Fermi surface of Mo(112) and indirect interaction between adsorbed atoms

A comprehensive examination of the Fermi surface of Mo(112) is presented. The Fermi surface contours for the Mo(112) surface, obtained by density functional theory calculations, agree well with the direct observations via angle-resolved photoemission spectroscopy and indicate the existence of flattened segments in the Fermi contours perpendicular to the direction of the atomic furrows. Both the calculation and the experiment indicate significant surface weight for these states. Such flattened Fermi contours at the surface can give rise to long-range charge density waves (CDW) and long-range indirect lateral interactions, especially in the case of adsorption of electropositive atoms. When mediated by the surface electrons, exhibiting flattened Fermi contours, the oscillatory potential of the indirect interaction between adsorbed atoms decays very slowly (∼1/r) in the direction along the furrows, which can explain the formation of long-period chain structures of electropositive adsorbates on the furrowed surface of Mo(112)

New view of the occupied band structure of Mo(112)

We present a comprehensive examination of the occupied surface-weighted band structure of Mo(112) along the two high-symmetry directions of the surface Brillouin zone, both from theoretical and experimental perspectives. The band structures are found to be significantly different for the states along the two high-symmetry directions and for the states with even and odd reflection parities with respect to the mirror planes. The present study suggests the existence of a number of surface-weighted bands along both high-symmetry directions. The complexity of the band structure near the Fermi level may impose potential difficulties in experimental determination of the electron-phonon coupling parameters based on the effective mass enhancement distortion (or kink) in the energy-band dispersion, in the vicinity of the Fermi level, for several surface resonance bands of Mo(112)

Electron-Phonon Coupling and Structural Phase Transitions on Au/Mo(112)

The electronic structures, many-body interactions and Fermi surface topologies of Au/Mo(112) were investigated in detail and were found to play important roles in the newly discovered order-disorder structural phase transition of the system. First, the high-resolution angle-resolved photoemission spectroscopy was utilized to characterize the electronic band structure of Mo(112) in far greater details than before. This elucidated the existence of several surface-derived states and their dispersion relations in high precisions near the Fermi level, as well as the symmetries of the bulk and surface electronic states, which are in good quantitative agreement with the ab-initio calculations. Such thorough understanding of the electronic states on Mo(112) made it possible to investigate the more complex electronic structure and many-body interactions in the Au overlayers formed on the Mo(112) surface and their interface. Upon the Au adsorption on Mo(112) substrate, the Au overlayer states are seen to hybridize with those of Mo substrate, which resulted in the formation of the several surface resonance bands, exhibiting high electronic localization near the surface and interface of the combined system. Furthermore, the electron-phonon coupling, involving these surface resonance states, is found to cause strong effective mass enhancement of the electrons near the Fermi level, which can contribute significantly to the surface lattice instability. In particular, for the (4x1) Au overlayer on Mo(112), the noticeable temperature-dependent changes in the Fermi surface contours were observed near the room temperature and were seen to act in favor of the stronger nesting condition and phonon-induced lattice distortions. The combination of the identified strong electron-phonon coupling and the critical Fermi surface topology near the room temperature likely relates to the overlayer lattice instability on the Au/Mo(112) system. In accord with the above general expectation, the order-disorder structural phase transitions were identified on Au/Mo(112) above the room temperature, which is characterized by the abrupt changes in the effective surface Debye temperature, indicative of significant softening of phonons on Au/Mo(112) across the transition. The sequence of these studies likely evidences that the strong electron-phonon coupling and the temperature-dependent Fermi surface topology are indispensable in driving the order-disorder transitions on Au/Mo(112). Advisor: Peter A. Dowbe

Electron-Phonon Coupling and Structural Phase Transitions on Gold/Molybdenum(112)

The electronic structures, many-body interactions and Fermi surface topologies of Au/Mo(112) were investigated in detail and were found to play important roles in the newly discovered order-disorder structural phase transition of the system. First, the high-resolution angle-resolved photoemission spectroscopy was utilized to characterize the electronic band structure of Mo(112) in far greater details than before. This elucidated the existence of several surface-derived states and their dispersion relations in high precisions near the Fermi level, as well as the symmetries of the bulk and surface electronic states, which are in good quantitative agreement with the ab-initio calculations. Such thorough understanding of the electronic states on Mo(112) made it possible to investigate the more complex electronic structure and many-body interactions in the Au overlayers formed on the Mo(112) surface and their interface. Upon the Au adsorption on Mo(112) substrate, the Au overlayer states are seen to hybridize with those of Mo substrate, which resulted in the formation of the several surface resonance bands, exhibiting high electronic localization near the surface and interface of the combined system. Furthermore, the electron-phonon coupling, involving these surface resonance states, is found to cause strong effective mass enhancement of the electrons near the Fermi level, which can contribute significantly to the surface lattice instability. In particular, for the (4x1) Au overlayer on Mo(112), the noticeable temperature-dependent changes in the Fermi surface contours were observed near the room temperature and were seen to act in favor of the stronger nesting condition and phonon-induced lattice distortions. The combination of the identified strong electron-phonon coupling and the critical Fermi surface topology near the room temperature likely relates to the overlayer lattice instability on the Au/Mo(112) system. In accord with the above general expectation, the order-disorder structural phase transitions were identified on Au/Mo(112) above the room temperature, which is characterized by the abrupt changes in the effective surface Debye temperature, indicative of significant softening of phonons on Au/Mo(112) across the transition. The sequence of these studies likely evidences that the strong electron-phonon coupling and the temperature-dependent Fermi surface topology are indispensable in driving the order-disorder transitions on Au/Mo(112)

