Band Maximum (band + maximum)

Distribution by Scientific Domains


Selected Abstracts


A Cyclic Porphyrin Tetramer Linked by Azo and Butadiyne Bridges

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2010
Bruno Ba
Abstract A soluble cyclic porphyrin oligomer (CPO) consisting of four 5,10-diarylporphyrins linked by alternating azo and butadiyne bridges has been synthesised via an aminated dinickel(II) butadiyne dimer. This is the first cyclic tetramer that combines both azo and butadiyne bridges and extends the azoporphyrin family, which comprises only a very few examples. The electronic absorption spectrum of the tetramer is more similar to spectra of azoporphyrins than to those of butadiyne-linked dimers or tetramer, exhibiting a two-component Soret band with a splitting of 4190 cm,1 and a strongly red-shifted Q band maximum at 735 nm. [source]


Reconstitution of Photosystem II Reaction Center with Cu-Chlorophyll a

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 11 2006
Shuang Liu
Abstract An isolated photosystem (PS) II reaction center (RC) with altered pigment content was obtained by chemical exchange of native chlorophyll a (Chl) with externally added Cu-Chl a (Cu-Chl). Pigment composition and spectroscopic properties of the RC exchanged with Cu-Chl were compared with native RC and RC treated with Chl in the same way. High-performance liquid chromatography analysis showed approximately 0.5 Cu-Chl per two pheophytin in the Cu-Chl-reconstituted RC preparation. Insertion of Cu-Chl resulted in a decrease in absorption at 670 nm and an increase at 660 nm, suggesting that the peripheral Chl may have been displaced. Fluorescence emission spectra of the Cu-Chl-reconstituted RC displayed a marked decrease in fluorescence yield and a blue shift of the band maximum, accompanied by the appearance of a broad peak at a shorter wavelength, indicating that energy transfer in the modified RC was disturbed by Cu-Chl, a quencher of the excited state. However, there were few differences in the circular dichroism (CD) spectra, suggesting that the arrangement of pigments and proteins responsible for the CD signal was not significantly affected. In addition, no obvious change in peptide components was found after the exchange procedure. (Managing editor: Ping He) [source]


Multiband optical photometry and bolometric light curve of the Type Ia supernova 2004S

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
Kuntal Misra
ABSTRACT We present BVRCIC broad-band CCD photometry of the Type Ia supernova SN 2004S, which appeared in the galaxy MCG,05-16-021, obtained during 2004 February 12 to March 22. We present multiband and bolometric light curves constructed using our data as well as other available data. The time of the B -band maximum and the peak magnitudes in different bands are obtained using fits of light-curve and colour templates. We clearly see a strong shoulder in the RC band and a second maximum in the IC band. SN 2004S closely resembles SN 1992al after maximum. From the peak bolometric luminosity, we estimate the ejected mass of 56 Ni to be 0.41 M,. [source]


Subgap states, doping and defect formation energies in amorphous oxide semiconductor a-InGaZnO4 studied by density functional theory

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2010
Toshio Kamiya
Abstract Amorphous In-Ga-Zn-O (a-IGZO) is expected for channel layers in thin-film transistors (TFTs). It is known that a-IGZO is sensitive to an O/H-containing atmosphere; therefore, it is important to clarify the roles of oxygen and hydrogen in a-IGZO. This paper provides atomic and electronic structures, formation energies of defects and bond energies in a-IGZO calculated by first-principles density functional theory (DFT). It was confirmed that oxygen deficiencies having small formation energies (2,3.6,eV) form either deep fully-occupied localized states near the valence band maximum or donor states, which depend on their local structures. All the hydrogen doping form OH bond and work as a donor. The stable OH bonds have small formation energy of ,0.45,eV and consist of three metal cations coordinated to the O ion. The bond energy of GaO is calculated to be ,2.0,eV, which is the largest among the chemical bonds in a-IGZO (1.7,eV for InO and 1.5,eV for ZnO). This result supports the idea that the incorporation of Ga stabilizes a-IGZO TFTs. [source]


