Publications by authors named "Zainul Aabdin"

10 Publications

  • Page 1 of 1

Dynamics of thin precursor film in wetting of nanopatterned surfaces.

Proc Natl Acad Sci U S A 2021 Sep;118(38)

Department of Physics, National University of Singapore, Singapore 117551;

The spreading of a liquid droplet on flat surfaces is a well-understood phenomenon, but little is known about how liquids spread on a rough surface. When the surface roughness is of the nanoscopic length scale, the capillary forces dominate and the liquid droplet spreads by wetting the nanoscale textures that act as capillaries. Here, using a combination of advanced nanofabrication and liquid-phase transmission electron microscopy, we image the wetting of a surface patterned with a dense array of nanopillars of varying heights. Our real-time, high-speed observations reveal that water wets the surface in two stages: 1) an ultrathin precursor water film forms on the surface, and then 2) the capillary action by nanopillars pulls the water, increasing the overall thickness of water film. These direct nanoscale observations capture the previously elusive precursor film, which is a critical intermediate step in wetting of rough surfaces.
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http://dx.doi.org/10.1073/pnas.2108074118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8463872PMC
September 2021

Nanoscale Elastocapillary Effect Induced by Thin-Liquid-Film Instability.

J Phys Chem Lett 2020 Apr 24;11(7):2751-2758. Epub 2020 Mar 24.

Centre for BioImaging Sciences and Department of Biological Sciences, National University of Singapore, Singapore 117557, Singapore.

Dense arrays of high-aspect-ratio (HAR) vertical nanostructures are essential elements of microelectronic components, photovoltaics, nanoelectromechanical, and energy storage devices. One of the critical challenges in manufacturing the HAR nanostructures is to prevent their capillary-induced aggregation during solution-based nanofabrication processes. Despite the importance of controlling capillary effects, the detailed mechanisms of how a solution interacts with nanostructures are not well understood. Using liquid cell transmission electron microscopy (TEM), we track the dynamics of nanoscale drying process of HAR silicon (Si) nanopillars in real-time and identify a new mechanism responsible for pattern collapse and nanostructure aggregation. During drying, deflection and aggregation of nanopillars are driven by thin-liquid-film instability, which results in much stronger capillary interactions between the nanopillars than the commonly proposed lateral meniscus interaction forces. The importance of thin-film instability in dewetting has been overlooked in prevalent theories on elastocapillary aggregation. The new dynamic mechanism revealed by visualization is essential for the development of robust nanofabrication processes.
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http://dx.doi.org/10.1021/acs.jpclett.0c00218DOI Listing
April 2020

Transient Clustering of Reaction Intermediates during Wet Etching of Silicon Nanostructures.

Nano Lett 2017 05 26;17(5):2953-2958. Epub 2017 Apr 26.

Department of Physics, National University of Singapore , 117551, Singapore.

Wet chemical etching is a key process in fabricating silicon (Si) nanostructures. Currently, wet etching of Si is proposed to occur through the reaction of surface Si atoms with etchant molecules, forming etch intermediates that dissolve directly into the bulk etchant solution. Here, using in situ transmission electron microscopy (TEM), we follow the nanoscale wet etch dynamics of amorphous Si (a-Si) nanopillars in real-time and show that intermediates generated during alkaline wet etching first aggregate as nanoclusters on the Si surface and then detach from the surface before dissolving in the etchant solution. Molecular dynamics simulations reveal that the molecules of etch intermediates remain weakly bound to the hydroxylated Si surface during the etching and aggregate into nanoclusters via surface diffusion instead of directly diffusing into the etchant solution. We confirmed this model experimentally by suppressing the formation of nanoclusters of etch intermediates on the Si surfaces by shielding the hydroxylated Si sites with large ions. These results suggest that the interaction of etch intermediates with etching surfaces controls the solubility of reaction intermediates and is an important parameter in fabricating densely packed clean 3D nanostructures for future generation microelectronics.
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http://dx.doi.org/10.1021/acs.nanolett.7b00196DOI Listing
May 2017

Nanodroplet-Mediated Assembly of Platinum Nanoparticle Rings in Solution.

Nano Lett 2016 Feb 7;16(2):1092-6. Epub 2016 Jan 7.

Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551.

Soft fluidlike nanoscale objects can drive nanoparticle assembly by serving as a scaffold for nanoparticle organization. The intermediate steps in these template-directed nanoscale assemblies are important but remain unresolved. We used real-time in situ transmission electron microscopy to follow the assembly dynamics of platinum nanoparticles into flexible ringlike chains around ethylenediaminetetraacetic acid nanodroplets dispersed in solution. In solution, these nanoring assemblies form via sequential attachment of the nanoparticles to binding sites located along the circumference of the nanodroplets, followed by the rearrangement and reorientation of the attached nanoparticles. Additionally, larger nanoparticle ring assemblies form via the coalescence of smaller ring assemblies. The intermediate steps of assembly reported here reveal how fluidlike nanotemplates drive nanoparticle organization, which can aid the future design of new nanomaterials.
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http://dx.doi.org/10.1021/acs.nanolett.5b04323DOI Listing
February 2016

Hydration Layer-Mediated Pairwise Interaction of Nanoparticles.

Nano Lett 2016 Jan 4;16(1):786-90. Epub 2016 Jan 4.

Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore, 117551.

