Inverse photoemission from Cu(001)

Bremsstrahlung ultraviolet spectra for Cu(001) are calculated for a photon energy ηω=9.7 eV within the framework of an inverse one-step model of photoemission for several angles of incidence of the electron beam. The comparison with recently reported experimental data shows that both the calculated energy dispersion of the peak in the spectra and the variation of the peak intensity are in reasonable agreement with the experiment.     

Evidence for an anisotropy-induced non-collinear spin state in exchange-coupled Co/Cu(001)

The magnetization behaviour of a Co/Cu/Co(001) sandwich has been studied by magneto-optical Kerr effect measurements. The sample was grown by molecular beam epitaxy onto a sapphire (1 .2) substrate with a Cu/Cr/Nb(001) buffer system. The copper layer had the form of a wedge with the thickness range chosen to be around the second region of antiferromagnetic exchange coupling. The hysteresis loops in the regime of weak antiferromagnetic coupling show characteristic steps, which can be explained by an anisotropy-induced non-collinear spin state. Indication for a similar behaviour is also found in the regime of strong antiferromagnetic coupling. This behaviour is explained by taking into account the competition between anisotropy, interlayer exchange coupling and external field energy. The nature of this metastable non-collinear magnetization state is in marked contrast to the biquadratic (90°) exchange coupling which was discovered in Fe/Cr(001).     

Step edge selection during ion erosion of Cu(001)

Upon Ar+ ion erosion of a Cu(001) surface, we observed with HR-LEED faceted structures on the surface oriented preferentially along <100> at 200 K and along <110> at 330 K. These results are evaluated with a geometric rule, relating under kinetic conditions the orientation of the surviving steps to their advance rates. Application of this generic rule demonstrates that the <100> steps advance slowest. This reveals enhanced interlayer mass transport across these steps. We also show that a transition from kinetically favored step orientation into the thermodynamically favored one occurs at very short time scales even near room temperature.     

Photon polarization effects in inverse photoemission from Cu(001)

A study of the polarization of Bremsstrahlung emitted from a Cu(001) single crystal surface helps to identify surface states and allows to determine the parity of bulk final states involved in a particular radiative transition if the angle of electron incidence is varied in a mirror plane of the crystal. In case of overlapping peaks with different polarization, a polarization dependent light detection increases in addition the apparent experimental resolution considerably.     

Mechanisms of high-order perturbative photoemission from Cu(001)

We observed high-order 2- to 4-photon photoemission and above threshold photoemission (ATP) processes with 3.07 eV light from the Cu(001) surface. The intensity of 3-photon photoemission via excitation through the n = 1 image potential state significantly exceeded that of the 2-photon process. The ATP occurs either via single photon transitions from the image potential resonances above the vacuum level or by multiphoton transitions from image potential states below the vacuum level. The experimental ratio of the m- to (m + 1)-photon process yields is sensitive to the electronic band structure of the solid.     

Femtosecond surface vibrational spectroscopy of CO adsorbed on Ru(001) during desorption

Using time-resolved sum-frequency generation spectroscopy, the C- O stretch vibration of carbon monoxide adsorbed on a single-crystal Ru(001) surface is investigated during femtosecond near-IR laser excitation leading to desorption. A large transient redshift, a broadening of the resonance, and a strong decrease in intensity are observed. These originate from coupling of the C- O stretch to low-frequency modes, especially the frustrated rotation, that are highly excited in the desorption process.     

Field desorption of Potassium from (001), (011) and (112) Tungsten planes

Field desorption of potassium from the (001), (011) and (112) tungsten planes in the temperature range 80–140 K and in the field range 0.10–0.55 V/Å has been investigated using the field emission micrscope with Faraday cage and a rotatable emitter. Generally good agreement with the results, obtained previously by other authors for other adsorbates and for the whole emitter tip, was found. However the temperature dependence of the desorption field is different for some crystal planes. The binding energy at zero coverage and zero field was determined. The values of 1.95 eV, 1.75 eV and 2.0 eV were obtained for the (001), (011) and (112) planes, respectively. The degree of desorption was also measured as a function of desorbing field and a significant difference of this dependence for the (001) and (011) planes was found.     

Evidence for F(-) formation by simultaneous double-electron capture during scattering of F(+) from a LiF(001) surface

Slow F(+) ions (v<0.1 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence exhibit a high probability for forming F(-) ions in the reflected beam, whereas no negative ions are found for neutral F(0) projectiles. From detailed studies of projectile energy loss and charge transfer, we find evidence for a correlated double-electron capture process in the formation of the F(-) ions.     

RHEED intensity oscillations during epitaxial growth of fcc Fe on Cu(001)

Up to 14 strong intensity oscillations of the specular beam in reflection high-energy electron diffraction (RHEED) have been observed during the epitaxial growth of face-centered (fcc) Fe on Cu(001) in the temperature range between 333–370 K. The amplitudes of these oscillations are strong even in the initial stages of growth. This provides evidence that the hetero-epitaxial growth of fcc Fe on Cu(001) proceeds predominantly layer-by-layer-like in that temperature regime. For growth at 300 K, initial Fe-bilayer-island formation followed by predominant layer-by-layer growth above 2 monolayers (ML) of Fe is observed. 3D growth prevails at ˜ 100 K.     

Experimental linewidth parameters and dipole moments for the propyne molecule in the V9 and V10 vibrationally excited states

Linewidth parameters were obtained for some rotational components in the ground, V₉ = 1, V₁₀ = 1, and V₁₀ = 2 vibrational states for the propyne (CH₃CCH) molecule at 300 K. A method employing the linewidth parameters to determine dipole moments of vibrationally excited species is presented and discussed.