Dysprosium Silicide Research Articles

Dynamics of dysprosium silicide nanostructures on Si(001) and (111) surfaces

The growth and coarsening dynamics of dysprosium silicide nanostructures are observed in real-time using photoelectron emission microscopy. The annealing of a thin Dy film to temperatures in the range of 700–1050 °C results in the formation of epitaxial rectangular silicide islands and nanowires on Si(001) and triangular and hexagonal silicide islands on Si(111). During continuous annealing, individual islands are observed to coarsen via Ostwald ripening at different rates as a consequence of local variations in the size and relative location of the surrounding islands on the surface. A subsequent deposition of Dy onto the Si(001) surface at 1050 °C leads to the growth of the preexisting islands and to the formation of silicide nanowires at temperatures above where nanowire growth typically occurs. Immediately after the deposition is terminated, the nanowires begin to decay from the ends, apparently transferring atoms to the more stable rectangular islands. On Si(111), a low continuous flux of Dy at 1050 °C leads to the growth of kinked and jagged island structures, which ultimately form into nearly equilateral triangular shapes.

Controlling the width of self-assembled dysprosium silicide nanowires on the Si(001) surface

We present STM data that show that it is possible to use a metal induced 2 × 7 reconstruction of Si(001) to narrow the width distribution of Dy silicide nanowires. This behavior is distinct from the effect of the 7 × 7 reconstruction on the Si(111) surface, where the 7 × 7 serves as a static template and the deposited metal avoids the unit cell boundaries on the substrate. In this case, the 2 × 7 is a dynamic template, and the nanowires nucleate at anti-phase boundaries between 2 × 7 reconstruction domains.

Electronic properties of self-assembled rare-earth silicide nanowires on Si(001)

To study the formation and the electronic properties of self-assembled dysprosium and erbium silicide nanowires on the vicinal Si(001) surface, we applied scanning tunneling microscopy and angle-resolved photoelectron spectroscopy. The formation of different types of nanowires was found, depending on the rare-earth exposure, postgrowth annealing temperature, and the rare-earth material itself. It is demonstrated that the so-called thin dysprosium silicide nanowires, which form close-packed arrays, are characterized by a nonmetallic band structure with negligible dispersion. In contrast to that, the so-called broad dysprosium silicide nanowires, which are lateral distances of several tens of nanometers apart, are metallic with one-dimensional electronlike bands crossing the Fermi energy. The effective masses of these bands amount to values ranging from 0.2 to 1.1 free-electron masses, and the overall band filling was found to be close to 1. It is shown that broad erbium silicide nanowires have a very similar electronic band structure compared to broad dysprosium silicide nanowires, while corresponding thin erbium silicide nanowires could not be found.

Phase selection in the rare earth silicides

The rare earth silicides form islands with a tetragonal or a hexagonal structure that coexist when grown on the Si(100) surface. We show using medium energy ion scattering that it is possible to selectively grow one of these as a pure phase by controlling the mobility of the rare earth atoms as they are deposited. When dysprosium, holmium, and erbium are deposited onto a liquid nitrogen cooled substrate the hexagonal structural phase is formed after annealing. When erbium and holmium are deposited onto a hot substrate only the tetragonal phase results. For dysprosium silicide growth under conditions of high mobility causes approximately equal numbers of hexagonal and tetragonal islands to form. The system offers a means to obtain fine control over physical properties such as the Schottky barrier height.

Electronic properties of dysprosium silicide nanowires on Si(557)

The electronic properties of self-assembled dysprosium silicide nanowires on Si(557) are studied by angle-resolved photoelectron spectroscopy. Using a toroidal electron energy analyzer, the energy surfaces of the nanostructures are imaged. At dysprosium coverages exceeding one monolayer, metallic nanowires with a two-dimensional electronic structure are formed on [111]-oriented terraces, consisting of hexagonal DySi2 monolayers or Dy3Si5 multilayers with the c-axis in [111] direction of the substrate.

