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The development of new modes at x-ray free electron lasers has inspired novel methods for studying fluctuations at different energies and timescales. For closely spaced x-ray pulses that can be varied on ultrafast time scales, we have constructed a pair of advanced instruments to conduct studies targeting quantum materials. We first describe a prototype instrument built to test the proof-of-principle of resonant magnetic scattering using ultrafast pulse pairs. This is followed by a description of a new endstation, the so-called fluctuation–dissipation measurement instrument, which was used to carry out studies with a fast area detector. In addition, we describe various types of diagnostics for single-shot contrast measurements, which can be used to normalize data on a pulse-by-pulse basis and calibrate pulse amplitude ratios, both of which are important for the study of fluctuations in materials. Furthermore, we present some new results using the instrument that demonstrates access to higher momentum resolution.

Understanding magnetic phase transitions from stripe to skyrmion textures provide fundamental scientific insights into the details of the intermediate topologies through which the system evolves. The solitonic nature of spin texture in both stripe and skyrmion phases has been observed in materials with Dzyaloshinskii-Moriya interaction. Here we show that the field evolution in a dipolar interaction mediated Fe/Gd multilayer that exhibits achiral stripe textures behaves similar to a finite-sized chiral soliton lattice. As a function of magnetic field, the stripes exhibit discrete jumps in periodicity indicative of intermediate topologies as the stripes get wound into skyrmions.

Low-dimensional and magnetic systems provide particularly clear-cut cases for the study of modified electron states that result from coupling with elementary excitations. Electronic quasiparticles of enhanced mass have been observed on the energy scale of phonons, and very recently on that of spin waves. Such mechanisms have bearing for superconducting pair formation, as spin fluctuations are being considered for high-temperature superconductivity. Phase transitions can occur if these interactions are accompanied by a nesting condition in the Fermi surface, leading to charge- or spin-density waves. The phase transition usually involves a structural distortion and is characterized by the opening of an energy gap. Special cases are the presence of multiple bands at the Fermi surface or the occurrence of thermal fluctuations. Recent progress in photoelectron spectroscopy and synchrotron-radiation instrumentation allow us to study these effects directly and resolved in k-space. Observations on surfaces, in magnetic materials, and in quasi-one-dimensional crystals are presented.

Spraying eggs with oil has been used as a method of decreasing the reproductive success of super abundant avian species. Double-crested Cormorant (Phalacrocorax auritus) abundances have created a potential disturbance to some endangered species of birds, sport fishing communities and aquaculture facilities. The hatching success of oil sprayed Double-crested Cormorant eggs was investigated. Oil spraying was done during the first, second, or third week of the egg’s incubation to determine the most effective time during the incubation period for a one-time treatment. The oil spraying technique was 95–98% effective at preventing hatching. Hatching success was independent of the week of incubation that an egg was sprayed with oil. The maximum number of eggs on the colony occurred four weeks after the first egg was laid. This would be the most efficient week to spray the colony to decrease hatching success.

Recently, we reported high resolution angle-resolved photoemission measurements that indicated unusually strong coupling between adsorbate vibrations and a surface-localized electron state in the system W(110)-(1×1)H. We have now extended these measurements to probe the electron–phonon coupling strength as a function of position on the relevant Fermi contour. We find that the strength of the coupling is strongly dependent on Fermi wave vector, with the electron–phonon coupling constant λ varying between zero and ∼0.8. Qualitatively, the strength of the coupling is related to the position of the surface band in the projected bulk band gap, and therefore to the degree of surface localization of the surface state wave function. Such effects should play an important role in all adsorbate vibronic interactions, since the vibrational modes are generally highly localized to the outermost surface layer. We discuss these results in relation to the surface phonon anomalies observed on this surface.

