133 research outputs found
Accessing surface Brillouin zone and band structure of picene single crystals
We have experimentally revealed the band structure and the surface Brillouin
zone of insulating picene single crystals (SCs), the mother organic system for
a recently discovered aromatic superconductor, with ultraviolet photoelectron
spectroscopy (UPS) and low-energy electron diffraction with laser for
photoconduction. A hole effective mass of 2.24 m_0 and the hole mobility mu_h
>= 9.0 cm^2/Vs (298 K) were deduced in Gamma-Y direction. We have further shown
that some picene SCs did not show charging during UPS even without the laser,
which indicates that pristine UPS works for high-quality organic SCs.Comment: 5 pages, 4 figures, Phys. Rev. Lett. 108, 226401 (2012
An organic borate salt with superior pâdoping capability for organic semiconductors
Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (optoâ) electronics. Beyond singleâcomponent molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes2B+; Mes: mesitylene) and the tetrakis(pentaâfluorophenyl)borate anion [B(C6F5)4]â is demonstrated as pâtype dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes2B+, and the positive charge on the polymer is stabilized by [B(C6F5)4]â. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C6F5)4]â even enables the stabilization of polarons and bipolarons in poly(3âhexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes2B+[B(C6F5)4]â is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors
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A diuranium carbide cluster stabilized inside a C80 fullerene cage.
Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing Ih(7)-C80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@Ih(7)-C80. This endohedral fullerene was prepared utilizing the KrĂ€tschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (NiII-OEP) to produce UCU@Ih(7)-C80·[NiII-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03âĂ
) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@Ih(7)-C80 and the covalent nature of the U(f1)=C double bonds were further affirmed through various spectroscopic and theoretical analyses
An Organic Borate Salt with Superior pâDoping Capability for Organic Semiconductors
Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (optoâ) electronics. Beyond singleâcomponent molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes2B+; Mes: mesitylene) and the tetrakis(pentaâfluorophenyl)borate anion [B(C6F5)4]â is demonstrated as pâtype dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes2B+, and the positive charge on the polymer is stabilized by [B(C6F5)4]â. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C6F5)4]â even enables the stabilization of polarons and bipolarons in poly(3âhexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes2B+[B(C6F5)4]â is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors.Peer Reviewe
Advanced Data Encryption âusing 2D Materials
Advanced data encryption requires the use of true random number generators (TRNGs) to produce unpredictable sequences of bits. TRNG circuits with high degree of randomness and low power consumption may be fabricated by using the random telegraph noise (RTN) current signals produced by polarized metal/insulator/metal (MIM) devices as entropy source. However, the RTN signals produced by MIM devices made of traditional insulators, i.e., transition metal oxides like HfO and AlO, are not stable enough due to the formation and lateral expansion of defect clusters, resulting in undesired current fluctuations and the disappearance of the RTN effect. Here, the fabrication of highly stable TRNG circuits with low power consumption, high degree of randomness (even for a long string of 2Â â 1 bits), and high throughput of 1 Mbit s by using MIM devices made of multilayer hexagonal boron nitride (h-BN) is shown. Their application is also demonstrated to produce one-time passwords, which is ideal for the internet-of-everything. The superior stability of the h-BN-based TRNG is related to the presence of few-atoms-wide defects embedded within the layered and crystalline structure of the h-BN stack, which produces a confinement effect that avoids their lateral expansion and results in stable operation.M.L. acknowledges generous support from the King Abdullah University of Science and Technology. This work was supported by the Ministry of Science and Technology of China (grants no. 2018YFE0100800, 2019YFE0124200), the National Natural Science Foundation of China (grants no. 61874075), the Collaborative Innovation Centre of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the 111 Project from the State Administration of Foreign Experts Affairs of China. A.A. and S.R. acknowledge the project: ModElling Charge and Heat trANsport in 2D-materIals based CompositesâMECHANIC reference number: PCI2018-093120 funded by Ministerio de Ciencia, InnovaciĂłn y Universidades. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya and is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). Y.S. acknowledges support from the European Union (Marie Sklodowska-Curie actions (grant no. 894840). The authors acknowledge technical advice from H.-S. Philip Wong from Stanford University and Xiaoming Xie from Chinese Academy of Sciences
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
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