808 research outputs found
Measurement of the Inclusive Cross Section \sigma(pp\rightarrow b\bar{b}X\rightarrow \mu\mu \mbox{X}^\prime) at TeV with the CMS Experiment at the LHC
No full textBeauty quarks are produced with a large cross section at a previously unreached center-of-mass energy at the Large Hadron Collider (LHC), enabling precision measurements to improve our understanding of heavy flavor physics.
This thesis presents the measurement of the inclusive cross section .
Di-muon events are selected in the pseudo-rapidity range
GeV or \pt>6 GeV. The amount of signal events is determined with a fit to the di-muon transverse impact parameter distribution.
The analysis is applied to data recorded by the CMS detector during proton-proton collisions at TeV centre-of-mass energies in the second half of year 2010, corresponding to an integrated luminosity of pb.
The -quark production cross section is determined and compared to leading-order and next-to-leading-order QCD predictions.Nel collisore adronico LHC i quark beauty sono prodotti
con un'elevata sezione d'urto ad una energia nel centro di massa mai raggiunta finora, consentendo misure di precisione in grado di migliorare la nostra comprensione della fisica del sapore.
Il presente lavoro di tesi riporta uno studio della misura della
produzione inclusiva dei quark tramite il processo .
Eventi di di-muoni sono selezionati nell'intervallo di pseudo-rapidità GeV or \pt>6 GeV. La frazione di eventi di segnale è determinata mediante un'interpolazione della distribuzione di parametro d'impatto trasverso. L'analisi e' applicata ai dati raccolti dal rivelatore CMS durante la fase di presa dati di collisioni ad energia di TeV nel centro di massa, avvenuta nella seconda metà del 2010, corrispondenti ad una luminosità integrata di pb.
La sezione d'urto di produzione dei -quark è misurata e confrontata cno le predizioni QCD al {\it leading-order} e
{\it next-to-leading-order}
Tunable sulfur desorption in exfoliated MoS2 by means of thermal annealing in ultra-high vacuum
No full textThe effects of thermal annealing in ultra-high vacuum on the electronic structures of bulk and liquid
exfoliated MoS2 have been studied by core level and valence band X-ray photoemission spectroscopy.
A quantitative analysis of core level spectra demonstrates, in the case of exfoliated MoS2, that, upon
annealing above 200 C, defect formation occurs in the form of sulfur single and double vacancies. Sulfur
vacancies introduce surface states in the band gap (determined by the analysis of the valence band spectra).
This determines a rigid shift of the core levels to lower binding energies, as a consequence of an
upward band bending
Exfoliated black phosphorus gas sensing properties at room temperature
No full textRoom temperature gas sensing properties of chemically exfoliated black phosphorus (BP) to oxidizing (NO2, CO2) and reducing (NH3, H-2, CO) gases in a dry air carrier have been reported. To study the gas sensing properties of BP, chemically exfoliated BP flakes have been drop casted on Si3N4 substrates provided with Pt comb-type interdigitated electrodes in N2 atmosphere. Scanning electron microscopy and x-ray photoelectron spectroscopy characterizations show respectively the occurrence of a mixed structure, composed of BP coarse aggregates dispersed on BP exfoliated few layer flakes bridging the electrodes, and a clear 2p doublet belonging to BP, which excludes the occurrence of surface oxidation. Room temperature electrical tests in dry air show a p-type response of multilayer BP with measured detection limits of 20 ppb and 10 ppm to NO2 and NH3 respectively. No response to CO and CO2 has been detected, while a slight but steady sensitivity to H-2 has been recorded. The reported results confirm, on an experimental basis, what was previously theoretically predicted, demonstrating the promising sensing properties of exfoliated BP
Role of substrate on interaction of water molecules with graphene oxide and reduced graphene oxide
No full textWe study local electronic properties of graphene oxide (GO) and reduced graphene oxide (RGO) on metallic (Pt) and insulating (Si3N4) substrates in controlled humidity environment. We demonstrate that the supporting substrate plays a crucial role in interaction of these materials with water, with Pt making both GO and RGO insensitive to humidity variations and change in environment. On the other hand, in the case of Si3N4substrate a significant difference between GO and RGO with respect to humidity variations is demonstrated, indicating complete water coverage at â1⁄460% R.H for RGO and â1⁄430% R.H. for GO. Irrespective of the substrate, both GO and RGO demonstrate relative independence of their electronic properties on the material thickness, with similar trends observed for 1 and 2 layers when subject to humidity variations. This indicates a relatively minor role of material thickness in GO-based humidity sensors