Lensless X-ray imaging techniques such as coherent diffraction imaging and ptychography, and Fourier transform holography can provide time-resolved, diffraction-limited images. Nearly all examples of these techniques have focused on transmission geometry, restricting the samples and reciprocal spaces that can be investigated. We report a lensless X-ray technique developed for imaging in Bragg and small-angle scattering geometries, which may also find application in transmission geometries. We demonstrate this by imaging a nanofabricated pseudorandom binary structure in small-angle reflection geometry. The technique can be used with extended objects, places no restriction on sample size, and requires no additional sample masking. The realization of X-ray lensless imaging in reflection geometry opens up the possibility of single-shot imaging of surfaces in thin films, buried interfaces in magnetic multilayers, organic photovoltaic and field-effect transistor devices, or Bragg planes in a single crystal.

The past two decades have experienced the development of angle-resolved photoemission to the point that it can now provide crucial information on an energy scale that is relevant to many key problems in condensed matter physics. At the same time, our ability to prepare and characterize surfaces, interfaces, and thin films has improved to the extent that many exotic phases can be produced with a high degree of perfection. The combination of these two developments suggests many interesting experiments can be performed that probe the coupling between charge, lattice, and spin degrees of freedom in the context of surface and interface physics. In this paper we briefly review a few groundbreaking experiments that have initiated this effort. We also speculate on future developments in this area.

We have applied a new differential method of photoelectron holography to both experimental and theoretical multiple-energy photoelectron diffraction data for Cu 3p bulk emission from Cu(001). Dominant forward-scattering effects contained in a normalized hologram χ k have been eliminated by taking the k -difference δχ k along each direction k . Two data sets that are different in k -space sampling ranges and densities have been analyzed to compare atomic images reconstructed from χ and δχ . In both cases, the original scheme has yielded only very weak images of back-scattering atoms and spurious features in the forward-scattering directions. On the other hand, the differential scheme has been found to be successful in suppressing the forward-scattering effects to image not only side-scattering and back-scattering atoms in either case, but also forward-scattering atoms in one of the two cases.

We report the observation of a Skyrmion lattice in the chiral multiferroic insulator Cu2OSeO3 using Cu L3-edge resonant soft x-ray diffraction. We observe the unexpected existence of two distinct Skyrmion sublattices that arise from inequivalent Cu sites with chemically identical coordination numbers but different magnetically active orbitals. The Skyrmion sublattices are rotated with respect to each other, implying a long wavelength modulation of the lattice. The modulation vector is controlled with an applied magnetic field, associating this moirélike phase with a continuous phase transition. Our findings will open up a new class of science involving manipulation of quantum topological states.

Thin films of oriented Fe and Cr intercalated (NbSe2)x(TiSe2)y superlattices have been synthesized by controlled annealing of elementally modulated reactants. Analytic techniques have been developed to extract the average c-axis structure of the unit cell, the distribution of c-axis crystal sizes, and the distribution of structural defects from X-ray diffraction data. High-resolution synchrotron source X-ray diffraction data were collected from a [(Fe0.33NbSe2)8(Fe0.33TiSe2)8]12 sample (i.e., 12 superlattice unit cells in the film, each cell containing 8 layers of Fe0.33NbSe2 followed by 8 layers of Fe0.33TiSe2) at three anomalously scattering wavelengths. Analysis determined structural parameters within 2% of published values for the parent compounds, typical crystal sizes of 200−500 A, and typical coherence losses over a unit cell of ±1%. Theoretical diffraction profiles calculated directly from the model structure are shown to agree satisfactorily with experiment. The flexibility offered by our growth ...

Valence-band spectra of Cr and Fe metal were measured with photon energies around their respective $2p$ energies. An Auger signal is found to be superimposed on the valence-band photoemission signal for photon energies at and above the $2p$ absorption energy, but also for excitation energies down to $\ensuremath{\sim}4$ eV below the $2p$ absorption energy. This is the radiationless resonance Raman (resonant Raman Auger) regime and gives rise to a signal that is equivalent, in terms of the final state, to the 6 eV satellite in Ni with energies at 3.5 eV below ${E}_{\mathrm{F}}$ in Cr and 3.2 eV below ${E}_{\mathrm{F}}$ in Fe.

Self-assembled indium linear chains on the Si(111) surface are found to exhibit instability of the metallic phase and 1D charge density wave (CDW). The room-temperature metallic phase of these chains undergoes a temperature-induced, reversible transition into a semiconducting phase. The 1D CDW along the chains is observed directly in real space by scanning tunneling microscopy at low temperature. The Fermi contours of the metallic phase measured by angle-resolved photoemission exhibit a perfect nesting predicting precisely the CDW periodicity.

