Selective scattering of blue and red light based on silver and gold nanocubes

Selective scattering of red-, green- and blue-light and transmitting other visible light to achieve transparent projection screen has been proposed recently based on metallic nanoparticle's localized surface plasmon resonance (LSPR). However, dielectric (TiO2) substrate/silver (Ag) nanocube structure was only demonstrated to selectively scatter blue-light in the backward direction. Given human eyes are sensitive to green-light, it is of interest to find out how to achieve selective forward-scattering of blue- and red-light and selective backward-scattering of red-light. In this work, through numerical simulation, forward and backward scattering properties of dielectric substrate/Ag (or gold) nanocube structures are investigated. And based on these properties, three designs are proposed which can achieve selective scattering of blue- and red-light in forward or backward or both directions

Nanocomposite Thin Films for both Mechanical and Functional Applications

The design methodology and realization of nanocomposite films aiming for mechanical (superhardness, toughness) and functional (optical, microelectronic) properties were discussed in this paper. Superhard TiCrCN and nc-TiN/a-SiNx films and super-tough nc-TiC/a-C(Al) films were prepared through co-sputtering method by optimal design of microstructure. The nanocrystalline silicon (nc-Si) passivated with a matrix of thermally grown silicon dioxide were prepared using implantation of Si into SiO₂ film, and showed improved photoluminescence and optical properties. Also discussed is the nano-composite design of thin film resistor with optimized temperature coefficient of resistivity.Singapore-MIT Alliance (SMA

Analyzing experiences of using effective feedback in the ESL classroom through the use of digital technologies

This article of systematic literature review presents the analysis of a series of experiences that use effective feedback in educational activities through the use and integration of digital technologies, specifically, in the classes of English as a second language in higher education. The revision analyzed 14 different experiences. As part of the analysis, criteria are defined to describe and compare them, linked with the possibilities of feedback to favor the formative processes at the higher education level. Criteria include: country of origin and level of education, design of feedback used, the timing of the feedback, the means of providing feedback, and the consideration of digital technologies. The main results indicate that the use of feedback, in the ESL classroom, allows learners to boost their capacity of analysis, critical thinking, and the resolution of problems linked with interlanguage. As a conclusion, the salience and positive impact of digital technologies are highlighted in favoring the positive and effective feedback, in the particular case of English as a second language. Finally, it is evident the use of computer -mediation, screencast, and web-based learning environments as the primary sources of authors used more frequently to implement effective feedback in higher education. It concludes that the set of experiences analyzed provides light in terms of the considerations needed to design and adjust formative processes that allow boosting effective feedback mediated by digital technologies. As future work, there will be the elaboration of a methodological proposal that helps to adjust the formative processes that enable the integration of digital technologies as mediators in the process of feedback between teachers and learners.UCR::Sedes Regionales::Sede del Atlántico::Recinto de GuápilesUCR::Sedes Regionales::Sede del Carib

The European Union counter-terrorism strategy origins, problems, and prospects

The European Union (EU) published its first Counter-Terrorism Strategy in December of 2005. After four years of reacting to the major terrorist attacks in the United States in 2001, Madrid in 2004, and London in 2005, the EU has enacted a substantial body of counterterrorism measures across multiple functional areas. The implementation of these actions, however, has not always been consistent or timely, due to a number of issues, including public threat perception, concern over social tensions, and competing national priorities. These roadblocks to a successful counterterrorism policy were often discovered upon new terrorist attacks and a renewed evaluation of EU counterterrorist activity. After the London bombings, the United Kingdom held the EU Presidency and immediately set to work on a strategy to counter terrorism, both similar and subordinate to the 2003 European Security Strategy, which specifically listed terrorism and weapons of mass destruction amoung the top five threats to the EU. The new strategy of 2005 outlines EU efforts over the long term and provides a tool for public information. Despite the EU's embrace of its new strategy, the document has many shortcomings. Evaluation of this strategy against a series of counterterrorism best practices accumulated from the work of functional and scholarly experts shows several areas in which the effectiveness of this strategy to successfully affect terrorism is severely limited. In all, the European Union Counter-Terrorism Strategy serves limited use as a strategy document, but does serve to guide the EU's efforts in fighting terrorism, as well as deepen EU integration in security affairs and in justice and law enforcement.http://archive.org/details/theeuropeunionco109452447Approved for public release; distribution is unlimited

Dual functional states of working memory realized by memristor-based neural network

Working memory refers to the brain's ability to store and manipulate information for a short period. It is disputably considered to rely on two mechanisms: sustained neuronal firing, and “activity-silent” working memory. To develop a highly biologically plausible neuromorphic computing system, it is anticipated to physically realize working memory that corresponds to both of these mechanisms. In this study, we propose a memristor-based neural network to realize the sustained neural firing and activity-silent working memory, which are reflected as dual functional states within memory. Memristor-based synapses and two types of artificial neurons are designed for the Winner-Takes-All learning rule. During the cognitive task, state transformation between the “focused” state and the “unfocused” state of working memory is demonstrated. This work paves the way for further emulating the complex working memory functions with distinct neural activities in our brains

