Direct Measurements of Island Growth and Step-Edge Barriers in Colloidal Epitaxy

Ganapathy, Rajesh; Buckley, Mark R.; Gerbode, Sharon J.; Cohen, Itai

doi:10.1126/science.1179947

Cited by 110 publications

(137 citation statements)

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“…Owing to the close similarity in the physics of GBs across diverse systems (4,8,27,37), we expect our results can be extended to atomic and block copolymeric polycrystals as well. Further, by combining the temperature-tunability of PNIPAm colloids with template-directed growth (25,41), in principle it should be possible to design bicrystals and polycrystals of controlled grain crystallography and size and investigate their response to shear deformation. More importantly, our experiments exemplify a multiscale approach that can be applied readily to elucidate fundamental as well as technologically relevant phenomena, such as grain rotation and coalescence, GB sliding, and texture evolution in driven polycrystals.…”

Section: Discussionmentioning

confidence: 99%

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Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Gokhale

Nagamanasa

Santhosh

et al. 2012

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

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The fabrication of functional materials via grain growth engineering implicitly relies on altering the mobilities of grain boundaries (GBs) by applying external fields. Although computer simulations have alluded to kinetic roughening as a potential mechanism for modifying GB mobilities, its implications for grain growth have remained largely unexplored owing to difficulties in bridging the widely separated length and time scales. Here, by imaging GB particle dynamics as well as grain network evolution under shear, we present direct evidence for kinetic roughening of GBs and unravel its connection to grain growth in driven colloidal polycrystals. The capillary fluctuation method allows us to quantitatively extract shear-dependent effective mobilities. Remarkably, our experiments reveal that for sufficiently large strains, GBs with normals parallel to shear undergo preferential kinetic roughening, resulting in anisotropic enhancement of effective mobilities and hence directional grain growth. Single-particle level analysis shows that the mobility anisotropy emerges from strain-induced directional enhancement of activated particle hops normal to the GB plane. We expect our results to influence materials fabrication strategies for atomic and block copolymeric polycrystals as well.colloids | grain boundary migration | anisotropic grain growth T he motion and rearrangement of grain boundaries (GBs) is central to our understanding of recrystallization (1), grain growth and its stagnation (2), and superplasticity (3) in a broad class of polycrystalline materials including metals (4), ceramics (5), colloidal crystals (6), and block copolymers (7,8). Polycrystals are pervasive as engineering materials and elucidating mechanisms that determine the structure and dynamics of their GBs continue to be a central goal of materials research (9). Advances in computer simulation methods (2, 10, 11) and experiments (12, 13) have provided substantial insights into the microscopic origins of these mechanisms. In conventional materials, nevertheless, establishing a direct link between the dynamics at the single/few atom length scale and the collective behavior of the many thousands of atoms that constitute GBs and grains poses a serious challenge (14).A bridging of length scales is vital for grain growth studies. The key parameter in grain growth and its stagnation is the mobility of GBs, which is determined by their roughness (2, 15). Although transmission electron microscopy (TEM) is well-suited for grain growth measurements, no technique exists that can nonintrusively quantify the atomic scale roughness of buried GBs (14). These experimental shortcomings are compounded in driven polycrystals, which assume practical significance in the fabrication of functional materials via grain growth engineering (2, 7). Driven GBs (16) are thought to kinetically roughen (17), which may result in significantly enhanced mobilities (15) and influence grain growth. Further, in nanocrystalline materials, which often possess superior mechanical propert...

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Section: Discussionmentioning

confidence: 99%

“…Most strikingly, by imaging the GB network under shear, we show that this shear-induced anisotropy in the mobility leads to directional grain growth. Because colloid models are valuable analogs of atomic systems (23)(24)(25)(26)(27), insights gained from the present studies should be relevant for atomic and block copolymeric polycrystals as well.…”

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confidence: 99%

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Gokhale

Nagamanasa

Santhosh

et al. 2012

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

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“…10,11 In particular, submicrometre silica spheres easily build inexpensive and versatile high-quality face-centered-cubic (fcc) ensembles. 12 These silica opals can contain a significant amount of physisorbed molecular water within the network formed between particles (depending on the silica hydrophilicity, up to ∼8 wt % under standard laboratory conditions 13,14 ).…”

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Nanoscale Morphology of Water in Silica Colloidal Crystals

