Real-time Atomic-resolution Probing of Lithium Ion Intercalation in TiO2-Related Anodes using Transmission Electron Microscopy.

Nanostructured TiO2 polymorphs such as rutile and bronze have been considered for lithium ion battery (LIB) application due to their chemical stability and accessibility. Despite their promising performance as anodes and coating materials, understanding of lithium ion behaviors in TiO2-related systems is still controversial, since most studies have relied on bulk characterization techniques which do not present local changes in morphology. Here, we employed in-situ transmission electron microscopy (TEM) and high-resolution scanning TEM (HRSTEM) to perform nano-scale structural studies of TiO2-related anodes upon Li intercalation. The electrochemical study of a single-crystalline rutile TiO2 nanowire (NW) was conducted under high-resolution TEM aided by selected area electron diffraction. The result demonstrates the two-step lithiation accompanied by the highly anisotropic volumetric expansion and phase transformation. An in-depth study of lithiation in bronze TiO2 (TiO2-B) had been possible by the growth of a high-quality TiO2-B thin film templated by Ca-modified bronze phase, CaTi5O11 (Ca:TiO2-B). Various interfaces and defects in TiO2-B and Ca:TiO2-B thin films deposited on (100) and (110) SrTiO3 substrates were first studied under HRSTEM. High crystallinity of (001) TiO2-B on a Ca:TiO2-B template motivated us to perform lithiation on the structure under HRTEM. Revealed by high-resolution observation of electrochemical lithiation into TiO2-B, many defects were induced by strain relaxation upon Li-induced TiO2-B lattice expansion. In fact, depending on Li intercalation direction into the structure, either high-symmetry structural transformation or plain shears was generated. The observations were corroborated by post-mortem HRSTEM characterization and theoretical calculation. The capability of a TiO2 nanostructure as a coating material for a LIB anode was also investigated via potentiostatic lithiation of a rutile TiO2-coated Si NW. It was found that lithium intercalation into this NW occurred locally by having each segment achieving full lithiation throughout the Li migration pathway. The TiO2 coating also influenced final lithiated morphology of a coated Si (Li15Si4) to be different from that of an uncoated one. The results discussed in this thesis provide the in-depth knowledge on the Li ion dynamics in two TiO2 polymorphs. The application of in-situ high-resolution TEM technique can be expanded towards other polymorphs of various different structural forms.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113420/1/sjkkorea_1.pd

The flavonoid luteolin prevents lipopolysaccharide-induced NF-kappaB signalling and gene expression by blocking IkappaB kinase activity in intestinal epithelial cells and bone-marrow derived dendritic cells

The nuclear factor (NF)-κB transcriptional system is a major effector pathway involved in inflammation and innate immune responses. The flavonoid luteolin is found in various herbal extracts and has shown anti-inflammatory properties. However, the mechanism of action and impact of luteolin on innate immunity is still unknown. We report that luteolin significantly blocks lipopolysaccharide (LPS)-induced IκB phosphorylation/degradation, NF-κB transcriptional activity and intercellular adhesion molecule-1 (ICAM-1) gene expression in rat IEC-18 cells. Using chromatin immunoprecipitation, we demonstrate that LPS-induced RelA recruitment to the ICAM-1 gene promoter is significantly reduced in luteolin-treated cells. Moreover, in vitro kinase assays show that luteolin directly inhibits LPS-induced IκB kinase (IKK) activity in IEC-18 cells. Using bone-marrow derived dendritic cells (BMDCs) isolated from interleukin (IL)-10−/− mice or from recently engineered transgenic mice expressing the enhanced green fluorescent protein (EGFP) under the transcriptional control of NF-κB cis-elements (cis-NF-κBEGFP), we found that luteolin blocks LPS-induced IκB phosphorylation and IKK activity, and decreases EGFP, IL-12 and tumour necrosis factor-α gene expression. Moreover, intraperitoneal administration of luteolin significantly inhibited LPS-induced EGFP expression in both peripheral blood mononuclear cells and splenocytes isolated from cis-NF-κBEGFP mice. These results indicate that luteolin blocks LPS-induced NF-κB signalling and proinflammatory gene expression in intestinal epithelial cells and dendritic cells. Modulation of innate immunity by natural plant products may represent an attractive strategy to prevent intestinal inflammation associated with dysregulated innate immune responses

Experimental Evidence of Ferroelectric Negative Capacitance in Nanoscale Heterostructures

We report a proof-of-concept demonstration of negative capacitance effect in a nanoscale ferroelectric-dielectric heterostructure. In a bilayer of ferroelectric, Pb(Zr0.2Ti0.8)O3 and dielectric, SrTiO3, the composite capacitance was observed to be larger than the constituent SrTiO3 capacitance, indicating an effective negative capacitance of the constituent Pb(Zr0.2Ti0.8)O3 layer. Temperature is shown to be an effective tuning parameter for the ferroelectric negative capacitance and the degree of capacitance enhancement in the heterostructure. Landau's mean field theory based calculations show qualitative agreement with observed effects. This work underpins the possibility that by replacing gate oxides by ferroelectrics in MOSFETs, the sub threshold slope can be lowered below the classical limit (60 mV/decade)

KINEMATIC ANALYSIS OF FRONT SQUAT IN RESPONSE TO LOADS

The purpose of this study was to examine the kinematics of lower extremity and spine in response to different mass loads in front squat exercise. Three experienced male varsity athletes were recruited to participate in this study, and each participant performed five trials of front squat exercise at three different loads (65%, 75%, and 85% of 1 repetition maximum). A standard two-dimensional kinematic analysis was conducted and the result showed that the participants had no significant difference on different loads in both lower extremity and spine. However, the knee joint demonstrated a strong sensitivity in response to load mass, so a strength training program may be prescribed focusing on the knee joint stability. Future research studies are warranted to examine the kinematic differences between a knee-braced front squat and a plain front squat