Department of Physics
Permanent URI for this communityhttps://repository.cuilahore.edu.pk/handle/123456789/24
Browse
16 results
Search Results
Item Particle Motion and Parametric Constraints of Spherically Symmetric Space-time Using Observational Data(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2024) Kashif Rehman; CIIT/SP23-RPH-023/LHR; Dr. Abdul Sattar; LHR TP 9642This study focuses on parameters of spherically symmetric PRZ space-time and observa- tional test and implications on various astrophysical phenomena, Classical solar system tests arpund S2 star and Supermassive BH SgrA* at center of Milky way and studying QPO. The main aim to constrain the PRZ spacetime parameters. This is contribute to our understanding of GR and potential deviation in strong gravitational regimes.Item Synthesis and Characterization of Devices Based on Atomically Thin 2D Materials(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) Umer Ahsan; CIIT/SP21-RPH-001/LHR; Dr. Abdul Sattar; LHR TP 8148Future two dimensional materials offer great promise for nanoelectronics as conventional semiconductor advancements are highly limited in terms of power and performance dissipation for new technology nodes. Since great carrier mobility is necessary for low voltage device operations and high performance, greatly scaled field-effect transistors with minimal short-channel effects are made possible by the atomic thickness of 2D materials. Interface engineering is essential for improving the performance of 2D layered semiconductor devices as well as conventional electronics. Defect free nature of Graphene, uniformity, inert nature and being very thin reduce the amount of interfacial interaction and provide well defined interfaces with MoS2. The work function of graphene and MoS2 has a very small difference which makes the charge carriers injection easy. Using Graphene as the source and drain electrodes results in an increase in the mobility. MoS2 based field-effect transistors (FETs) exhibit high threshold voltage hysteresis (VTH) due to interface traps present at their gate interfaces. In order to address the problem, the VTH of MoS2 FETs is dramatically decreased by adding a passivation layer made of 3-aminopropyltriethoxysilane (APTES) at the gate interface of MoS2/SiO2 due to the passivation of the interface traps. Verification by contact angle spectrometry confirms the successful deposition of self-assembled monolayers (SAMs). Two-dimensional graphene and MoS2 are produced via mechanical exfoliation and transferred using a dry transfer process with Polydimethylsiloxane (PDMS), while SAMs are created using the immersion method with PDMS. The layer count of two-dimensional materials is determined through Raman spectroscopy by analyzing the frequency difference between peaks. The electrical performance of the FET demonstrates an improvement in the mobility of the transistors, up to 103 cm2/Vs, when employing graphene electrodes. The mobility increases to 135 cm2/Vs and the threshold voltage decreases via APTES passivation. Both devices exhibit a modest on/off ratio. The insertion of an interfacial layer between the semiconductor and electrode results in a significant reduction of contact resistance. The use of n-type graphene as electrodes will lead to higher mobility. The channel of the field effect transistor (FET) can be protected from contamination through the utilization of hydrophobic self-assembled monolayers, which will passivate the channel from the top.Item DFT Studies of Organic-2D Material Heterostructures for Optoelectronic Devices(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) Muhammad Ikram; CIIT/FA20-RPH-035/LHR; Dr. Abdul Sattar; LHR TP 79922D nano materials have received a lot of attention in recent years due to their physical, chemical, electronic, and optical properties. After the discovery of graphene, more research is underway to understand the basics of these 2D materials. Because of their outstanding stability in the ambient conditions, they have become very popular in the research community. 2D materials such as monolayer MoS2 exhibit wide band gap and low carrier mobility in comparison to graphene. Such electrical and optical properties are hurdle on their use, especially in photo detectors. Therefore, some work needs to be done to improve them electrical and optical properties. Heterostructures of 2D materials have helped greatly in band gap engineering. However, due to the requirements of lattice matching in order to from a heterostructure between two 2D-layers, available combinations and possibilities become limited. Organic molecules readily form heterostructure with 2D materials and there is no limitation of lattice matching, there for making them ideal for future electronic devices. A lot of work has been done showing the formation of 2D structures of organic materials and 2D materials with exceptional qualities such as interlayer charge transfer and formation of exciton which are of critical importance in opto-electronic devices [1]. However, the mechanism and underlying physics is still not well understood. To improve their electronic structure, we must have a deeper understanding at the atomic level. DFT helps us to study the electronic properties such as band structure and density of states. It also provides an in-depth understanding of the electronic behavior of 2D objects with planer symmetry. In this study heterostructures of MoS2 with organic materials such as ZnPc, CuPc and pentacene will be studied using DFT. The Main goal of the study is to propose new organic material as a suitable candidate for optoelectronic devices. To investigate the electrical and physical properties of organic-2D materials, DFT calculations will be performed using the Atomistic Tool kit (ATK). The result will help guide future experimental work for optoelectronic devices [2].Item Fabrication of Electronic