Device physics and device mechanics for flexible MoS2 thin film transistors

textWhile there has been increasing studies of MoS2 and other two-dimensional (2D) semiconducting dichalcogenides on hard conventional substrates, experimental or analytical studies on flexible substrates has been very limited so far, even though these 2D crystals are understood to have greater prospects for flexible smart systems. In the first part, we report detailed studies of MoS2 transistors on industrial plastic sheets. Failure mechanisms under strain are studied with bending test and stretching test. Experimental investigation identifies that crack formation in the dielectric and the buckling delamination in MoS2 are responsible for the degradation of the device performance. Several approaches to improve device flexibility were discussed. In the second part, electronic transport properties in multilayer MoS2 are investigated with Y-function method. By combining experiments and analysis, we show that the Y-function method offers a robust route for evaluating the low-field mobility, threshold voltage and contact resistance even when the contact is a Schottky-barrier as is common in two-dimensional transistors. In addition, an independent transfer length method (TLM) evaluation corroborates the modified Y-function analysis. The last part, we demonstrate the first RF performance for transferred CVD-grown MoS2 FETs on the flexible substrate. Our result suggests that the large-area CVD-grown MoS2 provides a practical route to realize low-power, high speed electronics circuit applications in the future.Electrical and Computer Engineerin

Efficient 3D capacitance extraction solver using instantiable basis functions for VLSI interconnects

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 62-65).State-of-the-art capacitance extraction methods for Integrated Circuits (IC) involve scanning 2D cross-sections, and interpolating 2D capacitance values using a table lookup approach. This approach is fast and accurate for a large percentage of IC wires. It is however quite inaccurate for full 3D structures, such as crossing wires in adjacent metal layers. For such cases electrostatic field solvers are required. Unfortunately standard field solvers are inherently very time-consuming, making them completely impractical in typical IC design flows. Even fast matrix-vector product approaches (e.g., fastmultipole or precorrected FFT) are inefficient for these structures since they have a significant computational overhead and scale linearly with the number of conductors only for much larger structures with more than several hundreds of wires. In this talk we present therefore a new 3D extraction field solver that is extremely efficient in particular for the smaller scale extraction problem involving the ten to one hundred conductors in the 3D structures that cannot be handled by the 2D scanning and table look up approach. Because of highly restrictive design rules of the recent sub-micro to nano-scale IC technologies, smooth and regular charge distributions extracted from simple model structures can be stored beforehand as "templates" and instantiated and stretched to fit practical complicated cases as basis function building blocks. This "template-instantiated" strategy largely reduces the number of unknowns and computational time without additional overhead. Given that all basis functions are obtained by the same very few stretched templates, Galerkin coefficients can be readily computed from a mixture of analytical, numerical and table lookup approaches. Furthermore, given the low accuracy (i.e., 3%-5%) required by IC extraction and the specific aspect ratios and separations of wires on ICs, we have observed in our numerical experimentations that edge and corner charge singularities do not need to be included in our templates, hence reducing the complexity of our solver even further.by Yu-Chung Hsiao.S.M

Preface for the IJSME Special Issue: Metacognition for Science and Mathematics Learning in Technology-Infused Learning Environments

The final publication is available at Springer via http://dx.doi.org/10.1007/s10763-016-9727-9

Pt-decorated nanoporous gold for glucose electrooxidation in neutral and alkaline solutions

Exploiting electrocatalysts with high activity for glucose oxidation is of central importance for practical applications such as glucose fuel cell. Pt-decorated nanoporous gold (NPG-Pt), created by depositing a thin layer of Pt on NPG surface, was proposed as an active electrode for glucose electrooxidation in neutral and alkaline solutions. The structure and surface properties of NPG-Pt were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and cyclic voltammetry (CV). The electrocatalytic activity toward glucose oxidation in neutral and alkaline solutions was evaluated, which was found to depend strongly on the surface structure of NPG-Pt. A direct glucose fuel cell (DGFC) was performed based on the novel membrane electrode materials. With a low precious metal load of less than 0.3 mg cm-2 Au and 60 μg cm-2 Pt in anode and commercial Pt/C in cathode, the performance of DGFC in alkaline is much better than that in neutral condition

Primary Phacoemulsification and Intraocular Lens Implantation for Acute Primary Angle-Closure

Background: To investigate the effect of primary phacoemulsification on intraocular pressure (IOP) in patients with acute primary angle-closure (PAC) and coexisting cataract. Methodology: Sixteen eyes of 14 patients with acute PAC received phacoemulsification and intraocular lens implantation as initial management for medically uncontrolled IOP in a retrospective chart review. The effects on IOP, vision, anterior chamber depth (ACD), and number of antiglaucoma medications were evaluated. Principal Findings: The postoperative IOP was reduced in 16 eyes (100%). The mean 6 standard deviation preoperative IOP was 48.81616.83 mm Hg, which decreased postoperatively to 16.46610.67 mm Hg at 1 day, 9.4363.03 mm Hg at 1 week

A new human chromogranin A (CgA) immunoradiometric assay involving monoclonal antibodies raised against the unprocessed central domain (145-245)

