Fabio Grillo

Last Name

Grillo

First Name

Fabio

ORCID

0000-0003-1486-3117

Show all metadata

Search Results

Publications 1 - 10 of 14

Universality of breath figures on two-dimensional surfaces: An experimental study
Stricker, Laura; Grillo, Fabio; Marquez, E.A.; et al. (2022)
Physical Review Research
Droplet condensation on surfaces produces patterns, called breath figures. Their evolution into self-similar structures is a classical example of self-organization. It is described by a scaling theory with scaling functions whose universality has recently been challenged by numerical work. Here, we provide thorough experimental testing, where we inspect substrates with vastly different chemical properties, stiffness, and condensation rates. We critically survey the size distributions and the related time-asymptotic scaling of droplet number and surface coverage. In the time-asymptotic regime, they admit a data collapse: the data for all substrates and condensation rates lie on universal scaling functions.
Selectivity Enhancement for Ruthenium Atomic Layer Deposition in Sub-50 nm Nanopatterns by Diffusion and Size-Dependent Reactivity
Clerix, Jan-Willem J.; Marques, Esteban A.; Soethoudt, Job; et al. (2021)
Advanced Materials Interfaces
Area-selective deposition (ASD) is a promising bottom-up approach for fabricating nanoelectronic devices. However, a challenge is to prevent the undesired growth of nanoparticles in the nongrowth area. This work uses kinetic Monte Carlo (KMC) methods to investigate the defectivity in ruthenium ASD by (ethylbenzyl)(1-ethyl-1,4-cyclohexadienyl)Ru/O-2 (EBECHRu) atomic layer deposition (ALD) in line-space nanopatterns with different dimensions. Ru ASD is governed by adsorption as well as diffusion. The defectivity depends on the pattern dimensions, as nanoparticles can diffuse and reach the interface with the growth area where they aggregate. For linewidths of 50 nm and smaller, all Ru adspecies are captured at the growth interface before growth by precursor adsorption is catalyzed. The synergetic effect of diffusion and size-dependent reactivity reduces defectivity below 10(10) Ru atoms cm(-2) for at least 1000 ALD cycles. This is more than 1000 times lower than for patterns with a linewidth of 200 nm and larger, where the Ru content decreases significantly only near the interface with the growth surface. The predicted depletion zone is confirmed by experiments in nanoscale line-space patterns. Overall, this mechanism results in smaller and fewer Ru nanoparticles for smaller patterns, facilitating the development of passivation-deposition-etch ASD processes for nanoelectronic device fabrication.
Microswimmers from Scalable Galvanic Displacement
Bailey, Maximilian R.; Reichholf, Nico; Flechsig, Anne; et al. (2022)
Particle & Particle Systems Characterization
Microswimmers are small particles capable of converting available energy sources into propulsion owing to their compositional asymmetry, and are promising for applications ranging from targeted delivery to enhanced mixing at the microscale. However, current fabrication techniques demonstrate limited scalability and/or rely on the excessive use of expensive precursor materials. Here, a scalable Pickering-wax emulsion technique is combined with galvanic electrochemistry, to grow platinum films from copper nanoparticles asymmetrically seeded onto SiO₂ microparticle supports. In this manner, large quantities of Pt-SiO₂ Janus microswimmers are obtained. Utilizing copper as a templating material not only has the potential to reduce synthesis time, material costs, and toxic waste, but also facilitates the further extension of this methodology to a range of functional materials. This electrochemical approach builds upon previous attempts to overcome the current limitations in microswimmer synthesis and offers exciting opportunities for their future development.
Low efficiency of Janus microswimmers as hydrodynamic mixers
Bailey, Maximilian R.; Fedosov, Dmitry A.; Paratore, Federico; et al. (2024)
Physical Review E
The generation of fluid flows by autophoretic microswimmers has been proposed as a mechanism to enhance mass transport and mixing at the micro- and nanoscale. Here, we experimentally investigate the ability of model 2D active baths of photocatalytic silica-titania Janus microspheres to enhance the diffusivity of tracer particles at different microswimmer densities below the onset of collective behavior. Inspired by the similarities between our experimental findings and previous results for biological microorganisms, we then model our Janus microswimmers using a general squirmer framework, specifically treating them as neutral squirmers. The numerical simulations faithfully capture our observations, offer an insight into the microscopic mechanism underpinning tracer transport, and allow us to expand the parameter space beyond our experimental system. We find strong evidence that near-field interactions dominate enhancements in tracer diffusivity in active Janus baths, leading to the identification of an operating window for enhanced tracer transport by chemical microswimmers based on scaling arguments. Based on this argumentation, we suggest that for many chemically active colloidal systems, hydrodynamics alone is likely to be insufficient to induce appreciable mixing of passive components with large diffusion coefficients.