Although Gabor originally proposed using electrons in holography to form atomic-resolution images, it is only very recently that photoelectron diffraction data have been discussed as a practical method for achieving this. Such data enable recording both the amplitudes and phases of the scattered waves (relative to a direct reference wave), thus in principle permitting the holographic reconstruction of atomic positions. Photoelectron holography thus holds much promise of at least providing approximate starting structures that can be refined by more conventional comparisons of multiple-scattering calculations with experiment via R-factors. Criteria for optimizing the taking of such data and their holographic photoelectron diffraction patterns have been measured for surface and bulk core-level-shifted W 4f{sub 7/2} photoemission from W(110) on ALS beamline 7.0, yielding a data set of unprecedented size and quality. These data have been compared to multiple scattering theory, and used as a test case, since the W(110) surface is known not to exhibit significant relaxation in its interlayer spacings relative to the bulk. The authors have analyzed these experimental and theoretical results holographically in order to demonstrate the capabilities and limitations of photoelectron holography as a structural probe.

Two-dimensional Fermi contours of clean and hydrogen-induced surface electronic states have been systematically measured vs coverage of H on W(110) using angle-resolved photoemission. We observe a new pair of spin-orbit-interaction-split surface states, whose splitting grows systematically with hydrogen coverage and whose Fermi contours are strongly nested due to their opposing curvatures. Momentum-dependent electronic transitions between these states drive two previously observed anomalous behaviors: The phonon anomalies along {ovr {Gamma}H} and {ovr {Gamma}S} observed with inelastic helium scattering and electron energy loss spectroscopy, and the shifted-upper-layer reconstruction observed by low-energy electron diffraction for coverages greater than 0.5 monolayer. {copyright} {ital 1998} {ital The American Physical Society}

Using a combination of resonant soft x-ray scattering, magnetometry, x-ray reflectivity and microscopy techniques we have investigated the magnetic properties and microstructure of a series of perpendicular anisotropy Co/Pt multilayer films with respect to structural disorder tuned by varying the sputtering deposition pressure. The observed magnetic changes in domain size, shape and correlation length originate from structural and chemical variations in the samples, such as chemical segregation and grain formation as well as roughness at the surface and interfaces, which are all impacted by the deposition pressure. For low pressure samples we find evidence of a random "gas-like" distribution of magnetic domains, while in the higher pressure samples the domain structure exhibits only short range "liquid-like" positional ordering. The structural and chemical disorder induced by the higher deposition pressure first leads to an increase in the number of magnetic point defects that limit free domain wall propagation. Then, as the sputtering pressure is further increased, the domain wall energy density is lowered due to the formation of local regions with reduced magnetic moment, and finally magnetically void regions appear that confine the magnetic domains and clusters, similar to segregated granular magnetic recording media., 17 pages, 18 figures, submitted to Phys. Rev. B

We report a detailed experimental and theoretical study of the electronic structure of \(Mo_{1-x}Re_x\) random alloys. We have measured electronic band dispersions for clean and hydrogen-covered \(Mo_{1-x}Re_x\) ( 110) with x = 0-0.25 using angle-resolved photoemission spectroscopy. Our results suggest that the bulk and most surface electronic bands shift relative to the Fermi level systematically and approximately rigidly with Re concentration. We distinguish and quantify two contributions to these shifts: a raise of the Fermi energy and an increase of the overall bandwidth. Alloy bands calculated using the first-principles Korringa-Kohn-Rostoker coherent-potential-approximation method accurately predict both of these effects. As derived from the rigid band model, the Fermi energy shift is inversely related to the bulk density of states in this energy region. Using our results, we also characterize an electronic topological transition of the bulk Fermi surface and relate this to bulk transport properties. Finally, we distinguish effects beyond the rigid band approximation: a highly surface-localized state and a composition-dependent impact of the spin-orbit interaction.

