Roger Morin

Generating nanoliter to femtoliter microdroplets with ease

In this letter, we present a simply constructed and easy-to-use fluidic device that generates arrayed aqueous phase microdroplets in oil of controlled size with volumes ranging from nanoliter to femtoliter without surfactant. This can be applicable with a range of materials, allowing production and storage of monodisperse microdroplets. We illustrate the potential of our methodology in the field of nanoparticle generation

Proton and light ion nanobeams from field ionization of water

We observe emission of protons and Hn+ (n up to 4) at room temperature from field ionization of thick films of water adsorbed on Pt or Pd, not on W tips. This differs from previous field ionization experiments of water, all of which show hydrated proton emission. Our observations are explained by the ionic dissociation of water on Pt and Pd surfaces. These thick film experiments are made possible by a special local water supply arrangement. An ion point source based on this ionization process is shown to produce nanobeams of light ions suitable for high resolution ion microscopy.

Field nano-localization of gas bubble production from water electrolysis

Using a tip shaped electrode and ac voltages, we show that the production of micro bubbles of gas from water electrolysis is localized at the tip apex inside a domain in the voltage frequency phase space. A model taking into account the electrode shape and dimensions explains these results which suggest a field effect control of the electrolysis reaction rate at a nanometer scale.

Tunable microbubble generator using electrolysis and ultrasound

This letter reports on a method for producing on demand calibrated bubbles in a non-chemically controlled solution using localized micro-electrolysis and ultrasound. Implementing a feedback loop in the process leads to a point source of stable mono-dispersed microbubbles. This approach overcomes the inertial constraints encountered in microfluidics with the possibility to produce from a single to an array of calibrated bubbles. Moreover, this method avoids the use of additional surfactant that may modify the composition of the host fluid. It impacts across a broad range of scientific domains from bioengineering, sensing to environment.

Single mineral particle makes an electron point source

A mineral (celadonite, kaolinite) nanometer-thick particle deposited on a flat carbon film or at the apex of a carbon fiber provides electron emission at low applied fields. Voltage and time dependences of the emission intensity are studied, and a model of the underlying mechanism is proposed. An electron point source providing emission from a single particle is built and characterized.

High spatial resolution detection of low-energy electrons using an event-counting method, application to point projection microscopy

An event-counting method using a two-microchannel plate stack in a low-energy electron point projection microscope is implemented. 15 μm detector spatial resolution, i.e., the distance between first-neighbor microchannels, is demonstrated. This leads to a 7 times better microscope resolution. Compared to previous work with neutrons [Tremsin et al., Nucl. Instrum. Methods Phys. Res., Sect. A 592, 374 (2008)], the large number of detection events achieved with electrons shows that the local response of the detector is mainly governed by the angle between the hexagonal structures of the two microchannel plates. Using this method in point projection microscopy offers the prospect of working with a greater source-object distance (350 nm instead of 50 nm), advancing toward atomic resolution.

Addressing the Stochasticity of Nucleation: Practical Approaches

This chapter presents different practical ways to address nucleation stochasticity. The methods use either statistical studies on spontaneous nucleation or local control of nucleation. Techniques developed in our laboratory are described: droplet-based microfluidics, microinjectors in oil, and external electrical or mechanical fields in confined systems. Results of nucleation kinetics obtained on various molecules are presented in terms of metastable zone, critical supersaturation, nucleation rate, induction time, interfacial energy of the critical nucleus, polymorphism, and detection of the critical nucleus. These practical approaches show considerable potential to increase understanding and control of the nucleation mechanism.

Nanoporous metal film: An energy-dependent transmission device for electron waves

We measure electron transmission through free-standing ultrathin nanoporous gold films, using the coherent electron beam emitted by sharp field emission tips in a low energy electron projection microscope setup. Transmission coefficient versus electron wavelength plots show periodic oscillations between 75 and 850 eV. These oscillations result from the energy dependence of interference between paths through the gold and paths through the nanometer-sized pores of the film. We reveal that these films constitute high transmittance quantum devices acting on electron waves through a wavelength-dependent complex transmittance defined by the porosity and the thickness of the film.