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    Time-of-flight momentum microscopy reveals sixfold symmetric sharp features of decreased intensity (dark lines) in constant-energy maps for clean Ir(111) and graphene/Ir(111). The dark lines have been observed for p- and s-polarized light in the photon-energy range of 20–27 eV and result from scattering of photoelectrons at the surface potential barrier. The phenomenon is strongly related to threshold effects in low-energy electron diffraction. A quantitative analysis of the dark lines' positions shows that the relevant reciprocal-lattice vector corresponds to the lattice of the topmost layer (in our case graphene and Ir, respectively). The dark lines appear in the momentum patterns only in a certain photon-energy range satisfying the additional condition that the electron wavelength matches the lattice periodicity.
    This is sort of hoax, list of future contributions to Adv. Imag. Electron Physics was considered by an unqualified machine reader as a publication. Sorry to all who take this seriously, it is not my fault. ResGate should reconsider their algorithm.
    In emission electron microscope (EEM) energy distribution of emitted electrons can significantly affect the image contrast of microfields. This influence is the more the less energy of emitted electrons in volts differs from the residual of potentials of effective microfields. As usual it is accomplished in threshold photoelectron emission. Analytically this objective was solved for cases of contrast formation in EEM with using aperture or without that one. Determined from the obtained formulas and measurements built-in potential between Ag particles (thickness 30 nm, lateral size 20×20 µm2) and Si(100) substrate is 0.7 eV. Calculation shows that this value is two times higher without accounting of photoelectrons energy distribution (high pressure mercury lamp was used for excitation). Remarkable that the expression for correction that appeared in energy distribution of electrons emitted from the sample coincides with contrast defocus formula. It means that some initial energy of emitted electrons is equivalent to image defocus and thus can be compensated by some refocusing of images.
    Based on an analysis of literature data and results of research by high-resolution electron microscopy method, analyzed the question of the phase composition of Ge/Si nanostructure (100). It is concluded that the formation of solid solutions Ge(Si) in the Ge film and the Si(Ge) in the Si (100) substrate, which are separated by a thin pseudomorphic layer. This conclusion can correctly interpret the phase composition of the heterostructure based on Ge and Si. The density of the tips of the heterostructure (~1014 m – 2) and the electric field strength near their peaks (greater than 109 V/m), which causes cold emission of electrons from the tips were calculated.
    We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3-edges, F K-edge, C K-edge and Se M2/3-edges of the quasi-one-dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle () between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3-edges of (TMTSF)2PF6 do not exhibit a well resolved spectrum. Surprisingly, the C K-edge spectra contain three well defined peaks exhibiting strong and non-trivial and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor-anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts.
    We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3 edges, F K edge, C K edge, and Se M2/3 edges of the quasi one- dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3 edges of (TMTSF)2PF6 do not exhibit a well-resolved spectrum. Surprisingly, the C K-edge spectra contain three well-defined peaks exhibiting strong and nontrivial θ and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor−anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts.
    We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3 edges, F K edge, C K edge, and Se M2/3 edges of the quasi one- dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3 edges of (TMTSF)2PF6 do not exhibit a well-resolved spectrum. Surprisingly, the C K-edge spectra contain three well-defined peaks exhibiting strong and nontrivial θ and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor−anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts.
    Based on a general approach, we consider the regularities of forming contrast imaging of static and dynamic potential distribution on the surface of an object investigated with a scanning electron microscope (SEM). The feasibility of using specialized secondary electron detectors was demonstrated. The calculations were performed, showing the functional parameters of three detectors with different types of electron spectrometers. The design of a detector is described, which provides measurement accuracy close to the theoretical limit.
    Transition-density-fragment interaction combined with transfer integral approach for excitation-energy transfer via charge-transfer states J. Chem. Phys. 137, 034101 (2012); 10.1063/1.4733669 C–C bond unsaturation degree in monosubstituted ferrocenes for molecular electronics investigated by a combined near-edge x-ray absorption fine structure, x-ray photoemission spectroscopy, and density functional theory approach J. Chem. Phys. 136, 134308 (2012); 10.1063/1.3698283 Charging energy and barrier height of pentacene on Au(111): A local-orbital hybrid-functional density functional theory approach J. Chem. Phys. 135, 084702 (2011); 10.1063/1.3626522 Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces We have investigated the charge transfer mechanism in single crystals of DTBDT-TCNQ and DTBDT-F 4 TCNQ (where DTBDT is dithieno[2,3-d;2 ′ ,3 ′-d ′ ] benzo[1,2-b;4,5-b ′ ]dithiophene) using a combination of near-edge X-ray absorption spectroscopy (NEXAFS) and density functional theory calculations (DFT) including final state effects beyond the sudden state approximation. In particular, we find that a description that considers the partial screening of the electron-hole Coulomb correlation on a static level as well as the rearrangement of electronic density shows excellent agreement with experiment and allows to uncover the details of the charge transfer mechanism in DTBDT-TCNQ and DTBDT-F 4 TCNQ, as well as a reinterpretation of previous NEXAFS data on pure TCNQ. Finally, we further show that almost the same quality of agreement between theoretical results and experiment is obtained by the much faster Z+1/2 approximation, where the core hole effects are simulated by replacing N or F with atomic number Z with the neighboring atom with atomic number Z+1/2. Published by AIP Publishing. [http://dx.
    We find in the case of W(110) previously overlooked anomalous surface states having their spin locked at right angle to their momentum using spin-resolved momentum microscopy. In addition to the well known Dirac-like surface state with Rashba spin texture near the -point, we observe a tilted Dirac cone with circularly shaped cross section and a Dirac crossing at 0.28 × within the projected bulk band gap of tungsten. This state has eye-catching similarities to the spin-locked surface state of a topological insulator. The experiments are fortified by a one-step photoemission calculation in its density-matrix formulation.
    Single crystals of ludwigite Cu2MnBO5 were synthesized by flux growth technique. The detailed structural and magnetic characterizations of the synthesized samples have been carried out. The cations composition of the studied crystal was determined using X-ray diffraction and EXAFS technique, the resulting composition differ from the content of the initial Mn2O3–CuO components of the flux. Magnetic susceptibility measurements and the calculations of the exchange integrals in frameworks of indirect coupling model revealed that monoclinic distortions strongly affect exchange interactions and appearance of magnetic ordering phase at the temperature T=93 K. The hypothesis of the existence of several magnetic subsystems was supposed.
    The light emission spectra of individual Au nanoparticles induced by a scanning tunneling microscope (STM) have been investigated. Two-dimensional ensembles of tunnel-coupled Au particles were prepared by thermal evaporation onto a native oxide silicon wafer in ultrahigh vacuum (10-9 mbar). Our STM measurements show a single peak at photon energy 1.6 eV in the tunneling mode and two peaks at 2.2 eV (connected with the Mie plasmon) and 1.45 eV (a new peak which was not discussed in literature before) in the field emission mode.
    We investigated morphological features and magnetic properties of epitaxial Fe nanostructures (films, stripes and nanoparticles) on a W(110) surface with monoatomic steps preferentially along the direction. The nanostructures were prepared in ultra-high vacuum by using electron-beam evaporation and subsequent annealing at different temperatures. Scanning tunneling microscopy measurements in-situ revealed elongated Fe nanostructures with aspect ratios of up to . The observable shape and orientation (along or perpendicular to the monoatomic steps of the substrate) of the nanostructures depended substantially on the preparation parameters. By capping the system with 7 monolayers of Pt, the magnetic properties of selected Fe nanostructures could be analyzed ex-situ using Lorentz microscopy revealing diversified results. Depending on the size and shape, different magnetization structures, such as single domain, two domains and vortex, were observed. A precise intensity profile analysis demonstrated that the magnetic field values of different magnetic structures are close to each other and equal 2.4 T.