Devices Based on Near Percolation Nanotube Networks(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Muhammad Tayyab Idrees; CIIT/SP20-RPH-045/LHR; Dr. Abdul Sattar; LHR TP 7694Electronic gadgets that are efficient, compact, light, and cost-effective are in high demand. The fundamental objective of the researchers is to improve the performance of FETs, which are the building blocks of microelectronics. However, the trade-off between mobility and ION/IOFF remains a problem in today's FETs, lowering their performance. The Problems such as the instability of gate dielectric to withstand high threshold voltage in currently used CNTFETs are still unresolved. Also, single CNT based transistors are hard to realize for commercial used due to complexity of the fabrication method. To overcome these problems, firstly, self-assembled Monolayers (SAMs) can be used as a gate dielectric. Secondly to achieve single path CNT active region, lowest possible area coverage of carbon nanotubes much closer to percolation nanotube networks can be used. 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 different dielectric constants (Octanedithiol (ODT), Dodecanethiol (DDT), Cyclohexanethiol (CHT)) 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. The effective deposition of SWCNTs and SAMs in fabricated devices was confirmed by Raman and FTIR spectroscopy. When CNTFETs were analyzed with SAMs as the only gate dielectric, they performed exceptionally well. Using pure semiconducting CNTs as a channel and passivating the channel surface with SAMs to prevent oxidation and contamination from the environment can boost the device's performance even further.Item DFT Studies of Electrical and Optical Properties of Graphene Quantum Dot Based Devices(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Shabnum Rani; CIIT/SP20-RPH-013/LHR; Dr. Abdul Sattar; LHR TP 7710Graphene quantum dots (GQD) are tiny particles, which have novel properties. These properties play a vital role in innovative devices like sensors, energy storage and solar cell. Transition metal dichalcognised combining with graphene quantum dots have unique photoluminescence properties. Photovoltaic, photodectors and spintronic are examples of TMDCs with graphene quantum dot based devices. Density Functional Theory (DFT) is an essential tool to understand and explore the electronic and optical properties of TMDC/GQD. To study many-body electronic system Atomistic tool kit (ATK) package will be used along with local density approximation (LDA) and Generalized Gradient Approximation (GGA) as exchange and correlation function. Simulated data would be used to determine the I-V characteristic, density of states and structural arrangement. We will calculate the density of state, band structure, transmission spectra, optical spectrum, Eigen state and projected density of state, to understand the best results of TMDCs i.e. (MoS2, MoSe2, WS2, WSe2) with Graphene quantum dot. This project will try to pin-point the ideal configuration of a modified GDQs for its application in photodectors and spintronic.Item Synthesis and Characterization of Graphene Quantum Dots for Electronic and Photonics Devices(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Ammara Javed; CIIT/SP20-RPH-063/LHR; Dr. Abdul Sattar; LHR TP 7720People interpret the term "micro world" in a variety of ways. The surface-to-volume relationship is defined as the intermediary between atoms and solids. When chemists first introduced nanotechnology, no one knew what it was. They used physicists to alter the structures. Richard Feynman, a physicist, was awarded a Nobel prize for his contributions to nanotechnology in 1959. After winning the Nobel Prize for his amazing invention, the Noble Prize laureate declared during an American Physical Society meeting that "there is plenty of room at the bottom." Biology has traditionally been molecular, with important multidisciplinary study areas such as DNA, protein, and cellular machinery. The nanoworld idea is founded on the convergence of a genuine scientific or technological combination. Despite the fact that the wave-corpuscle duality-based principles of quantum physics are not clearly apparent. With the exception of semiconductors and lasers. Quantum effects will be applied in a variety of applications in the future. "Nano-Technology is a science, engineering, and technology that takes place on the nanoscale, which ranges from 1 to 10 nanometers." A billionth of a meter, or 10-9 of a meter, is one nanometer, which is difficult to comprehend. The capacity to observe and manipulate individual atoms and molecules is required. Atoms make up everything on the planet. However, seeing a nanometer-sized object with the naked eye is impossible. As a result, microscopes such as the Scanning Tunneling Microscope (STM).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 Electron transport properties of stacked 2 dimensional materials(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2017) Ali Raza; SP15-RPH-003; Dr. Abdul Sattar; LHR TP 6856Graphene; a material with a high carrier mobility, having zero band gap drawback. Whereas, Boron Nitride with an insulating behavior, having a wide band gap opening. To control the band gap of grapheme without affecting the carrier mobility, Graphene/ Boron Nitride (grapheme/BN) hetero bilayers (HBLs) are formed. In these HBLs the layer of graphene is already doped with BN as well. First Principles calculations show that the band gap and electron effective mass can be modulated according to the need by just changing their stacking arrangement and the inter layer spacing between BN and hybrid layer of graphene. The results show that the tunability of graphene band gap have a linear dispersion relation with handsome band gap opening for a specific stable stacking pattern and this is a promising feature for futuristic Nano devices.