New electronic orderings observed in cobaltates under the influence of misfit periodicities

We study with ARPES the electronic structure of CoO2 slabs, stacked with rock-salt (RS) layers exhibiting a different (misfit) periodicity. Fermi Surfaces (FS) in phases with different doping and/or periodicities reveal the influence of the RS potential on the electronic structure. We show that these RS potentials are well ordered, even in incommensurate phases, where STM images reveal broad stripes with width as large as 80\AA. The anomalous evolution of the FS area at low dopings is consistent with the localization of a fraction of the electrons. We propose that this is a new form of electronic ordering, induced by the potential of the stacked layers (RS or Na in NaxCoO2) when the FS becomes smaller than the Brillouin Zone of the stacked structure

Heavy ion beam measurement of the hydration of cementitious materials

The setting and development of strength of Portland cement concrete depends upon the reaction of water with various phases in the Portland cement. Nuclear resonance reaction analysis (NRRA) involving the 1H(15N,α,γ)12C reaction has been applied to measure the hydrogen depth profile in the few 100 nm thick surface layer that controls the early stage of the reaction. Specific topics that have been investigated include the reactivity of individual cementitious phases and the effects of accelerators and retarders

Hydrogen doppler spectroscopy using 15^{15}N ions

The energy spread of atomic and molecular ion beams from the 4 MV Dynamitron tandem accelerator at the Ruhr-Universität Bochum has been studied and in part minimized. Using the $E_R = 6.40$ MeV narrow resonance in $^1$H($^{15}$N,$\alpha\gamma$)$^{12}$C with an $^{15}$N energy spread of 4.55 keV, the Doppler broadening for several hydrogen-bearing gases was found to be in good agreement with expectation: e.g. for NH$_3$ gas a rotational-vibrational Doppler width of $10.41 \pm 0.25$ keV was observed (theory $=$ 10.4 keV). Studies of the vibrational Doppler widths of H-bonds on a Si $\langle 100 \rangle$ surface were performed using a $4\pi$ $\gamma$-ray detection system together with UHV-chambers for sample preparation, transport, and analysis. The results showed that further improvements in the experimental set-ups are needed for such investigations

Intelligent anvils applied to experimental investigations: state-of-the-art

Since a long time, efforts have been made to improve the accuracy of pressure and temperature measurements in diamond anvil cell experiments performed in experimental petrology and high-pressure physics. Here, we report on the state-of-the-art of the research carried out during past few years with the diamond anvils carrying implanted electronic structures (‘intelligent' anvils, iAnvils). The electronic structures are inserted a few microns below the diamond surface into the diamond lattice by high-energy implantation of boron. These structures can be used as pressure- and temperature-sensitive devices. Another useful application is the fabrication of micro-heaters integrated in the anvils. Pressure- and temperature-induced responses of the sensors (change of resistance) are quantified by low-current measurement equipment. Calibrations against pressure–temperature parameters are performed using well-known phase transitions or by using equation of state of pure substances. Results of in situ measurements performed on iAnvils under pressure and temperature are presented, together with calibration curves for pressure and temperature. Future experiments on in situ measurements of the conductivity dependence of the sensor structures are discussed

X-ray transmission properties of intelligent anvils in diamond anvil cells

International audienceHigh-pressure and/or high-temperature analysis of geo- and material science samples routinely employs diamond anvil cells (DACs) as a research instrument. In particular, DACs allow for various in situ characterizations (e.g. Raman and Fourier transform infra red spectroscopies, X-ray diffraction (XRD), X-ray spectroscopy including fluorescence (XRF) and absorption (XAS)) at elevated pressure and temperature. The measurement of pressure (P) and/or temperature (T) in the sample chamber is crucial, but not always accurate, more specifically in the case of low-pressure applications (a few GPa). The development of modified diamonds (intelligent anvils 'i-anvils') adapted to a new generation of DACs (intelligent diamond anvil cells: iDAC) can contribute to solve this problem, as the diamond itself serves as the PT sensor, being prepared, for example, by high-energy ion implantation [H. Bureau, M. Burchard, S. Kubsky et al., This volume (2006).] on a micrometric scale. Several most interesting measurement methods used with DACs are based on X-ray techniques (e.g. XRF, XRD, XAS). We present the first results of X-ray transmission measurements with iDACs, performed at the hard-X-ray microfocus beamline ID22 at the ESRF (European Synchrotron Radiation Facility), Grenoble, France. Sensor response to intense irradiation as a function of X-ray energy (Eph10;18.1 keV) was investigated. The values of the sensor were found to be independent of the irradiation in the investigated energy range and thus validate the use of these sensors for precise and reliable measurements on a wide range of applications with high-energy synchrotron radiation. No influence of the sensor on the X-ray transmission properties of the anvil has been found

In situ temperature measurements through i-anvils in diamond anvil cells

This study is devoted to in situ temperature measurement in diamond anvil cells (DAC) with implanted anvils (i-anvils). I-anvils consist of diamonds implanted with B and/or C ions, situated below the diamond’s surface at a depth of 1-3 µm; forming sensors which are placed below the culet at the location of the DAC’s sample chamber. I-anvils can be employed as temperature or pressure sensors, exploiting their electrical properties. We have tested the sensor’s behaviour with temperatures up to 900°C, at ambient pressure and up to 6 GPa in real-1- experimental conditions in two types of DAC. For this purpose, we performed experiments in four different i-anvils at temperatures up to 900°C. We have compared the signal measured by the sensors with the temperature measured by a thermocouple attached to the i-anvil. The temperature gradient between the sample chamber and the thermocouple position was taken into account by phase transition measurements of calibration standards. Reproducible laws of current variation with temperature have been established. We conclude that i-anvils are reliable and sensitive to measure the temperature in situ in diamond anvil cells with an accuracy of better than 1°C