    Low energy electron diffraction (LEED), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX), and electron energy loss spectroscopy (EELS) investigations of oxidation processes in (110)NiAl single crystal of wedge like shape, i.e., on the sample's areas of different thickness, were carried out. It was found that in the result of several cycles of ion etching, annealing and oxidation the upper layer of (110)NiAl is enriched with Ni. With the increase of Ni concentration from 50 to 100 at. %, the stoichiometry of the near surface area changes and the new phases of Ni3Al and Ni with Al doping are formed one after another. Up to Ni content of 75 at. % the defects concentration in the near-surface area increases and above 75 at. % it drops again. This leads to the change in orientation and azimuth direction of aluminum oxide (alumina). By varying the conditions of γ-Al2O3 epitaxial growth on (110)NiAl with (100), (110), and (111) orientations, we found that this oxide can be grown with different azimuthal directions, for example [440](111)γ-Al2O3 ∥ [002](110)NiAl and [440](111)γ-Al2O3 ∥ [022](110)NiAl.
    Nanoparticles emit electrons and photons when they are excited by electron injection via electric current; electromagnetic radiation via microwave fields; laser radiation in infrared, visible and synchrotron (X-ray) ranges; and electron and ion bombardment. In each case, the emission mechanism depends on characteristic length scales of the nanoparticle. If the particle size is commensurate with it or is smaller, a size dependence of emission is observed [1–3]. Also, it is interesting that nanoparticles may demonstrate properties absent in bulk material.
    The results of research the phase composition and electrophysical (resistivity, thermal coefficient of resistance, strain coefficient) and magnetoresistive properties (anisotropic magnetoresistance) of thin films (to 40 nm) high entropy alloys (HEA) based on Al, Cu, Ni, Cr, Fe, Co and Ti. It is established that after forming the layered samples by electron condensation on diffraction pattern fixed lines from the two phases of the fcc lattice and actually tracks the bcc phase. After homogenization by annealing the samples is one of the fcc phase s.s. HEA and traces bcc phase (likely s.s. (α-Fe, Cr)), that samples are single phase. The study electrical properties allowed watching the first double-stage plastic deformation of a large value of the coefficient gauge (300 units), watch probably, is typical for HEA. The character dependences MR from induction indicates to realization of anisotropic magnetoresistance.
    The electronic surface states on Mo(110) have been investigated using time-of-flight momentum microscopy with synchrotron radiation (hν=35eV). This novel angle-resolved photoemission approach yields a simultaneous acquisition of the E-vs-k spectral function in the full surface Brillouin zone and several eV energy interval. (kx,ky,EB)-maps with 3.4Å(-1) diameter reveal a rich structure of d-like surface resonances in the spin-orbit induced partial band gap. Calculations using the one-step model in its density matrix formulation predict an anomalous state with Dirac-like signature and Rashba spin texture crossing the bandgap at Γ¯ and EB=1.2eV. The experiment shows that the linear dispersion persists away from the Γ¯-point in an extended energy- and k∥-range. Analogously to a similar state previously found on W(110) the dispersion is linear along H¯-Γ¯-H¯ and almost zero along N¯-Γ¯-N¯. The similarity is surprising since the spin-orbit interaction is 5 times smaller in Mo. A second point with unusual topology is found midway between Γ¯ and N¯. Band symmetries are probed by linear dichroism.
    Using ferromagnetic resonance method, we performed measurements of two-dimensional periodic arrays of disc-shaped cobalt particles with different diameters a=450 and 900 nm and the distance between them l=2a and 3a with temperature variation in the range T = 140 −300 K. The first derivative of the microwave absorption spectrum was registered. With the increase of T additional peaks on both sides from the main peak that move aside from it, all peaks show an increase of the intensity and a decrease of the width. Dependences of the resonance field on T shows saturation-like behavior with increasing temperature. They move to higher temperatures and show sharper behavior with a increase and l decrease, respectively. An increase of a leads to the intensity decrease and width increase of all three adsorption peaks.
    We investigated the field emission current from a p-type silicon tip with large resistivity of 4 × 103 Ω cm for light illumination with a photon energy of 1.3 eV and tip-anode voltages of 0.7-5.0 kV. Additional AC voltage with amplitude 30-60 V and frequency varying in the range of 10-107 Hz was applied to the tip which resulted in variations of emission current. We investigated the dependence of this phenomenon on the AC signal parameters, light intensity and temperature. The resonant-like frequency dependence of the emission current is because the tip acts as a driven plasmonic resonator. The results represent an important step forward for the development of high-frequency display systems based on electron field emission.
    High-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the As M-edge, F K-edge and S L-edge of the Fabre salt (TMTTF)2AsF6 were performed from room temperature (RT) to 90 K, allowing to reach the charge localization regime below Tρ ≈ 230 K and to cross the charge ordering (CO) transition at TCO ≈ 102 K. The F K-edge and S L-edge spectra exhibit several transitions which have been indexed on the basis of first-principles DFT calculations. Upon cooling from RT significant energy shifts up to +0.8 eV and -0.4 eV were observed in transitions exhibited by the F 1s and S 2p spectra respectively, while the As 3p doublet does not show a significant shift. Opposite energy shifts found in the F 1s and S 2p spectra reflect substantial thermal changes in the electronic environment of F atoms of the anion and S atoms of TMTTF. The changes found around the charge localization crossover suggest an increase of the participation of the S d orbitals in the empty states of TMTTF as well as an increase of the strength of donor---anion interactions. A new F 1s pre-edge signal detected upon entry into the CO phase is a clear fingerprint of the symmetry breaking occurring at TCO. We propose that this new transition is caused by a substantial mixing between the HOMO of the AsF6- anion and the unoccupied part of the TMTTF HOMO conduction band. Analysis of the whole spectra also suggests that the loss of the inversion symmetry associated with the CO is due to an anion displacement increasing the strength of S---F interactions. Our data show unambiguously that anions are not, as previously assumed, innocent spectators during the electronic modifications experienced by the Fabre salts upon cooling. In particular the interpretation of the spectra pointing out a thermally dependent mixing of anion wave functions with those of the TMTTF chains demonstrates for the first time the importance of anion-donor interactions.
    We present the results of a soft X-ray emission spectroscopy study of a-C and CNx films on a Si(100) substrate. Also for the characterization of the homogeneity in depth of these films electron energy loss spectroscopy measurements with localization better than 4 nm were carried out. In case of CNx films the highest diamond-like modification occurs in the region close to the Si(100) substrate. The film density decreases with increasing distance from the substrate and becomes almost constant in range of thicknesses more than ~ 2 nm.
    We present the results of magnetic properties investigations of ferromagnetic nanoparticles which ensembled with ferromagnetic shell. The aim of this work is to study the connection of structure-phase composition and thermal treatment with the magnetic properties, partially, with the coercive force and the exchange bias field in a two-dimension spin system of core-shell type. It is found that the exchange bias field increases with the growth of the oxide shell thickness. This is realized by annealing in a dosed oxygen flow. The decrease of the coercive force with the increase of annealing temperature is connected with the concentration effect (the concentration of ferromagnetic particles decreases).
    Electron stimulated photon emission spectroscopy was used for the study of the electronic structure of Ge nanoparticles. A nanoparticle film was prepared by thermal deposition on a quartz substrate. Photon emission was stimulated by electron bombardment at energies of several hundred electron volts. Electron field emission from a W-tip was used at tip voltage Ut= 100-600 eV. A spectrometer in combination with a liquid nitrogen cooled charge-coupled device (CCD) camera was used for light detection. Light emission spectra were measured in the energy range 1.18-4.2 eV. They are characterized by features at ∼1.6 and ∼3.1 eV. A comparison with light emission spectra obtained with another excitation, i.e. by applying a voltage of Uf= 2 V to the Ge nanoparticle film gives further insight into the mechanism of photon emission.
    The resolution of emission electron microscopes approaches some nanometers, which leads to the need for new test objects. Microfields, which are almost always present at the sample surface, deform the trajectories of electrons forming the image. This leads to a distortion of the emission electron microscopy image and a decrease of lateral resolution. We propose a test object, where the influence of microfields conditioned by contact potential differences is compensated by a specially shaped relief of the sample surface.
    Phase characteristics of the partially oxidized cobalt particles were investigated. It is shown that the studied system consists of Co, CoO, and Co3O4 phases. The paper presents results for the magnetic characteristics of Co particles covered by a CoO shell. Magnetic measurements were performed at 77 K. It is shown that the shapes of the hysteresis loop of the investigated system are different for different cases of cooling, with and without applications of external magnetic field. Structural investigations were performed on single particles.