We present and analyze isothermal adsorption and desorption measurements for methane physisorbed on a Cu(100) surface to characterize the interplay between molecule–surface and molecule–molecule interactions. A 2D gas–liquid phase boundary for the methane layer is observed and partially mapped in coverage and temperature. Comparing our measured critical temperature of 66 K ±2 K to previous work on related systems implies an attractive well between physisorbed molecules of ∼130 K. This reduction compared to the gas phase well can be adequately understood in terms of dielectric screening of the dispersion interaction. By contrast, analyzing the low‐coverage adsorption and desorption isotherms using a quasiequilibrium model and imperfect gas statistics, we deduce a lateral attractive intermolecular potential well of only 40–50 K. This drastic reduction of the attractive well from the gas phase value is not consistent with image charge screening, and is difficult to reconcile with the observed critical temper...

In this paper we describe several uses of low angle X-ray diffraction to determine the structure and reactivity of thin films and interfaces, highlighting the sensitivity of these measurements to alignment of the sample with respect to the goniometer. A TiN film is used to demonstrate the ability of low angle diffraction to measure thickness without assuming optical constants or calibration data. The ability to extract density information via the critical angle and smoothness of deposited films from diffraction data is also detailed. Diffraction data from a silicon-germanium superlattice demonstrate the sensitivity of low angle diffraction to interfacial interdiffusion. Several features of this interdiffusion process are highlighted including the structural relaxation of the superlattice on initial annealing followed by the non-linear interdiffusion of the silicon and germanium layers. We only observe interdiffusion of the layers at higher temperatures and the crystallization of the thermodynamically stable solid solution rather than the elements as previously reported. The facile crystallization of the solid solution highlights the synthetic advantages of superlattices in avoiding stable reaction intermediates compared with the long annealing times required in conventional synthesis.

High spatial resolution magnetic x-ray spectromicroscopy at x-ray photon energies near the cobalt L3 resonance was applied to probe an amorphous 50 nm thin SmCo5 film prepared by off-axis pulsed laser deposition onto an x-ray transparent 200 nm thin Si3N4 membrane. Alternating gradient magnetometry shows a strong in-plane anisotropy and an only weak perpendicular magnetic anisotropy, which is confirmed by magnetic transmission soft x-ray microscopy images showing over a field of view of 10 μm a primarily stripe-like domain pattern but with local labyrinth-like domains. Soft x-ray ptychography in amplitude and phase contrast was used to identify and characterize local magnetic and structural features over a field of view of 1 μm with a spatial resolution of about 10 nm. There, the magnetic labyrinth domain patterns are accompanied by nanoscale structural inclusions that are primarily located in close proximity to the magnetic domain walls. Our analysis suggests that these inclusions are nanocrystalline Sm2...

The occurrence of magnetic domain memory has been observed in ferromagnets, either induced by structural defects or by exchange couplings. Being able to quantify the amount of memory as a function of length scale, field and temperature is both of fundamental and technological importance. A technique has been refined to statistically quantify the magnetic domain memory in ferromagnetic thin films by using coherent soft-X-ray scattering metrology. This technique, based on cross-correlating magnetic speckle patterns, provides a unique way to map out the behavior of domain memory. Here, the details of our correlation method and the necessary treatment of the X-ray scattering images to extract spatial and field dependences in the memory information are reviewed. The resulting correlation maps, measured on [Co/Pd]IrMn multilayers, show how magnetic domain memory evolves at various spatial scales, as a function of the field magnitude throughout magnetization cycles, but also as a function of field cycling and of temperature. This technique can easily be applied to a wide variety of systems presenting memory effects, in soft and hard matter, and also to dynamical studies.

International audience; We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic structure of an amorphous terbium-cobalt thin film with a spatial resolution of about 75 nm at the Co L 3 edge at 778 eV. In comparison with soft x-ray microscopy images recorded with Fresnel zone plate optics at better than 25 nm spatial resolution, we find qualitative agreement in the observed magnetic structure.

