6665 research outputs found
Sort by
Internal surface electric charge characterization of mesoporous silica
No full textPubMed: 30644430Mesoporous silica is an emerging technology to solve problems of existing and to support projected revolutionary applications ranging from targeted drug delivery to artificial kidney. However, one of the major driving mechanisms, electric charging of internal mesoporous surfaces, has not been characterized yet. In the nanoscale confinements of mesoporous structures made of pore throats and pore voids, surface charges diverge from existing theoretical calculations and show local variation due to two occurrences. First, when the size of pore throat becomes comparable with the thickness of ionic layering forming on throats' surfaces, ionic layers from opposite surfaces overlap so that ionic concentration on the surface becomes different than Boltzmann distribution predicts, and there will no longer be an equilibrium of zero electric potential at pore throat centers. Second, when this non zero potential inside throats becomes different than the potential of pore voids, ionic diffusion from void to throat creates axial ionic variation on surfaces. For such a case, we performed a pore level analysis on mesoporous internal surface charge at various porosities and ionic conditions. Pore parameters strongly affected the average internal charge which we characterized as a function of overlap ratio and porosity, first time in literature. Using this, a phenomenological model was developed as an extension of the existing theory to include nano-effects, to predict the average mesoporous internal surface charge as a function of EDL thickness, pore size and porosity
Azimuthal separation in nearly back-to-back jet topologies in inclusive 2-and 3-jet events in pp collisions at √s=13TeV
No full textPubMed: 31713548A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, Delta phi(12), is presented. The measurement considers events where the two leading jets are nearly collinear ("back-to-back") in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb(-1) are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with themeasurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177 degrees < Delta phi(12) < 180 degrees. The 2- and 3-jet measurements are not simultaneously described by any of models
Measurement of prompt ψ(2S) production cross sections in proton–lead and proton–proton collisions at √s NN =5.02TeV
No full textMeasurements of prompt psi(2S) meson production cross sections in proton-lead (pPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of root s(NN) = 5.02 TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb(-1) and 28.0 pb(-1), respectively. The nuclear modification factor R-pPb is measured for prompt psi(2S) in the transverse momentum range 4 < p(T) < 30 GeV/c and the center-of-mass rapidity range -2.4 < y(CM) < 1.93. The results on psi(2S) R-pPb are compared to the corresponding modification factor for prompt J/psi mesons. The results point to different nuclear effects at play in the production of the excited charmonium state compared to the ground state, in the region of backward rapidity and for PT < 10 GeV/c. (C) 2019 The Author. Published by Elsevier B.V
Grafen/silikon tabanlı Schottky fotodiyotun fabrikasyon ve karakterizasyonu
No full textThesis (Master)--Izmir Institute of Technology, Photonics, Izmir, 2019Includes bibliographical references (leaves: 46-56)Text in English; Abstract: Turkish and EnglishThis thesis focused on fabrication and characterization of CVD grown p-type graphene and n-type Si Schottky junction photodiode with rectification behavior. The device operated at wavelength range between 390 and 1100 nm at self-powered mode. The device was encapsulated with Epoxy Resin to prevent graphene from atmospheric adsorbates. The electronic and optoelectronic characterizations of the devices were done before and after coating the devices with ER. By encapsulation stability of the device was enhanced in terms of photoresponsivity. The maximum obtained photoresponsivity value of the bare device was 0.56 A/W. Also, time-resolved photocurrent spectroscopy measurements showed that the devices exhibited enhanced photodetector performance in terms of photo-switching characteristics. Furthermore, electrical characteristics of Gr/n-Si Schottky photodiode under various illumination power densities with 850 nm wavelength were investigated. The short circuit current showed linear response to power density. However, open circuit voltage exhibited two phased slow and fast increment with increased power density. Hall effect measurements were conducted in order to investigate hole carrier concentration and mobility of the graphene on n-Si. With increasing the power density the carrier concentration increased and the mobility decreased. Besides, light induced manipulation of the Schottky barrier height of Gr/n-Si photodiode was studied. Schottky barrier height of the graphene measured by KPFM method as 0.4 eV. With increasing power density we found that Schottky barrier height of the device increased from 0.4 eV to 0.5 eV and showed similar trend with the change in open circuit voltage.Bu tez, Kimyasal Buhar Biriktirme yöntemi ile üretilen p-tipi grafen ve n-tipi
Silikon (Gr/n-Si) Schottky eklem fotodiyotunun fabrikasyonu ve karakterizasyonuna
odaklanmıştır. Grafen ve n-Si Schottky eklemi doğrultucu bir davranış göstermiştir. Elde
edilen aygıt ile 390-1100 nm dalgaboyu aralığında ve fotovoltaik modda ölçümler
alınmıştır. Ayrıca cihaz Epoksi reçine ile kaplanarak hava ile teması kesilmiş ve böylece
aygıtın daha stabil hale getirilmesi amaçlanmıştır. Aygıt enkapsüle edilmeden önce ve
sonra elektriksel ve optoelektriksel karakterizasyonu yapılmıştır.