    The paper reports the epitaxial growth of cadmium telluride (CdTe) particles by thermal deposition on cleaved planes of (001)NaCl and (001)KBr. Using high resolution transmission electron microscopy and electron diffraction it was shown that CdTe particles could have different orientation and phase (cubic or hexagonal) depending on the substrate temperature. Their most common defects are twins and stacking faults. Cadmium telluride (CdTe) particles were grown by thermal deposition on cleaved planes of (001)NaCl and (001)KBr. Using high resolution transmission electron microscopy and electron diffraction it was shown that CdTe particles could have different orientation and phase (cubic or hexagonal) depending on the substrate temperature. Their most common defects are twins and stacking faults.
    As Stern-Gerlach type spin filters do not work with electrons, spin analysis of electron beams is accomplished by spin-dependent scattering processes based on spin-orbit or exchange interaction. Existing polarimeters are single-channel devices characterized by an inherently low figure of merit (FoM) of typically 10(-4)-10(-3). This single-channel approach is not compatible with parallel imaging microscopes and also not with modern electron spectrometers that acquire a certain energy and angular interval simultaneously. We present a novel type of polarimeter that can transport a full image by making use of k-parallel conservation in low-energy electron diffraction. We studied specular reflection from Ir (001) because this spin-filter crystal provides a high analyzing power combined with a "lifetime" in UHV of a full day. One good working point is centered at 39eV scattering energy with a broad maximum of 5eV usable width. A second one at about 10eV shows a narrower profile but much higher FoM. A relativistic layer-KKR SPLEED calculation shows good agreement with measurements.
    Ag clusters obtained by the gas-aggregation technique were deposited on the cleavage face (001)NaCl. The average size of the nanoparticles was varied in the range from 0.2 to 10 nm and the temperature was varied from room temperature to 470 K. Owing to the mobility of the clusters on the substrate, they coalesced with formation of larger particles, decorating atomic cleavage steps on (001)NaCl already at room temperature. It was shown that the step decoration is possible only when the average size of the deposited clusters is commensurable with the height of the cleavage steps.
    The structural investigations of fullerite films were performed using high-resolution electron microscopy, electron diffraction and electron energy loss spectroscopy and X-ray photoelectron spectroscopy. In particular defects such as dislocations, stacking faults and twins were studied in details. It was shown that fullerite films could be characterized by a face-centered cubic (f.c.c.) structure with lattice parameter a = 1.416 nm. They are distinguished for their rich polytypic structure that is caused by breaking of alteration of closely packed planes of (111) type. The quantitative method based on information theory using the “run-length encoding” algorithm was suggested to evaluate the degree of disorder in the f.c.c structure of thin fullerite films.
    One-dimensional chains and rings of equally sized ferromagnetic nanoparticles have been investigated using magnetic force microscopy. The one-dimensional structure of the Ni nanoparticles forms by self-assembled growth on a stepped surface of highly oriented pyrolytic graphite (HOPG). The nanoparticles show single-domain magnetization states with the magnetization aligned along the chain.
    We studied ordered arrays of magnetic nanoparticles (NPs) in a nonmagnetic matrix. The influence of annealing temperature and measurement geometry (varying angle between sample surface and external magnetic field direction) on magnetoresistance and coercive field values was established. Measurements were done on the Au(2 nm)/Cu(20 nm)/Fe3O4(NPs)/SiO2/Si system.
    We have investigated the magnetization structure and magnetization curves of individual rectangularity shaped permalloy particles using scanning X-ray microscopy in the ultrasoft X-ray regime. Magnetic contrast originates from X-ray magnetic circular dichroism and from the transverse magnetooptical Kerr effect. We studied magnetization curves in dependence on the field direction for particles of different shapes and sizes. Adjacent particles cause a significant dipole interaction. Asymmetric magnetization loops indicate the presence of non-linear magnetooptical effects.
    It is demonstrated that the near-edge X-ray absorption fine structure (NEXAFS) provides a powerful local probe of functional groups in novel charge transfer (CT) compounds and their electronic properties. Microcrystals of tetra-/hexamethoxypyrene as donors with the strong acceptor tetracyano-p-quinodimethane (TMP/HMP-TCNQ) were grown by vapor diffusion. The oxygen and nitrogen K-edge spectra are spectroscopic fingerprints of the functional groups in the donor and acceptor moieties, respectively. The orbital selectivity of the NEXAFS pre-edge resonances allows us to precisely elucidate the participation of specific orbitals in the charge transfer process. Upon complex formation, the intensities of several resonances change substantially and a new resonance occurs in the oxygen K-edge spectrum. This gives evidence of a corresponding change of hybridization of specific orbitals in the functional groups of the donor (those derived from the frontier orbitals 2e and 6a(1) of the isolated methoxy group) and acceptor (orbitals b(3g), a(u), b(1g), and b(2u), all located at the cyano group) with π*-orbitals of the ring systems. Along with this intensity effect, the resonance positions associated with the oxygen K-edge (donor) and nitrogen K-edge (acceptor) shift to higher and lower photon energies in the complex, respectively. A calculation based on density functional theory qualitatively explains the experimental results. NEXAFS measurements shine light on the action of the functional groups and elucidate charge transfer on a submolecular level.
    The contrast depth is analyzed as well, that is the sensitivity of electron mirror microscope to disorders of homogeneity on the object (local magnetic and electric fields, surface relief). Because of the latter ones, electron trajectories feel disturbances (electrons acquire additional increment velocity in radial and azimuthal directions), which leads to the shift of the observed point on the screen and, as a consequence, to the image contrast. Since the electron energy, when reflected, tends to zero, electrons are influenced by heterogeneities for a long time. It causes high sensitivity to heterogeneities, up to the crossing of electron trajectories (caustics are generated). The conditions of caustic generation at the expense of local electric or magnetic field are analyzed. Both the direct and the inverse problems are considered with regard to studies of objects with electric and magnetic fields. Derived equations provide opportunity for reconstruction of electric or magnetic fields distribution on the surface of the object from the images obtained by means of the mirror electron microscope.
    Abstract Texture constitutes one of the fundamental properties of objects besides color and shape. In several image analysis applications, it is often the only exploitable quality of objects. As such, it has been studied, described, segmented, synthesized, or in short, analyzed extensively. Among the plethora of texture description methods, mathematical morphology deserves special attention as it excels at the exploitation of spatial relationships among pixels, rendering it inherently suitable for texture description. In this chapter, we focus on morphological texture description methods for grey-scale and color images in an effort to spread the advantages of this framework in the context of texture analysis. We review several descriptors, ranging from the basic granulometries and pattern spectra to the most advanced multivariate and multidimensional size, shape, orientation, and distance distributions, providing application examples as well as experimental results.
    Specific effects observed in small metal particles due to their distinction from bulk material as well as phenomena inherent to an ensemble of these particles coupled by electron tunneling have attracted considerable attention to nanosized systems. Electron and photon emission was revealed as a power was fed into the metal nanoparticle films deposited on insulating substrates either by passage of an electrical current in the film plane or by laser irradiation in the infrared and visible range. The electrical conductivity of metal nanoparticle films close to the percolation threshold is sensitive to temperature, substrate bending and adsorption of various gases. Besides, the current–voltage characteristics of the conduction current of a system consisting of a metal nanoparticle film and an adsorbate exhibit a voltage-controlled negative resistance region. These peculiar properties enable nanosized particle systems to be used for various applications. The present review deals with a variety of sensors for physical properties and microelectronics elements based on nanoparticle films. The mechanisms underlying the special properties are discussed. Some technological methods ensuring better parameter definition and long-term stability of sensors are also described.
    By example of a Permalloy particle (40 × 40 μm2 size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cause a change of contrast and an image deformation of the particles geometry (curvature of its edge). The magnetic stray fields are calculated from a deformation of the X-ray magnetic circular dichroism (XMCD) images taken after the magnetic field pulse in a 1 ns interval. These measurements reveal a decrease of magnetic stray fields with time. An estimate of the lower limit of the domain wall velocity yields about 2 × 103 m s−1.
