Plasmonic devices based on transparent conducting oxides for near infrared applications

In the past decade, there have been many breakthroughs in the field of plasmonics and nanophotonics that have enabled optical devices with unprecedented functionalities. Even though remarkable demonstration of at photonic devices has been reported, constituent materials are limited to the noble metals such as gold (Au) and silver (Ag) due to their abundance of free electrons which enable the support of plasmon resonances in the visible range. With the strong demand for extension of the optical range of plasmonic applications, it is now a necessity to explore and develop alternative materials which can overcome intrinsic issues of noble metals such as integration challenges, considerable optical losses, and lack of tunability of their optical properties. As most promising alternative to noble metals, transparent conducting oxides (TCOs) have been proposed as a promising new class of plasmonic materials for the IR applications. The main objective of the thesis is to explore the various plasmonic devices based on TCOs in order to evaluate the capabilities of TCOs as alternative metallic component for plasmonic applications. By beginning with a discussion of the general (optical, electrical and morphological) properties of TCOs, we describe the demonstration of devices such as plasmonic resonator for bio-sensing and waveplate metasurfaces. In addition, we study the impact of TCOs to local antenna as epsilon-near-zero (ENZ) substrate. The technological importance of the IR range is apparent and growing, and as plasmonics develops a niche at these frequencies, I believe this study represents a scientific directive toward the quest to bring plasmonics into the IR

User Acceptance of the Next Generation Digital Signage: A Perspective of Perceived Value

The next generation digital signage (NGDS) has become extremely important as a new innovative information system that provides interactive information to users by capturing contextual information through the utilization of the state-of-the-art technologies. NGDS gets wide popularity from millions of people due to its advanced information services that fit in with the individual’s digitizing life style. Despite the increasing importance, however, there is a significant gap of our understanding on the user acceptance of NGDS. Motivated thus, this paper aims to develop a research model to explore the factors influencing the user acceptance of NGDS from the perspective of perceived value. The four dimensions of perceived value are proposed as key antecedents: utilitarian value, hedonic value, social value, and epistemic value. In particular, our interest is on their impacts on users’ satisfaction, continuance intention, and positive word-of-mouth (WOM). The pilot study results indicate that utilitarian value increases satisfaction, continuance intention, and positive WOM. Moreover, hedonic value increases satisfaction and positive WOM, while social value increases positive WOM only. Also, epistemic value increases satisfaction and positive WOM. This research is expected to advance the theoretical understanding on the user acceptance of NGDS and offer organizations useful insights to manage their NGDS

Ultrabroadband terahertz conductivity of highly doped ZnO and ITO

The broadband complex conductivities of transparent conducting oxides (TCO), namely aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO), were investigated by terahertz time domain spectroscopy (THz-TDS) in the frequency range from 0.5 to 18 THz using air plasma techniques, supplemented by the photoconductive antenna (PCA) method. The complex conductivities were accurately calculated using a thin film extraction algorithm and analyzed in terms of the Drude conductivity model. All the measured TCOs have a scattering time below 15 fs. We find that a phonon response must be included in the description of the broadband properties of AZO and GZO for an accurate extraction of the scattering time in these materials, which is strongly influenced by the zinc oxide phonon resonance tail even in the low frequency part of the spectrum. The conductivity of AZO is found to be more thickness dependent than GZO and ITO, indicating high importance of the surface states for electron dynamics in AZO. Finally, we measure the transmittance of the TCO films from 10 to 200 THz with Fourier transform infrared spectroscopy (FTIR) measurements, thus closing the gap between THz-TDS measurements (0.5-18 THz) and ellipsometry measurements (200-1000 THz). (C)2015 Optical Society of Americ

Domestication of Oryza species eco-evolutionarily shapes bacterial and fungal communities in rice seed

Abstract Background Plant-associated microbiomes, which are shaped by host and environmental factors, support their hosts by providing nutrients and attenuating abiotic and biotic stresses. Although host genetic factors involved in plant growth and immunity are known to shape compositions of microbial communities, the effects of host evolution on microbial communities are not well understood. Results We show evidence that both host speciation and domestication shape seed bacterial and fungal community structures. Genome types of rice contributed to compositional variations of both communities, showing a significant phylosymbiosis with microbial composition. Following the domestication, abundance inequality of bacterial and fungal communities also commonly increased. However, composition of bacterial community was relatively conserved, whereas fungal membership was dramatically changed. These domestication effects were further corroborated when analyzed by a random forest model. With these changes, hub taxa of inter-kingdom networks were also shifted from fungi to bacteria by domestication. Furthermore, maternal inheritance of microbiota was revealed as a major path of microbial transmission across generations. Conclusions Our findings show that evolutionary processes stochastically affect overall composition of microbial communities, whereas dramatic changes in environments during domestication contribute to assembly of microbiotas in deterministic ways in rice seed. This study further provides new insights on host evolution and microbiome, the starting point of the holobiome of plants, microbial communities, and surrounding environments. Video Abtract