Graphene oxide for gas detection under standard humidity conditions
No full textGraphene oxide (GO) synthesis is the easiest way to functionalize graphene, preserving the high graphene surface to volume ratio. Therefore, GO is a promising candidate for gas sensing applications. In this paper, an easy-to-fabricate and high sensitivity GO-based gas sensor is proposed. The device is fabricated by drop-casting a solution of GO flakes dispersed in water on a prepatterned Si3N4 substrate with 30 mu m spaced Pt electrodes. The sensing material has been studied using scanning electron microscopy and x-ray photoelectron spectroscopy. The large lateral dimensions of the flakes (tens of microns) allow single GO flake to bridge adjacent electrodes. The high quality of the synthesized flakes results in the gas sensor high sensitivity to and low detection limit (20 ppb) of NO2. The gas sensor response to NO2 has been studied in various relative humidity environments and it is demonstrated not to be affected by the presence of water vapor. Finally, the gas sensor responses to acetone, toluene, ethanol, and ammonia are reported
Few layered MoS2 lithography with an AFM tip: description of the technique and nanospectroscopy investigations
No full textA novel technique to lithograph the MoS2 surface is described here. Mechanically exfoliated MoS2 flakes have been patterned with an atomic force microscope tip. After the patterning process, the lithographed areas have been removed by selective chemical etching. The electronic properties of the MoS2 flakes have been analyzed with spatially resolved photoelectron spectroscopy, with tunable incident photon energy, provided by a synchrotron light source. Tens of meV core level shifts can be recorded in relation to the flakes edges, coming from both the exfoliation and from the lithography
Unravelling the Role of the Central Metal Ion in the Electronic Structure of Tris-(8-Hydroxyquinoline) Metal Chelates: Photoemission Spectroscopy and Hybrid Functional Calculations
No full textReduction dependent wetting properties of graphene oxide
No full textThis study reports contact angle measurements of standard, diol and aromatic solvents on graphene oxide thin films thermally reduced in ultra-high vacuum up to 900°C. The films were chemically and morphologically characterized using respectively X-ray photoemission spectroscopy and atomic force microscopy. The characterization shows that the wetting occurs in the chemically heterogeneous regime, namely the surface roughness (3 nm) does not influence the wetting properties of the samples. Zisman, Owens–Wendt and Neumann methods have been applied in order to calculate the surface free energy of the thin films showing that the Owens–Wendt method best fit the data trends. The surface free energy varies from 51 mN/m (pristine graphene oxide) to 39 mN/m (900 °C reduced graphene oxide). A correlation between the surface chemical composition, the surface free energy and its polar and dispersive components is reported, giving a rationale to the wetting properties of graphene oxide and reduced graphene oxide
Graphene Oxide as a Practical Solution to High Sensitivity Gas Sensing
No full textGraphene and its related materials have attracted much
interest in sensing applications because of their optimized ratio
between active surface and bulk volume. In particular, several forms of
oxidized graphene have been studied to optimize the sensing
efficiency, sometimes moving away from practical solutions to boost
performance. In this paper, we propose a practical, high-sensitivity,
and easy to fabricate gas sensor based on high quality graphene oxide
(GO), and we give the rationale to the high performance of the device.
The device is fabricated by drop-casting water-dispersed single-layer
GO flakes on standard 30 μm spaced interdigitated Pt electrodes. The
exceptional size of the GO flakes (27 μm mean size and ∼500 μm maximum size) allows single GO flake to bridge adjacent
electrodes. A typical p-type response is observed by testing the device in both reducing and oxidizing environments. The specific
response to NO2 is studied by varying the operating temperature and the gas concentration. Sensing activity is demonstrated to
be mainly mediated by the oxygen functional groups. A 20 ppb detection limit is measured. Besides illustrating a simple and
efficient approach to gas sensing, this work is an example of the versatility of graphene oxide, accomplishing tasks that are
complementary to graphene
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