M. Jałochowski

Quantum size effects in metallic nanostructures

Electrons confined in ultrathin metal films provide a window on the peculiar world of quantum mechanics.

Photoemission from ultrathin metallic films : quantum size effect, electron scattering, and film structure

The quantum-size-effect structure of ultrathin Pb and Pb-In alloy films on Si(111) surfaces is studied by photoemission spectroscopy in the thickness range from 0 to about 30 monolayers and analyzed, taking into account electron scattering and film structure, which is characterized by high-energy-reflection-electron diffraction

Gold-induced ordering on vicinal Si(111)

Abstract A vicinal Si(111) surface covered with a sub-monolayer amount of Au has been studied by RHEED. For a sample misoriented by 8.46° towards the [112] azimuthal direction at a coverage equal to 0.20 ML of Au, the RHEED pattern showed a regular distribution of monoatomic steps with the staircase width equal to 18.88 ± 0.33 A . Au-induced order was identified with a (755) facet of Si. Regularly spaced steps were stable within the investigated range of temperatures from 130 to 470 K. Upon further increase of the Au-coverage the periodicity was disturbed and at a coverage of about 0.50 ML of Au onset of (√3 × √3)R37° reconstruction was visible.

Double nonequivalent chain structure on a vicinal Si(557)-Au surface

We study electronic and topographic properties of the vicinal Si(557)-Au surface using scanning tunneling microscopy and reflection of high energy electron diffraction technique. STM data reveal double wire structures along terraces. Moreover behavior of the voltage dependent STM tip - surface distance is different in different chains. While the one chain shows oscillations of the distance which are sensitive to the sign of the voltage bias, the oscillations in the other chain remain unchanged with respect to the positive/negative biases. This suggests that one wire has metallic character while the other one - semiconducting. The experimental results are supplemented by theoretical calculations within tight binding model suggesting that the observed chains are made of different materials, one is gold and the other one is silicon chain.

Surface morphology and local magnetic properties of electrodeposited thin iron layers

Thin iron layers with different thickness were prepared by electrodeposition on the polycrystalline substrate. The surface morphology of the layers, their structure and local magnetic properties were studied using scanning tunneling microscopy (STM), X-ray diffraction (XRD) and conversion electron Mossbauer spectroscopy (CEMS). STM studies revealed the granular structure of the surface of the electrodeposited iron layers with the roughness up to 10 nm. XRD analysis proved that these layers were highly strained. The CEMS spectra showed an in-plane magnetic anisotropy in the iron layers. Isomer shift of the electrodeposited iron was different than that of the α-Fe. This difference was attributed to the internal stresses existing in the electrodeposited layers.

Infrared resonances of self-assembled Pb nanorods

The formation of self-assembled Pb nanorods on a vicinal Si(335)/Au surface at 305K was monitored in situ with polarization dependent infrared spectroscopy. The rods have formed from Pb evaporated on a single domain Au-stabilized Si(335) surface under ultrahigh vacuum conditions and reached lengths of about 1μm. As the rods are aligned almost parallel, a large optical anisotropy of the transmitted infrared light was detected. A plasmonic antennalike resonance appeared in the spectra. Since such resonance frequencies are mainly determined by the length of the rods, the growth process was directly monitored via the shift of the resonance frequency. The estimated extinction cross section at resonance frequency indicates field enhancement similar to that observed for gold nanorods.

Nitrogen doping of chemical vapor deposition grown graphene on 4H-SiC (0001)

We present optical, electrical, and structural properties of nitrogen-doped graphene grown on the Si face of 4H-SiC (0001) by chemical vapor deposition method using propane as the carbon precursor and N2 as the nitrogen source. The incorporation of nitrogen in the carbon lattice was confirmed by X-ray photoelectron spectroscopy. Angle-resolved photoemission spectroscopy shows carrier behavior characteristic for massless Dirac fermions and confirms the presence of a graphene monolayer in the investigated nitrogen-doped samples. The structural and electronic properties of the material were investigated by Raman spectroscopy. A systematical analysis of the graphene Raman spectra, including D, G, and 2D bands, was performed. In the case of nitrogen-doped samples, an electron concentration on the order of 5–10 × 1012 cm−2 was estimated based upon Raman and Hall effect measurements and no clear dependence of the carrier concentration on nitrogen concentration used during growth was observed. This high electron ...

Computer study of the influence of thermal vibrations on the RHEED intensity

Abstract The role of thermal vibrations in dynamical calculations of the RHEED intensity is analysed. It is found that the vibrations of the crystal lattice can cause large changes of the shapes of rocking curves.

Studies on gold atom chains and lead nanowires on silicon vicinal surfaces

The Si(557) vicinal surface is produced from Si(111) by cutting the crystal at a small angle of 9.45° along the [2] direction. By a special cleaning process performed under ultra-high vacuum conditions, Si(557) displays a perfect grating structure consisting of parallel narrow terraces, each of them composes of a silicon plane with half unit cell of the Si(111)-7x7 reconstruction and a silicon row. Such an atomic grating makes it possible to get self-assembled atomic wires by decorating the surface with an optimal amount of 0.2 monolayer (ML) of Au. In the first step of the study, Si(557) is used as a template for fabricating of Pb nanowires by self-assembling in which the steps on the Si(557) surface provide the high-oriented diffusion channels for Pb wires growth. By means of polarized infrared spectroscopy the optical response of the Pb nanowires is investigated. As a major consequence of the interaction between infrared light and nanostructures, an antenna-like resonance appears. We found the shift of the antenna resonance frequency to lower wavenumbers due to the development of the nanowires in length under parallel excitation, whereas there is no significant change due to perpendicular excitation observed.

Purely one-dimensional bands with a giant spin-orbit splitting: Pb nanoribbons on Si(553) surface

We report on a giant Rashba type splitting of metallic bands observed in one-dimensional structures prepared on a vicinal silicon substrate. A single layer of Pb on Si(553) orders this vicinal surface making perfectly regular distribution of monatomic steps. Although there is only one layer of Pb, the system reveals very strong metallic and purely one-dimensional character, which manifests itself in multiple surface state bands crossing the Fermi level in the direction parallel to the step edges and a small band gap in the perpendicular direction. As shown by spin-polarized photoemission and density functional theory calculations these surface state bands are spin-polarized and completely decoupled from the rest of the system. The experimentally observed spin splitting of 0.6 eV at room temperature is the largest found to now in the silicon-based metallic nanostructures, which makes the considered system a promising candidate for application in spintronic devices.