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We describe a setup of time-, spin-, and angle-resolved photoemission spectroscopy (tr-SARPES) employing a 10.7 eV (λ = 115.6 nm) pulse laser at a 1 MHz repetition rate as a probe photon source. This equipment effectively combines the technologies of a high-power Yb:fiber laser, ultraviolet-driven harmonic generation in Xe gas, and a SARPES apparatus equipped with very-low-energy-electron-diffraction spin detectors. A high repetition rate (1 MHz) of the probe laser allows experiments with the photoemission space-charge effects significantly reduced, despite a high flux of 1013 photons/s on the sample. The relatively high photon energy (10.7 eV) also brings the capability of observing a wide momentum range that covers the entire Brillouin zone of many materials while ensuring high momentum resolution. The experimental setup overcomes the low efficiency of spin-resolved measurements, which gets even more severe for the pump-probed unoccupied states, and affords the opportunity to investigate ultrafast electron and spin dynamics of modern quantum materials with energy and time resolutions of 25 meV and 360 fs, respectively. [ABSTRACT FROM AUTHOR]

We investigated structural and magnetic properties of FeNi ordered alloy thin films grown by nitrogen-surfactant assisted process using scanning tunneling microscopy and soft-X-ray absorption spectroscopy/magnetic circular dichroism. With the help of structurally controlled surface and interface by the N surfactant effect, the results successfully provide the layer-resolved spin magnetic moments of the Fe layer. Furthermore, the critical role of the topmost layer on the magnetic anisotropy is identified from a thickness dependence of the Fe orbital magnetic moment; the out-of-plane magnetization emerges when the Fe–N bonds, which favor the in-plane magnetization, break and the Ni–N bonds form in the NiN topmost layer. [ABSTRACT FROM AUTHOR]

We study submonolayer Ag deposited Ge(001) surfaces at 90 K by scanning tunneling microscopy (STM). Silver atoms and their small aggregates on the surface are found as bright dots on the surface at 78 K. The Ag aggregates form small clusters, and move with the change of the buckling phase in the adjacent Ge dimer row at 180 K as observed in successive STM images. These are transient processes to the formation of a surface alloy between Ag and Ge. [ABSTRACT FROM AUTHOR]

The size of structural vacancies and structural vacancy density of 1/1-Al–Re–Si approximant crystals with different Re compositions were evaluated by positron annihilation lifetime and Doppler broadening measurements. Incident positrons were found to be trapped at the monovacancy-size open space surrounded by Al atoms. From a previous analysis using the maximum entropy method and Rietveld method, such an open space is shown to correspond to the centre of Al icosahedral clusters, which locates at the vertex and body centre. The structural vacancy density of non-metallic Al73Re17Si10was larger than that of metallic Al73Re15Si12. The observed difference in the structural vacancy density reflects that in bonding nature and may explain that in the physical properties of the two samples. [ABSTRACT FROM PUBLISHER]

We report nonlinear terahertz (THz) effects in monolayer graphene, giving rise to transmission enhancement of a single-cycle THz pulse when the incident THz peak electric field is increased. This transmission enhancement is attributed to reduced photoconductivity, due to saturation effects in the field-induced current and increased intraband scattering rates arising from transient heating of electrons. We have developed a tight-binding model of the response using the length gauge interaction Hamiltonian that provides good qualitative agreement. The model fully accounts for the nonlinear response arising from the linear dispersion energy spectrum in graphene. The results reveal a strong dependence of the scattering time on the THz field, which is at the heart of the observed nonlinear response. [ABSTRACT FROM AUTHOR]

Hot carrier dynamics in the Dirac band of n-type epitaxial graphene on a SiC substrate were traced in real time using femtosecond-time-resolved photoemission spectroscopy. The spectral evolution directly reflects the energetically linear density of states superimposed with a Fermi-Dirac distribution. The relaxation time is governed by the internal energy dissipation of electron-electron scattering, and the observed electronic temperature indicates cascade carrier multiplication. [ABSTRACT FROM AUTHOR]

We have studied the electronic structure of Ag thin films of monoatomic height grown on a Ge(001) surface at 95 K by using photoelectron spectroscopy. All the surface states on the clean Ge surface vanished and Ag 5s derived state appeared in the bulk band gap just below the Fermi level. These suggest a strong interaction with the substrate. On the other hand, on three-dimensional (3D) islands formed on a room temperature substrate, small changes were found in Ge 3d spectrum from the clean surface. Each of the Ag 3D islands already had bulklike feature in the valence band structure. The results are consistent with recent observation by scanning tunneling microscopy. [ABSTRACT FROM AUTHOR]

The valence electronic states of Fe[sub 3]O[sub 4](111) films on Pt(111) were studied using temperature-dependent spin- and angle-resolved photoemission spectroscopy with synchrotron radiation. The majority- and minority-spin partial density of states (DOS) has been obtained at 300 K and 100 K, above and below the Verwey transition temperature (T[sub V] ∼ 120 K). The spectra still show substantial k-dependence at 100 K in the 3d region. This provides the most direct experimental evidence that the 3d electrons are itinerant even at T < T[sub V]. [ABSTRACT FROM AUTHOR]

Two types of square-shaped self-assembled CrN nanoislands of monoatomic layer are fabricated on the Cu(001) substrate. The island edges are commonly oriented along the <110> directions, and the islands locally form a two-dimensional square superstructure. The mean height is either 0.09 or 0.18 nm, and the average lateral size of the islands is 2.5 × 2.5 nm2 for the lower islands and 3.5 × 3.5 nm2 for the others. The formation of the higher CrN islands is attributed to an unconventional short-range attractive mechanism. The lower islands coexisting with the clean surface are made by the interplay between the long- and short-range interactions. [ABSTRACT FROM AUTHOR]

Epitaxial Rh-doped SrTiO3 thin film photocatalysts were fabricated by pulsed laser deposition under various deposition conditions. The oxygen pressure used during film growth was found to affect the valence of the Rh dopant in the Rh:SrTiO3 films, reproducing the known optical absorption behavior of powder samples. Evaporative Rh loss was observed at low growth pressures and high temperatures. Cyclic voltammetry measurements in a K2SO4 solution showed that Rh-doped SrTiO3 is a highly efficient hydrogen-producing photocathode with a characteristic p-type behavior under visible light irradiation. [ABSTRACT FROM AUTHOR]

A letter to the editor and a reply are presented regarding the scanning tunnelling microscopy and angle-resolved photoemission spectroscopy (ARPES) against one-dimensional (1D) metal in a gold (AU)-induced chain.