Suppression of electron scattering resonances in graphene by quantum dots

Transmission of low-energetic electrons through two-dimensional materials leads to unique scattering resonances. These resonances contribute to photoemission from occupied bands where they appear as strongly dispersive features of suppressed photoelectron intensity. Using angle-resolved photoemission we have systematically studied scattering resonances in epitaxial graphene grown on the chemically differing substrates Ir(111), Bi/Ir, Ni(111) as well as in graphene/Ir(111) nanopatterned with a superlattice of uniform Ir quantum dots. While the strength of the chemical interaction with the substrate has almost no effect on the dispersion of the scattering resonances, their energy can be controlled by the magnitude of charge transfer from/to graphene. At the same time, a superlattice of small quantum dots deposited on graphene eliminates the resonances completely. We ascribe this effect to a nanodot-induced buckling of graphene and its local rehybridization from sp$^{2}$ to sp$^{3}$ towards a three-dimensional structure. Our results suggest nanopatterning as a prospective tool for tuning optoelectronic properties of two-dimensional materials with graphene-like structure.Comment: The following article has been submitted to Applied Physics Letters. If it is published, it will be found online at http://apl.aip.or

Resilience Through Adversity: A Narrative Case Study of Students\u27 Experiences of Expulsion from School

Expulsion from school is life changing. This single event can alter the trajectory of a student\u27s life--for better or for worse. How life changes is unique for each individual student. Risk and protective factors that impact an individual student\u27s resilience determine the level of positive or negative outcomes experienced as a result of expulsion. Educators have the opportunity to take advantage of this disruption in students\u27 education to improve the trajectory of students\u27 lives. However, without thoughtful intervention from caring educators, this interruption in students\u27 education may have an irreparable destructive impact on students\u27 future. The purpose of this study was to understand the expulsion experience from the point of view of the student in order to represent this critical stakeholder group in future policy and program development, implementation, and decision-making. Students\u27 narratives are a means for members of the educational community to access students\u27 experiences and perceptions in order to understand the impact of expulsion on students\u27 lives. Students\u27 perspectives are presented through thick description in this narrative case study. The experience of these eight students is evidence that expulsion can change students\u27 lives in a positive way. Knowing this, responsible educators must develop interventions for expelled students that channel the positive life-changing potential of this experience. Educators must develop interventions focused on bringing forth protective factors that are documented to increase resilience and to make students less susceptible to the risks inherent in removing them from school. Recommendations for educators and policy-makers are presented to assist educators in preventing expulsion and improving educational and socio-emotional outcomes for expelled students

Седьмой Международный симпозиум по артишоку, кардону и их диким сородичам

Artichoke is a very promising culture in the world due to a wide range of horticulturally valuable characteristics. Each 3 year the international symposiums take place around the world to join scientists, breeders, company managers, industrial experts. In this year, The «Bretagne Biotechnologie Vegetale» institute (France) was bidding to host the 7th symposium on artichoke under the aegis of International Society for Horticulture Science ISHS, and other institutions.Седьмой Международный симпозиум по артишоку, кардону и их диким сородичам (7th International Symposium on Artichoke, Cardoon and their wild relatives) проходил с 16 по 19 июня 2009 года во Франции. Интерес к этой культуре в мире не случаен - это очень полезная, обладающая широким спектром целебных свойств культура. Для координации работы ученых, крупных производителей артишоков в решении проблем данной культуры каждые 3 года проходят симпозиумы в различных странах мира. Организатором 7-го симпозиума выступил институт Bretagne Biotechnologie Vegetale (BBV) под эгидой международной организации садоводства ISHS, и других международных организаций

Band Renormalization of Blue Phosphorus on Au 111

Most recently, theoretical calculations predicted the stability of a novel two dimensional phosphorus honeycomb lattice named blue phosphorus. Here, we report on the growth of blue phosphorus on Au 111 and unravel its structural details using diffraction, microscopy and theoretical calculations. Most importantly, by utilizing angle resolved photoemission spectroscopy we identify its momentum resolved electronic structure. We find that Au 111 breaks the sublattice symmetry of blue phosphorus leading to an orbital dependent band renormalization upon the formation of a 4 4 superstructure. Notably, the semiconducting two dimensional phosphorus realizes its valence band maximum at 0.9 eV binding energy, however, shifted in momentum space due to the substrate induced band renormalizatio

Laser Irradiation as a Tool to Control the Resonance Energy Transfer in Bacteriorhodopsin–Quantum Dot Bio-Nano Hybrid Material

 Bacteriorhodopsin (BR) is a natural photosensitive protein which can be considered promising in photovoltaics and optoelectronics because of its ability to produce a pronounced electrochemical response and controllably change its absorption spectrum under light excitation. However, its applicability is limited by its narrow absorption spectrum and low values of the absorption cross sections. Semiconductor quantum dots (QDs), which have high one- and two-photon absorption cross-sections in a UVand NIR spectral regions, respectively, can significantly improve the light sensitivity of BR by means of Förster resonance energy transfer (FRET) from QD to BR. In this work, we demonstrate the possibility to control the efficiency of FRET from QD to BR within electrostatically bound complexes of QD and purple membranes (PM) containing BR. We show that laser irradiation of QDs at different wavelengths leads to distinct changes (rise or decrease) of QD luminescence quantum yield (QY) without changing of QD structure. Such photo-induced changes in the QY of QD lead to a corresponding change in the efficiency of FRET. We have estimated efficiencies of FRET from QD to BR in the PM complexes composed of irradiated and non-irradiated QDs and found the increase in FRET efficiency with irradiated QDs

One-dimensional electronic structure of phosphorene chains

Phosphorene, a 2D allotrope of phosphorus, is technologically very appealing because of its semiconducting properties and narrow band gap. Further reduction of the phosphorene dimensionality may spawn exotic properties of its electronic structure, including lateral quantum confinement and topological edge states. Phosphorene atomic chains self-assembled on Ag(111) have recently been characterized structurally but were found by angle-resolved photoemission (ARPES) to be electronically 2D. We show that these chains, although aligned equiprobably to three directions of the Ag(111) surface, can be characterized by ARPES because the three rotational variants are separated in the angular domain. The dispersion of the phosphorus band measured along and perpendicular to the chains reveals pronounced electronic confinement resulting in a 1D band, flat and dispersionless perpendicular to the chain direction in momentum space. Our density functional theory calculations reproduce the 1D band for the experimentally determined structure of P/Ag(111). We predict a semiconductor-to-metal phase transition upon increasing the density of the chain array so that a 2D structure would be metallic

A Study of Emission Power and Spectrum of LT-GaAs Based THz Photoconductive Antennas

AbstractEmission spectra of LT-GaAs photoconductive antennas based on epitaxial films of “low-temperature” gallium arsenide (LT-GaAs) are measured in the terahertz frequency region by the Fourier transform spectroscopy

On a possible observation of "dihelion" in dissociation of relativistic 9^9C nuclei

Nuclear track emulsion is exposed to 1.2 A $^9$C GeV nuclei. Pairs of 2$^3$He nuclei having unusually narrow opening angles are observed in channel $^9$C $\rightarrow$ 3$^3$He pointing to the possible 2$^3$He resonance near the production threshold.Comment: Nuclear Physics in Astrophysics - V 2011 preprint Journal of Physics - Conference Serie