    Using carbon nanotubes filled with α-Fe, we have shown that aggregated ferronematic colloids demonstrate reliable and very effective response to a weak (<5 mT) magnetic field. The magnetic field realigns the aggregates of the particles which results in a non-threshold reorientation of the LC nearby, leading to the optically observed director distortions. The distortion regions expand with the increase of the magnetic field and achieve maximum size of several micrometres, comparable with the size of the agglomerates. In the non-distorted regions the reorientation of the director begins at the magnetic field reaching the Fréedericksz transition value. Taking into account the extreme sensitivity of aggregated ferronematics to magnetic field, the following experimental and theoretical studies of the individual response of the aggregated nanoparticles to magnetic field may became the topical task of the physics and applications of ferronematics.
    A dielectric matrix, containing metal nanoparticles with interparticle spacings of 1–2 nm, is a system with tunnel mechanism of electrical conductivity. Its electrical resistance is very sensitive to deforming of matrix because it leads to changes in spaces between particles and as a result the potential barrier transperancy is varied. Different metals (Mo, Cr, Ta, Au, Pt, Bi, Al) and their films morphology structure were studied in order to get high sensitive strain sensors. Metal nanoparticles were deposited on elastic dielectric substrates. Strain coefficients were measured for a wide range of strains and temperatures. Variation of matrix structure gives possibilities to produce strain sensors with high electrical resistance and weak temperature dependence. The matrix with Au nanoparticles was found to have maximum strain coefficient (>100). These sensors can be manufactured in the miniature scale (sensitive area around 1 micron or less).
    It is demonstrated that the near-edge X-ray absorption fine structure (NEXAFS) provides a powerful local probe of functional groups in novel charge transfer (CT) compounds. Microcrystals of tetra- and hexamethoxypyrene as donors with the strong acceptor tetracyanoquinodimethane (TMPx/HMPx - TCNQy) were grown from solution via vapour diffusion in different stoichiometries x:y = 1:1, 1:2 and 2:1. Owing to the element specificity of NEXAFS, the oxygen and nitrogen K-edge spectra are direct spectroscopic fingerprints of the donating and accepting moieties. The orbital selectivity of the NEXAFS resonances allows to precisely elucidate the participation of specific orbitals in the charge-transfer process. In the present case charge is transferred from methoxy-orbitals 2e (PI*) and 6a1 (SIGMA*) to the cyano-orbitals b3g and au (PI*) and - to a weaker extent - to b1g and b2u (SIGMA*). The occupation of 2e reflects the anionic character of the methoxy groups. Surprisingly, the charge transfer increases with increasing HMP content of the complex. As additional indirect signature, all spectral features of the donor and acceptor are shifted to higher and lower photon energies, respectively. Providing quantitative access to the relative occupation of specific orbitals, the approach constitutes the most direct probe of the charge-transfer mechanism in organic salts found so far. Although demonstrated for the specific example of pyrene-derived donors with the classical acceptor TCNQ, the method is very versatile and can serve as routine probe for novel CT-complexes on the basis of functionalized polycyclic aromatic hydrocarbons. Comment: 13 pages, 5 figures
    Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP1-TCNQ1) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d1=0.894 nm and d2=0.677 nm). A softening of the CN stretching vibration (redshift by 7 cm−1) of TCNQ is visible in the IR spectra, being indicative of a CT on the order of 0.3e from TMP to TCNQ in the complex. Characteristic shifts in the electronic level positions occur in UPS and STS that are in reasonable agreement with the prediction of density-functional theory (DFT) calculations (GAUSSIAN03 with hybrid functional B3LYP). STS reveals a highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of the CT complex of about 1.25 eV being much smaller than the gaps (>3.0 eV) of the pure moieties. The electron-injection and hole-injection barriers are 0.3 eV and 0.5 eV, respectively. Systematic differences in the positions of the HOMOs determined by UPS and STS are discussed in terms of the different information content of the two methods.
    Functionalized polcyclic aromatic hydrocarbons (PAHs) are an interesting class of molecules in which the electronic state of the graphene-like hydrocarbon part is tuned by the functional group. Searching for new types of donor and acceptor molecules, a set of new PAHs has recently been investigated experimentally using ultraviolet photoelectron spectroscopy (UPS). In this work, the electronic structure of the PAHs is studied numerically with the help of B3LYP hybrid density functionals. Using the DELTA-SCF method, electron binding energies have been determined which affirm, specify and complement the UPS data. Symmetry properties of molecular orbitals are analyzed for a categorization and an estimate of the related signal strength. While SIGMA-like orbitals are difficult to detect in UPS spectra of condensed film, calculation provides a detailed insight into the hidden parts of the electronic structure of donor and acceptor molecules. In addition, a diffuse basis set (6-311++G**) was used to calculate electron affinity and LUMO eigenvalues. The calculated electron affinity (EA) provides a classification of the donor/acceptor properties of the studied molecules. Coronene-hexaone shows a high EA, comparable to TCNQ, which is a well-known classical acceptor. Calculated HOMO-LUMO gaps using the related eigenvalues have a good agreement with the experimental lowest excitation energies. TD-DFT also accurately predicts the measured optical gap. Comment: Journal of Molecular Spectroscopy, 20 pages, 2 figures, 3 tables, 48 references
    The present paper is devoted to the investigation of exchange anisotropy of fine cobalt particles with oxidized surface. From the value of hysteresis loop shift the value of exchange magnetic anisotropy constant and its dependence of the particle size has been determined. X-ray structure analysis has shown, that cobalt core of the particle is surrounded by a thin layer of the CoO which, in turn, is covered by a layer of Co3O4.
    UHV-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP1-TCNQ1) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), X-ray-diffraction (XRD), infrared (IR) spectroscopy and scanning tunnelling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d1= 0.894 nm, d2= 0.677 nm). A softening of the CN stretching vibration (red-shift by 7 cm-1) of TCNQ is visible in the IR spectra, being indicative of a CT of the order of 0.3e from TMP to TCNQ in the complex. Characteristic shifts of the electronic level positions occur in UPS and STS that are in reasonable agreement with the prediction of from DFT calculations (Gaussian03 with hybrid functional B3LYP). STS reveals a HOMO-LUMO gap of the CT complex of about 1.25 eV being much smaller than the gaps (>3.0 eV) of the pure moieties. The electron-injection and hole-injection barriers are 0.3 eV and 0.5 eV, respectively. Systematic differences in the positions of the HOMOs determined by UPS and STS are discussed in terms of the different information content of the two methods. Comment: 20 pages, 6 figures
    Searching for new pi-conjugated charge-transfer systems, the electronic structure of a new acceptor-donor pair derived from coronene (C(24)H(12)) was investigated by ultraviolet photoelectron spectroscopy (UPS). The acceptor coronene-hexaone (C(24)H(6)O(6), in the following abbreviated as COHON) and the donor hexamethoxycoronene (C(30)H(24)O(6), abbreviated as HMC) were adsorbed as pure and mixed phases on gold substrates. At low coverage, COHON adsorption leads to the appearance of a charge-transfer induced interface state 1.75 eV below the Fermi energy. At multilayer coverage the photoemission intensity of the interface state drops and the valence spectrum of neutral COHON appears. The sample work function decreases from 5.3 eV (clean Au) to 4.8 eV (monolayer) followed by an increase to 5.6 eV (multilayer). The formation of a significant interface dipole due to charge-transfer at the metal-organic interface is possibly accompanied by a change in molecular orientation. HMC on Au exhibits no interface state and the sample work function decreases monotonically to ca. 4.8 eV (multilayer). The UPS spectra of individual donor and acceptor multilayers show good agreement with density functional theory modeling. In donor/acceptor mixed films the photoemission signal of the donor (acceptor) shifts to higher (lower) binding energy. This trend is predicted by the calculation and is anticipated when charge is transferred from donor to acceptor. We propose that mixed films of COHON and HMC constitute a weak charge-transfer system.