When any two surfaces in a solution come within a distance the size of a few solvent molecules, they experience a solvation force or a hydration force when the solvent is water. Although the range and magnitude of hydration forces are easy to characterize, the effects of these forces on the transient steps of interaction dynamics between nanoscale bodies in solution are poorly understood. Here, using in situ transmission electron microscopy, we show that when two gold nanoparticles in water approach each other at a distance within two water molecules (∼5 Å), which is the combined thickness of the hydration shell of each nanoparticle, they form a sterically stabilized transient nanoparticle dimer. The interacting surfaces of the nanoparticles come in contact and undergo coalescence only after these surfaces are fully dehydrated. Our observations of transient steps in nanoparticle interactions, which reveal the formation of hydration layer mediated metastable nanoparticle pairs in solution, have significant implications for many natural and industrial processes.
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http://dx.doi.org/10.1021/acs.nanolett.5b04808DOI Listing
January 2016

Nanodroplet Depinning from Nanoparticles.

ACS Nano 2015 Sep 24;9(9):9020-6. Epub 2015 Aug 24.

Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551.

Nanoscale defects on a substrate affect the sliding motion of water droplets. Using in situ transmission electron microscopy imaging, we visualized the depinning dynamics of water nanodroplets from gold nanoparticles on a flat SiNx surface. Our observations showed that nanoscale pinning effects of the gold nanoparticle oppose the lateral forces, resulting in stretching, even breakup, of the water nanodroplet. Using continuum long wave theory, we modeled the dynamics of a nanodroplet depinning from a nanoparticle of comparable length scales, and the model results are consistent with experimental findings and show formation of a capillary bridge prior to nanodroplet depinning. Our findings have important implications on surface cleaning at the nanoscale.
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http://dx.doi.org/10.1021/acsnano.5b03078DOI Listing
September 2015

Bonding pathways of gold nanocrystals in solution.

Nano Lett 2014 Nov 13;14(11):6639-43. Epub 2014 Oct 13.

Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore , 117551.

Nanocrystal bonding is an important phenomenon in crystal growth and nanoscale welding. Here, we show that for gold nanocrystals bonding in solution can follow two distinct pathways: (1) coherent, defect-free bonding occurs when two nanocrystals attach with their lattices aligned to within a critical angle; and (2) beyond this critical angle, defects form at the interfaces where the nanocrystals merge. The critical misalignment angle for ∼10 nm crystals is ∼15° in both in situ experiments and full-atom molecular dynamics simulations. Understanding the origin of this critical angle during bonding may help us predict and manage strain profiles in nanoscale assemblies and inspire techniques toward reproducible and extensible architectures using only basic crystalline blocks.
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http://dx.doi.org/10.1021/nl5032919DOI Listing
November 2014

Nanoparticle dynamics in a nanodroplet.

Nano Lett 2014 24;14(4):2111-5. Epub 2014 Mar 24.

Center for Bioimaging Sciences and Department of Biological Sciences, National University of Singapore , 14 Science Drive 4, Singapore 117543.

We describe the dynamics of 3-10 nm gold nanoparticles encapsulated by ∼30 nm liquid nanodroplets on a flat solid substrate and find that the diffusive motion of these nanoparticles is damped due to strong interactions with the substrate. Such damped dynamics enabled us to obtain time-resolved observations of encapsulated nanoparticles coalescing into larger particles. Techniques described here serve as a platform to study chemical and physical dynamics under highly confined conditions.
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http://dx.doi.org/10.1021/nl500766jDOI Listing
March 2015

Phonon spectroscopy in a Bi2Te3 nanowire array.

Nanoscale 2013 Nov 20;5(21):10629-35. Epub 2013 Sep 20.

Jülich Center for Neutron Science JCNS, Peter Grünberg Institut PGI, JARA-FIT, Forschungszentrum Jülich GmbH, D-52425 Jülich.

The lattice dynamics in an array of 56 nm diameter Bi2Te3 nanowires embedded in a self-ordered amorphous alumina membrane were investigated microscopically using (125)Te nuclear inelastic scattering. The element specific density of phonon states is measured on nanowires in two perpendicular orientations and the speed of sound is extracted. Combined high energy synchrotron radiation diffraction and transmission electron microscopy was carried out on the same sample and the crystallinity was investigated. The nanowires grow almost perpendicular to the c-axis, partly with twinning. The average speed of sound in the 56 nm diameter Bi2Te3 nanowires is ~7% smaller with respect to bulk Bi2Te3 and a decrease in the macroscopic lattice thermal conductivity by ~13% due to nanostructuration and to the reduced speed of sound is predicted.
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http://dx.doi.org/10.1039/c3nr02918bDOI Listing
November 2013

Switching of the natural nanostructure in Bi2Te3 materials by ion irradiation.

Adv Mater 2012 Sep 21;24(34):4605-8. Epub 2012 Jun 21.

Institut für Angewandte Physik, Eberhard Karls Universität Tübingen, Germany.

In Bi(2)Te(3) materials the natural nanostructure (nns) with a wavelength of 10 nm can be reproducibly switched ON and OFF by Ar(+) ion irradiation at 1.5 and 1 keV. Controlled formation of the nns in Bi(2)Te(3) materials has potential for reducing its thermal conductivity and could increase the thermoelectric figure of merit.
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http://dx.doi.org/10.1002/adma.201201079DOI Listing
September 2012
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