In-situ high pressure Raman spectroscopy is used to study monolayer, bilayer and few-layer graphene samples supported on silicon in a diamond anvil cell to 3.5 GPa. The results show that monolayer graphene adheres to the silicon substrate under compressive stress. A clear trend in this behaviour as a function of graphene sample thickness is observed. We also study unsupported graphene samples in a diamond anvil cell to 8 GPa, and show that the properties of graphene under compression are intrinsically similar to graphite. Our results demonstrate the differing effects of uniaxial and biaxial strain on the electronic bandstructure. ArticleThe discovery of graphene in 2004 [1] has led to many advances in solid state physics. Research into this new material is fuelled by interest in fundamental physics as the quantum Hall effect has been observed in graphene at room temperature [2] and electrons within graphene behave as massless dirac fermions, mimicking relativistic particles [3]. Graphene has been suggested as a candidate for a wide variety of applications in electronics (due to its ballistic transport at room temperature) and composite materials [2]. It is the first experimental realisation of a truly 2-dimensional material.To date there have been no studies published on graphene at high pressure. This is surprising in view of the huge interest in the mechanical properties of graphene [4-9] motivated particularly by its possible applications in nanoelectronics [4,5]. Strain monitoring is of critical importance [10,11] in this field. It should be of particular relevance in the case of graphene due to the predicted dependence of electronic bandgap on strain [12], and also due to the fact that some of the materials related to graphene are intrinsically stressed due to the presence of the substrate, for example graphene grown epitaxially on SiC [13]. The possibility of using graphene as an ultrasensitive strain sensor has also been suggested [9]. Study of graphene at high

The crystal structures, lattice vibrations, and electronic band structures of PbCrO4, PbSeO4, SrCrO4, and SrSeO4 were studied by ab initio calculations, Raman spectroscopy, X-ray diffraction, and optical-absorption measurements. Calculations properly describe the crystal structures of the four compounds, which are isomorphic to the monazite structure and were confirmed by X-ray diffraction. Information is also obtained on the Raman- and IR-active phonons, with all of the vibrational modes assigned. In addition, the band structures and electronic densities of states of the four compounds were determined. All are indirect-gap semiconductors. In particular, chromates are found to have band gaps smaller than 2.5 eV and selenates higher than 4.3 eV. In the chromates (selenates), the upper part of the valence band is dominated by O 2p states and the lower part of the conduction band is composed primarily of electronic states associated with the Cr 3d and O 2p (Se 4s and O 2p) states. Calculations also show that the band gap of PbCrO4 (PbSeO4) is smaller than the band gap of SrCrO4 (SrSeO4). This phenomenon is caused by Pb states, which, to some extent, also contribute to the top of the valence band and the bottom of the conduction band. The agreement between experiments and calculations is quite good; however, the band gaps are underestimated by calculations, with the exception of the bang gap of SrCrO4, for which theory and calculations agree. Calculations also provide predictions of the bulk modulus of the studied compounds.

Silane (SiH 4 ) is found to (partially) decompose at pressures above 50 GPa at room temperature into pure Si and H 2 . The released hydrogen reacts with surrounding metals in the diamond anvil cell to form metal hydrides. A formation of rhenium hydride is observed after the decomposition of silane. From the data of a previous experimental report (Eremets et al., Science 319, 1506), the claimed high-pressure metallic and superconducting phase of silane is identified as platinum hydride, that forms after the decomposition of silane. These observations show the importance of taking into account possible chemical reactions that are often neglected in high-pressure experiments.

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The outermost layer of spores of the Bacillus cereus family is a loose structure known as the exosporium. Spores of a library of Tn917-LTV1 transposon insertion mutants of B. cereus ATCC 10876 were partitioned into hexadecane; a less hydrophobic mutant that was isolated contained an insertion in the exsA promoter region. ExsA is the equivalent of SafA (YrbA) of Bacillus subtilis, which is also implicated in spore coat assembly; the gene organizations around both are identical, and both proteins contain a very conserved N-terminal cortexbinding domain of ca. 50 residues, although the rest of the sequence is much less conserved. In particular, unlike SafA, the ExsA protein contains multiple tandem oligopeptide repeats and is therefore likely to have an extended structure. The exsA gene is expressed in the mother cell during sporulation. Spores of an exsA mutant are extremely permeable to lysozyme and are blocked in late stages of germination, which require coatassociated functions. Two mutants expressing differently truncated versions of ExsA were constructed, and they showed the same gross defects in the attachment of exosporium and spore coat layers. The protein profile of the residual exosporium harvested from spores of the three mutants-two expressing truncated proteins and the mutant with the original transposon insertion in the promoter region-showed some differences from the wild type and from each other, but the major exosporium glycoproteins were retained. The exsA gene is extremely important for the normal assembly and anchoring of both the spore coat and exosporium layers in spores of B. cereus. Bacillus cereus, Bacillus anthracis, and Bacillus thuringiensisare very closely related (16,22), and the possession of an exosporium is a major characteristic of this group. This outermost layer of the spore is the least understood of all the spore integuments. The paradigm of sporeformers, B. subtilis, lacks a distinct, separate exosporium, although there has been a report that a very outermost tightly fitting layer of the spore coat can be visualized after extracting some of the coat material from spores with urea-mercaptoethanol and might be considered an exosporium (26). The exosporium of Bacillus cereus is first observed as a small lamellar structure in the mother cell cytoplasm in proximity to, but not in contact with, the outer forespore membrane; it is synthesized concurrently with the spore coat, although the two structures are clearly separate within the mature spore (16). The exosporium contains a hexagonal crystal-like basal layer and a hairy-nap outer layer (9). It has been estimated as containing 53% protein, 20% amino and neutral polysaccharide, 18% lipids, and approximately 4% ash. The whole structure makes up approximately 2% of the dry weight of the spore (14). A number of the proteins from the exosporia of B. cereus (7, 37) and B. anthracis (25,28,30) have been identified, most notably the B. anthracis surface-exposed glycoprotein antigen BclA (30, 31).The hydrophobic properties of Bacillus me...