    Emission electron microscopy was used to study the electron emission observed under the passage of a tunnel current through a silver nanoparticle film when a voltage is applied to it. The electron emission originates from separate emission centers emitting photons as well. The electron emission centers are visualized as separate spots in an emission electron microscope. A deformation of shape and size of these spots was studied at various applied voltages. It enables the energy spread of electrons emitted from an individual emission center or at least the width of its most intensive part ε as well as the magnitude of electric field E near this center to be estimated. It has been shown that ε comprises 0.5–0.6 eV, and E < < 107 V/cm. The latter result means that the electron emission is not the field emission.
    The quantitative theory of image contrast in an electron microscope in the mirror operation mode is given in this paper. This theory permits us to calculate the potential distribution on the object surface from the current density distribution on the microscope screen. The potential distribution results in image formation on the screen. Local electric fields existing on the object surface lead to a perturbation of electron trajectories above the object and to a redistribution of the current density on the screen, causing image contrast. Using the quantitative correlation between these fields and the function of current density distribution on the screen, it is possible to calculate the magnitude of these microfields as well. As illustration, a measured potential distribution on an object surface with spiral structures of adsorbates was analysed. These structures are formed during reaction of CO oxidation on Pt(110). The value of the measured contact potential difference comprised a few hundredths of volt.
    The possibility of measuring the height of an object in emission electron microscopy (EEM) is investigated. If the specimen is characterized by an equipotential surface with the relief h(x,y), the image is equivalent to a specimen with an ideal flat surface and a corresponding distribution of the electric potential φ(x,y)=−E ext h(x,y). As a consequence of the interaction with the microfields grad φ(x,y), the trajectories of electrons forming the image become deformed, which leads to characteristic image distortion. From EEM, images obtained at different voltages of the extractor V ext,φ(x,y) can be derived and thereby h(x,y) is reconstructed. If the surface of the specimen is characterized both by a distribution of the potential and in addition by a relief h(x,y), then for the reconstruction one needs an additional EEM image taken at a different voltage of the extractor. The maximal sensitivity to microfields/relief is exploited when using the electron microscope in the mirror operation mode. We illustrate the performance of the method by means of a test pattern of Au on Si. For quantitative comparison, the same structure was investigated by atomic force microscope.
    Spintronics is a research field involving a wide variety of different magnetic materials. Synchrotron radiation in the VUV and soft X-ray regime is ideally suited to investigate the relationships between magnetic properties and electronic structure of spintronics thin film stacks. Complex layered structures and nanomagnets are the main building blocks for current and future spintronics applications. In this contribution we describe the study of spintronics model systems with respect to the static and dynamic behavior with an emphasis on interfaces.
    The defocusing of images of ferromagnetic particles in the transmission electron microscope gives rise to magnetic contrast (Lorentz microscopy). We have developed a theory which allows from this contrast to determine quantitatively the distribution of the magnetic fields of the specimen. The measurements were performed on permalloy particles of disc (diameter 50nm), and rectangular (25×50nm2 and 50×50nm2) shapes, thickness of 21nm. These particles had a vortex and Landau–Lifshitz structure, respectively. The determined value of the magnetic induction in the material amounted to 1.1±0.1T. The stray fields in angular sectors of the rectangular particles reached 0.35±0.05T. The width of the 90° Néel wall between domains turned out to be equal to 4.5±0.5nm.
    We studied the dynamic magnetization response in rectangular polycrystalline Permalloy and also epitaxial Co structures (lateral sizes comprised tens of microns at a thickness of tens of nanometers) during the action of a magnetic field pulse, using time-resolved X-ray photoemission electron microscopy with a time resolution of 10 ps. In the case of Permalloy platelets the restoring torque that is necessary for the stroboscopic image acquisition is provided by the Landau flux closure structure representing a minimum of the free energy. We investigated the dynamic response of 90° Néel domain walls. The main results are: the maximum velocity of the domain wall is 1.5 × 104 m/s, the intrinsic frequency of the magnetization change in these structures is estimated to be several Gigahertz. For the case of epitaxial Co platelets grown on Mo(110) the magnetic uniaxial anisotropy with an easy axis along Mo[10] restores the homogeneous magnetization structure after each field pulse. We observed a rotation of the mean magnetization direction within the first 100 ps of the field pulse. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    This work describes the preparation of ternary nanoparticles based on the Heusler compound Co2FeGa. Nanoparticles with sizes of about 20 nm were synthesized by reducing a methanol impregnated mixture of CoCl2 6H2O, Fe(NO3)3 9H2O and Ga(NO3)3 xH2O after loading on fumed silica. The dried samples were heated under pure H2 gas at 900 °C. The obtained nanoparticles—embedded in silica—were investigated by means of x-ray diffraction (XRD), transmission electron microscopy, temperature dependent magnetometry and Mößbauer spectroscopy. All methods clearly revealed the Heusler-type L21 structure of the nanoparticles. In particular, anomalous XRD data demonstrate the correct composition in addition to the occurrence of the L21 structure. The magnetic moment of the particles is about 5μB at low temperature in good agreement with the value of bulk material. This suggests that the half-metallic properties are conserved even in particles on the 10 nm scale.
    Nanoparticles of solid solution Fe x Pt1−x , where 0.25≥x≥0 ( fcc lattice) with γ-Fe2O3 shell (lattice of the spinel type) were synthesised and characterised by high-resolution transmission electron microscopy, energy dispersive X-ray analysis, electron energy loss spectroscopy, Mössbauer spectroscopy and magnetometry. From the point of view of magnetic properties, such two-phase particles are interesting because their core is antiferromagnetic or paramagnetic (at very small values ofx) whereas the shell is ferrimagnetic. The size of the particles was in the range of several nanometers. The Mössbauer measurements revealed a blocking temperature of about 100K above which the particles are superparamagnetic. Towards lower temperatures, the magnetic characteristics of an ensemble of such particles show an increase of magnetic rigidity.
    Using electron holography (interference electron microscopy) we have made measurements of the magnetic flux and magnetic field distribution around a carbon nanotube filled with iron. At the surface of the carbon nanotube, an iron particle with a radius of 30nm and a length of 200nm created a magnetic flux of 10−15Wb (Weber) and a magnetic field of 0.3–0.4T (Tesla). The theory developed in this work is constrained to the case of cylindrical symmetry of the investigated ferromagnetic particles, but, in general, such studies can be made for ferromagnetic particles of any shape.
    Stroboscopic pump-probe measurements (a time-resolution of about 10 ps) have been conducted on a photoemission electron microscope by using the synchrotron radiation source UE46-PGM beamline at BESSY-II (Berlin) with low alpha bunch option (a photon pulse was characterized by the root mean square of 3 ps, and the repetition rate was 0.5 GHz). This technique was applied to studying the dynamics of 180° Neel walls between domains in rectangular permalloy (NisiFeig) particles (their lateral sizes comprised 16 μm X 32 μm, the thickness amounted to 10 nm) due to the action of an external magnetic field being a sum of pulse and constant magnetic fields directed oppositely. The velocity of 180° Neel walls comprises ~ 103 m/s, when the rate of change (increase) of a magnetic field is 1.2 • 106 T/s. The remagnetization fundamental frequency is estimated to be ~ 1.25 GHz.
    Electron emission from Ag and Au nanoparticle films was studied under excitation with femtosecond-laser pulses with photon energies of 1.55 and 3.1 eV. Films were grown on a glass substrate with particle sizes from the nanometer range to a continuous layer. The transition from a continuous film to a nanoparticle film is accompanied by an increase in photoemission current by more than an order of magnitude. Pump-and-probe experiments with variable delay gave information on the lifetime of the intermediate states. At a fixed pulse power, the emission yield increases as the temporal width of the laser pulses is decreased. Experimental results are interpreted in terms of two different electron emission mechanisms, i.e., multiphoton photoemission and thermionic emission or thermally assisted multiphoton photoemission. The first mechanism prevails for con-tinuous films and larger particles with sizes above several tens of nanometers; the second one prevails for smaller nanoparticles with sizes of a few nanometers.
