Zhian He

Dysprosium silicide nanowires on Si(110)

Dysprosium deposited on Si(110) at 720 °C is observed to form self-assembled silicide nanowire (NW) structures with a single orientation and average dimensions of 15 nm wide and microns long. The NW sides grow into the substrate along inclined Si{111} planes, forming a V-shaped cross section with an interface that is coherent on one side, described by DySi2(0001)//Si(111_) and DySi2[011_0]//Si[1_10], and incoherent on the other. This type of growth represents a physical mechanism for self-assembled NW formation that does not require anisotropic lattice mismatch.

Epitaxial titanium silicide islands and nanowires

The growth of titanium silicide islands formed by reactive deposition of Ti on Si(1 1 1) at T � 850 C has been studied using atomic force microscopy and transmission electron microscopy. The predominant shape is very long and narrow, and can be considered to be a nanowire (NW). Other flat-topped structures coexist with the NWs, including small equilateral triangles and large rectangular plates. Most NWs are oriented along Sih 220 i directions, with typical dimensions 20 nm wide, 10 nm high and several microns long. A minority of NWs are oriented along Sih 224 i. These latter tend to break up into chains of small segments with regular size and spacing. Growth at lower temperature or higher deposition rate results in smaller and more numerous NWs. Length appears to be limited by intersection with other NWs oriented 120 apart. The junction between NWs appears to be incoherent in most cases. The triangular islands are positively identified as fully relaxed C54 TiSi2, while the chains are relaxed C49 TiSi2. The dominant NW structure is incommensurate and is tentatively identified as C49 TiSi2. 2002 Elsevier Science B.V. All rights reserved.

Structure and orientation of epitaxial titanium silicide nanowires determined by electron microdiffraction

The crystal structure and epitaxial orientation of self-assembled titanium silicide nanowires (NWs) on Si (111) is determined using transmission electron microdiffraction. The NWs are formed by deposition of ∼1 monolayer Ti on Si(111) at ∼850 °C. Type 1 NWs are oriented with long axis along Si〈2-20〉 and are identified as C49 TiSi2. The most common orientation is C49 [01-3] || Si [112] and C49 (200) || Si (2-20), but several other orientations are also found. Type 2 NWs are oriented with long axis along Si〈224〉 and are identified as B27 TiSi, with orientation B27 [02-1] || Si [111] and B27 (-312) || Si (22-4) + 4°. Most of the NWs are incommensurate and fully strain relaxed. They generally extend below the surface with inclined incoherent interfaces.

Signatures of quantum transport in self-assembled epitaxialnickel silicide nanowires

We have measured the electrical properties of self-assembled epitaxial NiSi2 nanowires (NWs) formed on Si substrates. We find quantum corrections due to weak antilocalization and electron–electron interactions. Analysis of the magnetoresistance indicates that electron phase coherence in the NWs is limited by Nyquist dephasing below 10K, and by electron–phonon scattering at higher temperatures. The phase-breaking and spin–orbit scattering lengths are found to be ∼45nm and 3–7nm, at 4.2K, respectively, similar to reports for thin NiSi2 films.

Epitaxial DySi2 nanowire formation on stepped Si(111)

We report the growth of epitaxial DySi2 nanowires (NW) with a single orientation on miscut Si(111). Using high-resolution electron microscopy, we determine that the islands are hexagonal DySi2 with orientation DySi2(0001)‖Si(111), corresponding to a near-perfect lattice match. The NW islands develop extended defects that correlate perfectly with individual step bunches at the buried interface, produced during growth. By contrast, islands grown on step-free substrates develop a broad, two-dimensional shape with no defects. We suggest that the NW shape results from the energy cost of extended defects, which inhibits growth across step edges.

In situ observations of endotaxial growth of CoSi2 nanowires on Si(110) using ultrahigh vacuum transmission electron microscopy

We report in situ observations of the growth of endotaxial CoSi(2) nanowires on Si(110) using an ultrahigh vacuum transmission electron microscope with a miniature electron-beam deposition system located above the pole-piece of the objective lens. Metal deposition at 750-850 °C results in formation of coherently strained silicide nanowires with a fixed length/width (L/W) aspect ratio that depends strongly on temperature. Both dimensions evolve with time as L, W ∼ t(1/3). To explain this behavior, we propose a fixed-shape growth mode based on thermally activated facet-dependent reactions. A second growth mode is also observed at 850 °C, with dimensions that evolve as L ∼ t and W ∼ constant. This mode is accompanied by formation of an array of dislocations. We expect that other endotaxial nanowire systems will follow coherently strained growth modes with similar geometrical constraints, as well as dislocated growth modes with different growth kinetics.