Large-area epitaxial growth of InAs nanowires and thin films on hexagonal boron nitride by metal organic chemical vapor deposition

Large-area epitaxial growth of III-V nanowires and thin films on van der Waals substrates is key to developing flexible optoelectronic devices. In our study, large-area InAs nanowires and planar structures are grown on hexagonal boron nitride templates using metal organic chemical vapor deposition method without any catalyst or pre-treatments. The effect of basic growth parameters on nanowire yield and thin film morphology is investigated. Under optimised growth conditions, a high nanowire density of 2.1×109cm-2is achieved. A novel growth strategy to achieve uniform InAs thin film on h-BN/SiO2/Si substrate is introduced. The approach involves controlling the growth process to suppress the nucleation and growth of InAs nanowires, while promoting the radial growth of nano-islands formed on the h-BN surface. A uniform polycrystalline InAs thin film is thus obtained over a large area with a dominant zinc-blende phase. The film exhibits near-band-edge emission at room temperature and a relatively high Hall mobility of 399 cm-2/(Vs). This work suggests a promising path for the direct growth of large-area, low-temperature III-V thin films on van der Waals substrates.Aswani Gopakumar Saraswathy Vilasam, Sonachand Adhikari, Bikesh Gupta, Sivacarendran Balendhran, Naoki Higashitarumizu, Julie Tournet, Lily Li, Ali Javey, Kenneth B Crozier, Siva Karuturi, Chennupati Jagadish, and Hark Hoe Ta

Breath-hold fast recovery fast spin echo versus conventional non-breath-hold fast spin echo T2-weighted MR imaging of focal liver lesions

Annals of the Academy of Medicine Singapore324450 - 454AAMS

Fundamental aspects of light scattering and optical Kerr effect spectroscopy

We describe the principles of two spectroscopic methods of non-resonance light scattering (LS) and optical-Kerr-effect (OKE) spectroscopies in detail, and review basic but truly important phenomena observed by these two methods. Particularly, we focus on the following three experiments: 1) Response functions determined by frequency-domain LS and time-domain OKE spectroscopies, almost completely agree with each other, indicating that the quantum-mechanical fluctuation-dissipation theorem (QM-FDT) holds well in this system. 2) Femtosecond time responses of liquids clearly show an initial rise process even though they show an exponential response at a later time. This indicates that the Debye relaxation model does not hold in such an early time region. 3) From the measurement of the Stokes and anti-Stokes LS intensity ratios, it is found that the LS spectra of relaxation modes in liquids and solids are symmetric with respect to the spectral origin of the scattered light and hence the ratio does not satisfy the Boltzmann distribution rule expected from QM-FDT. These experimental results which contain apparently contradictory data are closely related with the nature of relaxation modes examined, which more or less assume a macroscopic character, and also with the physical basis of relaxation, which is inevitably connected to the observation problem of quantum mechanics. We discuss these points in relation to the physical reality of macroscopic quantity

Measurements with silicon photomultipliers of dose-rate effects in the radiation damage of plastic scintillator tiles in the CMS hadron endcap calorimeter

Measurements are presented of the reduction of signal output due to radiation damage for two types of plastic scintillator tiles used in the hadron endcap (HE) calorimeter of the CMS detector. The tiles were exposed to particles produced in proton-proton (pp) collisions at the CERN LHC with a center-of-mass energy of 13 TeV, corresponding to a delivered luminosity of 50 fb-1. The measurements are based on readout channels of the HE that were instrumented with silicon photomultipliers, and are derived using data from several sources: A laser calibration system, a movable radioactive source, as well as hadrons and muons produced in pp collisions. Results from several irradiation campaigns using 60Co sources are also discussed. The damage is presented as a function of dose rate. Within the range of these measurements, for a fixed dose the damage increases with decreasing dose rate

Search for dark matter produced in association with heavy-flavor quark pairs in proton-proton collisions at √s=13TeV