    Differently doped areas in silicon can show strong electron-optical contrast in dependence on the dopant concentration and surface conditions. Photoemission electron microscopy is a powerful surface-sensitive technique suitable for fast imaging of doping-induced contrast in semiconductors. We report on the observation of Si (100) samples with n- and p-type doped patterns (with the dopant concentration varied from 10(16) to 10(19) cm(-3)) on a p- and n-type substrate (doped to 10(15) cm(-3)), respectively. A high-pass energy filter of the entire image enabled us to obtain spectroscopic information, i.e. quantified photo threshold and related photoyield differences depending on the doping level. Measurements have confirmed the possibility of resolving areas at a high contrast even with the lowest dopant concentration when employing the energy filter. The influence of electron absorption phenomena on contrast formation is discussed.
    Fine particles of lead in the size of 3-40 nm are grown epitaxially on thin monocrystalline MgO substrate transparent for an electron beam in a column of a transmission electron microscope. Studying of their melting was carried out in situ. Particles of lead were heated by means of a heater containing a substrate with these particles and an electron beam. Size dependences of melting temperature qualitatively differ for different ways of heating. In the first case, the melting temperature goes down with reduction of the size of a particle. In the second case, the size of a particle there is less, the greater energy of an electron beam is necessary for its melting.
    The stray magnetic field of domains on the surface of Nd17Fe17Cu5B5 and SmFe10Ti89 samples was visualized by emission electron microscopy in the regime without restriction of the electron rays by a contrast aperture. The distribution of the tangential and normal components of the magnetic field on the surface under study was derived from the image contrast. The experimental uncertainty of the performed quantitative measurements of the magnetic field is estimated as 15–20%, however, the applied technique has a principal error that is several times smaller.
    Using synchrotron-based stroboscopic photoemission electron microscopy with X-ray circular dichroism as contrast method, we have investigated the high-frequency response of permalloy thin-film structures. Standing precessional modes have been studied in rectangular elements (16 × 32 μm2, 10 nm thick) with a high time resolution of about 15 ps in the low-α mode of BESSY. With increasing amplitude of the applied magnetic AC field the particle is driven from an initial symmetric Landau flux-closure state into an asymmetric state and finally into a single-domain state magnetized perpendicular to the applied field HAC. The electromagnetic microwave field thus can induces a net magnetization in a small particle. This behaviour is a result of the constant throughput of energy (open system) that allows for an increase of local order, contrary to the usual increase on entropy in closed systems. A propagating spinwave in an ultrathin elliptical particle (semi axes 6 × 12 μm2, 3 nm thick) was observed in a snapshot series with 25 ps time increment. The phase front of the spinwave with large precessional angle (bright contrast) propagates with a velocity of 8100 m/s, i.e. much faster than typical domain wall velocities in permalloy.
    Silver cluster films deposited on Si(1 1 1) were investigated by spectroscopic photoelectron microscopy using fs-laser excitation tuneable between hν = 1.45–1.65 eV and 2.9–3.3 eV. With increasing coverage the films grown as stepped wedges first exhibit clusters of few nanometers diameter with narrow size distributions that later agglomerate forming larger islands up to about 100 nm diameter. The cluster films have been characterized by SEM, AFM and HR-TEM. In the 3.1 eV range the small clusters emit more effectively and the dependence of electron yield on laser power follows a quadratic power law. Microspectroscopy reveals that the Fermi level onset is sharp(<150 meV width) and shifts by 2hν when the quantum energy is increased, thus confirming the predominance of two-photon-photoemission (2PPE). Under 1.6 eV excitation the situation is different: The power dependence is non-integer and the slope varies between 2.9 and 3.7 for different points on the sample. The Fermi edge appears smeared out and shifted by several hundred meV to lower final state energies. We attribute this deviation from pure 3PPE to thermally assisted nPPE of electrons from a transient “hot electron” gas in the nanoparticles.
    We have studied ultrafast magnetodynamics in micropatterned spin-valve structures using time-resolved x-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism. Exciting the system with ultrafast field pulses of 250 ps width, we find the dynamic response of the free layer to fall into two distinctly different contributions. On the one hand, it exhibits localized spin wave modes that strongly depend on the shape of the micropattern. A field pulse applied perpendicular to the exchange bias field along the diagonal of a square pattern leads to the excitation of a standing spin wave mode with two nodes along the field direction. This mode is strongly suppressed for a pattern of elliptical shape. On the other hand, the integrated response of the free layer roughly follows a single-spin model with a damping constant of alpha=0.025 independent of the shape and resembles the response of a critically damped forced oscillator.
    Interference electron microscopy was applied to measure the size dependence of the Curie temperature of small nickel particles. Nickel films consisting of particles of different sizes and distances between them were studied. We found a decrease of the Curie temperature with decreasing particle size for particles smaller than about 100 nm. The decay of the Curie temperature is stronger for particles being well separated from other particles, whereas the decay is much less pronounced in the case of small distances between the particles. This observation can be explained by interparticle interaction.
    The dynamic magnetic properties of two-dimensional periodic Co antidot arrays were studied by X-band ferromagnetic resonance. The experimental results on geometrically scaled antidot arrays reveal a strong attenuation of the uniform ferromagnetic resonance mode in comparison to a continuous film, but an excitation of nonuniform in-plane spin-wave modes. Micromagnetic finite-element simulations show that the static magnetic structure in an antidot array depends on the direction of the external field with respect to the symmetry axes of the antidot lattice, even if the external field is strong enough to enforce a technically saturated magnetization state. The analysis gives evidence that characteristic inhomogeneities in the magnetization distribution around the antidots give rise to the changes of the resonance modes with the in-plane direction of the magnetization.
    V{sub 2}O{sub 5} nanotubes synthesized via the sol-gel route has been studied by electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), and energy dispersive x-ray analysis, in order to understand the local structure of vanadium in the nanotubes. Contrary to our expectation, all the features of the XAS and EELS spectra of the V{sub 2}O{sub 5} nanotubes are in line with that of bulk layered vanadium oxide revealing that vanadium is present in the 5{sup +} oxidation state in the nanotubes. However, V{sub 2}O{sub 5} nanotubes exhibit additional surface states in their electronic structure in comparison with bulk V{sub 2}O{sub 5}. A comparison of measured and calculated spectra allows us to distinguish single-wall from multiwall V{sub 2}O{sub 5} nanotubes.
    The magnetic domain structure of a neodymium-iron-boron single crystal (Nd2Fe14B) was investigated in a photoemission electron microscope equipped with an aperture for partial restriction of the electron beam. As a result of the influence of magnetic microfields, electron trajectories are deflected in such a way that some of them are stopped by the aperture in the electron optical path. As a result, the contrast caused by the stray fields of the magnetic domains is significantly enhanced. The distribution of the local magnetic fields at the surface is reconstructed from the image by means of the proposed theory on the contrast mechanism. The size of the stray field close to the sample surface under study was 0.5–0.7T.
    Using a photoemission electron microscope we determined magnetic stray fields at the edges of permalloy (Ni80Fe20) particles. X-ray magnetic dichroism was used for visualization of magnetic domains. The values of the stray fields were deduced from the deflection of electrons in the image due to the Lorentz force. The stray fields are responsible for the magnetic interaction of adjacent particles with distances much larger than the thickness. The measured magnetic stray field is about 0.023T for rectangular particles with a thickness of 30nm and lateral sizes of tens of microns.
    The various aspects of time resolved photoemission electron microscopy (PEEM) such as surface and thin film magnetism are analyzed. The slow varying magnetic fields was analyzed by PEEM in which, magnetization followed the applied field through the nucleation and motion of domain walls and vortices. The magnetization in a ferromagnet is a collective phenomena of correlated electrons and can therefore be understood by models and wave functions. The nonmonotonous behavior of photoelectron emission intensity along the wedge shaped Ag film was explained as interplay between surface plasmon enhanced photoexcitation and variation of the coverage. It was observed that the absorption of laser radiation due to the excitation of collective modes followed by photoemission strongly increased while moving from a continuous film to the nanoparticles. The experiment showed that the novel time of flight based photoemission electron microscopy has a high potential for the study of nano-scale materials.