Development and characterization of light-emitting diodes (LEDs) based on ruthenium complex single layer for transparent displays

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008
G. Santos
Abstract In this work, two ruthenium complexes, [Ru(bpy)3](PF6)2 and [Ru(ph2phen)3](PF6)2 in poly(methylmethacrylate) matrix were employed to build single-layer light-emitting electrochemical cells by spin coating on indium tin oxide substrate. In both cases the electroluminescence spectra exhibit a relatively broad band with maxima near to 625 nm and CIE (x, y) color coordinates of (0.64, 0.36), which are comparable with the photoluminescence data in the same medium. The best result was obtained with the [Ru(bpy)3](PF6)2 device where the optical output power approaches 10 W at the band maximum with a wall-plug efficiency higher than 0.03%. The lowest driving voltage is about 4 V for an electrical current of 20 mA. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Doping-dependence of subband energies in quantized electron accumulation at InN surfaces

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2007
T. D. Veal
Abstract Electron tunnelling spectroscopy is used to investigate the quantized electron accumulation at the surfaces of wurtzite InN with different doping levels. The tunnelling spectra of InN-oxide-tip junctions recorded in air at room temperature exhibit a ,0.6 V plateau, corresponding to the band gap of InN, and a gap between onsets of 1.3 V, consistent with the separation between the valence band maximum and the pinned Fermi level at the oxidized InN surface. Also observed within the tunnelling spectra are additional features between the conduction band minimum and the pinned Fermi level. These features are attributed to surface-bound quantized states associated with the potential well formed by the downward band bending at the InN-oxide interface. Their energetic positions are dependent upon the doping level of the InN films and coincide with calculated subband energies. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Negative electron affinity on hydrogen terminated diamond

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2005
D. Takeuchi
Abstract Total photoyield spectroscopy (TPYS) is applied to characterize the surface electronic properties of p- and n-type chemical-vapour-deposited (111) homoepitaxial diamond films with hydrogen terminated (H-terminated) surfaces. All experiments on H-terminated high quality diamond show the same threshold energy of 4.4 eV and comparable spectra in the regime 4.4,5.5 eV. A H-terminated intrinsic IIa (100) sample also show the same result. The onset of electron emission at 4.4 eV on p-, intrinsic and n-type diamond indicates that Fermi levels do not affect the sub-band spectra. Obviously, direct excitation of valence-band electrons into the vacuum takes place in the close vicinity of the surface. If we assume a transition from valence band maximum the threshold energy of 4.4 eV gives a negative electron affinity (NEA) of ,1.07 eV (Eg, 5.47 eV). TPYS therefore allows a precise and direct detection of the NEA of H-terminated diamond. It is interesting that the expected rise of photoyield as NEA in the regime hv > 5.47 eV is missing in n-type diamond. We attribute this to a surface space charge region due to ionized phosphorus atoms. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Temperature dependence of photoluminescence from CdS nanoclusters formed in the matrix of Langmuir-Blodgett film

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006
E. A. Bagaev
Abstract In this paper photoluminescence from CdS nanoclusters formed in the matrix of Langmuir-Blodgett film has been investigated in the temperature range 5-300 K. The photoluminescence spectrum of the nanoclusters at 300 K consists of two bands at 2.9 and 2.1 eV. Temperature dependence of the high-energy band maximum deviates from the dependence of the energy bandgap of bulk CdS. The integrated PL intensity of this band decreases with increasing temperature up to 75 K, grows in a temperature range 150-230 K, and rapidly falls at temperatures higher 230 K. The experimental data have been explained within the framework of a model of recombination of carriers considering carrier transport between CdS nanoclusters. An energy of electron traps and activation energies of nonradiative recombination have been estimated to be about 120, 4 and 100 meV, respectively. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]