Superradiant lasing from J-aggregated molecules adsorbed onto colloidal silver

Cataloged from PDF version of article.The picosecond time-resolved emission spectrum of the cyanine dye 1,18-diethyl-3,38- bis-~3-sulfopropyl!-5,58,6,68-tetrachlorobenzimidazolocarbocyanine ~also known as BIC! adsorbed onto colloidal silver was examined as a function of laser pulse energy at room temperature. BIC is found to aggregate on colloidal silver, and the number of coherently responding molecules involved in the one-exciton state ~i.e., the coherence length! was estimated to involve 8–9 molecules. Lasing at a remarkably low incident pulse energy threshold was found for this system and explained in terms of a mechanism involving superradiant states created in coherently coupled adsorbed molecules that emit photons which stimulate emission from other spatially distributed superradiant states. © 1998 American Institute of Physics

Steady state and picosecond time-resolved photophysics of a benzimidazolocarbocyanine dye

Cataloged from PDF version of article.We report the steady-state and the excited state properties of 1, 3, 1', 3' -tetraethyl-5, 6, 5', 6' -tetrachlorobenzimidazolocarbocyanine iodide (TTBC) in various solvents. The magnitude of the Stokes shift and the average transition energy proves that the structure of the fluorescent state should be very similar to that of the ground-state structure. The fluorescence lifetimes and quantum yields indicate that non-radiative processes are collectively much more effective than the radiative processes. It is therefore suggested that the non-radiative processes, which are driven by the medium around the TTBC molecule control the excited state dynamics. r 2002 Elsevier Science B.V. All rights reserved

The effect of uncertainty on learning in game-like environments

Cataloged from PDF version of article.Considering the role of games for educational purposes, there has an increase in interest among educators in applying strategies used in popular games to create more engaging learning environments. Learning is more fun and appealing in digital educational games and, as a result, it may become more effective. However, few research studies have been conducted to establish principles based on empirical research for designing engaging and entertaining games so as to improve learning. One of the essential characteristics of games that has been unexplored in the literature is the concept of uncertainty. This study examines the effect of uncertainty on learning outcomes. In order to better understand this effect on learning, a game-like learning tool was developed to teach a database concept in higher education programs of software engineering. The tool is designed in two versions: one including uncertainty and the other including no uncertainty. The experimental results of this study reveal that uncertainty enhances learning. Uncertainty is found to be positively associated with motivation. As motivation increases, participants tend to spend more time on answering the questions and to have higher accuracy in these questions

Optical transition rates of a meso-substituted thiacarbocyanine in methanol-in-oil reverse miscelles

Cataloged from PDF version of article.We report the photophysical properties of 3,3′-diethyl-5,5′-dichloro-9-phenylthiacarbocyanine (DDPT) in methanol-in-oil (m/o) reverse micellar systems which form methanol droplets stabilized with anionic surfactant aerosol-OT (AOT) in n-heptane. The fluorescence quantum yield of DDPT is enhanced by a factor of 17 in the methanol droplet in comparison with bulk methanol. The fluorescence lifetimes of DDPT in m/o reverse micelles are prolonged up to 2.2 ns with increasing molar ratio of methanol to surfactant (w0=[MeOH]/[AOT]), whereas the fluorescence lifetime of DDPT in bulk methanol is 75 ps. The non-radiative rate constants of DDPT in the droplets are decreased by a factor of 40, resulting in a remarkable enhancement in quantum yields, indicating that internal motions of DDPT in the droplets are significantly reduced due to strong electrostatic interactions between the positively charged DDPT and the negatively charged sulfonate head-groups of AOT and the spatial confinement induced by the reverse micellar structure. © 2004 Elsevier B.V. All rights reserved

Epitaxial growth mechanisms of graphene and effects of substrates

Cataloged from PDF version of article.The growth process of single layer graphene with and without substrate is investigated using ab initio, finite temperature molecular dynamic calculations within density functional theory. An understanding of the epitaxial graphene growth mechanisms in the atomic level is provided by exploring the transient stages which occur at the growing edges of graphene. These stages are formation and collapse of large carbon rings together with the formation and healing of Stone-Wales like pentagon-heptagon defects. The activation barriers for the healing of these growth induced defects on various substrates are calculated using the climbing image nudge elastic band method and compared with that of the Stone-Wales defect. It is found that the healing of pentagon-heptagon defects occurring near the edge in the course of growth is much easier than that of Stone-Wales defect. The role of the substrate in the epitaxial growth and in the healing of defects are also investigated in detail, along with the effects of using carbon dimers as the building blocks of graphene growth

Structural and electrical characterizations of InxGa1-xAs/InP structures for infrared photodetector applications

Cataloged from PDF version of article.Three InGaAs/InP structures for photodetector applications were grown with different indium compositions by MBE technique. The structural properties of the samples have been obtained by means of high resolution X-ray diffraction and secondary ion mass spectrometry measurements. Three InGaAs/InP metal-semiconductor-metal devices were fabricated at room temperature. The experimental forward and reverse bias current-voltage characteristics of the devices such as ideality factor, barrier height, and saturation current were evaluated considering the structural properties of the grown structures. The carrier recombination lifetime and diffusion length in the devices were also calculated using carrier density and mobility data obtained with Hall effect measurement at room temperature. It was determined that all room temperature fabricated devices improved the Schottky barrier height. Especially, the device fabricated on the lower mismatched structure exhibited barrier height enhancement from 0.2 eV, which is the conventional barrier height to 0.642 eV. In addition, the obtained results show that the room temperature fabricated devices on InGaAs/InP structures can be convenient for infrared photodetector applications. (C) 2014 AIP Publishing LLC

