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synht

木虫 (正式写手)

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虫号: 237969
注册: 2006-04-04
性别: GG
专业: 中西医结合基础理论

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As seen in Fig. 2a, for the nanowires with diameter less
than 1 nm, the heats of formation for the different directions
are close to each other, showing no preferential
growth direction in this size range. As wire diameter further
increases, the preferential growth direction becomes
clear. Formation of Si nanowires along the [100] direction
costs the most energy, whereas the [111] and [112] directions
correspond to the smallest heat of formation. This
is in agreement with experimental observations [7,14] and
explains why [100] growth direction was found to be less
favorable than the [111] and [112] directions. Indeed, the
most commonly reported growth directions in literatures
are [111], [11 2] and [110] [1–4,7,14]. The thinnest hydrogenated
SiNWs in experiments, with 1 nm diameter, are oriented
along the [112] direction [7].
In addition to the [100] nanowires with quadrangular
cross-section and four (110) lateral surfaces shown in
Fig. 1, we also considered a series of [10 0] nanowires with
the octagonal cross-section, which have four (11 0) and
four (100) lateral surfaces, to further examine the effect
of morphology on the nanowires stability. After full optimization,
the heats of formation for the octagonal [10 0]
nanowires with 1.152 and 1.736 nm in diameters are 0.09
and 0.07 eV/atom, respectively, higher than those of the
quadrangular [100] nanowires with the same diameter by
0.066 and 0.058 eV/atom, respectively. The heat of formation
per atom for the octagonal [100] nanowire with
2.11 nm in diameter is 0.06 eV, higher than that of the quadrangular
[100] nanowires with a diameter of 2.0 nm by
0.05 eV. Thus, the [100] nanowires with the quadrangular
cross-section seems to be energetically favorable even with
four sharp edges.

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