517 research outputs found
In situ growth regime characterization of cubic GaN using reflection high energy electron diffraction
Cubic GaN layers were grown by plasma-assisted molecular beam epitaxy on
3C-SiC (001)substrates. In situ reflection high energy electron diffraction was
used to quantitatively determine the Ga coverage of the GaN surface during
growth. Using the intensity of the electron beam as a probe,optimum growth
conditions of c-GaN were found when a 1 ML Ga coverage is formed at the
surface. 1 micrometer thick c-GaN layers had a minimum surface roughness of 2.5
nm when a Ga coverage of 1 ML was established during growth. These samples
revealed also a minimum full width at half maximum of the (002)rocking curve.Comment: 3pages with 4 figure
Estimates of rates for dissociative recombination of NO + e via various mechanisms
We estimate rates for the dissociative recombination (DR) of NO +
e. Although accurate excited state potential energy curves for the excited
states of the neutral are not available, we estimate that the 1 {\Phi}
and the 1 {\Pi} states of the neutral may intersect the ground state
cation potential energy surface near its equilibrium geometry. Using fixed
nuclei scattering calculations we estimate the rate for direct DR via these
states and find it to be significant. We also perform approximate calculations
of DR triggered by the indirect mechanism, which suggest that the indirect DR
rate for NO is insignificant compared to the direct rate.Comment: Submitted to Phys Rev
Effect of growth conditions on optical properties of CdSe/ZnSe single quantum dots
In this work, we have investigated the optical properties of two samples of
CdSe quantum dots by using submicro-photoluminescence spectroscopy. The effect
of vicinal-surface GaAs substrates on their properties has been also assessed.
The thinner sample, grown on a substrate with vicinal surface, includes only
dots with a diameter of less than 10 nm (type A islands). Islands of an average
diameter of about 16 nm (type B islands) that are related to a phase transition
via a Stranski-Krastanow growth process are also distributed in the thicker
sample grown on an oriented substrate. We have studied the evolution of
lineshapes of PL spectra for these two samples by improving spatial resolution
that was achieved using nanoapertures or mesa structures. It was found that the
use of a substrate with the vicinal surface leads to the suppression of
excitonic PL emitted from a wetting layer.Comment: 2pages, 2 figures, Proceedings of International Conference On
Superlattices Nano-Structures And Nano-Devices, July, Toulouse, France, to
appear in the special issue of Physica
Ultrafast Excited-state Proton Transfer Processes: Energy Surfaces and On-the-fly Dynamics Simulations
The excited-state intramolecular proton transfer (ESIPT) is reviewed for several benchmark systems [o-hydroxybenzaldehyde (OHBA), salicylic acid and 2-(2′-hydroxyphenyl)-benzothiazole (HBT)] in order to verify the applicability of the time-dependent density functional theory (TDDFT) and the resolution-of-the-identity approximate second-order coupled cluster (RI-CC2) methods. It was found that these approaches are very well suited for the description of ESIPT processes. A comparative investigation of previous and new excited-state dynamics simulations is performed for HBT, 10-hydroxybenzo[h]quinoline (HBQ), and [2,2′-bipyridyl]-3,3′-diol (BP(OH)2). The time scale for the ESIPT process in these systems ranges in the time interval of 30−40 fs for HBT and HBQ and amounts to about 10 fs for the first proton transfer step in BP(OH)2. The dynamics simulations also show that the proton transfer in HBT is strongly supported by skeletal modes and the proton plays a rather passive role, whereas in HBQ a semipassive mechanism is found due to its increased rigidity in comparison to HBT. The special role of the double proton transfer in BP(OH)2 is discussed as well
Universality of electron accumulation at wurtzite c- and a-plane and zinc-blende InN surfaces
Electron accumulation is found to occur at the surface of wurtzite (112¯0), (0001), and (0001¯) and zinc-blende (001) InN using x-ray photoemission spectroscopy. The accumulation is shown to be a universal feature of InN surfaces. This is due to the low Г-point conduction band minimum lying
significantly below the charge neutrality level
Cycloaddition of Strained Cyclic Alkenes and Ortho-Quinones: A Distortion/Interaction Analysis
The chemistry of strained unsaturated cyclic compounds has experienced remarkable growth in recent years via the development of metal−free click reactions. Among these reactions, the cycloaddition of cyclopropenes and their analogues to ortho-quinones has been established as a highly promising click reaction. The present work investigates the mechanism involved in the cycloaddition of strained dienes to ortho-quinones and structural factors that would influence this reaction. For this purpose, we use B97D density functional theory calculations throughout, and for relevant cases, we use spin component−scaled MP2 calculations and single−point domain-based local pair natural orbital coupled cluster (DLPNO-CCSD(T)) calculations. The outcomes are analyzed in detail using the distortion/interaction model, and suggestions for future experimental work are made
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Shaping (non)-discursive social media spaces: Cross-national typologies of news organizations' heavy commenters
This study examines the role of heavy commenters on social media. We propose typologies of heavy commenters on Facebook pages of six news organizations in two systems that historically embraced different discourse cultures—the United States and Germany. We find that discourse cultures are impacted by news outlet and country: the US discourse is more participatory in terms of comment frequency, but further characterized by a strong non-discursive culture compared to a participatory liberal discourse culture in Germany. Frequency of commenting as normative ideal of social media sites (e.g. web traffic) does not lead to higher amounts of deliberation. On the contrary, it may contribute to what we conceptualize as the non-discursive model. As an expression of this, heavy commenters in the United States more often perform hate watching that manifests in hostile commenting on stories that are incongruent with their political ideologies. Implications for the democratic function of media organizations on social media are discussed
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