Günlere bağlı yapılan fotocevap ölçümleri enkapsülasyon işleminin aygıtın
stabilitesini arttırdığını göstermiştir. Elde edilen maksimum fotocevap değeri enkapsüle
edilmemiş aygıt için 0.56 A/W olarak ölçülmüştür. Ayrıca zamana bağlı fotoakım
spektrometresi ölçümleri aygıtların açma kapama performansları bakımından gelişmiş bir
fotodetektör performansı sergilediğini göstermiştir.
Buna ek olarak, Gr/n-Si Schottky fotodiyotun 850 nm dalga boyunda farklı
şiddetlere sahip ışık altında elektriksel karakteristiğindeki değişim incelenmiştir. Kısa
devre akımı artan ışık şiddeti ile doğru orantılı artmıştır. Fakat açık devre voltajı artan
ışık şiddetine bağlı olarak yavaş ve hızlı olmak üzere iki fazlı bir artış göstermiştir. Işık
şiddetine bağlı olarak n-Si üzerindeki grafenin deşik yoğunluğu konsantrasyonunu ve
mobilitesini ölçmek için Hall Etkisi ölçümleri yapılmıştır. Işık şiddetine bağlı olarak
deşik konsantrasyonu artmış fakat mobilite düşmüştür. n-Si üzerindeki grafenin Schottky
bariyer yüksekliği Kelvin Kuvvet Aygıtı Mikroskopu (KPFM) yöntemiyle 0.4 eV olarak
ölçülmüştür. Ayrıca, Gr/n-Si fotodiyotun Schottky bariyer yüksekliğinin ışık şiddeti ile
değişimi incelenmiştir. Artan ışık şiddetiyle birlikte, aygıtın Schottky bariyer
yüksekliğinin 0.4 eV'den 0.5 eV'ye yükselmiştir ve bu değişim açık devre voltajındaki
değişimle benzer bir eğilim göstermektedir
Green fabrication of lanthanide-doped hydroxide-based phosphors: Y(OH)(3):Eu3+ nanoparticles for white light generation
No full textPubMed: 31293857Phosphors can serve as color conversion layers to generate white light with varying optical features, including color rendering index (CRI), high correlated color temperature (CCT), and luminous efficacy. However, they are typically produced under harsh synthesis conditions such as high temperature, high pressure, and/or by employing a large amount of solvent. In this work, a facile, water-based, rapid method has been proposed to fabricate lanthanide-doped hydroxide-based phosphors. In this sense, sub-micrometer-sized Y(OH)(3):Eu3+ particles (as red phosphor) were synthesized in water at ambient conditions in <= 60 min reaction time. The doping ratio was controlled from 2.5-20 mol %. Additionally, first principle calculations were performed on Y(OH)(3):Eu3+ to understand the preferable doping scenario and its optoelectronic properties. As an application, these fabricated red phosphors were integrated into a PDMS/YAG:Ce3+ composite and used to generate white light. The resulting white light showed a remarkable improvement (approximate to 24%) in terms of luminous efficiency, a slight reduction of CCT (from 3900 to 3600 K), and an unchanged CRI (approximate to 60) as the amount of Y(OH)(3):Eu3+ was increased
Measurement of the top quark mass in the all-jets final state at √s=13TeV and combination with the lepton+jets channel
No full textPubMed: 31031568A top quark mass measurement is performed using 35.9 fb - 1 of LHC proton- proton collision data collected with the CMS detector at v s = 13 TeV. The measurement uses the tt all- jets final state. A kinematic fit is performed to reconstruct the decay of the tt system and suppress themultijet background. Using the ideogram method, the top quark mass ( mt) is determined, simultaneously constraining an additional jet energy scale factor ( JSF). The resulting value of mt = 172.34 +/- 0.20 ( stat+ JSF) +/- 0.70 ( syst) GeV is in good agreement with previous measurements. In addition, a combined measurement that uses the tt lepton+ jets and all- jets final states is presented, using the same mass extraction method, and provides an mt measurement of 172.26 +/- 0.07 ( stat+ JSF) +/- 0.61 ( syst) GeV. This is the first combined mt extraction from the lepton+ jets and all- jets channels through a single likelihood function
Observation of two excited B+c states and measurement of the B+c(2S) mass in pp collisions at √s=13 TeV
