Electronic structure of 1 ML NTCDA/Ag(1 1 1) studied by photoemission spectroscopy

We performed high-resolution photoemission experiments at different photon energies to investigate the valence band structure of 1 ML of 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) on Ag(1 1 1). Besides the known occupied molecular orbitals HOMO and HOMO − 1 we observe a new state close to the Fermi level, which results from the interaction between NTCDA and the substrate, partially filling the lowest unoccupied orbital of the free molecule (LUMO) in the monolayer system. By tuning the photon energy through the carbon K-edge, a resonance like change of the spectral intensity at the HOMO and HOMO − 1 energies is clearly revealed, which we use for an assignment of the individual spectral features to a predominant localization either at the naphthalene core or the anhydride group.     

Doping and STM tip-induced changes to single dangling bonds on Si(0 0 1)

We have studied single Si dangling bonds on the Si(0 0 1) surface using scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations. The Si dangling bonds are created by the chemisorption of single hydrogen atoms forming a Si-Si-H hemihydride. At room temperature, the hemihydride induces static buckling on adjacent Si-Si dimers. In the STM measurements, we observe that the orientation of the static buckling pattern can be reversed with tip-sample bias and influenced by the substrate doping. Our DFT calculations yield a correlation between the electron occupancy of the hemihydride Si dangling bond and the buckling orientation around it.     

Dynamically controlled dielectrophoresis using resonant tuning

Electrically polarizable micro- and nanoparticles and droplets can be trapped using the gradient electric field of electrodes. But the spatial profile of the resultant dielectrophoretic force is fixed once the electrode structure is defined. To change the force profile, entire complex lab-on-a-chip systems must be re-fabricated with modified electrode structures. To overcome this problem, we propose an approach for the dynamic control of the spatial profile of the dielectrophoretic force by interfacing the trap electrodes with a resistor and an inductor to form a resonant resistor–inductor–capacitor (RLC) circuit. Using a dielectrophoretically trapped water droplet suspended in silicone oil, we show that the resonator amplitude, detuning, and linewidth can be continuously varied by changing the supply voltage, supply frequency, and the circuit resistance to obtain the desired trap depth, range, and stiffness. We show that by proper tuning of the resonator, the trap range can be extended without increasing the supply voltage, thus preventing sensitive samples from exposure to high electric fields at the stable trapping position. Such unprecedented dynamic control of dielectrophoretic forces opens avenues for the tunable active manipulation of sensitive biological and biochemical specimen in droplet microfluidic devices used for single-cell and biochemical reaction analysis.     

Shape‐Persistent Two‐Component 2 D Networks with Atomic‐Size Tunability

Over the past few years, two‐dimensional (2D) nanoporous networks have attracted great interest as templates for the precise localization and confinement of guest building blocks, such as functional molecules or clusters on the solid surfaces. Herein, a series of two‐component molecular networks with a 3‐fold symmetry are constructed on graphite using a truxenone derivative and trimesic acid homologues with carboxylic‐acid‐terminated alkyl chains. The hydrogen‐bonding partner‐recognition‐induced 2D crystallization of alkyl chains makes the flexible alkyl chains act as rigid spacers in the networks to continuously tune the pore size with an accuracy of one carbon atom per step. The two‐component networks were found to accommodate and regulate the distribution and aggregation of guest molecules, such as COR and CuPc. This procedure provides a new pathway for the design and fabrication of molecular nanostructures on solid surfaces.     

Gearing of molecular swirls: columnar packing of nematogenic hexakis(4-alkoxyphenylethynyl)benzene derivatives

Through molecular design and straightforward synthesis, incorporating an additional alkoxy chain onto various numbers of peripheral phenyls in nematogenic hexakis(4-alkoxyphenylethynyl)benzene was achieved to generate columnar phases with significantly expanded temperature ranges. For the compound with two decyloxy chains on every peripheral phenyl, scanning tunnelling microscopic studies indicate the molecule adopts a preferred molecular-swirl geometry by restricting the conformational arrangement of the alkoxy side chains. Cooperative packing of the molecular swirls by a lock-in mechanism among columns results in a stable helical column packing evidenced by powder X-ray diffraction.     

Modeling and analysis of nonlinear rotordynamics due to higher order deformations in bending

A mathematical model incorporating the higher order deformations in bending is developed and analyzed to investigate the nonlinear dynamics of rotors. The rotor system considered for the present work consists of a flexible shaft and a rigid disk. The shaft is modeled as a beam with a circular cross section and the Euler Bernoulli beam theory is applied with added effects such as rotary inertia, gyroscopic effect, higher order large deformations, rotor mass unbalance and dynamic axial force. The kinetic and strain (deformation) energies of the rotor system are derived and the Rayleigh–Ritz method is used to discretize these energy expressions. Hamilton’s principle is then applied to obtain the mathematical model consisting of second order coupled nonlinear differential equations of motion. In order to solve these equations and hence obtain the nonlinear dynamic response of the rotor system, the method of multiple scales is applied. Furthermore, this response is examined for different possible resonant conditions and resonant curves are plotted and discussed. It is concluded that nonlinearity due to higher order deformations significantly affects the dynamic behavior of the rotor system leading to resonant hard spring type curves. It is also observed that variations in the values of different parameters like mass unbalance and shaft diameter greatly influence dynamic response. These influences are also presented graphically and discussed.     

Cation spectroscopy of 3,4-difluoroaniline by two-color resonant two-photon mass-analyzed threshold ionization

We applied the two-color resonant two-photon mass-analyzed threshold ionization technique to record the vibrationally resolved cation spectra of 3,4-difluoroaniline (34DFA) via the 0⁰, X¹, 6b¹, and I² levels of the S₁ state. The adiabatic ionization energy of this molecule was determined to be 64 195 ± 5 cm⁻¹. Most of the observed active modes of the 34DFA cation in the D₀ state are related to the in-plane ring deformation vibrations. Comparing these data with those of 3-fluoroaniline and 4-fluoroaniline, one can learn the effects of fluorine substitution on the electronic transition and molecular vibration.     

STM spectroscopy on superconducting FeSe1−xTex single crystals at 300 mK

We report cryogenic scanning tunneling spectroscopy measurements on single crystals of superconducting FeSe_1−xTe_x, at doping levels of x=0.5 and 0.7, with critical temperatures . Atomically resolved topographic images were obtained, showing large-scale density-of-state clustering which appears to have no periodicity and to vary with the doping. Conductance spectra taken at 300 mK showed a generally asymmetric V-shaped background, along with a sharp dip structure within . These spectra appeared to vary over ∼nm length scale, and not correlated with the topography. The overall spectral evolution versus temperature is consistent with the dip structure arising from a superconducting energy gap which closes above T_c, and with the spectral background having a non-superconducting origin. The persistence of finite zero-bias conductance down to 300 mK, well below T_c, indicates the presence of low-energy quasiparticles on parts of the Fermi surface. We discuss our data in light of some other recent spectroscopic measurements of FeSe_1−xTe_x, and in terms of its characteristic band structure.