Electronic structure of dysprosium silicide films grown on a Si(1 1 1) surface

The thickness-dependent electronic structures of Dy silicide films grown on a Si(1 1 1) surface have been investigated by angle-resolved photoelectron spectroscopy. Two ( 1 × 1 ) periodic bands, both of them cross the Fermi level, have been observed in the silicide films formed by Dy coverages of 1.0 monolayer and below, and more than five ( 3 × 3 ) periodic bands have been observed in thicker films. Taking the ( 2 3 × 2 3 ) periodic structure of Dy atoms in the submonolayer silicide film into account, the periodicity of the two metallic bands indicate that they mainly originate from the orbitals of Si atoms, which form a ( 1 × 1 ) structure. Of the ( 3 × 3 ) periodic bands observed in thick films, four of them are well explained by the folding of the ( 1 × 1 ) bands into a ( 3 × 3 ) periodicity. Regarding the other band, the three ( 3 × 3 ) periodic bands would originate from the electronic states related to the inner Si layers that form a ( 3 × 3 ) structure, and the one observed in the 3.0 ML film only might originate from the electron located at the interface between bulk Si and the Dy silicide film.

Structural and electronic properties of rare earth silicide nanowires on Si(557)

We report on the atomic structure and electronic properties of self-organized dysprosium and erbium silicide nanowires on Si(557), studied using scanning tunneling microcopy and angle-resolved photoelectron spectroscopy. The nanowires were prepared by deposition of different rare earth amounts and subsequent annealing for silicide formation. Due to the stepped structure of the Si(557) surface, nanowires form along the step edges, showing a variety of structurally and electronically different types, depending on the preparation conditions. At submonolayer dysprosium coverages, different chainlike structures dominate, showing one-dimensional dispersion with half-metallic properties. These nanowire regions are separated by $7\ifmmode\times\else\texttimes\fi{}7$ reconstructed Si(111) facets or submonolayer dysprosium silicide patches on these facets. At monolayer coverages, in contrast, mainly nanowires with lengths exceeding $1\text{ }\ensuremath{\mu}\text{m}$ and widths of a few nanometers are found, forming on the (111) facets of the Si(557) surface. Their electronic properties are characterized by a two-dimensional band structure with strong dispersion both parallel and perpendicular to the nanowires and clear metallic behavior, and it is demonstrated that they are formed from hexagonal ${\text{DySi}}_{2}$ monolayers. In the case of thicker silicide layers, metallic nanowires form again on the Si(111) facets, but with clear structural and electronic characteristics of hexagonal ${\text{Dy}}_{3}{\text{Si}}_{5}$ multilayers. At these coverages, additional structures are found, which show an intense signal in the photoelectron spectroscopy data. Related experiments on the growth of erbium silicides indicated the formation of very similar nanowire structures.

Formation of dysprosium silicide nanowires on Si(557) with two-dimensional electronic structure

The self-organized growth of dysprosium silicide nanowires on Si(557) has been studied using scanning tunneling microcopy and angle-resolved photoelectron spectroscopy. The nanowires grow on the (111) facets of the Si(557) surface with lengths exceeding 1000 nm and widths of 3–5 nm. Their metallic electronic structure shows a two-dimensional behavior with a strong dispersion, which is both parallel and perpendicular to the nanowires. For Dy coverages of around 2 Å, it is demonstrated that the nanowires consist of hexagonal DySi2 monolayers, while at higher coverages they are predominantly formed from Dy3Si5 multilayers.

Dysprosium disilicide nanostructures on silicon(001) studied by scanning tunneling microscopy and transmission electron microscopy

The microstructure of self-assembled dysprosium silicide nanostructures on silicon(001) has been studied by scanning tunneling microscopy and transmission electron microscopy. The studies focused on nanostructures that involve multiple atomic layers of the silicide. Cross-sectional high resolution transmission electron microscopy images and fast Fourier transform analysis showed that both hexagonal and orthorhombic/tetragonal silicide phases were present. Both the magnitude and the anisotropy of lattice mismatch between the silicide and the substrate play roles in the morphology and epitaxial growth of the nanostructures formed.

