645 research outputs found
HIV Denial in the Internet Era
The Internet has served as a fertile and un-refereed medium to spread HIV denialist beliefs, argue the authors
Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene
The non-covalent functionalisation of graphene is an attractive strategy to
alter the surface chemistry of graphene without damaging its superior
electrical and mechanical properties. Using the facile method of aqueous-phase
functionalisation on large-scale CVD-grown graphene, we investigated the
formation of different packing densities in self-assembled monolayers (SAMs) of
perylene bisimide derivatives and related this to the amount of substrate
contamination. We were able to directly observe wet-chemically deposited SAMs
in scanning tunnelling microscopy (STM) on transferred CVD graphene and
revealed that the densely packed perylene ad-layers adsorb with the conjugated
{\pi}-system of the core perpendicular to the graphene substrate. This
elucidation of the non-covalent functionalisation of graphene has major
implications on controlling its surface chemistry and opens new pathways for
adaptable functionalisation in ambient conditions and on the large scale.Comment: 27 pages (including SI), 10 figure
Raman-modes of index-identified free-standing single-walled carbon nanotubes
Using electron diffraction on free-standing single-walled carbon nanotubes we
have determined the structural indices (n,m) of tubes in the diameter range
from 1.4 to 3nm. On the same free-standing tubes we have recorded Raman spectra
of the tangential modes and the radial breathing mode. For the smaller
diameters (1.4-1.7nm) these measurements confirm previously established radial
breathing mode frequency versus diameter relations, and would be consistent
with the theoretically predicted proportionality to the inverse diameter.
However, for extending the relation to larger diameters, either a yet
unexplained environmental constant has to be assumed, or the linear relation
has to be abandoned.Comment: 4 pages, 4 figures, +additional materials (select PostScript to
obtain it
In vitro synthesis of full-length DNA transcripts of Rous sarcoma virus RNA by viral DNA polymerase.
Wide spectral photoresponse of layered platinum diselenide-based photodiodes
Platinum diselenide (PtSe2) is a group-10 transition metal dichalcogenide (TMD) that has unique electronic properties, in particular a semimetal-to-semiconductor transition when going from bulk to monolayer form. We report on vertical hybrid Schottky barrier diodes (SBDs) of two-dimensional (2D) PtSe2 thin films on crystalline n-type silicon. The diodes have been fabricated by transferring large-scale layered PtSe2 films, synthesized by thermally assisted conversion of predeposited Pt films at back-end-of-the-line CMOS compatible temperatures, onto SiO2/Si substrates. The diodes exhibit obvious rectifying behavior with a photoresponse under illumination. Spectral response analysis reveals a maximum responsivity of 490 mA/W at photon energies above the Si bandgap and relatively weak responsivity, in the range of 0.1–1.5 mA/W, at photon energies below the Si bandgap. In particular, the photoresponsivity of PtSe2 in infrared allows PtSe2 to be utilized as an absorber of infrared light with tunable sensitivity. The results of our study indicate that PtSe2 is a promising option for the development of infrared absorbers and detectors for optoelectronics applications with low-temperature processing conditions
Heterojunction Hybrid Devices from Vapor Phase Grown MoS
We investigate a vertically-stacked hybrid photodiode consisting of a thin
n-type molybdenum disulfide (MoS) layer transferred onto p-type silicon.
The fabrication is scalable as the MoS is grown by a controlled and
tunable vapor phase sulfurization process. The obtained large-scale p-n
heterojunction diodes exhibit notable photoconductivity which can be tuned by
modifying the thickness of the MoS layer. The diodes have a broad
spectral response due to direct and indirect band transitions of the nanoscale
MoS. Further, we observe a blue-shift of the spectral response into the
visible range. The results are a significant step towards scalable fabrication
of vertical devices from two-dimensional materials and constitute a new
paradigm for materials engineering.Comment: 23 pages with 4 figures. This article has been published in
Scientific Reports. (26 June 2014, doi:10.1038/srep05458
Direct Observationof DegenerateTwo-Photon Absorption and Its Saturation in WS2 and MoS2 Monolayer and Few-Layer Films
The optical nonlinearity of WS2, MoS2 monolayer and few-layer films was
investigated using the Z-scan technique with femtosecond pulses from the
visible to the near infrared. The dependence of nonlinear absorption of the WS2
and MoS2 films on layer number and excitation wavelength was studied
systematically. WS2 with 1~3 layers exhibits a giant two-photon absorption
(TPA) coefficient. Saturation of TPA for WS2 with 1~3 layers and MoS2 with
25~27 layers was observed. The giant nonlinearity of WS2 and MoS2 is attributed
to two dimensional confinement, a giant exciton effect and the band edge
resonance of TPA
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