    The importance of high resolution imaging of dopant contrast in semiconductor structures parallels the continuous increase in the degree of their integration and complexity and in the size of substrates. Some scanning electron microscopy modes show moderate contrast between differently doped areas, but its detailed interpretation remains questionable, in particular, as regards the measurement of the dopant concentration. Photoemission spectromicroscopy on silicon substrates with patterns of opposite-type dopants suggests that the p/n contrast is primarily related to local differences in the absorption of hot electrons along their trajectory toward the surface. This explanation is also expected to be valid in the interpretation of image contrasts formed by secondary electrons or very slow backscattered electrons. Wide-field photoemission electron microscopy has proven itself a fast imaging method providing large p-n contrast and the prospect of high-level resolution.
    There is a recent interest in nanoscale materials, in particular, nanotubes based not only on carbon. In this study, photoemission spectra of single MoS2 nanotubes deposited on a Si surface were recorded in order to explain their electronic structure. The photoelectrons were excited by a femtosecond laser oscillator resulting in two-photon photoemission. A spectromicroscopic technique based on imaging time-of-flight detection was used to record the spatially resolved photoelectron spectra. Self-consistent electronic structure calculations for MoS2 slabs using the full potential linear augmented plane wave method are used to explain the peculiarities of the observed spectra. It turns out that the MoS2 nanotubes are semiconducting with a band gap of about 1 eV. The two-photon transitions proceed through intermediate states in a region with high density of states; this gives rise to a high photoemission intensity.
    Being already well established as a versatile technique for high-resolution static magnetic domain imaging, X-ray photoemission electron microscopy (XPEEM) is now also capturing the field of time-resolved magnetic investigations. Using appropriate operation modes at synchrotron radiation sources, a time resolution of 10 ps and less can be achieved in recent magnetodynamics studies, giving access even to phenomena involving precessional processes.
    The response of multidomain flux-closure structures (Landau states) in micrometer-scale magnetic thin-film elements upon fast magnetic field pulses leads to the excitation of magnetic eigenmodes and to short-lived domain patterns that do not occur in quasi-static remagnetisation. Such transient spatio-temporal patterns and particular detail features are discussed. Examples are presented for permalloy platelets of various shapes and sizes. Dynamic series of domain patterns with variable delay between field pulse and photon pulse (synchrotron radiation) have been taken using stroboscopic XMCD-PEEM. Precessional remagnetisation starts at the domain boundaries. The damped precessional motion propagates into the domains magnetised perpendicular to the field pulse. Further, an apparent dynamical broadening of domain boundaries, the formation of transient vortices and domain walls as well as the fast formation of blocking patterns are discussed. An important feature is the action of the demagnetising field that develops via the damped precessional motion of the magnetisation on the nanosecond time scale. The effective field is constituted by the sum of the instantaneous external pulse field and the delayed response of the demagnetising field.
    Understanding the microscopic mechanisms governing fast magnetic switching processes is of high fundamental interest as well as of vital technological importance. A macrospin picture often fails to adequately describe the situation in extended systems. A detailed study of the magnetization dynamics in complex magnetic materials thus requires a real-space mapping of the magnetization distribution in the ground state and of its time evolution. Imaging these transient magnetization distributions on a sub-nanosecond time scale is an experimental challenge, which has been successfully addressed in recent years by time-resolved Kerr and X-ray photoemission microscopies. Soft X-ray photoemission electron microscopy (XPEEM) is known to be an extremely versatile tool to image static domain patterns in chemically complex magnetic systems, combining element selectivity with strong magnetic contrast and high lateral resolution. The choice of different magnetic contrast modes with circularly or linearly polarized light provides access to both ferro-and antiferromagnetically ordered structures. The technique can be extended into the sub-nanosecond time-domain by exploiting the intrinsic time structure of the synchrotron light.
    The measurement of electric fields on object surface in an emission electron microscope is studied. An inverse-problem is solved and a distortion of the image details caused by the local electric fields is investigated. The smallest resolvable distance is approximately 0.1 μm, and each point of an object image is a circle of diffusion with a current density being close to a Gaussian distribution. The results show that en emission electron microscope makes it possible to observe local electric fields on the object surface with very very high sensivity.
    We investigated the magnetodynamics in rectangular Permalloy platelets by means of time-resolved x-ray photoemission microscopy. 10 nm thick platelets of size 16 x 32 microm were excited by an oscillatory field along the short side of the sample with a fundamental frequency of 500 MHz and considerable contributions of higher harmonics. Under the influence of the oscillatory field, the Néel wall in the initial classical Landau pattern shifts away from the center, corresponding to an induced magnetic moment perpendicular to the exciting field. This phenomenon is explained by a self-trapping effect of the dominating spin-wave mode when the system is excited just below the resonance frequency. The basic driving mechanism is the maximization of entropy.
    A giant nonlinear optical response has been observed for nanoporous layers of titanium dioxide (anatase) under picosecond laser excitation with photon energy below the gap. At excitation intensity of 10 MW/cm2 the nonlinear refractive index variation at the wavelength of 1064 nm corresponds to χ(3)=2×10-5 esu which is six orders of magnitude higher than the respective value of bulk TiO2. This effect is explained by resonant excitation of electronic states of defects at the developed surface of anatase nanoparticles.
    Photoemission electron microscopy was used to image the electrons photoemitted from specially tailored Ag nanoparticles deposited on a Si substrate (with its native oxide SiO(x)). Photoemission was induced by illumination with a Hg UV lamp (photon energy cutoff homega(UV) = 5.0 eV, wavelength lambda(UV) = 250 nm) and with a Ti:sapphire femtosecond laser (homega(l) = 3.1 eV, lambda(l) = 400 nm, pulse width below 200 fs), respectively. While homogeneous photoelectron emission from the metal is observed upon illumination at energies above the silver plasmon frequency, at lower photon energies the emission is localized at tips of the structure. This is interpreted as a signature of the local electrical field therefore providing a tool to map the optical near field with the resolution of emission electron microscopy.
    We present recent results of time-resolved X-ray photoemission electron microscopy (TR-XPEEM) investigations on magnetic systems. Our studies of microstructured permalloy particles employ a magnetic pump XPEEM probe approach. The stroboscopic experiments feature a time resolution of  ps and yield magnetic domain images with a surprising richness of details. We observe a strong influence of incoherent magnetization rotation processes, which lead to complicated transient domain structures with a blocked relaxation behavior.
    Photoemission electron microscopy (PEEM) was exploited to observe the dynamics in local field distributions on microstrip-line devices with a best time resolution of 133 ps. A delayline detector system served as imaging unit capable of a time resolving data acquisition and processing. The setup can be operated at the resolution limit of the PEEM of about 20 nm while a continuously illuminating UV-lamp excites the photoelectrons in threshold photoemission. A pulsed photon source is not needed to obtain time resolved images, the time reference of the data acquisition was taken by a periodic signal (clock, here typ. 100 MHz) in phase with the pulse pattern applied to the microstrip-line device. Ultra-short current pulses passing the microstrip-line are associated with local changes of the magnetic field at the device surface and with a fast propagation of the electrical potential as well. The photoelectron imaging is immediately responding to small local field distortions due to the small kinetic energy of the electrons escaping from the surface. Thus, local field distortions can be detected as temporal changes between the 133 ps wide image-slices which are sorted by time in reference to the clock signal.
    Giant nonlinear optical response has been observed for nanoparticle TiO2 (anatase modification) layers within sub-gap photon energy excitation in picosecond range. The obtained effective cubic optical nonlinearity value χ(3)eff ∼10–5 esu is six orders of magnitude higher than the bulk response in transparency range. The effect can be explained with resonant excitation of oxygen vacancies and related defect states , which also act as photocatalytic active centers at the nanoparticle surface. The magnitude of the nonlinear optical response correlates with the photocatalytic activity and depends on the samples preparation conditions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Fast magnetization processes in a microstructured permalloy ring with 80 µm o.d. and 30 nm thickness have been observed by photoemission electron microscopy exploiting x-ray magnetic circular dichroism as the magnetic contrast mechanism. As a high speed probe we employed synchrotron radiation pulses at the ESRF (Grenoble) operated in 16-bunch mode, yielding photon pulses of 105 ps FWHM with a period of 176 ns. Fast magnetic field pulses have been generated by means of current pulses through coplanar waveguides with the magnetic structure being lithographically prepared on their surface. A stroboscopic pump-probe set-up with a variable time delay between the field pulse and photon pulse allowed us to take snapshots of the dynamic response of the magnetic domain structure. We observed coherent magnetization rotation during the leading edge part of the field pulse, the formation of a characteristic domain pattern ('onion state') in the plateau region of the pulse and the fast formation of a striped domain pattern (incoherent magnetization rotation) during the trailing edge part of the field pulse. A numerical simulation confirmed essential features of the stroboscopic image series.