Using coherent soft x-ray scattering we have measured slow magnetization fluctuations in an Au/Co/Au heterostructure near a thermally driven spin-reorientation phase transition. The intermediate scattering function is well described by a stretched exponential, suggesting cooperative motion through the transition. The decay times were found to exhibit a pronounced maximum as a function of temperature. We argue that the transition proceeds through a cone phase in which the local magnetization evolves continuously from a perpendicular to longitudinal orientation. Our results demonstrate a different and fruitful way to probe the complex spatiotemporal dynamics that arise in unusual magnetic phases with competing anisotropies.

We report time‐resolved electron energy loss spectroscopy results for the thermal desorption of CO physisorbed onto Ag(011). The measurements were performed isothermally and effectively at constant coverage. We observe that the logarithm of the measured pseudo‐first‐order desorption rate constant increases approximately linearly with coverage over the temperature and coverage ranges accessible to our measurements. The results are analyzed in terms of a quasiequilibrium model in which the desorption rate constant is expressed analytically as a virial expansion. Using this analysis, we determine that at low coverage the molecules adsorb with their axes parallel to the surface plane and are oriented with respect to the crystalline axes. We find that long‐range interactions extending out to 7–8 neighbor shells must be included to fit our results. The magnitude of these long‐range interactions is reasonably well described by the gas phase intermolecular potential if screening by substrate image charges is incl...

We present time‐resolved electron energy loss spectroscopy measurement of isothermal desorption of NH3 and ND3 from Cu(001) as a function of coverage. The desorption process is characterized by pseudo‐first‐order kinetics. The pseudo‐first‐order rate constant increases approximately exponentially as a function of adsorbed ammonia coverage. The results of an analysis based on a quasiequilibrium approximation which expresses the desorption rate in terms of a virial expansion in adsorbate coverage are reported. This demonstrates that the intermolecular interactions are dominated by short range repulsive lateral interactions, in qualitative accord with expectations of dipolar interactions. The results also suggest the existence of longer‐range attractive interactions.

The kinetics of NH3 and ND3 desorption from Cu(001) surface have been measured by time‐resolved electron energy loss spectroscopy. The desorption precess is observed to be characterized by pseudo‐first‐order kinetics. The desorption energy and the prefactor have been determined for both NH3 and ND3. The prefactors are unusually low as compared to those observed for simple diatomic molecules. Moreover, we observed an unusual behavior consistent with an isotope kinetic compensation effect. Both of these observations can be explained within the context of transition state theory by the interplay between isotopic masses and the shifts of frustrated vibrational modes of adsorbed molecules. Our results imply that the conventional Arrhenius form would not be precisely applicable to molecular desorption, if a large enough temperature range could be measured, particularly for hydrogen‐containing molecules.

The effects of a 3-h pulse exposure of rainbow trout ( Oncorhynchus mykiss ) eggs to thiocyanate (KSCN and NaSCN) were evaluated. Observations on fertilization success, mortality, incidence of deformaties and embryonic heartrate were recorded for 5 wk at 13.5°C. The eggs were exposed either immediately after fertilization (before water hardening) or 3 h later after water hardening had begun. Pulse exposure adversely affected the survival and development of the eggs, both before and after water hardening. Significant egg mortality occurred at SCN − concentrations ≥ 2,700 and 1,290 mg 1 −1 in the before and after treatments respectively. Alevins that hatched from treated eggs exhibited abnormalities of the tail and spine after exposure to KSCN and NaSCN. Deformities occurred at significantly higher frequencies, relative to controls, at SCN − concentrations ≥85 and 2,700 mg 1 −1 before and after water hardening respectively. Embryonic heart-rates were not significantly affected by NaSCN.

Angle-resolved photoemission measurements of the surface localized electronic states of the clean Pd(001) surface are presented. Several surface localized levels were observed, in qualitative agreement with an existing surface band-structure calculation. In particular, a state was observed which crosses the Fermi level (${\mathit{E}}_{\mathit{F}}$) near the X\ifmmode\bar\else\textasciimacron\fi{} point of the surface Brillouin zone. The segment of the Fermi contour derived from this crossing lies largely within a gap in the projected bulk Fermi surface and is parallel to the Brillouin-zone edge. The nesting properties of this segment of the Fermi contour suggest the possibility of a fairly strong electronic coupling to phonon excitations.

