Ludovico Cademartiri

Nanofabrication by self-assembly

The self-assembly paradigm in chemistry, physics and biology has matured scientifically over the past two-decades to a point of sophistication that one can begin to exploit its numerous attributes in nanofabrication. In what follows we will take a brief look at current thinking about self-assembly and with some recent examples taken from our own work examine how nanofabrication has benefited from self-assembly.

Programmable self-assembly.

Two conceptual strategies for encoding information into self-assembling building blocks highlight opportunities and challenges in the realization of programmable colloidal nanostructures.

Using Explosions to Power a Soft Robot

grasping and walking. Despite their advantages(simplicity of fabrication, actuation, and control; low cost;light weight), pneu-nets have the disadvantage that actuationusing them is slow, in part because the viscosity of air limitsthe rate at which the gas can be delivered through tubes to filland expand the microchannels. Herein, we demonstrate therapid actuation of pneu-nets using a chemical reaction (thecombustion of methane) to generate explosive bursts ofpressure.Althoughthecombustionofhydrocarbonsisubiquitousinthe actuation of hard systems (e.g., in the metal cylinder ofa diesel or spark-ignited engine

Large‐Scale Synthesis of Ultrathin Bi2S3 Necklace Nanowires

One of the most fascinating areas of nanoscience is the study of one-dimensional nanostructures. From our materials chemistry viewpoint the idea of bringing the size of nanowires down to a point where nanoscale colloidal analogues of polymers can be studied is most stimulating. This direction has been the subject of intense study that promises to develop a new class of materials in which the topological properties of polymers can be coupled with quantum size effects and inorganic crystalline materials. Our strategy goes in a singular direction: instead of connecting nanocrystals by ligand chemistry or dipole interactions we aim to synthesize colloidal nanowires thin enough to display polymer-like behavior. Colloidal chemistry has in recent years shown that virtually any composition can be obtained as colloidal nanocrystals of the most diverse shapes. Much work though still needs to be done in the area of pnictide chalcogenides for which very few syntheses are available for obtaining colloidally stable products and none to our knowledge has shown fully demonstrated quantum size effects. Pnictide chalcogenides (Bi2S3 in particular) are in fact known to show extremely wide changes in the bandgap energy and conductivity with changes in stoichiometry. In the present work we report a “low”-temperature, gramscale route to Bi2S3 nanowires of unprecedented thickness (< 2 nm), with a necklace architecture, strong excitonic features never before seen in bismuth chalcogenides, and extremely high extinction coefficients. The wires are colloidally stable for months even after extensive purification. The nanowires were obtained by injecting a solution of sulfur in oleylamine into a saturated solution of bismuth citrate in oleylamine at 130 8C (see Supporting Information). The nanowires start nucleating immediately after injection and are shown in Figure 1a. The wires are below 2 nm in diameter and display remarkable size uniformity as well as a lack of extensive branching (even though branching points can be seldomly observed). The length of the wires could not be measured rigorously due to their melting under e-beam irradiation, but light scattering measurements indicate their length can be in the order of several microns. Strikingly, the diameter of the wires does not change during growth (Supporting Information), as it will be later shown. In Figure 1b we show a Z-contrast TEM image, which indicates the melting the wires undergo upon e-beam irradiation. The inhomogeneity in the droplet spacing is a hint to the nanowire9s texture that will be highlighted later. The HRTEM image obtained from the wires (Figure 1c) shows some slightly elongated nanocrystals. The fact that only certain parts of the wires show lattice fringes at a given time indicates their polycrystalline microstructure. The lattice spacing that is evidenced in Figure 1c corresponds to the (021) planes of the Bi2S3 structure. The reaction is highly scalable due to the high concentration of the reagents and its high yield (> 60%): multigram quantities can be routinely obtained in a laboratory environment. Figure 1d depicts over 17 grams of nanowires produced in the course of a single reaction (ca. 350 mL). Unlike for single-crystalline ultrathin nanowires, the powder X-ray diffraction (XRD) pattern for the Bi2S3 nanowires (Figure 2a) is devoid of relatively sharp features, which seems to indicate a rather isotropic nanocrystalline component. In ultrathin nanowires, the different coherence lengths along the different crystallographic directions, which are due to the high aspect ratio and small size, give rise to sharp peaks on an broad background. In this case, the XRD pattern is more consistent with a spherical nanocrystal system: Rietveld refinement of the XRD pattern was successfully accomplished by using the Bi2S3 unit cell as well as a spherical particle model with a 1.6 nm size, consistent with the microscopy data (Supporting Information). It is important here not to overestimate the accuracy of Rietveld refinement when it comes to nanocrystal shape determination but it is safe to say that we are not dealing with a one-dimensional single crystal. [*] L. Cademartiri, R. Malakooti, Dr. S. Petrov, Prof. G. A. Ozin Lash Miller Chemical Laboratories Department of Chemistry, University of Toronto 80 St. George Street, Toronto, ON, M5S 3H6 (Canada) Fax: (+1)416-971-2011 E-mail: gozin@chem.utoronto.ca Homepage: http://www.chem.toronto.edu/staff/GAO/group.html

Cross-linking Bi2S3 ultrathin nanowires: a platform for nanostructure formation and biomolecule detection.

