Mechanism of the nanoscale localization of Ge quantum dot nucleation on focused ion beam templated Si(001) surfaces

Portavoce, A.; Kammler, M.; Hull, R.; Reuter, M. C.; Ross, FM

doi:10.1088/0957-4484/17/17/028

Cited by 53 publications

(51 citation statements)

References 25 publications

(56 reference statements)

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“…Topography is known to promote crystallization directly from a vapor (2)(3)(4)(5), because these systems typically exhibit low contact angles. Crystallization from the melt, in contrast, is associated with very high contact angles such that topography is usually ineffective (6).…”

mentioning

confidence: 99%

Observing the formation of ice and organic crystals in active sites

Campbell

Meldrum

Christenson

2016

Proc. Natl. Acad. Sci. U.S.A.

112

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Heterogeneous nucleation is vital to a wide range of areas as diverse as ice nucleation on atmospheric aerosols and the fabrication of high-performance thin films. There is excellent evidence that surface topography is a key factor in directing crystallization in real systems; however, the mechanisms by which nanoscale pits and pores promote nucleation remain unclear. Here, we use natural cleavage defects on Muscovite mica to investigate the activity of topographical features in the nucleation from vapor of ice and various organic crystals. Direct observation of crystallization within surface pockets using optical microscopy and also interferometry demonstrates that these sharply acute features provide extremely effective nucleation sites and allows us to determine the mechanism by which this occurs. A confined phase is first seen to form along the apex of the wedge and then grows out of the pocket opening to generate a bulk crystal after a threshold saturation has been achieved. Ice nucleation proceeds in a comparable manner, although our resolution is insufficient to directly observe a condensate before the growth of a bulk crystal. These results provide insight into the mechanism of crystal deposition from vapor on real surfaces, where this will ultimately enable us to use topography to control crystal deposition on surfaces. They are also particularly relevant to our understanding of processes such as cirrus cloud formation, where such topographical features are likely candidates for the "active sites" that make clay particles effective nucleants for ice in the atmosphere.nucleation | confinement | topography | pores | active sites T he growth of a new phase is almost always dependent on a nucleation event. Nucleation is therefore fundamental to a number of processes including crystallization, freezing, condensation, and bubble formation and is typically described in terms of classical nucleation theory. However, because this theory was developed to describe the nucleation of liquid droplets in vapor it cannot give a complete understanding of all nucleation processes, and in particular the formation of crystalline materials. Nucleation in the real world is also usually heterogeneous, occurring on seeds, impurities, or container surfaces. Although simple models consider nucleation to occur on perfectly flat, uniform surfaces, it is clear that real surfaces inevitably vary in chemistry and topography. We focus here on the effects of surface topography. Classical nucleation theory predicts a lower free energy barrier to nucleation in surface cracks or pores on the length scale of a critical nucleus (1). The extent of the reduction is contact-angle-dependent, such that nuclei with a low contact angle experience a more significant reduction from topography.Topography is known to promote crystallization directly from a vapor (2-5), because these systems typically exhibit low contact angles. Crystallization from the melt, in contrast, is associated with very high contact angles such that topography is usually ineff...

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mentioning

confidence: 99%

Observing the formation of ice and organic crystals in active sites

Campbell

Meldrum

Christenson

2016

Proc. Natl. Acad. Sci. U.S.A.

112

View full text Add to dashboard Cite

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“…This is in strong contrast to the previous reports on directed self-assembly of Ge using pit patterns where the formation occurs preferentially within the pits. 23,[27][28][29][30] Furthermore, we find that the patterns where optimal QD formation occurs are not in fact composed of isolated pits in the flat (001) terrace; rather, the surface appears to be continuously height modulated with no flat terrace regions between the pits. The striking resemblance between the before/after micrographs raises the question of whether Ge QDs are self-assembling, or instead, Ge just conformally coats the patterned Si surface.…”

Section: Resultsmentioning

confidence: 74%

“…27 The growth of Ge QDs in the TEM was accomplished using chemical vapor deposition at 550°C. For optimal patterning dose and postannealing conditions, small Ge QDs % 20 nm in diameter are obtained, on ultrasmall pits found (by ex situ AFM) to be only 10 nm in diameter, 1 nm deep, and 200 nm apart.…”

Section: Discussionmentioning

confidence: 99%

Highly uniform arrays of epitaxial Ge quantum dots with interdot spacing of 50 nm

Duska

Floro

2014

J. Mater. Res.

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Periodic, highly uniform arrays of dome-like Ge quantum dots (QDs) with 50 nm interdot pitch have been achieved on Si (001). The Si surface was patterned using ultra-low-dose focused ion beam and defect-selective etching, resulting in a continuously height-modulated, "egg-carton" morphology. The directed self-assembly process is robust, occurring across a range of ion doses, growth temperatures, and deposition rates. By selectively etching off the Ge dots to reveal the underlying Si surface just prior to Ge growth, we showed that Ge QDs preferentially formed on crowns (regions of negative curvature) rather than pits (regions of positive curvature) as is mostly seen in the literature. The width of the QD size distribution mimics that of the underlying substrate pattern, indicative of a complete lack of coarsening during the Ge growth, despite the small length scales, and extensive mass transport leading to QD formation.

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“…QDMCs of this description have been fabricated using EUV lithography. [7,19,74] Our first step was to develop a process using focused ion beam patterning to control the initial QD layer, [22,24,25,80,83] and then develop the necessary growth protocols to extend the QDMC in the third dimension. Specific challenges include: directing nucleation at reduced length scales, i.e.…”

Section: Scanning Electron Microscopy (Sem)mentioning

confidence: 99%

“…Modification of the surface has been achieved by means of lithography, [18][19][20] nano-indentation [21] and ion-beam processing. [22][23][24][25] The various techniques and experiments cover a large range of surface features to direct the growth including pits, [18,19,22] stripes, [26][27][28] mesas, [29,30] and oxide windows, [31] as well as a wide range of QD areal density, growth temperatures, composition and deposition thickness. We have investigated the use of a Ga+ focused ion beam (FIB) to direct write patterns on Si (001) surfaces to direct precise positioning of Ge QDs at sub-100 nm lengthscales.…”

Section: Introductionmentioning

confidence: 99%

Towards Directed Self-Assembly of Quantum Dot Mesocrystals of Ge/Si Using Focused Ion Beam Patterning

Duska

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Mechanism of the nanoscale localization of Ge quantum dot nucleation on focused ion beam templated Si(001) surfaces

Cited by 53 publications

References 25 publications

Observing the formation of ice and organic crystals in active sites

Observing the formation of ice and organic crystals in active sites

Highly uniform arrays of epitaxial Ge quantum dots with interdot spacing of 50 nm

Towards Directed Self-Assembly of Quantum Dot Mesocrystals of Ge/Si Using Focused Ion Beam Patterning

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