129 research outputs found

    Evidence for the coexistence of Dirac and massive carriers in a-(BEDT-TTF)2I3 under hydrostatic pressure

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    Transport measurements were performed on the organic layered compound \aI3 under hydrostatic pressure. The carrier types, densities and mobilities are determined from the magneto-conductance of \aI3 . While evidence of high-mobility massless Dirac carriers has already been given, we report here, their coexistence with low-mobility massive holes. This coexistence seems robust as it has been found up to the highest studied pressure. Our results are in agreement with recent DFT calculations of the band structure of this system under hydrostatic pressure. A comparison with graphene Dirac carriers has also been done.Comment: 5 pages 5 figure

    Behavioral Interactions Of Opioid Agonists And Antagonists With Serotonergic Systems

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    Morphine interacts with brain serotonergic (5-HT) systems; these systems have been implicated in morphine analgesia and dependence (see Cervo et al., 1981). The 5-HT agonist quipazine induces analgesia in rats that is attenuated by naloxone and 5-HT antagonists (Minnema et al., 1980; Samanin et al., 1976). Behavioral disruption by the hallucinogens LSD, DMT and mescaline, mediated primarily through brain 5-HT effects (Rech and Commissaris, 1982), is potentiated by naloxone and naltrexone (Commissaris et al., 1980; Ruffing and Domino, 1981) and is variably antagonized or potentiated by morphine and methadone (Ruffing and Domino, 1981). Cyclazocine causes a disruption of operant behavior similar to that of the hallucinogens which is reversed in part by nalozone and the 5-HT antagonist metergoline, and to a greater extent by the combination of maloxone and metergoline (Henck et al., 1983). These studies indicate that indole and phenethylamine hallucinogens interact to some extent with brain opioid mechanisms as well as brain 5-HT components, whereas opioid drugs influence behavior in part by actions on 5-HT systems. We have extended these drug studies in an attempt to characterize interactions with 5-HT mechanisms and to identify the various types of opioid receptors involved

    Large area molybdenum disulphide-epitaxial graphene vertical Van der Waals heterostructures

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    International audienceTwo-dimensional layered transition metal dichalcogenides (TMDCs) show great potential for optoelectronic devices due to their electronic and optical properties. A metal-semiconductor interface, as epitaxial graphene - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science, as it constitutes an outstanding platform to investigate the interlayer interaction in van der Waals heterostructures. Here, we study large area MoS2-graphene-heterostructures formed by direct transfer of chemical-vapor deposited MoS2 layer onto epitaxial graphene/SiC. We show that via a direct transfer, which minimizes interface contamination, we can obtain high quality and homogeneous van der Waals heterostructures. Angle-resolved photoemission spectroscopy (ARPES) measurements combined with Density Functional Theory (DFT) calculations show that the transition from indirect to direct bandgap in monolayer MoS2 is maintained in these heterostructures due to the weak van der Waals interaction with epitaxial graphene. A downshift of the Raman 2D band of the graphene, an up shift of the A1g peak of MoS2 and a significant photoluminescence quenching are observed for both monolayer and bilayer MoS2 as a result of charge transfer from MoS2 to epitaxial graphene under illumination. Our work provides a possible route to modify the thin film TDMCs photoluminescence properties via substrate engineering for future device design

    Van der Waals epitaxy of two-dimensional single-layer h-BN on graphite by molecular beam epitaxy: electronic properties and band structure

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    We report on the controlled growth of h-BN/graphite by means of molecular beam epitaxy. X-Ray photoelectron spectroscopy suggests the presence of an interface without any reaction or intermixing, while the angle resolved photoemission spectroscopy (ARPES) measurements show that the h-BN layers are epitaxially aligned with graphite. A well-defined band structure is revealed by ARPES measurements, reflecting the high quality of the h-BN films. The measured valence band maximum located at 2.8 eV below the Fermi level reveals the presence of undoped h-BN films (band gap 6 eV). These results demonstrate that, although only weak van der Waals interactionsare present between h-BN and graphite, a long range ordering of h-BN can be obtained even on polycrystalline graphite via van der Waals epitaxy, offering the prospect of large area, single layer h-BN

    Fizikokemijska karakterizacija čvrstih disperzijskih sustava tadalafila s poloksamerom 407

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    Dissolution behaviour of a poorly water-soluble drug, tadalafil, from its solid dispersion systems with poloxamer 407 has been investigated. Solid dispersion systems of tadalafil were prepared with poloxamer 407 in 1:0.5, 1:1.5 and 1:2.5 ratios using the melting method. Characterization of binary systems with FTIR and powder XRPD studies demonstrated the presence of strong hydrogen bonding interactions, a significant decrease in crystallinity and the possibility of existence of amorphous entities of the drug. In the binary systems tested, 1:0.5 proportion of tadalafil/poloxamer 407 showed rapid dissolution of tadalafil (DE30 70.9 ± 3.6 %). In contrast, higher proportions of poloxamer 407 (1:1.5 and 1:2.5) offered no advantage towards dissolution enhancement of the drug from corresponding binary systems indicating altered rheological characteristics of the polymer, at its higher concentration, which might have retarded the release rate of tadalafil.U radu je ispitivano oslobađanje u vodi teško topljivog lijeka tadalafila iz čvrstih disperzijskih sustava. Ti sustavi pripravljeni su s poloksamerom 407 u omjeru lijeka i polimera 1:0,5, 1:1,5 i 1:2,5, koristeći metodu taljenja. Karakterizacija binarnih sustava s FTIR i rendgenskom difrakcijom praha XRD ukazuje na prisutnost snažnih vodikovih veza, značajno smanjenje kristaliničnosti i moguću prisutnost amorfnog lijeka. Iz binarnog sustava tadalafil/poloksamer 1:0,5 oslobađanje ljekovite tvari je brzo (DE30 70,9 ± 3,6 %). Nasuprot tome, iz pripravaka s višim omjerima lijeka i polimera (1:1,5 i 1:2,5) oslobađanje ljekovite tvari nije povećano. Usporavanje oslobađanja tadalafila moglo bi biti posljedicom promjene reoloških svojstava polimera pri višim koncentracijama

    Terahertz spectroscopy of explosives and drugs

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    Terahertz frequency radiation possesses a unique combination of desirable properties for noninvasive imaging and spectroscopy of materials. This includes the ability to obtain chemical and structural information about substances concealed within dry packaging, such as paper, plastics, and cardboard. As a result, the application of terahertz frequency spectroscopy for the sensing and identification of materials of security interest, such as explosives and, to a lesser extent, drugs-of-abuse, has caught the attention of a number of researchers and security agencies. We describe terahertz time-domain spectroscopy and examine the terahertz spectra of a wide range of drugs-of-abuse, pure explosives, and plastic explosives
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