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Electron States (electron + states)
Selected AbstractsPhotoluminescence effects on gold nano- particles modified by short single stranded DNA moleculesMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4 2009O. Kysil Gold-Nanopartikel; Einzelstrang DNA; sichtbare Photolumineszenz; Photosensor Abstract The concept for a function of gold nanoparticle photosensor based on gold nanoparticle optical properties, depending on the size and architecture of their self , assemblies, is revised from the studies of modified by short ssDNA (5.4 nm length) selected gold nanoparticle (8.6 nm diameter) assembling in biosuspensions. Biosensing effect, collective photoluminescence in visible range of different size 2D, 3D assemblies from these nanoparticles, is revealed due to their controlled assembling in biosuspesions, dependent on ssDNA conformation, that changes gold core capping and therefore a force of interparticle interaction. Nanophotosensor is characterized by intensive photoluminescence maxima in two regions of visible range for tested biosuspensions due to detected difference in the self - assemblies' architecture of gold nanoparticles with different gold core capping by the ssDNA molecules. The emission maxima are 4.2x103 pps and 4.1x104 pps in (525,780) nm and (780,920) nm regions mainly for 2D assemblies as nanowires and 3D assemblies as circle holms, correspondently, in DNA buffer suspensions with different biomolecules. The results are explained addressing photoluminescence of gold nanoparticle assemblies to system of discrete electron states in valence and conductivity bands for gold nanoparticle model. Photolumineszenz-Effekt auf Gold Nanopartikel vermittelt durch kurze Einzelstrang DNA Moleküle Das Konzept für die Funktion der Goldpartikel Nanophotosensoren basiert auf den optischen Eigenschaften der Gold Nanopartikel abhängig von der Größe und Architektur ihrer ,Self-Assemblies", und wird auf Basis von Studien von kurzen ssDNA (5.4 nm Länge) mit ausgewählten sich in Biosuspensionen versammelnden Gold Nanopartikeln (8.6 nm Durchmesser) revidiert. Der Biosensoreffekt, sichtbar durch die gesammelte Photolumineszenz im sichtbaren Spektrum von verschieden großen 2D und 3D-Aggregaten von diesen Nanopartikeln, wird wegen ihrer kontrollierten Ansammlung in Biosuspensionen, welche in Abhängigkeit zu den kurzen ssDNA Konformation, dem Ändern der monomolekularen Bedeckungsschicht des Goldkerns und somit durch eine Kraft der Teilchen-Wechselwirkung offenbart. Der Nanophotosensor ist durch zwei intensive Photolumineszenz-Maxima im Bereich des sichtbaren Spektrums für derart geprüfte Biosuspensionen wegen des meßbaren Unterschieds in der Selbstanordnung von Gold Nanopartikeln mit dem verschiedenen Goldkernbedeckungen durch die ssDNA Stränge charakterisiert: Emissionsmaxima liegen bei 4.2x103 pps und 4.1x104 pps in den Wellenlängenbereichen von (525,780) nm und (780,920) nm, jeweils hauptsächlich für 2D-Aggregate als Nanodrähte und 3D-Aggregate in kreisförmiger Anordnung in DNA-Puffersuspendierungen mit verschiedenen Biomolekülen. Die Ergebnisse werden Mithilfe der Adressierung der Photolumineszenz von Gold Nanopartikel-Aggregaten zu System von getrennten Elektronzuständen in Valenz und Leitungsbändern entsprechend den Gold Nanopartikel-Modellen erklärt. [source] Effect of hydrogen on electronic structure of fcc iron in relation to hydrogen embrittlement of austenitic steelsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007S. M. Teus Abstract The total structural energy per primitive lattice cell, density of electron states, spatial distribution of electrons and elastic modulus in fcc Fe,H solid solutions are studied using the density functional theory and Wien2k program package. It is shown that hydrogen increases the density of electron states at the Fermi level. The density of conduction electrons is increased in the vicinity of hydrogen atoms, which suggests that the latter migrate over the crystal lattice surrounded by the clouds of conduction electrons. Calculations of elastic modulus show that hydrogen decreases the shear modulus c44. The consequences for mechanical properties of hydrogen-charged austenitic steels are analysed taking into account the stress for activation of dislocation sources, the line tension of dislocations and the distance between dislocations in pile-ups. It is concluded that hydrogen-induced brittleness of austenitic steels can be satisfactorily interpreted in terms of the hydrogen effect on