Faulted surface layers in dysprosium silicide nanowires

The crystallography and microstructure of epitaxial dysprosium silicide nanowires on Si(001) have been studied using high-resolution transmission electron microscopy. Islands grown at $750\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ have a compact three-dimensional shape and are identified as hexagonal $\mathrm{Dy}{\mathrm{Si}}_{2}$. Islands grown at $650\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ have an elongated nanowire (NW) shape. They contain one or two layers of hexagonal silicide at the buried interface and two to three surface layers with faulted stacking similar to tetragonal $\mathrm{Dy}{\mathrm{Si}}_{2}$. The faulted layers are believed to provide stress relief during growth of the coherently strained NW islands.

Structural studies of two- and three-dimensional dysprosium silicides using medium-energy ion scattering

Medium-energy ion scattering has been used to determine the atomic structure of two-dimensional and three-dimensional (3D) dysprosium silicide films on the Si(1 1 1) surface. A quantitative study of the ion yield from the dysprosium has enabled the positions of the atoms in the top three layers of the Si(1 1 1)1×1–Dy to be precisely determined. For the case of the Si(1 1 1)(√3×√3) R30°–Dy 3D silicide surface the experimental blocking curves are in agreement with simulations for the structural model determined by surface X-ray diffraction for the Si(1 1 1)(√3×√3) R30°–Er 3D silicide surface. A contraction of 2.0±0.6% in the c-axis lattice constant compared to bulk dysprosium disilicide is found.

Structure of DySi2 nanowires on Si(001)

Free-standing dysprosium–silicide nanowires can be formed on Si(001) by self assembly. It is shown that the wires consist of anisotropically strained hexagonal DySi2 with the c axis aligned perpendicular to the wires. The surface is characterized by a 2×1 reconstruction due to the formation of Si dimer chains.

Epitaxial dysprosium silicide films on silicon: growth, structure and electrical properties

Dysprosium silicide layers were grown epitaxially on Si(100) and (111). Electron microscopy results showed that DySi 2− x layers grown on Si(100) have tetragonal crystalline structure and on Si(111) are hexagonal. Electrical resistivity measurements show that the two crystalline phases of DySi 2− x are metallic and have slightly different electronic and magnetic properties.

Growth and electronic structure of dy silicide on Si(111)

We report on a study of core-level photoemission spectroscopy and scanning tunneling microscopy of dysprosium silicide grown on n-type Si(111). The structure of the silicide was found to be different for submonolayers and thicker films. In the monolayer regime, an extremely low Schottky-barrier height was observed.

In situ characterization of epitaxially grown thin layers.

A method of characterization of ultrathin layers based on analysis of reflection high-energy electron diffraction (RHEED) azimuthal plots using dynamical diffraction theory is presented. Dysprosium silicide thin films are grown on a Si(111)-7\ifmmode\times\else\texttimes\fi{}7 substrate. Layers obtained following deposition of Dy on a hot (600 \ifmmode^\circ\else\textdegree\fi{}C) substrate demonstrate a high-quality crystallographic structure. RHEED azimuthal plots collected experimentally for those samples at Bragg reflections show reproducible fine structure. A series of calculations is carried out to analyze the experimental data, and detailed agreement is found between the numerical and measured azimuthal plots. The structure below the surface resembles bulk ${\mathrm{DySi}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$ with alternate planes of Dy and Si. At the surface the structure is terminated with Si atoms which, however, do not form a single plane (as in the bulk) but form two subplanes separated by a distance of about 0.5 \AA{}. It is concluded that analysis of RHEED azimuthal plots can be very useful for simple in situ characterization of growing layers. \textcopyright{} 1996 The American Physical Society.

Direct observation of rare-earth silicide epilayer formation by RHEED technique

The solid phase reaction of yttrium thin film and silicon substrate was investigated in situ with help of RHEED technique. For the first time, we have measured directly yttrium silicide formation temperature which can be as low as 120 °C for a thin (60 Å) metal layer deposited on a Si(111) substrate. For this purpose, we developed a new experimental technique. A study of the growth of thin (10–150 Å) silicon overlayers on yttrium and dysprosium silicide films epitaxially grown on Si(111) was also made. In this paper, an in situ reflection high energy electron diffraction (RHEED) pattern and also azimuthal plot investigation of Si/RE-silicide/Si double heterostructures grown by solid phase epitaxy and reactive deposition method are presented.