D. Y. Petrovykh

Formation of regular step arrays on Si(111)7×7

Highly regular arrays of steps are produced on vicinal Si(111)7×7 surfaces. A tilt of the surface normal from (111) toward (112) produces single steps (0.3 nm high and typically 15 nm apart). The opposite tilt toward (112) produces bunched steps with adjustable height (1–5 nm) and a spacing of 70 nm. Preparation criteria for straight edges and regular spacings are determined, taking into account the miscut angle (azimuthal and polar), annealing sequence, current direction, and applied stress.

Atomic scale memory at a silicon surface

The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of five atom rows. The memory can be initialized and reformatted by controlled deposition of silicon. The writing process involves the transfer of Si atoms to the tip of a scanning tunnelling microscope. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.

Self-assembly of one-dimensional nanostructures at silicon surfaces

Nanostructures at surfaces and interfaces are a fertile testing ground for bringing the idea of ‘tailored solids’ towards reality. Electronic properties can be controlled systematically by confinement or by interface effects. The presence of a single crystal substrate allows for the self-assembly of highly regular nanoobjects, such as stripes and strings of dots with sizes of about 10 nm. Using silicon as substrate facilitates the electronic integration of nanodevices into micro-electronics. We speculate how such structures might evolve into future devices, such as data storage arrays with densities of Terabits/cm 2 and self-assembled,

Self-assembled Fe nanowires using organometallic chemical vapor deposition and CaF2 masks on stepped Si(111)

Linear arrays of 3 nm wide Fe stripes with 15 nm spacing are fabricated by self-assembly. They are formed by photolysis of ferrocene that is selectively adsorbed between CaF2 stripes. An ultraviolet nitrogen laser removes the organic ligands from ferrocene. Arrays of CaF2 stripes serve as masks, which are self-assembled on a stepped Si(111) surface. Scanning tunneling microscopy is used to investigate the surface morphology during growth. A generalization of this method to other wire materials is discussed.

Functionalization of silicon step arrays I: Au passivation of stepped Si(111) templates

The growth mode of Au on stepped Si(111)7×7 surfaces is determined by scanning tunneling microscopy, with the goal of providing a continuous gold layer that replicates the step morphology. Functionalization with gold allows attaching organic and biomolecules via thiol groups (e.g., alkanes and DNA). On clean Si(111), gold grows in the Stranski–Krastanov mode and produces islands with a size comparable to the step spacing. A Ti wetting layer produces smooth Au films that preserve the step topography down to a scale of a few nanometers.

UNOCCUPIED SURFACE STATES ON SI(111)3X3-AG

A nearly metallic surface state band is detected on Si~111!)3) Ag by inverse photoemission, Si 2p core level photoemission, and scanning tunneling spectroscopy. The band spans most of the bulk band gap of Si, from the Fermi level at 0.25 eV above the valence band maximum all the way to the conduction band minimum. The Fermi level is pinned over a wide doping range ~7310 cm p type to 1.2310 cm n type!. The data suggest that the surface band gap expected from the even electron count is filled in at room temperature, possibly due to thermal disorder or due to the finite domain size of 10–20 nm. A second, prominent surface feature at 2.2 eV above the valence band maximum is assigned to surface umklapp from K to Ḡ via a )3) reciprocal lattice vector. @S0163-1829~98!03204-4#

Single domain Ca-induced reconstruction on vicinal Si(1 1 1)

High-quality vicinal Si(1 1 1) surfaces are used as templates to create single domains of the Si(1 1 1)3 � 1-Ca reconstruction which exhibit atomic chains parallel to Si steps. Scanning tunneling microscope images support the formation of honeycomb chains of Si atoms, rather than zigzag chains proposed in earlier models. Angle-resolved photoemission is used to map out the dispersion of valence band states parallel and perpendicular to the chains. A gap of � 0.9 eV is found below the Fermi level with both in-plane and out-of-plane polarization of the synchrotron light. The observed semiconducting behavior suggests that the honeycomb chain channel model proposed for the alkaliinduced 3 � 1 reconstruction be modified for divalent alkaline earths, e.g. a 3 � 2 structure with 1/6 monolayer coverage. 2002 Elsevier Science B.V. All rights reserved.

Silicon adatoms on the Si(1 1 1)5×2–Au surface

Abstract Scanning tunneling microscopy images of the Si(1xa01xa01)5×2–Au surfaces exhibit irregularly distributed protrusions of atomic size. They are identified as silicon adatoms by evaporating small amounts of silicon and gold onto the reconstructed surface. While extra silicon increases the density of protrusions, extra gold transforms the reconstruction partially into a Si(1xa01xa01)√3×√3 reconstruction.

Enhanced spin polarization of conduction electrons in Ni explained by comparison with Cu

The spin-split Fermi-level crossings of the conduction band in Ni are mapped out by high-resolution photoemission and compared to the equivalent crossing in Cu. The area of the quasiparticle peak decreases rapidly below EF in Ni, but not in Cu. Majority spins have larger spectral weight at EF than minority spins, thereby enhancing the spin polarization beyond that expected from the density-of-states. A large part of the effect can be traced to a rapid variation of the matrix element with k at the point where the s, p band begins to hybridize with the dz state. However, it is quite possible that the intensity drop in Ni is reinforced by a transfer of spectral weight from single-particle to many-electron excitations. The results suggest that the matrix element should be considered for explaining the enhanced spin polarization observed for Ni in spin-polarized tunneling.

Connection between Structure and Electronic Properties in Epitaxial Magnetic Layers

This study explores the consequences of structure on the electronic properties of magnetic multilayers. Epitaxial layers of Co and Cu are grown on Cu(100) in a new deposition system that couples sputter-deposition with MBE and contains a wide range of characterization tools, including RHEED, LEED, and Kerr effect. This system can be coupled in situ to spin-polarized, angle-resolved photoemission and to resonant, magnetic X-ray scattering, both employing synchrotron radiation. The interface structure turns out to be critical in determining the coercivity and the presence of quantum well states, which determine oscillatory magnetic coupling.