A Hexagonal (Wurtzite) Form of Silicon

Jennings, Hamlin M.; Richman, M. H.

doi:10.1126/science.193.4259.1242

Cited by 35 publications

(22 citation statements)

References 9 publications

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“…This is particularly true for group IV based materials for which the existence of phases other than the cubic-diamond cannot be achieved in standard conditions. [6][7][8] Nevertheless, in group IV nanowires, the stability of novel polytypes -previously theoretically predicted 9 but experimentally observed only very locally in the form of crystal imperfections [10][11][12][13] is now supported by clear experimental evidences. [14][15][16][17][18][19] For instance, Vincent et al 14 reported the synthesis of quasi-periodic allotrope Ge heterostructures of hexagonal-diamond (wurtzite structure with single atom type) and cubic-diamond domains.…”

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confidence: 90%

Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Amato¹,

Kaewmaraya²,

Zobelli³

et al. 2016

Nano Lett.

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Recent experimental investigations have confirmed the possibility to synthesize and exploit polytypism in group IV nanowires. Driven by this promising evidence, we use first-principles methods based on density functional theory and many-body perturbation theory to investigate the electronic and optical properties of hexagonal-diamond and cubic-diamond Si NWs as well as their homojunctions. We show that hexagonal-diamond NWs are characterized by a more pronounced quantum confinement effect than cubic-diamond NWs. Furthermore, they absorb more light in the visible region with respect to cubic-diamond ones and, for most of the studied diameters, they are direct band gap materials. The study of the homojunctions reveals that the diameter has a crucial effect on the band alignment at the interface. In particular, at small diameters the band-offset is type-I whereas at experimentally relevant sizes the offset turns up to be of type-II. These findings highlight intriguing possibilities to modulate electron and hole separations as well as electronic and optical properties by simply modifying the crystal phase and the size of the junction.

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confidence: 90%

Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Amato¹,

Kaewmaraya²,

Zobelli³

et al. 2016

Nano Lett.

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“…As will be explained below, this type of Si polymorph has been observed in Si submitted to nanoindentation experiments and in nanoparticles nucleated in the gas phase. [8][9][10] Interestingly, two slightly different Si IV structures were observed (see Table 1 for the crystallographic parameters): Si IV A [11] and Si IV B , [12] with 22 % and 78 % of the total NW amount, respectively. However, on NWs with a radius below 10 nm (which in fact represents less than 10 % of the total amount in our samples) we found 44 % of Si I, 44 % of Si IV B , and 12 % of Si IV A NWs.…”

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confidence: 95%

“…In contrast, an error of less than 5 % was obtained when using a crystalline structure similar to the one observed by Jennings and Richman (Si IV B ). [12] The lattice parameters differ from the other wurtzite polymorph Si IV A , for which the calculated fitting errors were greater than 11 %. The c/a ratio in the Si IV B structure is 1.63, which is exactly the same as the c/a ratio reported for a similar form of carbon.…”

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confidence: 98%

Synthesis of Silicon Nanowires with Wurtzite Crystalline Structure by Using Standard Chemical Vapor Deposition

et al. 2007

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“…Prudent approaches should be taken when analyzing nanostructured Si, however, particularly for chemically synthesized samples. In addition to the lattice-fringe-resolved high-resolution (HR) images, the diffraction pattern must be examined with caution using a calibrated camera length, as the difference between various polymorphs can be easily overlooked [4,5,9]. The following discussion pertains to SiNWs prepared by the vapor-liquid-solid (VLS) mechenism, evidenced in Figs.…”

Section: Hrtem Characterization Of Diamond and Wurtzite Sinwsmentioning

confidence: 99%

Kinetically-induced hexagonality in chemically grown silicon nanowires

Liu

Wang

2009

Nano Res.

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Various silicon crystal structures with different atomic arrangements from that of diamond have been observed in chemically synthesized nanowires. The structures are typified by mixed stacking mismatches of closely packed Si dimers. Instead of viewing them as defects, we defi ne the concept of hexagonality and describe these structures as Si polymorphs. The small transverse dimensions of a nanowire make this approach meaningful. Unique among the polymorphs are cubic symmetry diamond and hexagonal symmetry wurtzite structures. Electron diffraction studies conducted with Au as an internal reference unambiguously confi rm the existence of the hexagonal symmetry Si nanowires.Cohesive energy calculations suggest that the wurtzite polymorph is the least stable and the diamond polymorph is the most stable. Cohesive energies of intermediate polymorphs follow a linear trend with respect to their structural hexagonality. We identify the driving force in the polymorph formations as the growth kinetics. Fast longitudinal elongation during the growth freezes stacking mismatches and thus leads to a variety of Si polymorphs. The results are expected to shed new light on the importance of growth kinetics in nanomaterial syntheses and may open up ways to produce structures that are uncommon in bulk materials.

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A Hexagonal (Wurtzite) Form of Silicon

Cited by 35 publications

References 9 publications

Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions

Synthesis of Silicon Nanowires with Wurtzite Crystalline Structure by Using Standard Chemical Vapor Deposition

Kinetically-induced hexagonality in chemically grown silicon nanowires

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