Complexes of Copper with a Flexible Bis-benzimidazole Ligand

The flexible bidentate ligand 1,3-bis(benzimidazol-2-yl)propane, L3, and its N-methylated derivative L4, form complexes with CUI and CUII. The X-ray crystal structure of [Cu(L4)(MeCN)] (PF6) (1) shows a trigonal coordination of the CuI with the eight-membered chelate ring adopting a half-chair conformation. With CuII in EtOH, L3 forms dimeric [(L3)Cu(μ-EtO)2Cu(L3)](ClO4)2 · 2EtOH (2) whose X-ray crystal structure shows CuII in a distorted square-planar environment with one bidentate ligand and two bridging ethoxides. The chelate ring now has a boat-chair conformation which forms a hydrophobic pocket around the metal

Non-sequential double ionization with near-single cycle laser pulses

A three-dimensional semiclassical model is used to study double ionization of Ar when driven by a near-infrared and near-single-cycle laser pulse for intensities ranging from 0.85 x 10(14) W/cm(2) to 5 x 10(14) W/cm(2). Asymmetry parameters, distributions of the sum of the two electron momentum components along the direction of the polarization of the laser field and correlated electron momenta are computed as a function of the intensity and of the carrier envelope phase. A very good agreement is found with recently obtained results in kinematically complete experiments employing near-single-cycle laser pulses. Moreover, the contribution of the direct and delayed pathways of double ionization is investigated for the above observables. Finally, an experimentally obtained anti-correlation momentum pattern at higher intensities is reproduced with the three-dimensional semiclassical model and shown to be due to a transition from strong to soft recollisions with increasing intensity

Early deformation mechanisms in the shear affected region underneath a copper sliding contact

Dislocation mediated plastic deformation decisively influences the friction coefficient and the microstructural changes at many metal sliding interfaces during tribological loading. This work explores the initiation of a tribologically induced microstructure in the vicinity of a copper twin boundary. Two distinct horizontal dislocation traces lines (DTL) are observed in their interaction with the twin boundary beneath the sliding interface. DTL formation seems unaffected by the presence of the twin boundary but the twin boundary acts as an indicator of the occurring deformation mechanisms. Three concurrent elementary processes can be identified: simple shear of the subsurface area in sliding direction, localized shear at the primary DTL and crystal rotation in the layers above and between the DTLs around axes parallel to the transverse direction. Crystal orientation analysis demonstrates a strong compatibility of these proposed processes. Quantitatively separating these different deformation mechanisms is crucial for future predictive modeling of tribological contacts

Critical Discussion of Ex situ and In situ TEM Measurements on Memristive Devices

Memristors are promising candidates for new memory technologies and are capable to mimic synapses in artificial neural networks. The switching in memristive devices occurs typically in few nanometer thin dielectric layers. The direct observation of the switching mechanism is crucial for better comprehension and improvements of memristors. Therefore, in situ experiments are conducted in a transmission electron microscope (TEM). However, sample preparation processes and electron beam irradiation can lead to a chemical and structural modification of the active layers. Moreover, devices may show significant device-to-device variability due to the details of processing parameters. Thus, it is essential to characterize the identical device electrically before microstructural analysis

Carrier-envelope phase control over pathway interference in strong-field dissociation of H2+_2^+

The dissociation of an H$_2^+$ molecular-ion beam by linearly polarized, carrier-envelope-phase-tagged 5 fs pulses at 4$\times10^{14}$W/cm$^2$ with a central wavelength of 730 nm was studied using a coincidence 3D momentum imaging technique. Carrier-envelope-phase-dependent asymmetries in the emission direction of H$^+$ fragments relative to the laser polarization were observed. These asymmetries are caused by interference of odd and even photon number pathways, where net-zero photon and 1-photon interference predominantly contributes at H$^+$+H kinetic energy releases of 0.2 -- 0.45 eV, and net-2-photon and 1-photon interference contributes at 1.65 -- 1.9 eV. These measurements of the benchmark H$_2^+$ molecule offer the distinct advantage that they can be quantitatively compared with \textit{ab initio} theory to confirm our understanding of strong-field coherent control via the carrier-envelope phase