the electronic structure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006Hamid Haratizadeh Abstract We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time-resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Symmetry of electron states and optical transitions in GaN/AlN hexagonal quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2004P. Tronc Abstract The exact symmetry of hexagonal quantum dots (QDs) made of materials with the wurtzite structure such as GaN/AlN QDs for example, is described by the C3v point group and does not depend on the existence of a wetting layer. We have determined the possible exact symmetries of electron states and vibration modes in the dots and derived the optical selection rules. The vibration modes involved in the Frölich interaction are totally symmetric with respect to the C3v group and can induce transitions only between states with the same symmetry. The not totally symmetric modes provide other channels for lowering the energy of excited carriers and excitons by connecting states with symmetries different one from another. The rapid decay of created polarons, due to the short lifetime of vibration modes, releases the carriers and excitons into ground levels. In the envelope function approximation (EFA), the symmetry of the dots is represented by the C6v point group. Interband transitions are allowed only between states whose envelope functions have the same symmetry. EFA artificially increases the number of dark exciton symmetries. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Angle-resolved photoelectron spectroscopy study of the GaN(0001)-2×2 surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010P. Lorenz Abstract GaN(0001)-2×2 surfaces were investigated by angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) as well as X-ray photoelectron spectroscopy (XPS). Contamination- and metal-free GaN thin films with a 2×2 reconstruction and a rms roughness below 1 nm were grown on 6H-SiC(0001) by plasma assisted molecular beam epitaxy (PAMBE). The valence band structure of the surface was investigated in-situ with ARUPS along the and directions of the surface Brillouin zone. Weak dispersive surface states related to the unreconstructed GaN surface or to the 2×2 superstructure as well as the dispersion of electron states of the bulk band structure are identified and compared to available results from density functional theory (DFT) calculations [Phys. Rev. B 77, 115120 (2008)] for GaN(0001). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of electronic correlations on the frequency-dependent hopping transport in Si:PPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008Elvira Ritz Abstract At low energy scales charge transport in the insulating Si:P is dominated by activated hopping between the localized donor electron states. Thus, theoretical models for a disordered system with electron-electron interaction are appropriate to interpret the electric conductivity spectra. With a newly developed technique we have measured the complex broadband microwave conductivity of Si:P from 100 MHz to 5 GHz in a broad range of phosphorus concentration n /nc from 0.56 to 0.95 relative to the critical value nc = 3:5 × 1018 cm,3 corresponding to the metal-insulator transition driven by doping. At our base temperature of T = 1.1 K the samples are in the zero-phonon regime where they show a super-linear frequency dependence of the conductivity indicating the influence of the Coulomb gap in the density of the impurity states. At higher doping n , nc, an abrupt drop in the conductivity power law ,1(,) , ,, is observed. The dielectric function ,1 increases upon doping following a power law in (1 , n /nc). Dynamic response at elevated temperatures has also been investigated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Deep electron states in indium-doped Cd0.93Mn0.07Te DLTS studyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006A. Hajdusianek Abstract Electron traps in indium doped Cd0.93Mn0.07Te were studied with Deep Level Transient Spectroscopy. Five electron traps were found (labeled as E1 - E5). Energy levels ET of related defects are equal to ET 1 = 0.09 eV, ET 2 = 0.12 eV, ET 3 = 0.18 eV, ET 4 = 0.56 eV and ET 5 = 0.65 eV. Three of them (E1, E2, E3 ) are related to the defects with thermally activated capture cross section. Electric field enhanced electron emission from the trap E4 was observed and described in the terms of the Poole-Frenkel - mechanism. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||