Uncooled infrared imaging face recognition using kernel-based feature vector selection

A considerable amount of research has been recently conducted on face recognition tasks, due to increasing demands for security and authentication applications. Recent technological developments in uncooled IR imagery technology have boosted IR face recognition research applications. Our study is part of an on-going research initiated at the Naval Postgraduate School that considers an uncooled low-resolution and low-cost IR camera used for face recognition applications. This work investigates a recent approach which approximates nonlinear kernel-based methods at a significantly reduced computational cost. Our research was applied to an IR database. Results show that this scheme may perform sufficiently close to its â kernelizedâ version considered in a previous study, at a fraction of the computational cost, provided that the associated parameters are well tuned. The thesis considers a relative comparison between the two algorithms, based on identification and verification experiments and considers a statistical test to investigate whether classification performance differences may be considered statistically significant. Results show that, from a cost perspective, a low-resolution uncooled IR camera in conjunction with a low computational-cost classification scheme can be embedded in a robust face recognition system to efficiently address the issue of authentication in security-related tasks

Study of Si-nanocrystals-based light-emitting devices

In this project, Si nanocrystals embedded in dielectric matrix have been synthesized with the technique of Si ion implantation and plasma enhanced vapor deposition (PECVD). The resulting structure of the synthesized films embedded with nc-Si have been characterized by the techniques of transmission electron microscopy (TEM), x-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS), and x-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and photoluminescence (PL) and electroluminescence (EL) measurements. XPS has been employed to study the evolution of chemical structures corresponding to the oxidation states as a function of annealing. Optical properties, including the optical constants and dielectric functions, of Si nanocrystals in the photon energy range of 1-5 eV have been experimentally determined and modeled for the first time from the SE analysis. The bandgap expansion and dielectric suppression of Si nanocrystals have been also investigated. Strong room-temperature PL emission has been observed from SiO2 thin films embedded with nc-Si synthesized with Si ion implantation and subsequent thermal annealing. It has been found that thermal annealing at 1100 degree Celcius exhibits PL related to the formation of nc-Si. In this work, size-dependent PL bands with the peak wavelength ranging from ~720 to ~960 nm have been realized through adjusting the implantation energy and implanted Si ion dose. The PL energy decreases with the increasing nanocrystal size in accordance with the quantum confinement concepts. However, the size-dependent PL could not originate from the direct band to band transition of nc-Si. Based on the knowledge of band structure of nc-Si obtained in this work, the size-dependent PL band could be attributed to the indirect band-to-band transition of the nc-Si assisted by the Si-O vibration at the interface of nc-Si/SiO2. In addition, the evolution of PL mechanisms of Si+-implanted SiO2 thin films under different annealing conditions has been investigated. Visible and near infrared (IR) EL has been observed from a metal–oxide–semiconductor-like (MOS-like) structure with Si nanocrystals embedded in the gate oxide fabricated with low-energy ion implantation. Different nanocrystal distributions are achieved by varying the implanted Si ion dose and implantation energy. The nanocrystal distribution is found to play an important role in the EL. The influence of the applied voltage, the implantation dose, and implantation energy on the luminescence bands has been investigated. The current transport in the material system follows a power law, and it is determined by the concentration and distribution of the nc-Si in the oxide film. A linear relationship between the EL intensity and the current transport is observed. The current transport evolves with both the concentration and distribution of the nc-Si, and so does the EL. With the knowledge of the dependence of the transport on the concentration and distribution of the nc-Si, one can predict the effect of the implantation recipe on the EL intensity.T204A201 (ARC 1/04

Development of nanocrystal memory devices

In this project, we have fabricated non-volatile memory (NVM) devices based on silicon nanocrystals. The nanocrystals are synthesized with very-low energy ion beam technique, and the size of the nanocrystals is ~ 4 nm as determined from TEM measurement. The fabrication of the memory devices is fully compatible with the conventional CMOS process. The memory characteristics, reliability, and the effects of tunnel oxide thickness and programming mechanisms have been investigated. Channel-hot-electron programming is found to yield a better memory performance and reliability. Promising device results have been presented, demonstrating low-voltage operation for comparable memory windows, and good thin tunnel oxide retention performance that suggests to meet long-term nonvolatility requirements. An important issue for nanocrystal memory found in this work is the charge trapping in the control oxide during the programming operation. The charge trapping leads to an increase in the threshold voltage for both the programmed and erased states during repeated programming/erasing operations. This problem could be overcome by development of high quality oxides and/or device design solutions

Studies of metal - semiconductor contacts: current transport, photovoltage, schottky barries heights and fermi level pinning

published_or_final_versionPhysicsDoctoralDoctor of Philosoph

Post stress reliability in submicron MOSFET devices

In this project, we have conducted a systematic investigation of post-breakdown conduction and its instability in ultrathin SiO2 films as well as various studies of interface degradation, charge trapping and oxide barrier height change in deep submicron MOS devices with ultrathin gate oxide caused by electrical stress.RG 52/9