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Atomic-scale imaging of few-layer black phosphorus and its reconstructed edge
Lee, Yangjin,Yoon, Jun-Yeong,Scullion, Declan,Jang, Jeongsu,Santos, Elton J G,Jeong, Hu Young,Kim, Kwanpyo IOP 2017 Journal of Physics. D, Applied Physics Vol.50 No.8
<P>Black phosphorus (BP) has recently emerged as an alternative 2D semiconductor owing to its fascinating electronic properties such as tunable bandgap and high charge carrier mobility. The structural investigation of few-layer BP, such as identification of layer thickness and atomic-scale edge structure, is of great importance to fully understand its electronic and optical properties. Here we report atomic-scale analysis of few-layered BP performed by aberration corrected transmission electron microscopy (TEM). We establish the layer-number-dependent atomic resolution imaging of few-layer BP via TEM imaging and image simulations. The structural modification induced by the electron beam leads to revelation of crystalline edge and formation of BP nanoribbons. Atomic resolution imaging of BP clearly shows the reconstructed zigzag (ZZ) edge structures, which is also corroborated by van der Waals first principles calculations on the edge stability. Our study on the precise identification of BP thickness and atomic-resolution imaging of edge structures will lay the groundwork for investigation of few-layer BP, especially BP in nanostructured forms.</P>
Lee, Tae Hoon,Kim, Kwanpyo,Kim, Gwangwoo,Park, Hyo Ju,Scullion, Declan,Shaw, Leo,Kim, Myung-Gil,Gu, Xiaodan,Bae, Won-Gyu,Santos, Elton J. G.,Lee, Zonghoon,Shin, Hyeon Suk,Nishi, Yoshio,Bao, Zhenan American Chemical Society 2017 Chemistry of materials Vol.29 No.5
<P>Organic field-effect transistors have attracted much attention because of their potential use in low-cost, large area, flexible electronics. High-performance organic transistors require a low density of grain boundaries in their organic films and a decrease in the charge trap density at the semiconductor dielectric interface for efficient charge transport. In this respect, the role of the dielectric material is crucial because it primarily determines the growth of the film and the interfacial trap density. Here, we demonstrate the use of chemical vapor-deposited hexagonal boron nitride (CVD hBN) as a scalable growth template/dielectric for highperformance organic field-effect transistors. The field-effect transistors based on C-60 films grown on single-layer CVD h-BN exhibit an average mobility of 1.7 cm(2) V-1 s(-1) and a maximal mobility of 2.9 cm(2) s(-1) with on/off ratios of 10(7). The structural and morphology analysis shows that the epitaxial, two-dimensional growth of C-60 on CVD h-BN is mainly responsible for the superior charge transport behavior. We believe that CVD h-BN can serve as a growth template for various organic semiconductors, allowing the development of large-area, high-performance flexible electronics.</P>
New light‐travel time models and orbital stability study of the proposed planetary system HU Aquarii
Hinse, T. C.,Lee, J. W.,Goź,dziewski, K.,Haghighipour, N.,Lee, C.‐,U.,Scullion, E. M. Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society Vol.420 No.4
<P><B>ABSTRACT</B></P><P>In this work we propose a new orbital architecture for the two proposed circumbinary planets around the polar eclipsing binary HU Aquarii. We base the new two‐planet, light‐travel time model on the result of a Monte Carlo simulation driving a least‐squares Levenberg–Marquardt minimization algorithm on the observed eclipse egress times. Our best‐fitting model with <IMG src='/wiley-blackwell_img/equation/MNR_20283_mu1.gif' alt ='inline image'/> resulted in high final eccentricities for the two companions leading to an unstable orbital configuration. From a large ensemble of initial guesses, we examined the distribution of final eccentricities and semimajor axes for different <IMG src='/wiley-blackwell_img/equation/MNR_20283_mu2.gif' alt ='inline image'/> parameter intervals and encountered qualitatively a second population of best‐fitting parameters. The main characteristic of this population is described by low‐eccentric orbits favouring long‐term orbital stability of the system. We present our best‐fitting model candidate for the proposed two‐planet system and demonstrate orbital stability over one million years using numerical integrations.</P>
Ultrashort PW laser pulse interaction with target and ion acceleration
Ter-Avetisyan, S.,Singh, P.K.,Kakolee, K.F.,Ahmed, H.,Jeong, T.W.,Scullion, C.,Hadjisolomou, P.,Borghesi, M.,Bychenkov, V. Yu. Elsevier 2018 Nuclear Instruments & Methods in Physics Research. Vol.909 No.-
<P><B>Abstract</B></P> <P>We present the experimental results on ion acceleration by petawatt femtosecond laser solid interaction and explore strategies to enhance ion energy. The irradiation of micrometer thick (0.2–6.0 μ m ) Al foils with a virtually unexplored intensity regime (8 × 10<SUP>19</SUP> W/cm<SUP>2</SUP> – 1 × 10<SUP>21</SUP> W/cm<SUP>2</SUP>) resulting in ion acceleration along the rear and the front surface target normal direction is investigated. The maximum energy of protons and carbon ions, obtained at optimized laser intensity condition (by varying laser energy or focal spot size), exhibit a rapid intensity scaling as <SUP> I 0 . 8 </SUP> along the rear surface target normal direction and <SUP> I 0 . 6 </SUP> along the front surface target normal direction. It was found that proton energy scales much faster with laser energy rather than the laser focal spot size. Additionally, the ratio of maximum ion energy along the both directions is found to be constant for the broad range of target thickness and laser intensities.</P> <P>A proton flux is strongly dominated in the forward direction at relatively low laser intensities. Increasing the laser intensity results in the gradual increase in the backward proton flux and leads to almost equalization of ion flux in both directions in the entire energy range. These experimental findings may open new perspectives for applications.</P>
Ter-Avetisyan, S.,Andreev, A.,Platonov, K.,Sung, J. H.,Lee, S. K.,Lee, H. W.,Yoo, J. Y.,Singh, P. K.,Ahmed, H.,Scullion, C.,Kakolee, K. F.,Jeong, T. W.,Hadjisolomou, P.,Borghesi, M. The Optical Society 2016 Optics express Vol.24 No.24
<P>A significant level of back reflected laser energy was measured during the interaction of ultra-short, high contrast PW laser pulses with solid targets at 30 degrees incidence. 2D PIC simulations carried out for the experimental conditions show that at the laser-target interface a dynamic regular structure is generated during the interaction, which acts as a grating (quasi-grating) and reflects back a significant amount of incident laser energy. With increasing laser intensity above 1018 W/cm(2) the back reflected fraction increases due to the growth of the surface modulation to larger amplitudes. Above 1020 W/cm(2) this increase results in the partial destruction of the quasi-grating structure and, hence, in the saturation of the back reflection efficiency. The PIC simulation results are in good agreement with the experimental findings, and, additionally, demonstrate that in presence of a small amount of pre-plasma this regular structure will be smeared out and the back reflection reduced. (C) 2016 Optical Society of America</P>
Solar Science with the Atacama Large Millimeter/Submillimeter Array-A New View of Our Sun
Wedemeyer, S.,Bastian, T.,Brajš,a, R.,Hudson, H.,Fleishman, G.,Loukitcheva, M.,Fleck, B.,Kontar, E. P.,De Pontieu, B.,Yagoubov, P.,Tiwari, S. K.,Soler, R.,Black, J. H.,Antolin, P.,Scullion, E.,Gu Springer-Verlag 2016 Space science reviews Vol.200 No.1
<P>The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere-a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases.</P>