Topmost Band Research Articles

Grass Flora along Altitudinal Gradient of the Phulchoki Hill, Central Nepal

Phulchoki hill on the southern part of Kathmandu Valley (1550-2750 m) presents a unique opportunity to study the diversity of grasses along the altitudinal gradient. During the present study, 73 species of grasses belonging to 5 sub families, 16 tribes and 48 genera were recorded, out of which 28 species are new to this area. Among the recorded species 89% of the species were terrestrial, 7% lithophytes and remaining 4% aquatic. The lowest elevation (1550-1950 m) has highest diversity with 49 species whereas the topmost band (2351-2750 m) has least diversity with only 19 species. The total species richness of grass has decreasing trend along the altitudinal gradient of species, with r2 =0.97 and p=0.04, which indicates significant relation.

PORTRAYAL OF WOMAN IN THE CAVE PAINTINGS OF AJANTA

The thirty rock cut cave temples of Ajanta located near a village named “Ajistha” in Aurangabad district of Maharashtra state. The caves are carved in a half crescent shape overlooking the Waghora river. The caves are located at a picturesque location having beautiful natural surroundings. Because of this peace and godly environment Buddhist monks might have chosen this place for their artistic endeavour. The caves possess well carved sculptures, pillars, entrances and walls are embellished with beautiful paintings. The art of Ajanta flourished from 1st century BC to 7th century AD. The Ajanta art is considered as the classical age of Indian painting. The artists of Ajanta did not follow the law of perspective and represented the figures in its entirety rather than appeared through a normal eye. Ajanta artists tried to depict the whole view through horizontal bands. In the paintings at Ajanta, the background was painted at the topmost band, the middle part of the painting below it and the foreground below the middle ground.

Fractionation of Gold Nanorod Dimers by Stepwise Density Gradient Centrifugation

Gold nanorod dimers were prepared in aqueous solution. The nanorod dimers were separated from other nanorod assemblies by a stepwise density-gradient centrifugation using sucrose (20, 30, 40, 50, and 60% w/w). The centrifugation step (3400 × g, 20 min) produced two bands, a side-wall sediment, and a bottom precipitate. The topmost band contained nanorod monomers. The bottom precipitate was redispersed in water, and its surface plasmon band was consistent with that of a theoretical model of a nanorod dimer. Thus, density gradient centrifugation is effective in fractionizing nanorod dimers.

Polarization of defect related optical transitions in chalcopyrites

We investigate the symmetry of shallow acceptors in Cu chalcopyrites by polarization dependent photoluminescence measurements and density functional calculations. We determine the influence of the band symmetry versus the site symmetry. The polarization of the emitted or absorbed light is parallel to the c-axis in the case of CuGaSe2 and perpendicular to the c-axis in the case of CuInSe2. The symmetry of the defects depends in each case on the symmetry of the topmost band. Neither does the site symmetry affect the defect symmetry nor do the defects change the symmetry of the band.

Optical polarization of m ‐plane In‐GaN/GaN light‐emitting diodes characterized via confocal microscope

AbstractA confocal microscope was applied to characterize near‐field optical polarization of light emission from InGaN‐based light‐emitting diodes prepared on a nonpolar orientation. Detection of stray light was significantly reduced as a result of the confocal technique compared to broad‐area measurements. The confocal measurement required no special sample preparation and obtained data was directly interpretable. A polarization ratio of 0.83 was measured on long‐wavelength emitting devices and was sustained over two orders of magnitude of low current range. Energy shifts and separation of emission peaks for the two polarization components were evaluated to discuss the valence‐band structure. Energy shifts indicated that the topmost band |X 〉 had a heavier effective mass than the lower band |Z 〉. Splitting energy of InGaN was estimated to be 30 meV. Results were consistent with the past reports, thus it was confirmed that the confocal microscope is a valid technique to characterize near‐field optical polarization. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Valence band engineering for remarkable enhancement of surface emission in AlGaN deep‐ultraviolet light emitting diodes

