Browsing by Subject "lithography"
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Item Computational Study of the Development of Graphene Based Devices(2012-02-14) Bellido Sosa, EdsonGraphene is a promising material for many technological applications. To realize these applications, new fabrication techniques that allow precise control of the physical properties, as well as large scale integration between single devices are needed. In this work, a series of studies are performed in order to develop graphene based devices. First, using MD simulations we study the effects of irradiating graphene with a carbon ion atom at several positions and energies from 0.1 eV to 100 keV. The simulations show four types of processes adsorption, reflection, transmission, and vacancy formation. At energies below 10 eV the dominant process is reflection, between 10 and 100 eV is adsorption, and between 100 eV and 100 keV the dominant process is transmission. Vacancy formation is a low rate process that takes place at energies above 30 eV. Three types of defects were found: adatom, single vacancy, and 5-8-5 defect formed from a double vacancy defect. Also a bottom-up fabrication method is studied, in this method, the controlled folding of graphene structures, driven by molecular interactions with water nanodroplets, is analyzed considering the interactions with substrates such as SiO2, HMDS and IPA on SiO2. When the graphene is supported on SiO2, the attraction between graphene and the substrate prevents graphene from folding but if the substrate has HMDS or IPA, the interaction between graphene and the substrate is weak, and depending on the geometry of the graphene structure, folding is possible. Finally, to evaluate the characteristics of graphene based devices, we model the vibrational bending modes of graphene ribbons with different dimensions. The resonant frequencies of the ribbons and relations between the size of the ribbon and their resonant frequencies are calculated. The interaction of a graphene vibronic device with water and IPA molecules are simulated and demonstrate that this device can be used as a sensitive vibronic molecular sensor that is able to distinguish the chemical nature of the detected molecule. Also, the electrical properties of the graphene vibronic with armchair and zigzag border are calculated; the latter has the potential to generate THz electrical signals as demonstrated in this work.Item Nanofabrication, Plasmon Enhanced Fluorescence and Photo-oxidation Kinetics of CdSe Nanoparticles(2011-08-08) Chen, JixinUnconventional nanofabrication techniques; both those which have been newly developed and those under development, had brought inexpensive, facile, yet high quality means to fabricate nanostructures that have feature sizes of less than 100 nm in industry and academia. This dissertation focuses on developing unconventional fabrication techniques, building studying platforms, and studying the mechanisms behind them. The studies are divided into two main facets and four chapters. The first facet, in Chapter II and Chapter III, deals with the research and development of different nanofabrication techniques and nanostructures. These techniques include litho-synthesis, colloidal lithography, and photolithography. The nanostructures that were fabricated by these techniques include the metal nanoparticle arrays, and the self-assembled CdSe nanoring arrays. At the same time, the dissertation provides mechanisms and models to describe the physical and chemical nature of these techniques. The second area of this study, in Chapter III to Chapter V, presents the applications of these nanostructures in fundamental studies, i.e. the mechanisms of plasmon enhanced fluorescence and photo-oxidation kinetics of CdSe quantum dots, and applications such as molecular sensing and material fabrication. More specifically, these applications include tuning the optical properties of CdSe quantum dots, biomodification of CdSe quantum dots, and copper ion detection using plasmon and photo enhanced CdSe quantum dots. We have successfully accomplished our research goals in this dissertation. Firstly, we were able to tune the emission wavelength of quantum dots, blue-shifted for up to 45 nm, and their surface functionalization with photo-oxidation. A kinetic model to calculate the photo-oxidation rates was established. Secondly, we established a simple mathematical model to explain the mechanism of plasmon enhanced fluoresce of quantum dots. Our calculation and experimental data support the fluorescence resonance energy transfer (FRET) mechanism between quantum dots and the metal nanoparticles. Thirdly, we successfully pattered the CdSe quantum dots (diameter ~4 nm) into nanorings with tunable diameters and annular sizes on different substrates. We also established a physical model to quantitatively explain the mechanism with the forces that involved in the formation of the nanorings.Item Optical modeling and resist metrology for deep-UV photolithography(Texas A&M University, 2006-10-30) Liu, ChaoThis thesis first presents a novel and highly accurate methodology for investigating the kinetics of photoacid diffusion and catalyzed-deprotection of positive-tone chemically amplified resists during post exposure bake (PEB) by in-situ monitoring the change of resist and capacitance (RC) of resist film during PEB. Deprotection converts the protecting group to volatile group, which changes the dielectric constant of resist. So the deprotection rate can be extracted from the change of capacitance. The photoacid diffusivity is extracted from the resistance change because diffusivity determines the rate of change of the acid distribution. Furthermore, by comparing the R and C curves, the dependence of acid diffusivity on reaction state can be extracted. The kinetics of non-Fickean acid transportation, deprotection, free volume generation and absorption/escaping, and resist shrinkage is analyzed and a comprehensive model is proposed that includes these chemical/physical mechanisms. Then in this thesis a novel lithographic technique, liquid immersion contact lithography (LICL) is proposed and the simulations are performed to illustrate its main features and advantages. Significant depth-of-field (DOF) enhancement can be achieved for large pitch gratings with deep-UV light (????=248nm) illumination with both TM and TE polarizations by liquid immersion. Better than 100nm DOF can be achieved by when printing 70nm apertures. The simulation results show that it is very promising to apply this technique in scanning near field optical microscopy. Finally, a rigorous, full vector imaging model of non-ideal mask is developed and the simulation of the imaging of such a mask with 2D roughness is performed. Line edge roughness (LER) has been a major issue limiting the performance of sub-100nm photolithography. A lot of factors contribute to LER, including mask roughness, lens imperfection, resist chemistry, process variation, etc. To evaluate the effect of mask roughness on LER, a rigorous full vector model has been developed by the author. We calculate the electromagnetic (EM) field immediately after a rough mask by using TEMPEST and simulate the projected wafer image with SPLAT. The EM field and wafer image deviate from those from an ideal mask. LER is finally calculated based on the projected image.Item Spin hall effect in paramagnetic thin films(2009-05-15) Xu, HuachunSpintronics, an abbreviation of spin based electronics and also known as magneto electronics, has attracted a lot of interest in recent years. It aims to explore the role of electrons? spins in building next generation electric devices. Using electrons? spins rather than electrons? charges may allow faster, lower energy cost devices. Spin Hall Effect is an important subfield of spintronics. It studies spin current, spin transport, and spin accumulation in paramagnetic systems. It can further understanding of quantum physics, device physics, and may also provide insights for spin injection, spin detection and spin manipulation in the design of the next generation spintronics devices. In this experimental work, two sets of experiments were prepared to detect the Spin Hall Effect in metallic systems. The first set of experiments aims to extract Spin Hall Effect from Double Hall Effect in micrometer size metal thin film patterns. Our experiments proved that the Spin Hall Effect signal was much smaller than the theoretically calculated value due to higher electrical resistivity in evaporated thin films. The second set of experiments employs a multi-step process. It combines micro fabrication and electrochemical method to fabricate a perpendicular ferromagnet rod as a spin injector. Process description and various techniques to improve the measurement sensitivity are presented. Measurement results in aluminum, gold and copper are presented in Chapters III, IV and V. Some new experiments are suggested in Chapters V and VI.