Feedback-controlled active brownian colloids with space-dependent rotational dynamics
Fernandez Rodriguez, Miguel Angel; Grillo, Fabio; Alvarez, Laura; et al. (2020)
Nature Communications
The non-thermal nature of self-propelling colloids offers new insights into non-equilibrium physics. The central mathematical model to describe their trajectories is active Brownian motion, where a particle moves with a constant speed, while randomly changing direction due to rotational diffusion. While several feedback strategies exist to achieve position-dependent velocity, the possibility of spatial and temporal control over rotational diffusion, which is inherently dictated by thermal fluctuations, remains untapped. Here, we decouple rotational diffusion from thermal fluctuations. Using external magnetic fields and discrete-time feedback loops, we tune the rotational diffusivity of active colloids above and below its thermal value at will and explore a rich range of phenomena including anomalous diffusion, directed transport, and localization. These findings add a new dimension to the control of active matter, with implications for a broad range of disciplines, from optimal transport to smart materials.
Tracking Janus microswimmers in 3D with machine learning
Bailey, Maximilian Robert; Grillo, Fabio; Isa, Lucio (2022)
Soft Matter
Advancements in artificial active matter systems heavily rely on our ability to characterise their motion. Yet, the most widely used tool to analyse the latter is standard wide-field microscopy, which is largely limited to the study of two-dimensional motion. In contrast, real-world applications often require the navigation of complex three-dimensional environments. Here, we present a Machine Learning (ML) approach to track Janus microswimmers in three dimensions, using Z-stacks as labelled training data. We demonstrate several examples of ML algorithms using freely available and well-documented software, and find that an ensemble Decision Tree-based model (Extremely Randomised Decision Trees) performs the best at tracking the particles over a volume spanning more than 40 μm. With this model, we are able to localise Janus particles with a significant optical asymmetry from standard wide-field microscopy images, bypassing the need for specialised equipment and expertise such as that required for digital holographic microscopy. We expect that ML algorithms will become increasingly prevalent by necessity in the study of active matter systems, and encourage experimentalists to take advantage of this powerful tool to address the various challenges within the field.
Fitting an active Brownian particle's mean-squared displacement with improved parameter estimation
Bailey, Maximilian R.; Sprenger, Alexander R.; Grillo, Fabio; et al. (2022)
Physical Review E
The active Brownian particle (ABP) model is widely used to describe the dynamics of active matter systems, such as Janus microswimmers. In particular, the analytical expression for an ABP's mean-squared displacement (MSD) is useful as it provides a means to describe the essential physics of a self-propelled, spherical Brownian particle. However, the truncated or "short-time"form of the MSD equation is typically fitted, which can lead to significant problems in parameter estimation. Furthermore, heteroscedasticity and the often statistically dependent observations of an ABP's MSD lead to a situation where standard ordinary least-squares regression leads to biased estimates and unreliable confidence intervals. Instead, we propose here to revert to always fitting the full expression of an ABP's MSD at short timescales, using bootstrapping to construct confidence intervals of the fitted parameters. Additionally, after comparison between different fitting strategies, we propose to extract the physical parameters of an ABP using its mean logarithmic squared displacement. These steps improve the estimation of an ABP's physical properties and provide more reliable confidence intervals, which are critical in the context of a growing interest in the interactions of microswimmers with confining boundaries and the influence on their motion.