We report time‐resolved electron energy loss spectroscopy results for the desorption of CO from Cu(001) and Cu(011). The measurements were performed isothermally and effectively at constant coverage. We present an analysis based on a quasiequilibrium model that expresses the pseudo‐first‐order desorption rate constant in terms of a virial expansion. The results of this analysis demonstrate the existence of small, long‐range attractive interactions as well as the expected short‐range repulsive interactions between adsorbed molecules. The interplay between these two types of interactions leads to a kinetic compensation effect that can be easily understood in terms of vanishing virial coefficients. Thus, in these simple systems, the origin of the kinetic compensation effect lies in the statistical thermodynamics of the adsorbed phase, while the dynamical events associated with the desorption event apparently play a lesser role. The relationship of this analysis technique to others is investigated, and its generality is emphasized.

We demonstrate the ability to control the magnetic phase diagram of Cr 1-x V x (110) thin films grown on a W(110) substrate. Using angle-resolved photoemission, we have mapped paramagnetic and commensurate and incommensurate antiferromagnetic phases as a function of temperature, film thickness, and composition. We show that surface-localized electron states play a key role in the observed phase behaviors and suggest from this that it might be possible to control the magnetic phase by applying an external electric field.

We demonstrate the ability to control the magnetic phase diagram of Cr1-x Vx(110) thin films grown on a W(110) substrate. Using angle-resolved photoemission, we have mapped paramagnetic and commensurate and incommensurate antiferromagnetic phases as a function of temperature, film thickness, and composition. We show that surface-localized electron states play a key role in the observed phase behaviors and suggest from this that it might be possible to control the magnetic phase by applying an external electric field.

We have studied the atomic and electronic structure of the $\mathrm{Cu}(001)\text{\ensuremath{-}}(\sqrt{20}\ifmmode\times\else\texttimes\fi{}\sqrt{20})R26.6\ifmmode^\circ\else\textdegree\fi{}\text{\ensuremath{-}}\mathrm{In}$ surface, which undergoes a reversible transition to a $p(2\ifmmode\times\else\texttimes\fi{}2)$ phase at high temperature. Low temperature scanning-tunneling microscopy indicates a $p(2\ifmmode\times\else\texttimes\fi{}2)$ structure modulated at the $(\sqrt{20}\ifmmode\times\else\texttimes\fi{}\sqrt{20})$ periodicity. Angle-resolved photoelectron spectroscopy shows a surface resonance exhibiting gap opening and backfolding along a $(\sqrt{20}\ifmmode\times\else\texttimes\fi{}\sqrt{20})$ zone boundary. We suggest that the $(\sqrt{20}\ifmmode\times\else\texttimes\fi{}\sqrt{20})$ structure is stabilized due to the Fermi surface nesting accompanying a surface charge density wave.

One dimensional (1D) metals are unstable at low temperature undergoing a metal-insulator transition coupled with a periodic lattice distortion, a Peierls transition. Angle-resolved photoemission study for the 1D metallic chains of In on Si(111), featuring a metal-insulator transition and triple metallic bands, clarifies in detail how the multiple band gaps are formed at low temperature. In addition to the gap opening for a half-filled ideal 1D band with a proper Fermi surface nesting, two other quasi-1D metallic bands are found to merge into a single band, opening a unique but k-dependent energy gap through an interband charge transfer. This result introduces a novel gap-opening mechanism for a multiband Peierls system where the interband interaction is important.

Using coherent x-ray speckle metrology, we have measured the influence of disorder on major loop return point memory (RPM) and complementary point memory (CPM) for a series of perpendicular anisotropy Co/Pt multilayer films. In the low disorder limit, the domain structures show no memory with field cycling--no RPM and no CPM. With increasing disorder, we observe the onset and the saturation of both the RPM and the CPM. These results provide the first direct ensemble-sensitive experimental study of the effects of varying disorder on microscopic magnetic memory and are compared against the predictions of existing theories., Comment: 4 pages, 4 figures. Accepted for publication in Physical Review Letters in Nov. 2004

We present measurements of the Fermi surface and underlying band structure of a single layer of indium on Si(111) with square root 7 x square root 3 periodicity. Electrons from both indium valence electrons and silicon dangling bonds contribute to a nearly free, two-dimensional metal on a pseudo-4-fold lattice, which is almost completely decoupled at the Fermi level from the underlying hexagonal silicon lattice. The mean free path inferred from our data is quite long, suggesting the system might be a suitable model for studying the ground state of two-dimensional metals.

