Effect of atomic layer deposition on the quality factor of silicon nanobeam cavities

In this work we study the effect of thin-film deposition on the quality factor (Q) of silicon nanobeam cavities. We observe an average increase in the Q of 38±31% in one sample and investigate the dependence of this increase on the initial nanobeam hole sizes. We note that this process can be used to modify cavities that have larger than optimal hole sizes following fabrication. Additionally, the technique allows the tuning of the cavity mode wavelength and the incorporation of new materials, without significantly degrading Q

Profiling of promoter occupancy by PPARα in human hepatoma cells via ChIP-chip analysis

The transcription factor peroxisome proliferator-activated receptor α (PPARα) is an important regulator of hepatic lipid metabolism. While PPARα is known to activate transcription of numerous genes, no comprehensive picture of PPARα binding to endogenous genes has yet been reported. To fill this gap, we performed Chromatin immunoprecipitation (ChIP)-chip in combination with transcriptional profiling on HepG2 human hepatoma cells treated with the PPARα agonist GW7647. We found that GW7647 increased PPARα binding to 4220 binding regions. GW7647-induced binding regions showed a bias around the transcription start site and most contained a predicted PPAR binding motif. Several genes known to be regulated by PPARα, such as ACOX1, SULT2A1, ACADL, CD36, IGFBP1 and G0S2, showed GW7647-induced PPARα binding to their promoter. A GW7647-induced PPARα-binding region was also assigned to SREBP-targets HMGCS1, HMGCR, FDFT1, SC4MOL, and LPIN1, expression of which was induced by GW7647, suggesting cross-talk between PPARα and SREBP signaling. Our data furthermore demonstrate interaction between PPARα and STAT transcription factors in PPARα-mediated transcriptional repression, and suggest interaction between PPARα and TBP, and PPARα and C/EBPα in PPARα-mediated transcriptional activation. Overall, our analysis leads to important new insights into the mechanisms and impact of transcriptional regulation by PPARα in human liver and highlight the importance of cross-talk with other transcription factors

Comparative Analysis of Gene Regulation by the Transcription Factor PPARα between Mouse and Human

Studies in mice have shown that PPARalpha is an important regulator of hepatic lipid metabolism and the acute phase response. However, little information is available on the role of PPARalpha in human liver. Here we set out to compare the function of PPARalpha in mouse and human hepatocytes via analysis of target gene regulation

Light-Matter Interactions in Various Semiconductor Systems

Semiconductors provide an interesting platform for studying light-matter interactions due to their unique electrically conductive behavior which can be deliberately altered in useful ways with the controlled introduction of confinement and doping, which changes the electronic band structure. This area of research has led to many important fundamental scientific discoveries that have in turn spawned a plethora of applications in areas such as photonics, microscopy, single-photon sources, and metamaterials. Silicon is the prevalent semiconductor platform for microelectronics because of its cost and electrical properties, while III-V materials are optimal for optoelectronics because of the ability to engineer a direct bandgap and create versatile heterojunctions by growing binary, ternary, or quaternary compounds.Release after 11-May-201

Polarization dependent femtosecond laser modification of MBE-grown III-V nanostructures on silicon

We report a novel, polarization dependent, femtosecond laser- induced modification of surface nanostructures of indium, gallium, and arsenic grown on silicon via molecular beam epitaxy, yielding shape control from linear and circular polarization of laser excitation. Linear polarization causes an elongation effect, beyond the dimensions of the unexposed nanostructures, ranging from 88 nm to over 1 mu m, and circular polarization causes the nanostructures to flatten out or form loops of material, to diameters of approximately 195 nm. During excitation, it is also observed that the generated second and third harmonic signals from the substrate and surface nanostructures increase with exposure time. (C) 2017 Optical Society of AmericaAir Force Office of Scientific Research (AFOSR) [FA9550-15-1-0389]Open access journal.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

TEM EDS analysis of epitaxially-grown self-assembled indium islands

International audienceEpitaxially-grown self-assembled indium nanostructures, or islands, show promise as nanoantennas. The elemental composition and internal structure of indium islands grown on gallium arsenide are explored using Transmission Electron Microscopy (TEM) Energy Dispersive Spectroscopy (EDS). Several sizes of islands are examined, with larger islands exhibiting high (>94%) average indium purity and smaller islands containing inhomogeneous gallium and arsenic contamination. These results enable more accurate predictions of indium nanoantenna behavior as a function of growth parameters. 1. Background As the field of plasmonic nanostructures develops, there is increasing demand for epitaxially-grown metallic nanostructures. Metal-on-semiconductor nanoantennas, which operate at optical and near-infrared wavelengths, have a wide range of potential applications, from low-cost photodetectors1 to higher-efficiency solar cells.2 Currently, nanoantenna fabrication is often performed separately from substrate preparation;3-8 this discontinuity can adversely affect the finished product through contamination and impurities introduced during fabrication. One method for avoiding these issues is to epitaxially grow both the substrate and plasmonic nanostructure, with the structure self-assembling from a uniformly-deposited metal layer such as silver or indium.9,10 Self-assembled nanostructures can additionally benefit from a better contact interface between structure and substrate compared to other fabrication methods. Epitaxially-grown nanostructures may also have applications in quantum computing.11,12 Majorana fermions, a candidate for qubit construction, have been observed in InSb nanowires coupled to superconducting NbTiN.13 Other s-wave superconductor-1D semiconductor systems are also expected to generate Majorana fermions; InAs and indium have been identified as a potential semiconductor and superconductor, respectively.14,15 InAs nanowires can be grown epitaxially, suggesting that self-assembled indium islands may allow for the epitaxial growth of entire Majorana fermion-generating heterostructures. While epitaxially-grown self-assembled indium islands show promise as nanoantennas,16 the internal structure of these islands has not been thoroughly explored. Prior work has indicated that these structures may contain impurities unique to the epitaxial growth process.17 This paper seeks to describe and analyze the internal structure of indium islands grown under three different sets of growth conditions, in order to better predict the behavior and future applications of these plasmonic nanostructures. 2. Experimen