Optical Properties of Gallium-Doped Zinc Oxide-A Low-Loss Plasmonic Material: First-Principles Theory and Experiment

Searching for better materials for plasmonic and metamaterial applications is an inverse design problem where theoretical studies are necessary. Using basic models of impurity doping in semiconductors, transparent conducting oxides (TCOs) are identified as low-loss plasmonic materials in the near-infrared wavelength range. A more sophisticated theoretical study would help not only to improve the properties of TCOs but also to design further lower-loss materials. In this study, optical functions of one such TCO, gallium-doped zinc oxide (GZO), are studied both experimentally and by first-principles density-functional calculations. Pulsed-laser-deposited GZO films are studied by the x-ray diffraction and generalized spectroscopic ellipsometry. Theoretical studies are performed by the total-energy-minimization method for the equilibrium atomic structure of GZO and random phase approximation with the quasiparticle gap correction. Plasma excitation effects are also included for optical functions. This study identifies mechanisms other than doping, such as alloying effects, that significantly influence the optical properties of GZO films. It also indicates that ultraheavy Ga doping of ZnO results in a new alloy material, rather than just degenerately doped ZnO. This work is the first step to achieve a fundamental understanding of the connection between material, structural, and optical properties of highly doped TCOs to tailor those materials for various plasmonic applications

Adiabatic frequency shifting in epsilon-near-zero materials:The role of group velocity

The conversion of a photon’s frequency has long been a key application area of nonlinear optics. It has been discussed how a slow temporal variation of a material’s refractive index can lead to the adiabatic frequency shift (AFS) of a pulse spectrum. Such a rigid spectral change has relevant technological implications, for example, in ultrafast signal processing. Here, we investigate the AFS process in epsilon-near-zero (ENZ) materials and show that the frequency shift can be achieved in a shorter length if operating in the vicinity of Re

P-TEFb Regulates Transcriptional Activation in Non-coding RNA Genes

Many non-coding RNAs (ncRNAs) serve as regulatory molecules in various physiological pathways, including gene expression in mammalian cells. Distinct from protein-coding RNA expression, ncRNA expression is regulated solely by transcription and RNA processing/stability. It is thus important to understand transcriptional regulation in ncRNA genes but is yet to be known completely. Previously, we identified that a subset of mammalian ncRNA genes is transcriptionally regulated by RNA polymerase II (Pol II) promoter-proximal pausing and in a tissue-specific manner. In this study, human ncRNA genes that are expressed in the early G1 phase, termed immediate early ncRNA genes, were monitored to assess the function of positive transcription elongation factor b (P-TEFb), a master Pol II pausing regulator for protein-coding genes, in ncRNA transcription. Our findings indicate that the expression of many ncRNA genes is induced in the G0–G1 transition and regulated by P-TEFb. Interestingly, a biphasic characteristic of P-TEFb-dependent transcription of serum responsive ncRNA genes was observed: Pol II carboxyl-terminal domain phosphorylated at serine 2 (S2) was largely increased in the transcription start site (TSS, -300 to +300) whereas overall, it was decreased in the gene body (GB, > +350) upon chemical inhibition of P-TEFb. In addition, the three representative, immediate early ncRNAs, whose expression is dependent on P-TEFb, metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), nuclear enriched abundant transcript 1 (NEAT1), and X-inactive specific transcript (XIST), were further analyzed for determining P-TEFb association. Taken together, our data suggest that transcriptional activation of many human ncRNAs utilizes the pausing and releasing of Pol II, and that the regulatory mechanism of transcriptional elongation in these genes requires the function of P-TEFb. Furthermore, we propose that ncRNA and mRNA transcription are regulated by similar mechanisms while P-TEFb inhibition unexpectedly increases S2 Pol II phosphorylation in the TSSs in many ncRNA genes.One Sentence Summary: P-TEFb regulates Pol II phosphorylation for transcriptional activation in many stimulus-inducible ncRNA genes

funRNA : a fungi-centered genomics platform for genes encoding key components of RNAi

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