Thermal atomic layer deposition of gold nanoparticles: Controlled growth and size selection for photocatalysis
Hashemi, Fatemeh S.M.; Grillo, Fabio; Ravikumar, Vikram R.; et al. (2020)
Nanoscale
Gold nanoparticles have been extensively studied for their applications in catalysis. For Au nanoparticles to be catalytically active, controlling the particle size is crucial. Here we present a low temperature (105 °C) thermal atomic layer deposition approach for depositing gold nanoparticles on TiO2 with controlled size and loading using trimethylphosphino-trimethylgold(III) and two co-reactants (ozone and water) in a fluidized bed reactor. We show that the exposure time of the precursors is a variable that can be used to decouple the Au particle size from the loading. Longer exposures of ozone narrow the particle size distribution, while longer exposures of water broaden it. By studying the photocatalytic activity of Au/TiO2 nanocomposites, we show how the ability to control particle size and loading independently can be used not only to enhance performance but also to investigate structure–property relationships. This study provides insights into the mechanism underlying the formation and evolution of Au nanoparticles prepared for the first time via vapor phase atomic layer deposition. Employing a vapor deposition technique for the synthesis of Au/TiO2 nanocomposites eliminates the shortcomings of conventional liquid-based processes opening up the possibility of highly controlled synthesis of materials at large scale.
Area-Selective Deposition of Ruthenium by Area-Dependent Surface Diffusion
Grillo, Fabio; Soethoudt, Job; Marques, Esteban A.; et al. (2020)
Chemistry of Materials
Area-selective deposition (ASD) enables the growth of materials on target regions of patterned substrates for applications in fields ranging from microelectronics to catalysis. Selectivity is often achieved through surface modifications aimed at suppressing or promoting the adsorption of precursor molecules. Here, we show instead that varying the surface composition can enable ASD by affecting surface diffusion rather than adsorption. Ru deposition from (carbonyl)-(alkylcyclohexadienyl)Ru and H2 produces smooth films on metal nitrides, and nanoparticles on SiO2. The latter form by surface diffusion and aggregation of Ru adspecies. Kinetic modeling shows that changing the surface termination of SiO2 from −OH to −CH3, and thus its surface energy, leads to larger and fewer nanoparticles because of a 1000-fold increase in surface diffusion rates. Kinetic Monte Carlo simulations show that even surface diffusion alone can enable ASD because adspecies tend to migrate from high- to low-diffusivity regions. This is corroborated by deposition experiments on three-dimensional (3D) TiN–SiO2 nanopatterns, which are consistent with Ru migrating from SiO2 to TiN. Such insights not only have implications for the interpretation of experimental results but may also inform new ASD protocols, based on chemical vapor and atomic layer deposition, that take advantage of surface diffusion. © 2020 American Chemical Society.
Sequential capillarity-assisted particle assembly in a microfluidic channel
Pioli, Roberto; Fernandez Rodriguez, Miguel Angel; Grillo, Fabio; et al. (2021)
Lab on a Chip
Colloidal patterning enables the placement of a wide range of materials into prescribed spatial arrangements, as required in a variety of applications, including micro- and nano-electronics, sensing, and plasmonics. Directed colloidal assembly methods, which exploit external forces to place particles with high yield and great accuracy, are particularly powerful. However, currently available techniques require specialized equipment, which limits their applicability. Here, we present a microfluidic platform to produce versatile colloidal patterns within a microchannel, based on sequential capillarity-assisted particle assembly (sCAPA). This new microfluidic technology exploits the capillary forces resulting from the controlled motion of an evaporating droplet inside a microfluidic channel to deposit individual particles in an array of traps microfabricated onto a substrate. Sequential depositions allow the generation of a desired spatial layout of colloidal particles of single or multiple types, dictated solely by the geometry of the traps and the filling sequence. We show that the platform can be used to create a variety of patterns and that the microfluidic channel easily allows surface functionalization of trapped particles. By enabling colloidal patterning to be carried out in a controlled environment, exploiting equipment routinely used in microfluidics, we demonstrate an easy-to-build platform that can be implemented in microfluidics labs.

Publications 1 - 10 of 14

Fabio Grillo

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results