Browsing by Subject "Quantum Dot"
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Item Spectral multiplexing using quantum dot tagged microspheres with diffusing colloidal probe microscopy(2009-05-15) Muthukumar, ShankarapandianThis work involves the development of a new technique that integrates Diffusing Colloidal Probe Microscopy (DCPM) and luminescence to simultaneously measure multiple particle-wall interactions. DCPM can be used to map potential energy profiles of multiple particle-surface interactions simultaneously and accurately. Colloidal semiconductor quantum dots were used for spectral multiplexing to enable monitoring of multiple analytes at the same time. DCPM combines Total Internal Reflection Microscopy (TIRM) and Video Microscopy to simultaneously measure multiple particle-surface interactions with nanometer resolution in particle-surface separation. By acquiring the scattered intensity emitted by the particles, the separation distance can be calculated and subsequently the forces of interactions between the particle and the surface. This work demonstrates the use of luminescence instead of scattering as the mode of detection in DCPM. The luminescence is provided by quantum dots which are incorporated into polystyrene microspheres. The unique optical properties of quantum dots enable the creation of an optically multiplexed system where microspheres are tagged by quantum dots of different emission wavelengths. Scattering in DCPM may result in erroneous calculation of the potential energy profiles because of particle polydispersity. Since scattering is dependent on particle size, luminescence is introduced into the system and some interesting results are obtained. These results illustrate that the effect of particle polydispersity is significantly reduced when luminescence is used as the mode of detection. This combined with the DCPM system?s sensitivity would enable the monitoring of multiple functionalized particlesurface interactions simultaneously and accurately.Item Technology computer aided design and analysis of novel logic and memory devices(2012-08) Hasan, Mohammad Mehedi; Register, Leonard F.; Banerjee, Sanjay K.; Bank, Seth; MacDonald, Allan H.; McDermott, Mark W.Novel logic and memory device concepts are proposed and analyzed. For the latter purpose the commercial technology computer aided design (TCAD) simulators Taurus and Sentaurus Device by Synopsys are used. These simulators allow ready definition of complex device geometries. Moreover, while not all device physics models are state-of-the-art, the wide variety of device physics considered is advantageous here when not all of the critical device physics is known a priori. The initial device concept analyzed was a one transistor (1T), one capacitor (1C) – pseudo-static random access memory (SRAM). Simulations indicate that tri-gate pass-transistors will offer better gate control and reduced leakage, and tri-gate capacitors will offer increased capacitance, making the overall device performance comparable to SRAM. The second device analyzed was a quantum dot non-volatile memory. In principle, such memories become more reliable for a given tunnel oxide thickness by localizing any leaks to individual dots. However, simulations illustrate limits on dot packing density to retain this advantage due to inter-dot tunneling. The final device, proposed and extensively analyzed here, is a novel tunnel field-effect transistor (TFET), the “hetero-barrier TFET” (HetTFET). In complementary metal-oxide-semiconductor (CMOS) logic, while switching power decreases with voltages, standby power increases due to thermionic emission of charge carriers over the source-to-channel barrier in the constituent metal-oxide-semiconductor field-effect transistors (MOSFETs). As a result, CMOS voltage and, thus, power scaling is approaching an impasse. Because TFETs are not subject to thermionic emission, they are being considering as a replacement for MOSFETs. Various materials systems and device geometries have been considered. However, even in simulation, balancing switching and standby power at low voltages while still providing sufficient transconductance for rapid switching has not proven straightforward. HetTFETs are intended to achieve high on-to-off current ratios via a threshold defined by the onset of band overlap, and high ON-state transconductances via tunneling through thin barriers defined by crystal growth, rather than relying on gate-controlled barrier narrowing in whole or part for either purpose as with other designs. Simulations of n and p-channel HetTFETs suggest the possibility of current CMOS-like performance at much lower voltages.