21 research outputs found
Theoretical Understanding and Material Design towards Next-generation Data Storage Devices
Ph.DDOCTOR OF PHILOSOPH
Effect of interfacial strain on spin injection and spin polarization of Co2CrAl/NaNbO3/Co2CrAl magnetic tunneling junction
First-principles calculations were carried out to investigate interfacial
strain effects on spin injection and spin polarization of a magnetic tunnel
junction consisting of half-metallic full-Heusler alloy Co2CrAl and
ferroelectric perovskite NaNbO3. Spin-dependent coherent tunneling was
calculated within the framework of non-equilibrium Green's function technique.
Both spin polarization and tunnel magnetoresistance (TMR) are affected by the
interfacial strain but their responses to compressive and tensile strains are
different. Spin polarization across the interface is fully preserved under a
compressive strain due to stronger coupling between interfacial atoms, whereas
a tensile strain significantly enhances interface states and lead to
substantial drops in spin polarization and TMR
Interface Controlled Thermal Resistances of Ultra-Thin Chalcogenide-Based Phase Change Memory Devices
Phase change memory (PCM) is a rapidly growing technology that not only offers advancements in storage-class memories but also enables in-memory data processing to overcome the von Neumann bottleneck. In PCMs, data storage is driven by thermal excitation. However, there is limited research regarding PCM thermal properties at length scales close to the memory cell dimensions. Our work presents a new paradigm to manage thermal transport in memory cells by manipulating the interfacial thermal resistance between the phase change unit and the electrodes without incorporating additional insulating layers. Experimental measurements show a substantial change in interfacial thermal resistance as GST transitions from cubic to hexagonal crystal structure, resulting in a factor of 4 reduction in the effective thermal conductivity. Simulations reveal that interfacial resistance between PCM and its adjacent layer can reduce the reset current for 20 and 120 nm diameter devices by up to ~ 40% and ~ 50%, respectively. These thermal insights present a new opportunity to reduce power and operating currents in PCMs
Transition Metal Atoms Pathways on Rutile TiO2 (110) Surface: Distribution of Ti3+ States and Evidence of Enhanced Peripheral Charge Accumulation
Charge transfer between metal nanoparticles and the supported TiO2 surface is
primarily important for catalytic applications as it greatly affects the
catalytic activity and the thermal stability of the deposited nanoparticles on
the surface. Herein, a systematic spin-polarized density functional calculation
is performed to evaluate the adsorption, diffusion, and charge state of several
transition metal monomers on both stoichiometric and reduced rutile TiO2 (110)
surface. The role of oxygen vacancy (Ov) with its accompanying excess electrons
in influencing the activation of the monomers is examined. For pristine reduced
surface, our hybrid functional calculation shows that only a small portion
(around 5%) of the excess electrons occupy the topmost surface, which are
mainly delocalized at the second nearest and third nearest fivefold coordinated
Ti (Ti5c) atoms. The small amounts of excess electrons populating at the Ti5c
atoms can be transferred to strongly electronegative adsorbates like Au and Pt
thus enabling a moderate adsorption, whereas no stable adsorption at the Ti5c
site is found for other less electronegative TM adatoms(Ag, Cu, Fe, Co, Ni and
Pd) on the reduced surface and for all the adatoms on stoichiometric surface.
This finding clarify the origin of the experimental observation of the
adsorption of O2 and CO molecules at Ti5c sites in connection with charge
transfer. In addition, the spatial redistribution of the excess electrons at
Ti5c sites around the Ov upon the adsorption of the monomers is thoroughly
examined. Our finding of an accumulation of excess electrons at the Ti5c sites
around the monomers explains the critical role of the perimeter interface of
the deposited nanoparticles in promoting the adsorption and activation of
reactants observed in experiments.Comment: Some more complete results will be presente
A new mutation of the Atoh1 gene in mice with normal life span allows analysis of inner ear and cerebellar phenotype in aging.
Atoh1 is a transcription factor that regulates neural development in multiple tissues and is conserved among species. Prior mouse models of Atoh1, though effective and important in the evolution of our understanding of the gene, have been limited by perinatal lethality. Here we describe a novel point mutation of Atoh1 (designated Atoh1(trhl) ) underlying a phenotype of trembling gait and hearing loss. Histology revealed inner ear hair cell loss and cerebellar atrophy. Auditory Brainstem Response (ABR) and Distortion Product Otoacoustic Emission (DPOAE) showed functional abnormalities in the ear. Normal lifespan and fecundity of Atoh1(trhl) mice provide a complementary model to facilitate elucidation of ATOH1 function in hearing,central nervous system and cancer biology