AbstractValence band engineering for remarkable enhancement of surface emission in AlGaN deep‐ultraviolet (UV) light emitting diodes (LEDs) has been theoretically investigated by the calculation using the 6×6 k·p Hamiltonian. It has already been pointed out that the topmost valence band in deep‐UV AlGaN material has a Z‐like character and this causes the c‐axis polarized emission unfavourable for light extraction from c‐plane based LEDs. We have found, in this study, that this unfavourable polarization can be switched into favourable in‐plane polarization by decreasing quantum well (QW) width and/or introducing in‐plane compressive strain, which cause band‐crossing and change the character of the topmost band. It is also shown that such polarization changes occur in the QWs on semipolar substrates although that does not take place in those on nonpolar substrates. Furthermore, we have derived the condition of the polarization switch as an approximate analytical expression which could be useful for device structural design. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoemission and optical studies ofZrSe3,HfSe3, andZrS3

Angle-resolved photoemission spectroscopy (ARPES) and optical measurements were performed on single crystal samples of ZrSe3, HfSe3, and ZrS3, which belong to the class of low-dimensional band insulators. By ARPES, we traced the dispersion of the (S 3p, Se 4p) p-derived valence states. In all cases, the topmost band exhibits energy splitting increasing from S to Se, which we attribute to the spin-orbit interaction, similar to recent observations in the related layered dichalcogenides. The combination of optical and photoemission results allows us to address the issue of the gap feature in the absorption spectra and to characterize the electronic and vibrational properties of ZrSe3, HfSe3, and ZrS3.

Simulation study of angle-resolved photoemission spectra and intramolecular energy-band dispersion of a poly(tetrafluoroethylene) oligomer film.

Theoretical simulations of the angle-resolved ultraviolet photoemission spectra (ARUPS) for the oligomer of poly(tetrafluoroethylene) [(CF(2))(n); PTFE] were performed using the independent-atomic-center approximation combined with ab initio molecular orbital calculations. Previously observed normal-emission spectra for the end-on oriented sample (with long-chain axis perpendicular to the surface) showed the incident photon-energy (hnu) dependence due to the intramolecular energy-band dispersion along the one-dimensional chain, and the present simulations successfully reproduced this hnu dependence of the observed spectra. We employed the experimentally observed helical structure for PTFE oligomers for the simulations. We also calculated the density of states (DOS) for the planar zigzag structure, and examined the changes in the electronic structure due to the difference in the molecular structure by comparing the DOS for the helical and planar zigzag structures. Only a small change in the DOS was found between these structures, showing little change of the electronic structure between these conformations. We also evaluated the inner potential V(0), which is the parameter defining the energy origin of the free-electron-like final state, and checked the validity of the value of -10 eV estimated in our previous study using the experimentally observed hnu dependence of the peak intensity. The estimation of V(0) was performed by pursuing the best agreement between the energy-band dispersion [E=E(k)] relation along the chain direction obtained from the simulated spectra and the experimentally deduced one. An excellent agreement in the topmost band was achieved when the assumed inner potential V(0) was set at about zero. This value of V(0) is much different from the value of V(0)=-10 eV in the previous study, suggesting the invalidity of the previous assumption at the estimation of V(0) from the peak intensity variation with hnu. Using the presently obtained V(0), we could derive more reliable E=E(k) dispersion relation from the observed ARUPS spectra. The comparison of this newly derived relation gave good agreement with theoretically calculated E=E(k) relations, in contrast to the poor agreement for the previous results with V(0)=-10 eV.

Effect of dietary protein on calpastatin in canine skeletal muscle.

The cysteine proteinases, mu- and m-calpain, along with their inhibitor, calpastatin, have been hypothesized to play a role in skeletal muscle protein degradation. Because nutrition has previously been shown to influence the expression of calpastatin, the working hypothesis of this study was that the quantity and source of dietary protein could influence regulation of the calpain system in muscle. The objectives to support this hypothesis were to determine the effects of dietary protein (amount and source) on the expression of calpastatin in canine skeletal muscle. This study comprised eight diets with seven dogs per diet. A biopsy was taken from the biceps femoris of all 56 dogs before and after 10 wk on their respective diets. This experimental design allowed examination of change within individual dogs. Diets 1 to 4 contained 12% total protein derived from chicken and/or corn gluten meal in ratios of 100:0, 67:33, 33:67, and 0:100%, respectively. Diets 5 to 8 contained 28% total protein with protein sources and ratios identical to Diets 1 to 4. Differences in calpastatin were examined qualitatively using SDS-PAGE and immunoblotting, and semiquantitatively with densitometric analyses. The majority of the calpastatin blots showed three distinct calpastatin bands, the uppermost appearing at approximately 110 kDa. Diet 5 (28% CP, 100% chicken) resulted in an increase in the expression of the 110-kDa calpastatin band compared with the other two lower molecular weight bands in the same samples. Muscle from dogs fed Diet 5 showed greater increase in (P < 0.05) calpastatin intensity of the topmost band than those fed Diet 8 (0:100; chicken:corn gluten meal). Diet 5 (100:0; chicken:corn gluten meal) showed greater total calpastatin intensity than Diet 8 (0:100; chicken:corn gluten meal). These data suggest that dogs fed a diet containing a higher total percentage of chicken protein may have a greater potential to regulate calpain-mediated degradation of muscle protein than dogs fed diets containing corn gluten meal.

