Defects induced by liquid-phase exfoliation of graphite using sonication were studied. It was shown that localized impact by cavitation shock waves can produce bulk ripplocations and various types of ...dislocations in graphite nanoplatelets. Formation of ripples is more pronounced in large aspect (length/width) ratio platelets or nanobelts. Quasi-periodical ripple systems were observed in many nanobelts after sonication. Mechanism of formation of ripples and dislocations during sonication was proposed. Surprisingly, fast high-temperature processing was found to anneal most of defects. This is consistent with our observations that defects associated with ripplocations are strongly localized and thus can be fast annealed.
Bioinspired self-assembled structures are increasingly important for a variety of applications ranging from drug delivery to electronic and energy harvesting devices. An important class of these ...structures is diphenylalanine microtubes which are potentially important for optical applications including light emitting diodes and optical biomarkers. In this work we present the data on their photoluminescent properties at low temperatures (down to 12 K) and discuss the origin of the emission in the near ultraviolet (UV) range seen earlier in a number of reports. UV luminescence increases with decreasing temperature and exhibits several equidistant lines that are assigned to zero-phonon exciton emission line and its phonon replicas. We infer that the exciton is localized on the defect sites and significant luminescence decay is due to thermal quenching arising from the carrier excitation from these defects and non-radiative recombination.
•Low-temperature luminescence is studied in bioinspired self-assembled FF peptide microtubes.•The mechanism of the optical emission is assigned to the luminescence of excitonic states localized at defects.•Luminescence in FF microtubes can be used as an absolute temperature probe at low temperature.
Originating from relativistic quantum field theory, Dirac fermions have been invoked recently to explain various peculiar phenomena in condensed-matter physics, including the novel quantum Hall ...effect in graphene, the magnetic-field-driven metal-insulator-like transition in graphite, superfluidity in 3He (ref. 5) and the exotic pseudogap phase of high-temperature superconductors. Despite their proposed key role in those systems, direct experimental evidence of Dirac fermions has been limited. Here, we report the first direct observation of relativistic Dirac fermions with linear dispersion near the Brillouin zone (BZ) corner H, which coexist with quasiparticles that have a parabolic dispersion near another BZ corner K. In addition, we also report a large electron pocket that we attribute to defect-induced localized states. Thus, graphite presents a system in which massless Dirac fermions, quasiparticles with finite effective mass and defect states all contribute to the low-energy electronic dynamics.
Room temperature superconductivity under normal conditions has been a major challenge of physics and material science since its very discovery. Here we report the global room-temperature ...superconductivity observed in cleaved highly oriented pyrolytic graphite carrying dense arrays of nearly parallel surface line defects. The multiterminal measurements performed at the ambient pressure in the temperature interval 4.5 K < T < 300 K and at magnetic fields 0 < B < 9 T applied perpendicular to the basal graphitic planes reveal that the superconducting critical current I_c(T,B) is governed by the normal state resistance RN(T, B) so that I_c(T,B) is proportional to 1/R_N(T, B). Magnetization M(T, B) measurements of superconducting screening and hysteresis loops together with the critical current oscillations with temperature that are characteristic for superconductor-ferromagnet-superconductor Josephson chains, provide strong support for occurrence of superconductivity at T > 300 K. We develop a theory of global superconductivity emerging in the array of linear structural defects which well describes the experimental findings and demonstrate that global superconductivity arises as a global phase coherence of superconducting granules in linear defects promoted by the stabilizing effect of underlying Bernal graphite via tunneling coupling to the three dimensional (3D) material.
Magnetic carbon Makarova, Tatiana L; Sundqvist, Bertil; Höhne, Roland ...
Nature (London),
10/2001, Letnik:
413, Številka:
6857
Journal Article
Recenzirano
The discovery of nanostructured forms of molecular carbon has led to renewed interest in the varied properties of this element. Both graphite and C60 can be electron-doped by alkali metals to become ...superconducting; transition temperatures of up to 52 K have been attained by field-induced hole-doping of C60 (ref. 2). Recent experiments and theoretical studies have suggested that electronic instabilities in pure graphite may give rise to superconducting and ferromagnetic properties, even at room temperature. Here we report the serendipitous discovery of strong magnetic signals in rhombohedral C60. Our intention was to search for superconductivity in polymerized C60; however, it appears that our high-pressure, high-temperature polymerization process results in a magnetically ordered state. The material exhibits features typical of ferromagnets: saturation magnetization, large hysteresis and attachment to a magnet at room temperature. The temperature dependences of the saturation and remanent magnetization indicate a Curie temperature near 500 K.