    Solid gas surfaces The porosity of frozen rare-gas layers (Ar, Kr, and Xe) was visualized by a replica technique. Ag films were produced by condensation of Ag atoms onto freshly prepared solid (frozen) rare-gas layers. The resulting replicas of the rare-gas surfaces were investigated by atomic force (see two- and three-dimensional pictures) and scanning electron microscopy.
    The ferromagnetic resonance (FMR) method is used to study the collective phenomena in two-dimensional periodic arrays of disk-shaped Co particles. A study of geometrically similar structures with different periods reveals a broadening of the FMR resonance lines due to the excitation of additional size-dependent non-uniform spin waves. It is shown that these collective spin-wave modes are based on dipole–dipole interactions between the ferromagnetic particles in the array. Qualitative and quantitative data on magnetic interparticle interactions can thus be obtained from FMR spectra for two-dimensional periodic arrays of ferromagnetic particles.
    The lateral resolution of a time-of-flight photoemission electron microscope has been theoretically analyzed. It has been shown that the resolution limit can reach a few nanometers. The lateral resolution will be higher if the photoelectrons forming the image are characterized by a smaller acceptance angle obtained with the help of diaphragms in the crossover plane, a higher initial energy and a narrower interval of electron energies. The experimental results are in good agreement with the theoretical predictions.
    Silver cluster films deposited on glass or sapphire have been investigated using an emission electron microscope when a voltage was applied across the film. The electric field distribution in the silver cluster film was measured exploiting the image distortion with increasing voltage. The electron and photon emission originating from the cluster film was visualized. The latter phenomena are correlated with a deviation from Ohmic behavior of the conductivity curve.
    Photoemission electron microscopy was used to visualize the motion of magnetic domains on a sub-nanosecond timescale. The technique exploits the imaging of magnetic domains using soft X-ray circular dichroism, with the special feature that the instrument utilizes a fast image acquisition system with intrinsic 125 ps time resolution. The overall time resolution used is about 500 ps. Different domains and domain movements have been observed in lithographically-produced Permalloy structures on a copper microstrip-line. A current pulse of I = 0.5A with rise times of about 300 ps switched the Permalloy islands from a Landau-Lifshitz type domain configuration into metastable s-state domain configurations. A pulse with opposite direction could reverse these s-type patterns. Photoemission electron microscopy was employed to observe the domain movements while repeating current pulses passed the microstrip-line. Using small unipolar amplitudes, only the cross-tie walls of the s-type patterns disappear and the pattern becomes “fuzzy”, e.g. the domain rims are not sharp and some domains change their size. Before the structure switches at a current threshold, it is more fluctuating as shown by significant differences in sharpness of the islands rim and the inter-domain boundaries show. The device behavior complicates when a bi-polar pulse is applied. Switching and oscillating of domains is observed in various manners, e.g. very tiny domains appear and unify again.
    Time-of-flight photoemission electron microscopy was used to measure spatially resolved energy distribution curves of electrons emitted from Ag nanoparticle films with different mass thicknesses. Two-photon photoemission (2PPE) was induced by femtosecond laser pulse excitation with 3.1 eV photon energy and 200 fs pulse width. Regions of Ag nanoparticles with different average sizes and one region with a continuous 100 nm thick Ag film were deposited as a stepped wedge on a Si(1 1 1) substrate. Upon laser excitation the nanoparticle films exhibit a very high electron emission yield in the images, whereas the uncovered Si surface and the continuous Ag film are dark. The time-of-flight electron spectra obtained from the nanoparticle films are remarkably different from the spectra of the continuous film, well-known from literature. The nanoparticle spectra are up to a factor of 160 more intense than the spectrum of the continuous film. They reveal different widths, overall shape and a shift and broadening of the Fermi edge. The results are discussed in terms of Mie plasmon assisted two-photon photoemission of the nanoparticles.
    The dynamical evolution of magnetic stray fields has been investigated at the initial stage of magnetization reversal of a microstructured cobalt film (Co dots). Quantitative measurements of the domain magnetization and of the shift of the domain boundaries have been performed at 1ns intervals. The measurements were performed using an emission electron microscope. The photoelectrons were excited from a sample using well-defined synchrotron-radiation pulses in single bunch operation mode (UE56/1-PGM at BESSY II, Berlin). The magnetization movement was initiated by an external magnetic field pulse, the pulse width being 8ns. The magnetic field pulse was synchronized with the synchrotron single bunch radiation pulses. The lateral and time resolutions of the applied pulses were 50nm and 500ps, respectively.
    We present recent results of time-resolved x-ray photoemission electron microscopy on permalloy microstructures. The stroboscopic experiments feature a time-resolution of 130 ps. We observe a strong influence of incoherent magnetization rotation processes, leading to a significant transient stray-field formation at the edges of the microstructure.
    Heusler compounds are promising candidates for future spintronics device applications. The electronic and magnetic properties of Co2Cr0.6Fe0.4Al, an electron-doped derivative of Co2CrAl, are investigated using circularly polarized synchrotron radiation and photoemission electron microscopy (PEEM). Element specific imaging reveals needle shaped Cr rich phases in a homogeneous bulk of the Heusler compound. The ferromagnetic domain structure is investigated on an element-resolved basis using x-ray magnetic circular dichroism (XMCD) contrast in PEEM. The structure is characterized by micrometre-size domains with a superimposed fine ripple structure; the lateral resolution in these images is about 100 nm. The domains look identical for Co and Fe giving evidence of a ferromagnetic coupling of these elements. No ferromagnetic contrast is observed at the Cr line. Magnetic spectroscopy exploiting XMCD reveals that the lack of magnetic moment, detected in a SQUID magnetometer, is mainly due to the moment of the Cr atom.
    An emission electron microscope without restriction of the electron beams was used to visualize and measure the distribution of electric fields and potentials on the surface under study. Investigations of this kind can be performed in an emission electron microscope without any aperture diaphragm. The potentialities of this method have been demonstrated using measurements with a silicon p-n junction to which a voltage has been applied in the reverse direction. The quantitative analysis becomes more complicated if the specimen is characterized by a heterogeneous intensity distribution of the electron emission from different areas of its surface. In the latter case two images obtained at different accelerating voltages (i.e. different voltages of the microscope extractor) provide the information necessary for an analysis of electric field and potential distributions.
    Pt clusters deposited on a γ-Al2O3(1 1 1)/NiAl(1 1 0) substrate under ultra-high vacuum conditions were studied by transmission electron microscopy. Cluster size and density were varied by altering substrate temperature during deposition and the platinum coverage. The average cluster size was found to increase monotonically with increasing platinum coverage whereas the cluster density exhibits a maximum. It was also found that the deposition temperature strongly affects the cluster growth. When the temperature increases between 300 and 600 K, the aspect ratio (the relationship between the cluster height and its lateral size) increases as well.
    The plasmon energy of Ag clusters produced on an amorphous carbon substrate by gas-aggregation technique has been measured. It has been determined from the plasmon peak position in the light emission spectrum obtained during bombardment of Ag clusters by low-energy electrons. For Ag cluster films with maximum of the cluster size distribution at 30, 8 and 2.5 nm, the plasmon energy comprised 3.76, 4.13 and 4.28 eV (the wavelength was 330, 300 and 290 nm), respectively. The blue shift of the plasmon energy is probably related to the effect of confounding of collective and single-particle excitations.
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