On the profile of frequency and voltage dependent interface states and series resistance in (Ni/Au)/Al0.22Ga0.78N/AlN/GaN heterostructures by using current–voltage (I–V) and admittance spectroscopy methods

Cataloged from PDF version of article.In order to explain the experimental effect of interface states (N-ss) and series resistance (R-s) of device on the non-ideal electrical characteristics, current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/omega-V) characteristics of (Ni/Au)/Al0.22Ga0.78N/AlN/GaN heterostructures were investigated at room temperature. Admittance measurements (C-V and G/omega-V) were carried out in frequency and bias voltage ranges of 2 kHz-2 MHz and (-5 V)-(+5 V), respectively. The voltage dependent R-s profile was determined from the I-V data. The increasing capacitance behavior with the decreasing frequency at low frequencies is a proof of the presence of interface states at metal/semiconductor (M/S) interface. At various bias voltages, the ac electrical conductivity (sigma(ac)) is independent from frequencies up to 100 kHz, and above this frequency value it increases with the increasing frequency for each bias voltage. In addition, the high-frequency capacitance (C-m) and conductance (G(m)/omega) values measured under forward and reverse bias were corrected to minimize the effects of series resistance. The results indicate that the interfacial polarization can more easily occur at low frequencies. The distribution of N-ss and R-s is confirmed to have significant effect on non-ideal I-V. C-V and G/omega-V characteristics of (Ni/Au)/Al0.22Ga038N/AlN/GaN heterostructures. (C) 2011 Elsevier Ltd. All rights reserved

The exon 13 duplication in the BRCA1 gene is a founder mutation present in geographically diverse populations

Cataloged from PDF version of article.Recently, a 6-kb duplication of exon 13, which creates a frameshift in the coding sequence of the BRCA1 gene, has been described in three unrelated U.S. families of European ancestry and in one Portuguese family. Here, our goal was to estimate the frequency and geographic diversity of carriers of this duplication. To do this, a collaborative screening study was set up that involved 39 institutions from 19 countries and included 3,580 unrelated individuals with a family history of the disease and 934 early-onset breast and/or ovarian cancer cases. A total of 11 additional families carrying this mutation were identified in Australia (1), Belgium (1), Canada (1), Great Britain (6), and the United States (2). Haplotyping showed that they are likely to derive from a common ancestor, possibly of northern British origin. Our results demonstrate that it is strongly advisable, for laboratories carrying out screening either in English-speaking countries or in countries with historical links with Britain, to include within their BRCA1 screening protocols the polymerase chain reaction-based assay described in this report

Dissociative adsorption of molecules on graphene and silicene

Cataloged from PDF version of article.We study the interaction of H-2 , O-2 , CO, H-2 O and OH molecules with the vacancy defects of graphene and silicene. Atoms around the bare vacancy reconstruct and specific chemically active sites are created. While H-2 , O-2 and CO remain intact on both pristine graphene and silicene, these molecules can dissociate when they are placed at the close proximity of these chemically active sites and nucleate centers for the hydrogenation and oxygenation. Saturation of the dangling bonds at the defect sites by constituent atoms of dissociated molecules gives rise to significant modification of electronic and magnetic properties. We analyzed the mechanism of the dissociation and revealed a concerted action of surrounding host atoms together with dissociated molecules to lower the energy barrier needed for dissociation. The dissociations of H-2 O and OH are hindered by high energy barriers. Our study suggests that graphene and silicene can be functionalized by creating meshes of single vacancy, where specific molecules can dissociate, while some other molecules can be pinned

The profile of temperature and voltage dependent series resistance and the interface states in (Ni/Au)/Al0.3Ga0.7N/AlN/GaN heterostructures

Cataloged from PDF version of article.The profile of the interface state densities (N(ss)) and series resistances (R(s)) effect on capacitance-voltage (C-V) and conductance-voltage (G/omega-V) of (Ni/Au)/Al(x)Ga(1-x)N/AlN/GaN heterostructures as a function of the temperature have been investigated at 1 MHz. The admittance method allows us to obtain the parameters characterizing the metal/semiconductor interface phenomena as well as the bulk phenomena. The method revealed that the density of interface states decreases with increasing temperature. Such a behavior of N(ss) can be attributed to reordering and restructure of surface charges. The value of series R(s) decreases with decreasing temperature. This behavior of R(s) is in obvious disagreement with that reported in the literature. It is found that the N(ss) and R(s) of the structure are important parameters that strongly influence the electrical parameters of (Ni/Au)/Al(x)Ga(1-x)N/AlN/GaN(x = 0.22) heterostructures. In addition, in the forward bias region a negative contribution to the capacitance C has been observed, that decreases with the increasing temperature. Copyright (C) 2010 John Wiley & Sons, Ltd