Chromogranin A (CgA), a major protein of chromaffin granules, has been described as a potential marker for neuroendocrine tumours. Because of an extensive proteolysis which leads to a large heterogeneity of circulating fragments, its presence in blood has been assessed in most cases either by competitive immunoassays or with polyclonal antibodies. In the present study, 24 monoclonal antibodies were raised against native or recombinant human CgA. Their mapping with proteolytic peptides showed that they defined eight distinct epitopic groups which spanned two-thirds of the C-terminal part of human CgA. All monoclonal antibodies were tested by pair and compared with a reference radioimmunoassay (RIA) involving CGS06, one of the monoclonal antibodies against the 198–245 sequence. It appears that CgA C-terminal end seems to be highly affected by proteolysis and the association of C-terminal and median-part monoclonal antibodies is inadequate for total CgA assessment. Our new immunoradiometric assay involves two monoclonal antibodies, whose contiguous epitopes lie within the median 145–245 sequence. This assay allows a sensitive detection of total human CgA and correlates well with RIA because dibasic cleavage sites present in the central domain do not seem to be affected by degradation. It has been proved to be efficient in measuring CgA levels in patients with neuroendocrine tumours. © 1999 Cancer Research Campaig

Investigating the influence of product perception and geometric features

Research in emotional design and Kansei Engineering has shown that aesthetics play a significant role in the appeal of a product. This paper contributes to establishing a methodology to identify the relationships between perceptions, aesthetic features, desire to own and background of consumers. Surveys were conducted with 71 participants to gather their perceptions of 11 vase concepts. Advanced statistical analyses, including mixed models, were applied to allow generalisation of the results beyond the data sample. Significant relations between the desire to own a product and how the product is perceived were found (the desire to own was found to be related to beautiful, expensive, elegant, exciting, feminine, common and dynamic vases), as well as between the perceptions and the parameters describing the form of the vases (a vase was perceived as beautiful if it had many curved lines and was simple and tall). An automated mixed model analysis was conducted and revealed that general rules can be found between aesthetic features, perceptions and ownership, which can apply across gender and culture. The findings include design rules that link aesthetic features with perceptions. These contribute to research as guidelines for design synthesis and can either be implemented via shape grammars or parametric modelling approaches. These rules are also interesting for 3D printing applications, especially important when the consumer is the designer. Some of these design rules are linked to the desire to own a product, they have implications for industry, and they offer guidelines to creating attractive products that people want to own

Effects of maternal immune activation on gene expression patterns in the fetal brain

We are exploring the mechanisms underlying how maternal infection increases the risk for schizophrenia and autism in the offspring. Several mouse models of maternal immune activation (MIA) were used to examine the immediate effects of MIA induced by influenza virus, poly(I:C) and interleukin IL-6 on the fetal brain transcriptome. Our results indicate that all three MIA treatments lead to strong and common gene expression changes in the embryonic brain. Most notably, there is an acute and transient upregulation of the α, β and γ crystallin gene family. Furthermore, levels of crystallin gene expression are correlated with the severity of MIA as assessed by placental weight. The overall gene expression changes suggest that the response to MIA is a neuroprotective attempt by the developing brain to counteract environmental stress, but at a cost of disrupting typical neuronal differentiation and axonal growth. We propose that this cascade of events might parallel the mechanisms by which environmental insults contribute to the risk of neurodevelopmental disorders such as schizophrenia and autism

S100A7, a Novel Alzheimer's Disease Biomarker with Non-Amyloidogenic α-Secretase Activity Acts via Selective Promotion of ADAM-10

Alzheimer's disease (AD) is the most common cause of dementia among older people. At present, there is no cure for the disease and as of now there are no early diagnostic tests for AD. There is an urgency to develop a novel promising biomarker for early diagnosis of AD. Using surface-enhanced laser desorption ionization-mass spectrometry SELDI-(MS) proteomic technology, we identified and purified a novel 11.7-kDa metal- binding protein biomarker whose content is increased in the cerebrospinal fluid (CSF) and in the brain of AD dementia subjects as a function of clinical dementia. Following purification and protein-sequence analysis, we identified and classified this biomarker as S100A7, a protein known to be involved in immune responses. Using an adenoviral-S100A7 expression system, we continued to examine the potential role of S100A7 in AD amyloid neuropathology in in vitro model of AD. We found that the expression of exogenous S100A7 in primary cortico-hippocampal neuron cultures derived from Tg2576 transgenic embryos inhibits the generation of β-amyloid (Aβ)1–42 and Aβ1–40 peptides, coincidental with a selective promotion of “non- amyloidogenic” α-secretase activity via promotion of ADAM (a disintegrin and metalloproteinase)-10. Finally, a selective expression of human S100A7 in the brain of transgenic mice results in significant promotion of α-secretase activity. Our study for the first time suggests that S100A7 may be a novel biomarker of AD dementia and supports the hypothesis that promotion of S100A7 expression in the brain may selectively promote α-secretase activity in the brain of AD precluding the generation of amyloidogenic peptides. If in the future we find that S1000A7 protein content in CSF is sensitive to drug intervention experimentally and eventually in the clinical setting, S100A7 might be developed as novel surrogate index (biomarker) of therapeutic efficacy in the characterization of novel drug agents for the treatment of AD