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Nanoscale magnetic skyrmions have interesting static and transport properties that make them candidates for future spintronic devices. Control and manipulation of the size and behavior of skyrmions is thus of crucial importance. Using a Ginzburg-Landau approach, we show theoretically that skyrmions and skyrmion lattices can be stabilized by a spatial modulation of the uniaxial magnetic anisotropy in a thin film of centro-symmetric ferromagnet. Remarkably, the skyrmion size is determined by the ratio of the exchange length and the period of the spatial modulation of the anisotropy, at variance with conventional skyrmions stabilized by dipolar and Dzyaloshinskii--Moriya interactions (DMIs)., Comment: 9 pages (single column), 3 figures

A large quantity of nanosized ZnO tubular structures was prepared using a very simple thermal evaporation of mixed Zn–ZnO powders under a wet oxidation condition. The ZnO nanotubes have a hollow core with crystalline wall of 8–20 nm in thickness. Optical properties of ZnO nanotubes were studied at room temperature. Raman peaks arising from the ZnO nanotubes were analyzed, which correspond well to that of the bulk ZnO sample. The photoluminescence measurements of ZnO nanotubes revealed an intensive UV peak at 377 nm corresponding to the free exciton emission, and a broad peak at about 500 nm arising from defect-related emission.

Porous silicon (PS) samples were alternately oxidized in an ozone atmosphere and etched in HF solution. The variation of the corresponding photoluminescence (PL) implies that there is more than one origin responsible for the PL of PS. These results are explained by a multiple source quantum well model, where the nanoscale Si units and their covering oxide layers both contribute to the PL in different situations.

The phase formation during rapid thermal annealing of a Ti/Mo bilayer sequentially deposited on Si substrates has been studied. The Mo layer varied from 0.5 to 2 nm and the Ti layer was always 60 nm thick. The presence of the Mo interposing layer enhances the formation of the C54 of TiSi2 by first forming a Mo‐bearing silicide phase of hexagonal structure. The desired C54 phase then nucleates and grows on top of this Mo‐bearing silicide phase at a temperature as low as 650 °C via Si diffusion through the growing silicide layers. This is about 100 °C lower than what is usually needed for the C49–C54 transformation. The significance of this finding is that the usual route for the formation of TiSi2, i.e., the C49 phase forms as a result of the Ti–Si interaction and the C54 phase forms as the product of phase transformation, is altered by the interposition of a thin refractory metal (here Mo) layer between Ti and Si.

Tungsten (W) films are deposited on sputter‐deposited TiN adhesion layers in a cold‐wall chemical vapor deposition reactor, initiated with the deposition of a W nucleation layer by SiH4 reduction of WF6. H2 is also introduced in the reactor for some depositions. The electrical resistivity and mechanical stress of the W films are found to be dependent on the underlying TiN layers as well as on the presence of H2 during W nucleation layer deposition. A higher resistivity is obtained when the W is deposited on the TiN prepared at 250 °C than on the TiN prepared at 450 °C. For the W deposited on the low‐temperature TiN, the resistivity is reduced by adding H2 to the reactants during W nucleation layer deposition; while for the W deposited on the high‐temperature TiN, the resistivity is almost insensitive to the H2 addition. More oxygen and fluorine are found at the W–TiN interface for the W deposited on the low‐temperature TiN than on the high‐temperature TiN. Introduction of H2 to the reactants during W nucl...

In spite of much work, the formation of epitaxial CoSi2 from Ti/Co on (100) Si remains something of a mystery. It has been proposed that epitaxy occurs via the formation of an intermediate phase of CoSi with a (311) preferred orientation. In the absence of sufficient information it is impossible to validate or to invalidate the specific original claim. However, one shows that the formation of preferably oriented CoSi is not a necessary condition for the subsequent growth of epitaxial CoSi2. Careful measurements of diffraction intensities reveal the probable, temporary formation of a metastable form of CoSi2, based on a diamond cubic rather than the usual CaF2 structure.

Phosphorus doping of polycrystalline silicon by direct diffusion of PH3 at 685 and 785 °C followed by rapid thermal annealing (RTA) has been investigated. Unlike at 785 °C, the dopant profile is not uniform at 685 °C but becomes so after RTA at 1050 °C for 10 s, as revealed by secondary ion mass spectroscopy (SIMS). In the absence of any protection layer, RTA in N2 causes an out‐diffusion of ∼50% of P from the sample diffused at 785 °C, although it activates ∼100% of the remaining P atoms as indicated by Hall and SIMS measurements. In contrast, RTA in O2 results in 95% activation of the incorporated P from the same sample, accompanying an oxidation of ∼7 nm polycrystalline Si. As regards the sample diffused at 685 °C, RTA in N2 does not cause any out‐diffusion but activates less than 80% of the incorporated P atoms. This difference in behavior is attributed to the tendency to attain equilibrium concentrations of P in the crystallites and at the grain boundaries at the RTA temperature. The highest active P...

Contactless and accurate measurement of the temperature is an important issue in rapid thermal processing. In this letter we report on the variation of the emissivity of the surface during chemical vapor deposition of polycrystalline silicon onto oxidized silicon wafers. The observed periodic change in the emissivity of the polycrystalline silicon/silicon dioxide/silicon structure is due to interference phenomena in the growing layer. In these experiments the silicon wafers were heated by direct absorption of microwaves in a single wafer reactor. It is shown that with this method of heating, the change of emissivity does not influence the actual temperature of the substrate.

Mass fabrication of directly accessible, ultralong, uniform Si nanowires is realized by employing a controllable and reproducible method based on standard Si technology. High-conductivity polycrystalline Ni-silicide nanowires around 30 nm by 30 nm in cross section, able to support extremely high currents at ∼108A∕cm2, are obtained by means of solid-state reaction of the Si nanowires with subsequently deposited Ni films. By properly adjusting the Ni film thickness, NiSi, Ni2Si, and Ni31Si12 nanowires characterized with distinct resistivity and temperature coefficient of resistance are obtained. Upon annealing, the electrical continuity of the nanowires breaks at temperatures about 0.7 times the melting points of the silicides.

Lateral growth of Ni silicide towards the channel region of metal-oxide-semiconductor transistors (MOSFETs) fabricated on ultrathin silicon-on-insulator (SOI) is characterized using SOI wafers with a 20-nm-thick surface Si layer. With a 10-nm-thick Ni film for silicide formation, p-channel MOSFETs displaying ordinary device characteristics with silicided p+ source/drain regions were demonstrated. No lateral growth of NiSix under gate isolation spacers was found according to electron microscopy. When the Ni film was 20 nm thick, Schottky contact source/drain MOSFETs showing typical ambipolar characteristics were obtained. A severe lateral encroachment of NiSix into the channel region leading to an increased gate leakage was revealed, while no detectable voiding at the silicide front towards the Si channel was observed.

We report microscopic photoluminescence images and corresponding spectra of epitaxial GaAs on Si substrates, prepared by molecular beam epitaxy. High magnification (3000×) images directly reveal dislocations present in the epilayer. Several substrate orientations are investigated including nominal (001) tilted 4° toward 〈110〉. The GaAs samples include structures grown with and without superlattice buffer layers. Some samples were annealed at several temperatures from 650 to 850 °C. The dislocation density versus depth is studied by varying the optical probe wavelength and by studying samples that had been beveled and etched. In addition, the images and spectra are studied over a wide temperature range.