We propose differential holography as a method to overcome the long-standing forward-scattering problem in photoelectron holography and related techniques for the three-dimensional imaging of atoms. Atomic images reconstructed from experimental and theoretical Cu 3p holograms from Cu(001) demonstrate that this method suppresses strong forward-scattering effects so as to yield more accurate three-dimensional images of side- and back-scattering atoms., revtex, 4 pages, 2 figures

Low-temperature electronic properties of the charge-density-wave system NbSe3 are reported from angle-resolved photoemission at 15 K. The effect of two instabilities q(1) and q(2) on the k-resolved spectral function is observed for the first time. With a pseudogap background, the gap spectra exhibit maxima at Delta*(1) approximately 110 meV and Delta*(2) approximately 45 meV. Imperfectly nested sections of the Fermi surface lack a Fermi-Dirac edge, and show the signature of a dispersion that is modified by self-energy effects. The energy scale is of the order of the effective gap 2 Delta*(2). The effect disappears above T2, suggesting a correlation with the charge-density-wave state.

We present measurements of the Fermi surface and underlying band structure of a single layer of indium on Si(111) with $\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ periodicity. Electrons from both indium valence electrons and silicon dangling bonds contribute to a nearly free, two-dimensional metal on a pseudo-4-fold lattice, which is almost completely decoupled at the Fermi level from the underlying hexagonal silicon lattice. The mean free path inferred from our data is quite long, suggesting the system might be a suitable model for studying the ground state of two-dimensional metals.

The electron bands of the Peierls compound NbSe 3 are mapped with angle-resolved photoemission. Data of the Fermi level crossings show the nesting condition responsible for the charge density wave along the one-dimensional axis. The instability with periodicity q =0.44 A −1 induces a remnant backfolding of the electron bands in the nominally metallic state high above the critical temperature.

We report a simple and nondestructive method to determine directly the spatial profiles of the constituent elements in a synthetic multilayered material with a resolution of 10–20 A. This has been accomplished by measuring the x‐ray diffraction Bragg peak intensities over a large range of energies, and interpreting these data using a dynamical theory to deduce the first few Fourier coefficients of the relevant spatial profiles. We present initial results for Ti‐Si multilayer samples grown by thermal deposition. These results demonstrate extensive interdiffusion of the silicon into the titanium layers, even without annealing.

The electronic band structure of the Peierls compound NbSe3 has been explored for its symmetries with microspot synchrotron photoemission. The Fermi level crossings and deviations from one-dimensional behavior are identified. Density-functional calculations of the Fermi surfaces confirm the nesting conditions relevant for the two phase transitions. The instability along the chains with superstructure periodicity q = 0.44 A(-1) induces a backfolding of the electronic bands, and the Fermi level crossings appear suppressed. This broken symmetry is observed in the fluctuation regime at more than twice the critical temperature, where the correlation length is strongly reduced.

Angle-resolved photoemission (ARP) of valence bands is a mature technique that has achieved spectacular success in band-mapping metals, semiconductors, and insulators. The purpose of the present study was the development of experimental and analytical techniques in ARP which take advantage of third generation light sources. Here the authors studied the relatively simple Cu surface in preparation for other metals. Copper and related metals themselves are of current interest, especially due to its role as an interlayer in spin valves and other magnetic heterostructures. A major goal of this study was the development of a systematic technique to quickly (i.e. in a few hours of synchrotron beamtime) measure the FS and separate it into bulk and surface FS`s. Often, one needs to avoid bulk features altogether, which one can achieve by carefully mapping their locations in k-space. The authors will also show how they systematically map Fermi surfaces throughout large volumes of k-space, and, by processing the resulting volume data sets, provide intuitive pictures of FS`s, both bulk and surface.