A search is presented for an excess of events with heavy-flavor quark pairs (tt¯ and bb¯) and a large imbalance in transverse momentum in data from proton–proton collisions at a center-of-mass energy of 13TeV. The data correspond to an integrated luminosity of 2.2fb-1 collected with the CMS detector at the CERN LHC. No deviations are observed with respect to standard model predictions. The results are used in the first interpretation of dark matter production in tt¯ and bb¯ final states in a simplified model. This analysis is also the first to perform a statistical combination of searches for dark matter produced with different heavy-flavor final states. The combination provides exclusions that are stronger than those achieved with individual heavy-flavor final states. © 2017, CERN for the benefit of the CMS collaboration

Measurement of differential cross sections for Z boson production in association with jets in proton-proton collisions at √s=13TeV

The production of a Z boson, decaying to two charged leptons, in association with jets in proton-proton collisions at a centre-of-mass energy of 13TeV is measured. Data recorded with the CMS detector at the LHC are used that correspond to an integrated luminosity of 2.19fb-1. The cross section is measured as a function of the jet multiplicity and its dependence on the transverse momentum of the Z boson, the jet kinematic variables (transverse momentum and rapidity), the scalar sum of the jet momenta, which quantifies the hadronic activity, and the balance in transverse momentum between the reconstructed jet recoil and the Z boson. The measurements are compared with predictions from four different calculations. The first two merge matrix elements with different parton multiplicities in the final state and parton showering, one of which includes one-loop corrections. The third is a fixed-order calculation with next-to-next-to-leading order accuracy for the process with a Z boson and one parton in the final state. The fourth combines the fully differential next-to-next-to-leading order calculation of the process with no parton in the final state with next-to-next-to-leading logarithm resummation and parton showering. © 2018, CERN for the benefit of the CMS collaboration

Measurements of triple-differential cross sections for inclusive isolated-photon+jet events in p p collisions at √s=8TeV

Measurements are presented of the triple-differential cross section for inclusive isolated-photon+jet events in p p collisions at s=8 TeV as a function of photon transverse momentum (pTγ), photon pseudorapidity (ηγ), and jet pseudorapidity (ηjet). The data correspond to an integrated luminosity of 19.7fb-1 that probe a broad range of the available phase space, for | ηγ| < 1.44 and 1.57 < | ηγ| < 2.50 , | ηjet| < 2.5 , 40<pTγ<1000GeV, and jet transverse momentum, pTjet, > 25GeV. The measurements are compared to next-to-leading order perturbative quantum chromodynamics calculations, which reproduce the data within uncertainties. © 2019, CERN for the benefit of the CMS collaboration

Measurement of single-diffractive dijet production in proton–proton collisions at √s=8Te with the CMS and TOTEM experiments

Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss ξ and the four-momentum transfer squared t. Both processes pp→pX and pp→Xp, i.e. with the proton scattering to either side of the interaction point, are measured, where X includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton–proton collisions at s=8Te during a dedicated run with β∗=90m at low instantaneous luminosity and correspond to an integrated luminosity of 37.5nb-1. The single-diffractive dijet cross section σjjpX, in the kinematic region ξ< 0.1 , 0.03<|t|<1Ge2, with at least two jets with transverse momentum pT>40Ge, and pseudorapidity | η| < 4.4 , is 21.7±0.9(stat)-3.3+3.0(syst)±0.9(lumi)nb. The ratio of the single-diffractive to inclusive dijet yields, normalised per unit of ξ, is presented as a function of x, the longitudinal momentum fraction of the proton carried by the struck parton. The ratio in the kinematic region defined above, for x values in the range - 2.9 ≤ log 10x≤ - 1.6 , is R=(σjjpX/Δξ)/σjj=0.025±0.001(stat)±0.003(syst), where σjjpX and σjj are the single-diffractive and inclusive dijet cross sections, respectively. The results are compared with predictions from models of diffractive and nondiffractive interactions. Monte Carlo predictions based on the HERA diffractive parton distribution functions agree well with the data when corrected for the effect of soft rescattering between the spectator partons. © 2020, CERN for the benefit of the CMS and TOTEM collaborations