Steering proton migration in hydrocarbons using intense few-cycle laser fields

Proton migration is a ubiquitous process in chemical reactions related to biology, combustion, and catalysis. Thus, the ability to control the movement of nuclei with tailored light, within a hydrocarbon molecule holds promise for far-reaching applications. Here, we demonstrate the steering of hydrogen migration in simple hydrocarbons, namely acetylene and allene, using waveform-controlled, few-cycle laser pulses. The rearrangement dynamics are monitored using coincident 3D momentum imaging spectroscopy, and described with a quantum-dynamical model. Our observations reveal that the underlying control mechanism is due to the manipulation of the phases in a vibrational wavepacket by the intense off-resonant laser field.Comment: 5 pages, 4 figure

Phase- and intensity-resolved measurements of above threshold ionization by few-cycle pulses

We investigate the carrier-envelope phase and intensity dependence of the longitudinal momentum distribution of photoelectrons resulting from above-threshold ionization of argon by few-cycle laser pulses. The intensity of the pulses with a center wavelength of 750\,nm is varied in a range between $0.7 \times 10^{14}$ and \unit[5.5 \times 10^{14}]{W/cm^2}. Our measurements reveal a prominent maximum in the carrier-envelope phase-dependent asymmetry at photoelectron energies of 2\,$U_\mathrm{P}$ ($U_\mathrm{P}$ being the ponderomotive potential), that is persistent over the entire intensity range. Further local maxima are observed at 0.3 and 0.8\,$U_\mathrm{P}$. The experimental results are in good agreement with theoretical results obtained by solving the three-dimensional time-dependent Schr\"{o}dinger equation (3D TDSE). We show that for few-cycle pulses, the carrier-envelope phase-dependent asymmetry amplitude provides a reliable measure for the peak intensity on target. Moreover, the measured asymmetry amplitude exhibits an intensity-dependent interference structure at low photoelectron energy, which could be used to benchmark model potentials for complex atoms

Defect-mediated curvature and twisting in polymer crystals

Crystalline polymer solids almost inevitably exhibit defects due to chain ends, chain folding and the limited molecular mobility. The defects result in local (dislocations, grain boundaries) or global (bending, twisting) distortions of the molecular symmetry with pronounced implications on materials properties. Depending on the localization of the deformation, continuous molecular distortions or chain scission are expected, resulting in distinct differences for the mechanical (crack formation) and optoelectronic properties (charge transport and delocalization), which become especially important in the light of the recent extraordinary developments in molecular electronics. Further studies of defect structure and properties in polymers are expected to result in an increasingly sophisticated understanding of the microstructure and microstructural evolution during processing necessary to control and optimize the nano- and micrometerscale structure of organic materials. Copyright © 2000 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35029/1/322_ftp.pd

Single-shot velocity-map imaging of attosecond light-field control at kilohertz rate

High-speed, single-shot velocity-map imaging (VMI) is combined with carrier- envelope phase (CEP) tagging by a single-shot stereographic above-threshold ionization (ATI) phase-meter. The experimental setup provides a versatile tool for angle-resolved studies of the attosecond control of electrons in atoms, molecules, and nanostructures. Single-shot VMI at kHz repetition rate is realized with a highly sensitive megapixel complementary metal-oxide semiconductor camera omitting the need for additional image intensifiers. The developed camerasoftware allows for efficient background suppression and the storage of up to 1024 events for each image in real time. The approach is demonstrated by measuring the CEP-dependence of the electron emission from ATI of Xe in strong (≈1013 W/cm2) near single-cycle (4 fs) laser fields. Efficient background signal suppression with the system is illustrated for the electron emission from SiO2nanospheres