Search results for "Microscopy"
showing 10 items of 3390 documents
Time- and energy resolved photoemission electron microscopy-imaging of photoelectron time-of-flight analysis by means of pulsed excitations
2010
Abstract The present work enlightens the developments in time- and energy resolved photoemission electron microscopy over the past few years. We describe basic principles of the technique and demonstrate different applications. An energy- and time-filtering photoemission electron microscopy (PEEM) for real-time spectroscopic imaging can be realized either by a retarding field or hemispherical energy analyzer or by using time-of-flight optics with a delay line detector. The latter method has the advantage of no data loss at all as all randomly incoming particles are measured not only by position but also by time. This is of particular interest for pump–probe experiments in the femtosecond an…
Discriminating short-range from van der Waals forces using total force data in noncontact atomic force microscopy
2014
Noncontact atomic force microscopy (NC-AFM) features the measurement of forces with highest spatial resolution and sensitivity, resolving forces of the order of pico-Newtons with submolecular resolution. However, the measured total force is a mixture composed of various interactions. While some interactions such as electrostatic or magnetic forces can be excluded by a careful design of the experiment, the subtraction of van der Waals forces, which mainly originate from London dispersion interactions between the macroscopic tip shank and the bulk sample, remains a challenge. We present the determination of the inherently present van der Waals forces in total interaction force data from fitti…
Two-photon exchange correction in elastic unpolarized electron-proton scattering at small momentum transfer
2015
We evaluate the two-photon exchange (TPE) correction to the unpolarized elastic electron-proton scattering at small momentum transfer $ Q^2 $. We account for the inelastic intermediate states approximating the double virtual Compton scattering by the unpolarized forward virtual Compton scattering. The unpolarized proton structure functions are used as input for the numerical evaluation of the inelastic contribution. Our calculation reproduces the leading terms in the $ Q^2 $ expansion of the TPE correction and goes beyond this approximation by keeping the full $ Q^2 $ dependence of the proton structure functions. In the range of small momentum transfer, our result is in good agreement with …
Near Field of Strongly Coupled Plasmons: Uncovering Dark Modes
2012
Strongly coupled plasmons in a system of individual gold nanoparticles placed at subnanometer distance to a gold film (nanoparticle-on-plane, NPOP) are investigated using two complementary single particle spectroscopy techniques. Optical scattering spectroscopy exclusively detects plasmon modes that couple to the far field via their dipole moment (bright modes). By using photoemission electron microscopy (PEEM), we detect in the identical NPOPs near-field modes that do not couple to the scattered far field (dark modes) and are characterized by a strongly enhanced nonlinear electron emission process. To our knowledge, this is the first time that both far- and near-field spectroscopy are carr…
Atomic-resolution imaging of the polar (0001¯) surface of LiNbO3in aqueous solution by frequency modulation atomic force microscopy
2012
S. Rode,1 R. Holscher,2 S. Sanna,2 S. Klassen,1 K. Kobayashi,3 H. Yamada,3 W. G. Schmidt,2 and A. Kuhnle1,* 1Institut fur Physikalische Chemie, Fachbereich Chemie, Johannes Gutenberg-Universitat Mainz, Jakob-Welder-Weg 11, 55099 Mainz, Germany 2Lehrstuhl fur Theoretische Physik, Universitat Paderborn, 33095 Paderborn, Germany 3Department of Electronic Science and Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan (Received 31 March 2012; revised manuscript received 12 June 2012; published 29 August 2012)
Atomistic Simulations of Solid Friction
2002
Friction between two solid bodies in relative sliding motion takes place on a large spectrum of length and time scales: From the nanometer/second scale in an atomic force microscope up to the extremely macroscopic scales of tectonic motion. Despite our familiarity with the effects of friction, fundamental questions remain unanswered. The atomistic origins of well-established phenomenological friction laws are controversial. Many explanations, seemingly well-established, have recently been called into question by new experimental results. Computer simulations have also revealed flaws in previous theoretical approaches and led to new insights into the atomistic processes responsible for frict…
Common-path phase-shifting lensless holographic microscopy
2010
We present an approach capable of high-NA imaging in a lensless digital in-line holographic microscopy layout even outside the Gabor's regime. The method is based on spatial multiplexing at the sample plane, allowing a common-path interferometric architecture, where two interferometric beams are generated by a spatial light modulator (SLM) prior to illuminating the sample. The SLM allows phase-shifting interferometry by phase modulation of the SLM diffracted beam. After proper digital processing, the complex amplitude distribution of the diffracted object wavefront is recovered and numerically propagated to image the sample. Experimental results are reported that validate the proposed metho…
Two-photon spectroscopy of mercury and velocity-selective double resonances
2009
Two-photon laser spectroscopy of the $6\text{ }{^{1}S}_{0}\ensuremath{-}7\text{ }{^{1}S}_{0}$ transition in mercury has been performed using two copropagating continuous-wave laser beams. One laser beam is at 254 nm wavelength and can be tuned to the $6\text{ }{^{1}S}_{0}\ensuremath{-}6\text{ }{^{3}P}_{1}$ resonance. The other laser beam is at 408 nm. Two very different regimes can be distinguished, one far off resonance and one near resonance with the one-photon resonance. A resonance which is not Doppler broadened has been observed for low Rabi frequencies. This velocity-selective double resonance in a three-level ladder system is analogous to the dark resonance in three-level $\ensuremat…
Charge compensation by long-period reconstruction in strongly polar lithium niobate surfaces
2013
The microscopic structure of the polar (000$\overline{1}$) and (0001) surfaces of lithium niobate is investigated by atomic-resolution frequency modulation atomic force microscopy and first-principles calculations. It is found that the surface reconstructs at annealing temperatures sufficiently high to drive off external adsorbates. In particular a ($\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$)$R$19.1${}^{\ensuremath{\circ}}$ reconstruction is found for the (000$\overline{1}$) surface. Density-functional theory calculations show that---apart from the $(\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7})$---a series of adatom-induced surface reconstructions exist that lower the surfa…
Status of the EPIC thin and medium filters on-board XMM-Newton after more than 10 years of operation I: laboratory measurements on back-up filters
2013
After more than ten years of operation of the EPIC camera on board the X-ray observatory XMM-Newton, we have reviewed the status of its Thin and Medium filters by performing both laboratory measurements on back-up filters, and analysis of data collected in-flight. We have selected a set of Thin and Medium back-up filters among those still available in the EPIC consortium, and have started a program to investigate their status by different laboratory measurements including: UV/VIS transmission, X-ray transmission, RAMAN IR spectroscopy, X-Ray Photoelectron Spectroscopy, and Atomic Force Microscopy. We report the results of the measurements conducted up to now, and point out some lessons lear…