No full textPubMed: 31012626Signals consistent with the B-c(+)(2S) and B-c*(+)(2S) states are observed in proton-proton collisions at root s = 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb(-1), collected by the CMS experiment during the 2015-2018 LHC running periods. These excited (b) over barc states are observed in the B-c(+)pi(+)pi(-) invariant mass spectrum, with the ground state B-c(+) reconstructed through its decay to J/psi pi(+). The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 +/- 1.5(stat) +/- 0.7(syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B-c(+)(2S) meson is measured to be 6871.0 +/- 1.2(stat) +/- 0.8(syst) +/- 0.8(B-c(+)) MeV, where the last term corresponds to the uncertainty in the world-average B-c(+) mass
Single-layer Janus-type platinum dichalcogenides and their heterostructures
No full textUltrathin two-dimensional Janus-type platinum dichalcogenide crystals formed by two different atoms at opposite surfaces are investigated by performing state-of-the-art density functional theory calculations. First, it is shown that single-layer PtX2 structures (where X = S, Se, or Te) crystallize into the dynamically stable IT phase and are indirect band gap semiconductors. It is also found that the substitutional chalcogen doping in all PtX2 structures is favorable via replacement of surface atoms with a smaller chalcogen atom, and such a process leads to the formation of Janus-type platinum dichalcogenides (XPtY, where X and Y stand for S, Se, or Te) which are novel single-layer crystals. While all Janus structures are indirect band gap semiconductors as their binary analogues, their Raman spectra show distinctive features that stem from the broken out-of-plane symmetry. In addition, it is revealed that the construction of Janus crystals enhances the piezoelectric constants of PtX2 crystals significantly both in the in plane and in the out-of-plane directions. Moreover, it is shown that vertically stacked van der Waals heterostructures of binary and ternary (Janus) platinum dichalcogenides offer a wide range of electronic features by forming bilayer heterojunctions of type-I, type-II, and type-III, respectively. Our findings reveal that Janus-type ultrathin platinum dichalcogenide crystals are quite promising materials for optoelectronic device applications
Measurements of properties of the Higgs boson decaying to a W boson pair in pp collisions at √s=13TeV
No full textMeasurements of the production of the standard model Higgs boson decaying to a W boson pair are reported. The W+ W- candidates are selected in events with an oppositely charged lepton pair, large missing transverse momentum, and various numbers of jets. To select Higgs bosons produced via vector boson fusion and associated production with a W or Z boson, events with two jets or three or four leptons are also selected. The event sample corresponds to an integrated luminosity of 35.9 fb(-1), collected in pp collisions at root s = 13 TeV by the CMS detector at the LHC during 2016. Combining all channels, the observed cross section times branching fraction is 1.28(-0.17)(+0.18) times the standard model prediction for the Higgs boson with a mass of 125.09 GeV. This is the first observation of the Higgs boson decay to W boson pairs by the CMS experiment. (c) 2019 The Author(s). Published by Elsevier B.V
Search for the associated production of the Higgs boson and a vector boson in proton-proton collisions at √s = 13 TeV via Higgs boson decays to τ leptons
No full textA search for the standard model Higgs boson produced in association with a W or a Z boson and decaying to a pair of leptons is performed. A data sample of proton-proton collisions collected at p s = 13TeV by the CMS experiment at the CERN LHC is used, corresponding to an integrated luminosity of 35.9 fb. The signal strength is measured relative to the expectation for the standard model Higgs boson, yielding = 2: 5 +1:4. These results are combined with earlier CMS measurements targeting Higgs boson decays to a pair of leptons, performed with the same data set in the gluon fusion and vector boson fusion production modes. The combined signal strength is = 1: 24 +0:29 (1: 00 +0:24 expected), and the observed signi fi cance is 5.5 standard deviations (4.8 expected) for a Higgs boson mass of 125GeV