ABSTRACT
Superlattice induced minigaps in graphene band structure due to underlying one-dimensional nanostructuration has been demonstrated. A superperiodic potential can be introduced in graphene if the substrate is periodically structured. The successful preparation of a periodically nanostructured substrate in large scale can be obtained by carefully studying the electronic structure with a spatial averaging technique such as high-energy resolution photoemission. In this work, we present two different growth methods such as temperature programmed growth (TPG) and chemical vapor deposition (CVD) studied by scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). In both methods, we show that the original steps of Ir(332) have modified with (111) terraces and step bunching after graphene growth. Graphene grows continuously over the terrace and the step bunching areas. We observe that while TPG growth does not give rise to a well-defined surface periodicity required for opening a bandgap, the CVD growth does. By combining with angle-resolved photoemission spectroscopy (ARPES) measurements, we correlate the obtained spatial periodicity to observed band gap opening in graphene.
ABSTRACT
Carbon contamination is a general problem of under-vacuum optics submitted to high fluence. In soft X-ray beamlines carbon deposit on optics is known to absorb and scatter radiation close to the C K-edge (280â eV), forbidding effective measurements in this spectral region. Here the observation of strong reflectivity losses is reported related to carbon deposition at much higher energies around 1000â eV, where carbon absorptivity is small. It is shown that the observed effect can be modelled as a destructive interference from a homogeneous carbon thin film.
ABSTRACT
This study is devoted to in situ temperature measurement in diamond anvil cells (DACs) with intelligent 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 microm; 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 behavior with temperatures up to 900 degrees C, at ambient pressure and up to 6 GPa in real experimental conditions in two types of DAC. For this purpose, we performed experiments in four different i-anvils at temperatures up to 900 degrees 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 DACs with an accuracy of better than 1 degree C.
ABSTRACT
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 (1)H((15)N,alpha,gamma)(12)C 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.