Electronic structure of wurtzite- and zinc blende-GaN studied by angle-resolved photoemission

The valence band structures of both wurtzite- and zinc blende-GaN were investigated by angle-resolved photoemission spectroscopy. It was found the k dispersions of the upper valence bands show band structures corresponding to wurtzite or zinc blende structure. In wurtzite-GaN, band width of the upper valence band is 6.7 eV in good agreement with the theoretically predicted value. However, the binding energy of Ga 3d level was found to be 15.7 eV relative to the valence band maximum, which is about 2 eV higher binding energy than those predicted by local density approximation calculations. In zinc blende-GaN, some discrepancies in the binding energy of the topmost bands around the valence band maximum was observed. We discuss the cause of these discrepancies by taking into account the strain effect.

Electronic Band Structure of Monolayer Bi on GaP(110)

The two-dimensional electronic band structure of monolayer Bi on GaP(110) has been mapped using angle-resolved UV photoelectron spectroscopy (ARUPS) with synchrotron radiation. Surface photovoltage effects are corrected for by simultaneous second-order core spectroscopy. From valence-band spectra along the four symmetry directions of the surface Brillouin zone at three photon energies it is possible to distinguish three states as surface related. The topmost band is found to be inside the fundamental band gap, at ca 0.75 eV above the bulk valence-band maximum. Comparison with other V/III-V(110) systems shows that this system is not significantly different, despite the relatively large size of the Bi atoms with respect to the GaP lattice; in a selective comparison with InP and GaAs it would appear that Bi-substrate anion bonding is a more important factor than strain.

Surface electronic structure of monolayer Bi on InP(110)

The two-dimensional electronic bandstructure of monolayer Bi on InP(110) has been mapped by angle resolved ultra violet photoelectron spectroscopy using synchrotron radiation. The dispersion of the features in the valence band spectra was followed along the four symmetry directions of the surface Brillouin zone. It is possible to distinguish five states as surface related. The topmost band is found to be inside the fundamental band gap, at about 0.45 eV above the valence band maximum. Limited application of polarisation effects was made to probe the nature of the states. In the absence of a suitable calculation, the results are compared to measurements and calculations of other V/III–V(110) systems.

Surface electronic structure of monolayer Bi on InP(110)

Abstract The two-dimensional electronic bandstructure of monolayer Bi on InP(110) has been mapped by angle resolved ultra violet photoelectron spectroscopy using synchrotron radiation. The dispersion of the features in the valence band spectra was followed along the four symmetry directions of the surface Brillouin zone. It is possible to distinguish five states as surface related. The topmost band is found to be inside the fundamental band gap, at about 0.45 eV above the valence band maximum. Limited application of polarisation effects was made to probe the nature of the states. In the absence of a suitable calculation, the results are compared to measurements and calculations of other V/III–V(110) systems.

Petrology of a Wealden Sandstone at Clock House, Capel, Surrey

The topmost band of sandstone in the Weald Clay at Capel (6) is now exposed for 100 yards, and varies in thickness from 8 inches at the southern end of the face to 1 foot at the northern end. The stone is glauconitic and highly micaceous, and carries so much fresh biotite on certain bedding-planes that they are heavily darkened. Flakes of biotite and muscovite commonly reach 2 mm. in diameter, and occasionally 3 mm. No petrological facies like it is known in the older Hastings Beds outcropping to the south and south-east. The petrography of the sandstone therefore merits description, and some discussion of the problems which it raises.