The electron–phonon coupling at the Mo(112) surface

We investigated the electron–phonon coupling (EPC), in the vicinity of the Fermi level, for the surface-weighted states of Mo(112) from high resolution angle-resolved photoemission data taken parallel to the surface corrugation (i.e. (111)). The surface-weighted bandwidth may be discussed in terms of electron–electron interactions, electron impurity scattering and electron–phonon coupling and exhibits a mass enhancement factor λ = 0.42, within the Debye model, determined from the experimentally derived self-energy. Gold overlayers suppress the mass enhancement of the Mo(112) surface-weighted band crossing the Fermi level at 0.54 Å-1

Isomeric effects with di-iodobenzene (C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e4\u3c/sub\u3eI\u3csub\u3e2\u3c/sub\u3e) on adsorption on graphite

Differences are seen in the adsorption of 1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene on graphite, as a function of exposure, using core level photoemission. The isomer 1,3-di-iodobenzene exhibits significant differences from 1,2-di-iodobenzene, and 1,4-di-iodobenzene in apparent sticking coefficients and core level binding energies. 1,3-Di-iodobenzene adsorb on graphite at 110 K in a strongly Stranski–Krastanov or Volmer–Weber (island) growth mode. The implication is that, even for small molecules adsorption, the adsorbate dipole in the plane of surface and the choice of isomer may matter

Haloform adsorption on crystalline copolymer films of vinylidene fluoride with trifluoroethylene

Reversible bromoform adsorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF–TrFE 70:30) was examined by photoemission and inverse photoemission spectroscopies. The adsorption of bromoform on this polymer surface is associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state, whose intensity scales with the unscreened photoemission final state

Steep-Slope Threshold Switch Enabled by Pulsed-Laser-Induced Phase Transformation

Super-steep two-terminal electronic devices using NbO2, which abruptly switch from insulator to metal at a threshold voltage (Vth), offer diverse strategies for energy-efficient and high-density device architecture to overcome fundamental limitation in current electronics. However, the tight control of stoichiometry and high-temperature processing limit practical implementation of NbO2 as a component of device integration. Here, we demonstrate a facile room-temperature process that uses solid-solid phase transformation induced by pulsed laser to fabricate NbO2-based threshold switches. Interestingly, pulsed laser annealing under a reducing environment facilitates a two-step nucleation pathway (a-Nb2O5 → o-Nb2O5-δ → t-NbO2) of the threshold-enabled NbO2 phase mediated by oxygen vacancies in o-Nb2O5-δ. The laser-annealed devices with embedded NbO2 crystallites exhibit excellent threshold device performance with low off-current and high on/off current ratio. Our strategy that exploits the interactions of pulsed lasers with multivalent metal oxides can guide the development of a rational route to achieve NbO2-based threshold switches that are compatible with current semiconductor fabrication technology. © 2019 American Chemical Societ

Growth of Transition-Metal Cobalt Nanoclusters on 2D Covalent Organic Frameworks

Two-dimensional (2D) covalent organic frameworks (COFs) fabricated through on-surface synthesis were investigated as a honeycomb nanopore template for the growth of 3d-transition-metal nanoclusters (NCs) with a size of 2 nm on a metallic substrate. The evolution of these NCs and their electronic characteristics were studied employing scanning tunneling microscopy/spectroscopy (STM/STS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS), and X-ray photoelectron spectroscopy (XPS) under an ultrahigh-vacuum (UHV) condition at room temperature. The 2D COFs were synthesized on Cu(111) substrate utilizing 1,3,5-tris(4-bromo­phenyl)benzene (TBB) precursors, which engendered a honeycomb nanopore array of approximately 2 nm in size. In contrast to the behavior observed in the Co/Cu(111) system producing triangular-shaped bilayer-stacking nanoclusters measuring 10–20 nm, STM imaging of Co/COFs/Cu(111) revealed the growth of Co NCs of approximately 1.5 nm within a single COF nanopore. This growth occurred without forming a monolayer film beneath the COFs, providing direct evidence that the 2D COFs on Cu(111) can effectively entrap Co atoms within the nanopore, giving rise to Co NCs. Spectroscopy measurements, including STS/UPS/XPS, confirmed the different local densities of states for Co NCs and COFs, corroborating the coexistence of Co NCs and COFs on the surface

Association between floating toe and toe grip strength in school age children: a cross-sectional study

[Purpose] This study investigated the association between floating toe and toe grip strength. [Subjects and Methods] A total of 635 Japanese children aged 9-11 years participated in this study. Floating toe was evaluated using footprint images, while toe grip strength was measured using a toe grip dynamometer. All 1, 270 feet were classified into a floating toe group and a normal toe group according to visual evaluation of the footprint images. Intergroup differences in toe grip strength were analyzed using the unpaired t-test and logistic regression analysis adjusted for age, gender, and Rohrer Index. [Results] There were 512 feet (40.3%) in the floating toe group. Mean toe grip strength of the feet with floating toe was significantly lower than that of normal feet (floating toe group, 12.9 ± 3.7 kg; normal toe group, 13.6 ± 4.1 kg). In addition, lower toe grip strength was associated with floating toe on logistic regression analysis after adjustment for age, gender, and Rohrer Index (odds ratio, 0.954; 95% confidence interval, 0.925-0.984). [Conclusion] This study revealed that lower toe grip strength was significantly associated with floating toe. Therefore, increasing toe grip strength may play a role in preventing floating toe in school age children