Defects induced by liquid-phase exfoliation of graphite using sonication were studied. It was shown that localized impact by cavitation shock waves can produce bulk ripplocations and various types of ...dislocations in graphite nanoplatelets. Formation of ripples is more pronounced in large aspect (length/width) ratio platelets or nanobelts. Quasi-periodical ripple systems were observed in many nanobelts after sonication. Mechanism of formation of ripples and dislocations during sonication was proposed. Surprisingly, fast high-temperature processing was found to anneal most of defects. This is consistent with our observations that defects associated with ripplocations are strongly localized and thus can be fast annealed.
Magnetoelectric nanoparticles (NPs) present an important class of nanomaterials with a wide interest in piezocatalytic and biomedical applications. Herein, the results of magnetoelectric and ...magnetization measurements performed on core–shell NPs having magnetic core (MnFe 2 O 4 , MFO) and ferroelectric shell (Ba 0.85 Ca 0.15 Ti 0.5 Zr 0.5 O 3 , BCZT) synthesized by the microwave hydrothermal method are reported. Magnetic results are compared with the measurements on reference MFO NPs prepared under identical conditions. Detailed SQUID magnetometer measurements of the magnetization hysteresis loops M ( H ) down to 2 K reveal the existence of a clear exchange bias effect in pure MFO NPs attributed to the coexistence of ferromagnetic and antiferromagnetic short‐range interactions. When the magnetic core is covered by the thin ferroelectric BCZT shell, it is observed that 1) the shell suppresses the apparent bias effect and 2) induces an “extra” ferromagnetic magnetization at T < 20 K. The results indicate that this “extra” ferromagnetism has a 2D character and it is most likely related to the interface interactions between the MFO core and BCZT shell. Ferroelectric properties and strong magnetoelectric effect in core–shell NPs are revealed via piezoresponse force microscopy under magnetic field. The mechanisms of the observed effects are discussed.
This study was aimed at identifying the locations of the submarine groundwater discharge (SGD) on the shelf of Southwestern Taiwan by means of oceanographic measurements, quantifying its influence on ...the hydrographic conditions in the area, and estimating the volume rates of the discharge. Two high resolution hydrographic surveys of the region, including water and bottom sediment sampling campaigns, were completed in February and October of 2009. Water samples were also collected from the neighboring on-land groundwater wells.
At some locations in the study regions, the vertical profiles exhibited a slight but detectable (0.009 to 0.105
psu) decrease of salinity manifested in the near-bottom portion of the water column. Although convectively unstable, this feature appeared robust and persisted for the eight months between the surveys. The salinity anomalies in the near-bottom layer were often accompanied by the maxima of fluorescence, chlorophyll, silica, nitrate, and iron concentrations, as well as the minima of turbidity. In February, 2009, the n-alkane composition of organic matter in the water collected from an on-land groundwater well exhibited high content of C
24 alkane. A similar anomalously high concentration of C
24 alkane was encountered in the bottom sediment samples from the suspected SGD sites. In October, 2009, the dominant marker of SGD signature was the C
16 alkane.
Based on these data, we specified the likely locations of the SGD sources in the study area, all of which were restricted to the inner shelf at the depths less than 8
m. We argue that the influence of the SGD on oceanographic regime in the region is small but observable. Its signature is confined to the lowermost 0.1–2.1
m layer of the water column. The groundwater seepage rates roughly estimated under the assumption of the advection–diffusion balance based on the eddy diffusivity values typical for the bottom layer, are of the order of 0.1 to 1
g
m
−2
s
−1.
► The study is aimed at identifying the locations of SGD by means of routine oceanographic measurements. ► At SGD locations, there was a 0.009 to 0.105
psu drop of salinity in the lowermost 0.1–2.1
m layer. ► SGD resulted in local maxima of dissolved substances and minima of turbidity. ► N-alkane composition of sediments at SGD sites resembled that of the groundwater taken from a well. ► The groundwater seepage rates estimated from advection–diffusion balance were 1 to 10
cm day
−1.
Testing the magnetism of polymerized fullerene Boukhvalov, D. W.; Karimov, P. F.; Kurmaev, E. Z. ...
Physical review. B, Condensed matter and materials physics,
03/2004, Letnik:
69, Številka:
11
Journal Article
PDF