Blanco

Gallego-Gómez

López

2013

J. Phys. Chem. Lett.

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We show a simple method to visualize the morphology of water adsorbed within the pore network of colloidal crystals made of submicrometer silica spheres. Water is replicated into silica by modified silicon tetrachloride hydrolysation under standard ambient conditions, making it visible to standard electronic microscopy and thus allowing one to discern the original water distribution. Different distribution patterns are identified depending on the water content, surface condition, and spheres arrangement. The dimension and shape of wetting layers (covering the submicrometer spheres) and capillary bridges (joining them) are measurable at the nanoscale. We finally use these findings to demonstrate proof-of-principle of fabrication of isolated and freestanding silica nanorings by using hydrophobic polymeric templates and selective etching. SECTION: Physical Processes in Nanomaterials and NanostructuresH ow water distributes between solid particles drastically affects the physical properties of many colloidal and granular systems present in nature. 1−3 Direct visualization is an ideal tool for exploring the liquid morphology in such environments, but it has revealed a very difficult task, especially in three-dimensional cases and at ever-smaller scales. 4 Progress has been accomplished in at best submillimeter range using wetting liquids different than water or immersion fluids replacing the air to achieve enough contrast 5,6 and demanding techniques such as X-ray microtomography. 7 These critical drawbacks preclude the study of the most natural case: air and water between small particles. Here we demonstrate a straightforward method to visualize water distributed within the pore network between submicrometre spheres down to the nanoscale. Thereby, water is aimed to be faithfully replicated into silica by modified chemical vapor deposition (CVD) under standard ambient conditions, which can be then inspected by standard field emission scanning electron microscopy (FESEM), so the original water morphology can be discerned. To prove our method, we use colloidal crystals, a well-described system whose properties facilitate cross-checking, exploring the limits of the technique and expanding the available morphological description of such test systems. Specifically, colloidal silica is chosen because of its ability to adsorb water, versatile surface chemistry, and biocompatibility. Differences in the distribution pattern are explored under diverse spheres arrangements, silica surface hydrophilicity and ambient conditions. The morphology of the water structures (wetting layers on the spheres and capillary bridges between them) are quantifiable at the nanoscale. Calculation of the capillary forces, which depend on the accurate determination of these geometrical parameters, 8 is provided. This will allow comparison with experimental measurements by other techniques and testing of theoretical aspects not entirely understood at this scale. Finally, we use the one-pulse CVD technique on polymeric templates to demonstra...

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“…Theoretical distributions are frequently compared to experimental data from various materials and processes or with simulation data from atomistic models, providing estimates of parameters such as critical nucleus sizes and binding energies. Recent works on submonolayer growth of organic molecules [5][6][7] and colloidal epitaxy [8] increase the interest in the subject for the possibility of extending the knowlegde on atomic epitaxy.However, the exact forms of the CZD and ISD still remain unknown and, consequently, the basic mechanisms governing their kinetics are unclear. Most theoretical approaches assume irreversible aggregation of adatoms to islands whose size exceeds a critical value i.…”

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Scaling of island size and capture zone distributions in submonolayer growth

Oliveira

Reis

2011

Phys. Rev. B

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Island size and capture zone distributions (ISD, CZD) are studied numerically in submonolayer growth with various critical island sizes and shapes. CZD scaled by the variance show excellent agreement with the Wigner surmise, confirming the Pimpinelli-Einstein approach for large CZs / large island dynamics. The ISD decay as exp (−s γ ), with γ = 4, ≈ 2.4 and 2 for point, fractal, and square islands, respectively. A scaling approach explains the values of γ from the Gaussian decay of CZD and the efficiency of islands to capture diffusing adatoms. Since island nucleation in the submonolayer regime determines several features of the subsequent growth of a thin film [1][2][3][4], it motivated many theoretical works to explain the island size distributions (ISD) and the capture zone distributions (CZD). Theoretical distributions are frequently compared to experimental data from various materials and processes or with simulation data from atomistic models, providing estimates of parameters such as critical nucleus sizes and binding energies. Recent works on submonolayer growth of organic molecules [5][6][7] and colloidal epitaxy [8] increase the interest in the subject for the possibility of extending the knowlegde on atomic epitaxy.However, the exact forms of the CZD and ISD still remain unknown and, consequently, the basic mechanisms governing their kinetics are unclear. Most theoretical approaches assume irreversible aggregation of adatoms to islands whose size exceeds a critical value i.Important examples are that of Amar and Family (AF), who proposed an empirical formula for the ISD [9], the Mulheran and Blackman (MB) approach to relate ISD to distributions of areas of Voronoi polygons [10], and the recent proposal of Pimpinelli and Einstein (PE)[11] that CZD are described by the Wigner surmise (WS) from random matrix theory [12].The AF formula is widely used to fit the peaks of experimental ISD and to estimate critical island sizes (see e. g. Ref.[13]), but deviations from point island model distributions are significant [1,14]. The solution of equations from the MB approach provides ISD very close to point island model simulations, but it is not so popular as the AF formula for fitting experimental data. The WS works better than the MB curves for fitting simulated CZD of point and circular islands [11], but recent numerical work by Amar and Evans groups [15,16] showed deviations in the peaks and in the left tails. Alternatively, a Gamma distribution was used to fit CZD [17].Here we will analyze very accurate simulation data of ISD and CZD of growth models of point and extended (fractal and square) islands with irreversible aggregation (i = 1 and 2). The CZD are fitted by the WS after rescaling by the variance, which reduces deviations in the peaks and left tails and hightlights the Gaussian right tail predicted by PE for all island shapes. The ISD shows deviations from the AF formula, but have universal right tail decays dependent on the island shape and related to the Gaussian CZD. This confirms the PE ...

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Direct Measurements of Island Growth and Step-Edge Barriers in Colloidal Epitaxy

Cited by 110 publications

References 32 publications

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

Nanoscale Morphology of Water in Silica Colloidal Crystals

Scaling of island size and capture zone distributions in submonolayer growth

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