This paper describes the use of chemical cross-linking of ultrathin inorganic nanowires as a bottom-up strategy for nanostructure fabrication as well as a chemical detection platform. Nanowire microfibers are produced by spinning a nanowire dispersion into a cross-linker solution at room temperature. Nanomembranes with thicknesses down to 50 nm were obtained by injecting the nanowire dispersion at the cross-linker-solution/air interface. Furthermore, the sensitivity of the nanowire to amine cross-linkers allowed development of a novel sensing platform for small molecules, like the neurotransmitter serotonin, with detection limits in the picomolar regime.

Using shape for self-assembly

A 1980 poem by Alan Mackay outlines his aspiration ‘to see what all have seen but think what none have thought’: a daunting task, which he accomplished not once, but several times. A ‘truly myriadminded, manysided man—a veritable triacontahedron’ in the words of his colleagues and friends, Alan Mackay pursued a lifelong interest in the problems of morphogenesis and form, a comprehension of which necessitated him crisscrossing the borders of the inanimate and animate world of soft and hard materials, through the integration of concepts and methods of chemistry, physics, mathematics and biology. In other words, he realized in his time a genuinely interdisciplinary approach to complex problems that still to this day remains beyond much of the academic community. Being invited to contribute a paper on the theme ‘beyond crystals’, we naturally wondered how Alan Mackay would think about the world of nanoscale self-assembly where so much depends on shape and form.

Thermal Processing of Silicones for Green, Scalable, and Healable Superhydrophobic Coatings.

The thermal degradation of silicones is exploited and engineered to make super-hydrophobic coatings that are scalable, healable, and ecofriendly for various outdoor applications. The coatings can be generated and regenerated at the rate of 1 m(2) min(-1) using premixed flames, adhere to a variety of substrates, and tolerate foot traffic (>1000 steps) after moderate wear and healing.

Ultrathin Bi2S3 nanowires: surface and core structure at the cluster-nanocrystal transition.

Herein, we present the structural characterization of the core and surface of colloidally stable ultrathin bismuth sulfide (Bi(2)S(3)) nanowires using X-ray Absorption Spectroscopy (EXAFS and XANES), X-ray Photoelectron Spectroscopy (XPS), and Nuclear Magnetic Resonance (NMR). These three techniques allowed the conclusive structural characterization of the inorganic core as well as the coordination chemistry of the surface ligands of these structures, despite the absence of significant translational periodicity dictated by their ultrathin diameter (1.6 nm) and their polycrystallinity. The atomic structure of the inorganic core is analogous to bulk bismuthinite, but Bi atoms display a remarkably higher coordination number than in the bulk. This can be only explained by a model in which each bismuth atom at the surface (or in close proximity to it) is bound to at least one ligand at any time.

Ultrathin Sb2S3nanowires and nanoplatelets

Ultrathin (thickness < 2.2 nm) colloidal Sb2S3nanowires and nanoplatelets were synthesized via a simple solution synthesis. The nanowires and platelets were stable in solution for months and were characterized viaSAED, XRD, UV-VIS spectroscopy, SAXS, XPS and EDAX.

Electric winds driven by time oscillating corona discharges

We investigate the formation of steady gas flows—so-called electric winds—created by point-plane corona discharges driven by time oscillating (ac) electric fields. By varying the magnitude and frequency of the applied field, we identify two distinct scaling regimes: (i) a low frequency (dc) regime and (ii) a high frequency (ac) regime. These experimental observations are reproduced and explained by a theoretical model describing the transport and recombination of ions surrounding the discharge and their contribution to the measured wind velocity. The two regimes differ in the spatial distribution of ions and in the process by which ions are consumed. Interestingly, we find that ac corona discharges generate strong electric forces localized near the tip of the point electrode, while dc corona discharges generate weaker forces distributed throughout the interelectrode region. Consequently, the velocity of the electric winds (>1 m/s) generated by ac discharges is largely independent of the position of the co...