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Jonathan Wyrick,
Dae-Ho Kim,
Dezheng Sun,
Zhihai Cheng,
Wenhao Lu,
Yeming Zhu,
Kristian Berland, Yong Su Kim,
Eli Rotenberg,
Miaomiao Luo,
Per Hyldgaard,
T L Einstein,
Ludwig Bartels
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ABSTRACT: Anthraquinone self-assembles on Cu(111) into a giant honeycomb network with exactly three molecules on each side. Here we propose that the exceptional degree of order achieved in this system can be explained as a consequence of the confinement of substrate electrons in the pores, with the pore size tailored so that the confined electrons can adopt a noble-gas-like two-dimensional quasi-atom configuration with two filled shells. Formation of identical pores in a related adsorption system (at different overall periodicity due to the different molecule size) corroborates this concept. A combination of photoemission spectroscopy with density functional theory computations (including van der Waals interactions) of adsorbate-substrate interactions allows quantum mechanical modeling of the spectra of the resultant quasi-atoms and their energetics.
Nano Letters 06/2011; 11(7):2944-8. · 13.20 Impact Factor
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Andrew L. Walter,
Ki-Joon Jeon,
Aaron Bostwick,
Florian Speck,
Markus Ostler,
Thomas Seyller,
Luca Moreschini, Yong Su Kim,
Young Jun Chang,
Karsten Horn,
Eli Rotenberg
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ABSTRACT: We present a method for decoupling epitaxial graphene grown on SiC(0001) by intercalation of a layer of fluorine at the interface. The fluorine atoms do not enter into a covalent bond with graphene but rather saturate the substrate Si bonds. This configuration of the fluorine atoms induces a remarkably large hole density of p≈4.5×10<sup>13</sup> cm <sup>-2</sup> , equivalent to the location of the Fermi level at 0.79 eV above the Dirac point E<sub>D</sub> .
Applied Physics Letters 06/2011; · 3.84 Impact Factor
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ABSTRACT: By using high resolution x-ray photoelectron spectroscopy, we show that inelastic scattering of photoelectron at low temperature (30-50 K) generates two kinds of oxygen species on Pt (111) surface. Intense synchrotron radiation source dissociates oxygen molecules into chemisorbed atomic oxygen and induces the formation of PtO on the surface. Estimated coverage of dissociated atomic oxygen is 0.5 ML, suggesting possible formation of p(2 x 1) surface structure, while PtO coverage shows saturation coverage of 0.5 ML. Molecular oxygen dosed at 30 K undergoes thermally activated transition from physisorbed to chemisorbed state at around 40 K.
The Journal of chemical physics 07/2010; 133(3):034501. · 3.09 Impact Factor
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ABSTRACT: We have investigated the effects of structure change and electron correlation on SrTiO3 single crystals using angle-resolved photoemission spectroscopy. We show that the cubic to tetragonal phase transition at 105 K is manifested by a charge transfer from in-plane (dyz and dzx) bands to out-of-plane (dxy) band, which is opposite to the theoretical predictions. Along this second-order phase transition, we find a smooth evolution of the quasiparticle strength and effective masses. The in-plane band exhibits a peak-dip-hump lineshape, indicating a high degree of correlation on a relatively large (170 meV) energy scale, which is attributed to the polaron formation.
Phys. Rev. B. 02/2010; 81(23).
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ABSTRACT: Magnetic random access memory (MRAM) is one of the most promising candidates to provide energy-efficient and nonvolatile memory. We present a new MRAM design using a pair of cells where each cell can store two bits of information. The pair cells have a parallelogram shape to induce broken-shape magnetic anisotropy along the short axis of the cell. One important advantage of the pair cells is that they can share the same word- and bit-lines intersection in the MRAM architecture. This means that the number of electrical current lines can be reduced and lead to higher recording density. Such design is successfully demonstrated using finite-element micromagnetic simulation.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: This paper introduces flux-reversal machine (FRM) and presents the design of a FRM to reduce the cogging torque. The effect of the design parameters on the characteristic and cogging torque is analyzed by finite element method (FEM). The considered design parameters are bifurcated teeth, chamfered magnet poles, chamfered rotor tooth tips and rotor skewing. As a result, we can find the optimum model reduced cogging torque and torque ripple in 6/8 FRM.
Electrical Machines and Systems, 2005. ICEMS 2005. Proceedings of the Eighth International Conference on; 10/2005
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ABSTRACT: This paper presents a characteristic analysis of switched reluctance motor (SRM) considering hard chopping and dc link voltage ripple by using time-stepped voltage source finite element method in which the magnetic field is combined with drive circuit. We also examine the influence of freewheeling diodes and dc link voltage ripple on the performance of a SRM such as torque ripples and radial force on the surface of the teeth. The freewheeling diodes and dc link voltage ripples must be taken into account in predicting the performance of the SRM.
IEEE Transactions on Magnetics 06/2005; · 1.36 Impact Factor
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ABSTRACT: The authors present a retrospective clinical analysis of meningeal hemangiopericytomas. The long-term outcome and biologic behavior, including local recurrence and extraneural distant metastasis, are elucidated.
Clinical records and radiologic findings of 31 cases with meningeal hemangiopericytoma treated at Seoul National University Hospital and Asian Medical Center between 1982 and 1999 were carefully reviewed. The final outcome was determined by direct or phone contact and questionnaire by mail. The duration of follow-up was from 1 to 216 months (mean 77). All patients underwent craniotomy and Simpson Grade I or II resection was possible in 24 patients. Conventional radiotherapy was given in 11 patients (in 5 after total excision and in 6 for residual mass) and stereotactic radiosurgery was conducted in 6 cases.
Intracranial recurrence was seen in 12 cases (38.7%) and the mean period before the first recurrence was 104 months. The recurrence was at the primary site in 11 cases and diffuse leptomeningeal seeding occurred in the remaining case. The 5-year recurrence free rate was 59.2% and the extent of excision was the significant factor (72.7% in total excision group and 20.8% in the incomplete excision group, p = 0.006). In four patients (12.9%), extraneural metastases developed at an average of 107 months. Six patients died during the follow-up period; however, 2 of these died of unrelated causes.
Complete excision is the most important factor in reducing recurrence. However, recurrence may occur even after complete excision. Careful long-term follow-up is mandatory because of the long disease-free interval.
Surgical Neurology 02/2003; 59(1):47-53; discussion 53-4. · 1.67 Impact Factor
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Physical Review B, v.81 (2010).
