Helical magnetic order and Fermi surface nesting in non-centrosymmetric ScFeGe

An investigation of the structural, magnetic, thermodynamic, and charge transport properties of non-centrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below $T_N = 36$ K. Neutron diffraction measurements discovered a temperature and field independent helical wavevector \textbf{\textit{k}} = (0 0 0.193) with magnetic moments of 0.53 $\mu_{B}$ per formula unit confined to the {\it ab}-plane. Density functional theory calculations are consistent with these measurements and find several bands that cross the Fermi level along the {\it c}-axis with a nearly degenerate set of flat bands just above the Fermi energy. The anisotropy found in the electrical transport is reflected in the calculated Fermi surface, which consists of several warped flat sheets along the $c$-axis with two regions of significant nesting, one of which has a wavevector that closely matches that found in the neutron diffraction. The electronic structure calculations, along with a strong anomaly in the {\it c}-axis conductivity at $T_N$, signal a Fermi surface driven magnetic transition, similar to that found in spin density wave materials. Magnetic fields applied in the {\it ab}-plane result in a metamagnetic transition with a threshold field of $\approx$ 6.7 T along with a sharp, strongly temperature dependent, discontinuity and a change in sign of the magnetoresistance for in-plane currents. Thus, ScFeGe is an ideal system to investigate the effect of in-plane magnetic fields on an easy-plane magnetic system, where the relative strength of the magnetic interactions and anisotropies determine the topology and magnetic structure.Comment: 15 pages, 13 figure

Scaling the state: Egypt in the third millennium BC

Discussions of the early Egyptian state suffer from a weak consideration of scale. Egyptian archaeologists derive their arguments primarily from evidence of court cemeteries, elite tombs, and monuments of royal display. The material informs the analysis of kingship, early writing, and administration but it remains obscure how the core of the early Pharaonic state was embedded in the territory it claimed to administer. This paper suggests that the relationship between centre and hinterland is key for scaling the Egyptian state of the Old Kingdom (ca. 2,700-2,200 BC). Initially, central administration imagines Egypt using models at variance with provincial practice. The end of the Old Kingdom demarcates not the collapse, but the beginning of a large-scale state characterized by the coalescence of central and local models

Remote Microwave Plasma Enhanced Chemical Vapour Deposition of SiO2 Films : Oxygen Plasma Diagnostic

Silicon oxide is deposited by remote microwave plasma enhanced chemical vapour deposition (RMPECVD). The silica films are produced by exciting oxygen in a microwave discharge while a mixture of 5% of silane diluted in argon is introduced downstream. In the afterglow, double Langmuir probe measurements and rotational temperatures deduced from optical emission spectroscopy (OES), show that the electron energy is transferred to the gas when the pressure increases (19 - 26 Pa). Therefore the electronic temperature decreases from 22000 to 11000 K and the gas temperature increases from 400 to 500 K. Moreover the microwave power (180 - 480 W) has an influence on the deposition rate and on the quality of SiO2 coatings (density and etch rate in an HF solution). This effect can be correlated with the increase in the electron density (0.7.1010 to 3.7.1010 cm-3) and of the gas temperature (400 to 460 K)

Remote Microwave Plasma Enhanced Chemical Vapour Deposition of Amorphous Carbon : Optical Emission Spectroscopy Characterisation of the Afterglow and Growth Rates

Amorphous carbon films were obtained by remote microwave plasma enhanced chemical vapour deposition (RMPECVD). In this process, a mixture of argon and hydrogen is excited in the microwave discharge while methane is injected in the afterglow. The substrates are radio-frequency (RF) biased in order to improve the film properties. Three configurations have been compared : microwave, RF, and mixed microwave-RF coupling. Optical emission spectroscopy allowed to compare intensities of a few spectral lines in the afterglow (CH, C2, H, and Ar lines) as a function of process conditions. Films have been characterised by infra-red (IR) spectroscopy and electron recoil detection analysis (ERDA). Stress in the films is in the range of -0.7 to -0.3 GPa (compressive). The influence of the hydrogen presence in the plasma, microwave power and radio-frequency bias voltage is discussed

RMPECVD of silica films with a high microwave power (1600 W) parametric studies

In a large scale plasma reactor, a high microwave power of 1600 W is necessary to obtain a homogeneous distribution of the plasma source. The increase of the microwave power allows to decrease the substrate temperature during the process (150 °C) with the formation of a dense silicon oxide layer. In the range of variation of the parameters studied (pressure, temperature, R (oxygen flow rate / silane flow rate)) little variations of the film characteristics (density, etch rate, ...) are observed. However, the ERDA analysis shows that a low pressure (0.13 mbar) and a limitation of the deposition rate (R = 160) allow to reduce the incorporation of impurities (H,C) in the oxide films. The FTIR spectra, systematically studied by the position, the full width at half-maximum and the area of the Si-O-Si band, enable to point out the composition and the morphology evolution of silicon oxide coatings and corroborate the previous results

Egypt at its Origins 4. Proceedings of the Fourth International Conference “Origin of the State. Predynastic and Early Dynastic Egypt”, New York, 26th-30th July 30, 2011

International audienc

Initial stage of C 60 cation formation in superacids

International audienceWhile superacids are solvents for individualizing carbon nanotubes, the behavior of insulating C 60 is different. The final ionization state depends on the superacid used. With chlorosulfonic acid, chlorination is observed while with fuming sulfuric acid, sulfonation has been reported. Both reactions are fast and it is important to characterize the first step to understand the involved reaction mechanisms. Employing Raman spectroscopy and first-principles calculations, we show that C 60 + is present with chlorosulfonic acid and surprisingly C 60 2+ ions are predominantly formed during the first seconds after immersion in fuming sulfuric acid