FET. Two different concentrations of SWCNTs were used. SAMs were grown by immersion method while SWCNTs were deposited by the drop-casting method. After the preparation of SWCNT-FET, various analyses were performed using different characterization tools. Electrical measurements were done by Keithley source meter. It was observed that CNTFETs with low concentrations had ten times better properties as compared to high concentration ones. Among SAMs, DDT with low concentration showed an optimum balance between ION/IOFF ratio and mobility. Raman and FTIR spectroscopy was used to confirm the successful deposition of SWCNTs and SAMs in fabricated devices. Analysis of CNTFETs showed that they performed very well considering SAMs as the only gate dielectric. Devices performance can be further improved by taking pure semiconducting CNTs as a channel, and passivation of channel surface with SAMs to avoid oxidation and contamination from the environment.Item Preparation and Analysis of Cd Doped ZnO Nanostructures for Third Generation Solar Cell(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Hamna Kanwal; FA19-RPH-048; Dr. Abdul Sattar; LHR TP 7241The third-generation solar cells are one of the leading candidates for photovoltaic applications, due to its low cost and commercial characteristics which are based on III-IV group materials, especially dye sensitized solar cells (DSSCs). In this dissertation, Sol-gel synthesis is used to prepare the Zinc oxide (ZnO) nanoparticles (NPs), Cadmium (Cd) doped ZnO NPs (with different concentrations), and their thin films for cell fabrication. X-Ray diffraction (XRD) was used to investigate the structural properties (crystalline structure and grain morphology) of nanostructured materials. The results showed that the XRD pattern demonstrates that the ZnO nanostructures are crystalline and have a hexagonal structure, as all diffraction peaks match the crystalline structure of pure ZnO. The decreased crystallinity of the Cd-doped ZnO samples, shows that the doping causes increase in 2𝜃 which represents a steady decrease in the lattice, thereby increasing the crystallite size. Optical properties (absorption, transmission, band gap) of doped and undoped materials were analyzed using UV/Vis spectrophotometer. UV/Vis findings indicate that for nanoparticles with 4% Cd doped ZnO maximum absorption is found. The calculated undoped ZnO band gap is 3.25 eV, whereas the band gap for doped materials shows improved outcome (2% Cd doped ZnO has a band gap of 3.12 eV and 4% Cd doped ZnO has a band gap of 3.04% eV). UV/Vis data depicts that the optical band gap decreases as we increase Cd doping. Scanning Electron Microscope (SEM) is used to study the surface morphology of prepared samples. In the analysis of undoped ZnO, the spherical nanoparticles of 100 nm diameter approximately found whereas 2% Cd doped nanostructures are in cubic and hexagonal forms having 120 nm and bigger size clusters. The 4% Cd doped ZnO indicates that as the doping increases, the diameter of the particles grows, and fused together to produce colonies. The solar simulations (J-V measurements) were performed, the photovoltaic parameters such as open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and efficiency (𝜂) were calculated. Simultaneous improvements in photovoltaic performance were achieved by Cd doping. In comparison to others, the ZnO doped with 4% Cd exhibits the higher efficiency (𝜂) of 1.14%Item DFT Study of Electronic Devices Based on Quantum Anomalous Hall Effect(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Ammara Fatima; FA19-RPH-057; Dr. Abdul Sattar; LHR TP 7240The density functional theory (DFT) has been used to a wide range of physics problems, but nothing more effectively than in solid-state physics. Since its original conception in condensed matter physics, it has enlarged materials science, high-pressure physics and mineralogy, solid-state chemistry, and other domains, allowing entire computational sub disciplines to be established [ 1 ]. A broad range of structural, chemical, optical, spectroscopic, elastic, vibrational, and thermodynamic phenomena may be calculated using modern DFT modeling tools. A novel direction is recommended to maintain development to the excellence of findings expected by today's “ab initio” quantum chemistry [ 2 ]. Because of their swiftness and precision, “ab initio” simulations have become an important tool in most materials research, assisting in the clarification of new results as well as influencing new project. DFT is used in variety of applications, one of which is Quantum Anomalous Hall (QAH) Effect.Item Computational Understandings in Voltage and Diffusion Properties for Lithium Battery Cathode Materials.(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Mehreen Tahir; CIIT/FA19-RPH-035/LHR; Dr. Abdul Sattar; LHR TP 7270For the rechargeable lithium ion batteries, a stable olivine material LiMnPO4 has achieved great importance due to its use as a cathode material. In this work, we have studied the electronic structure of LiMnPO4 in the framework of density functional theory (DFT). By using PBE spin polarized SGGA technique with Monkhorst - pack K- point sampling also the basis set FHI Pseudopotentials and Double Zeta polarized, diffusion properties of LiMnPO4, DOS, band structure and surface chemistry of this material by optical absorption spectrum are studied. The electronic conductivity of the LiMnPO4 is demonstrated by density of states. With the help of HTST, the simulated energy barrier for lithium manganese phosphate is 1.8879 eV and calculated is Climbing image Nudged elastic band method is applied to calculate the barrier activation energy of this olivine material and 0.793 eV is obtained. The band gap of 3.69 eV is calculated by applying DFT approximation.