Victor Boureau

École Polytechnique Fédérale de Lausanne | EPFL · Interdisciplinary Center for Electron Microscopy (CIME)

Single‐crystal diamond substrates presenting a high concentration of negatively charged nitrogen‐vacancy centers (NV ⁻ ) are on high demand for the development of optically pumped solid‐state sensors such as magnetometers, thermometers, or electrometers. While nitrogen impurities can be easily incorporated during crystal growth, the creation of vac...

Nature provides a wide range of self-assembled structures from the nanoscale to the macroscale. Under the right thermodynamic conditions and with the appropriate material supply, structures like stalactites, icicles, and corals can grow. However, the natural growth process is time-consuming. This work demonstrates a fast, nature-inspired method for...

Single-crystal diamond substrates presenting a high concentration of negatively charged nitrogen-vacancy centers (NV-) are on high demand for the development of optically pumped solid-state sensors such as magnetometers, thermometers or electrometers. While nitrogen impurities can be easily incorporated during crystal growth, the creation of vacanc...

The development of hemoglobin (Hb)-based oxygen carriers (HBOCs) holds a lot of potential to overcome important drawbacks of donor blood such as a short shelf life or the potential risk of infection. However, a crucial limitation of current HBOCs is the autoxidation of Hb into methemoglobin (metHb), which lacks oxygen-carrying capacity. Herein, we...

The atomically dispersed transition metal with nitrogen-doped carbon (M-N-C) has been studied as a possible replacement for platinum group metal (PGM) catalysts in fuel cell electrodes. In this work, the Fe-N-C and Co-N-C are used as a hydrogen peroxide reduction reaction (PRR) catalysts in direct borohydride fuel cells (DBFCs). Using half-cell and...

Graphene Nanopores In article number 2206627, Kumar Varoon Agrawal and co-workers describe how ångstrom-scale pores are generated in graphene at a desired site, on demand, by controlled gasification of pre-formed epoxy clusters. This strategy allows independent control of pore density and pore size. The illustration shows CO2 released from the gasi...

Generating pores in graphene by decoupled nucleation and expansion is desired to achieve a fine control over the porosity, and is desired to advance several applications. Herein, we introduce epoxidation, the formation of nanosized epoxy clusters on the graphitic lattice as nucleation sites without forming pores. In situ gasification of clusters in...

Perpendicular shape anisotropy (PSA) and double magnetic tunnel junctions (DMTJs) offer practical solutions to downscale spin-transfer-torque Magnetic Random-Access Memory (STT-MRAM) beyond 20 nm technology nodes, while retaining their thermal stability and reducing critical currents applied. However, as these modern devices become smaller and thre...

Perpendicular shape anisotropy (PSA) and double magnetic tunnel junctions (DMTJ) offer practical solutions to downscale spin-transfer-torque Magnetic Random-Access Memory (STT-MRAM) beyond 20 nm technology nodes, whilst retaining their thermal stability and reducing critical currents applied. However, as these modern devices become smaller and thre...

Efficient catalytic water splitting demands advanced catalysts to improve the slow kinetics of the oxygen evolution reaction (OER). Earth-abundant transition metal oxides show promising OER activity in alkaline media. However, most experimental information available is either from post-mortem studies or in-situ space-averaged X-ray techniques in th...

In strained mechanical resonators, the concurrence of tensile stress and geometric nonlinearity dramatically reduces dissipation. This phenomenon, called dissipation dilution, is employed in mirror suspensions of gravitational-wave interferometers and at the nanoscale, where soft clamping and strain engineering have allowed extremely high quality f...

We investigate the use of ultrafast lasers exposure to induce localized crystallization and elemental redistribution in amorphous dielectric multi-layers, composed of alternating Si3N4 and SiO2 layers of sub-micrometer thickness. Specifically, we report on the occurrence of a laser-induced elemental intermixing process and the presence of silicon n...

We investigate the use of ultrafast lasers exposure to induce localized crystallization and elemental redistribution in amorphous dielectric multi-layers, composed of alternating Si3N4and SiO2layers of sub-micron thickness. Specifically,we report on the occurrence of a laser-induced elemental intermixing process and on the presence of silicon nanoc...

Significance The energy efficiency of gas separation is expected to benefit from the development of membranes yielding selective but large permeance. The ultimate limit of this is two-dimensional films hosting a high density of molecular-selective apertures (e.g., nanoporous single-layer graphene). Currently, pores are incorporated in single-layer...

In strained mechanical resonators, the concurrence of tensile stress and geometric nonlinearity dramatically reduces dissipation. This phenomenon, dissipation dilution, is employed in mirror suspensions of gravitational wave interferometers and at the nanoscale, where soft-clamping and strain engineering have allowed extremely high quality factors....

We compare two transmission electron microscopy (TEM) based techniques that can provide highly spatially resolved quantitative measurements of magnetic induction fields at high sensitivity. To this end, the magnetic induction of a ferromagnetic NiFe nanowire has been measured and compared to micromagnetic modeling. State-of-the-art off-axis electro...

The internal fields in 2.2 nm thick InGaN quantum wells in a GaN LED structure have been investigated by using aberration-corrected off-axis electron holography with a spatial resolution of better than 1 nm. To improve the spatial resolution, different types of off-axis electron holography acquisitions have been used, including pi phase shifting an...

We compare two transmission electron microscopy (TEM) based techniques that can provide highly spatially resolved quantitative measurements of magnetic induction fields at high sensitivity. To this end, the magnetic induction of a ferromagnetic NiFe nanowire has been measured and compared to micromagnetic modelling. State-of-the-art electron hologr...

Micro LEDs have been grown by metal organic vapor phase epitaxy on standard GaN and partly relaxed InGaNOS substrates with the purpose of incorporating higher concentrations of indium for identical growth conditions. Green emission has been demonstrated at wavelengths of 500 nm for the GaN template and 525 and 549 nm for the InGaNOS substrates, res...

Diffraction-based techniques, with either electrons or photons, are commonly used in materials science to measure elastic strain in crystalline specimens. In this paper, the focus is on two advanced techniques capable of accessing strain information at the nanoscale: high-resolution X-ray diffraction (HRXRD) and the transmission electron microscopy...

The fabrication of muti-gigabit magnetic random access memory (MRAM) chips requires the patterning of magnetic tunnel junctions at very small dimensions (sub-30 nm) and very dense pitch. This remains a challenge due to the difficulty in etching magnetic tunnel junction stacks. We earlier proposed a strategy to circumvent this problem by depositing...

The electric field in a silicon p–n junction has been measured using pixelated scanning transmission electron microscopy. By using a convergence angle of 3.2 mrad, a spatial resolution better than 1 nm can be achieved leading to a rigid shift of the transmitted beam as it passes through an electric field. By precessing the beam around the optical a...

Iron electrocoagulation (EC) can be used for decentralized treatment of arsenic(As)-contaminated groundwater. Iron EC involves the electrolytic dissolution of an Fe(0) electrode to Fe(II). This process produces reactive oxidants, which oxidize As(III) and Fe(II) to As(V) and a range of Fe(III) (oxyhydr)oxide phases. Here, we investigated the impact...

The distribution and electrical activity of p-type doping (Mg) in gallium nitride (GaN) grown by metal organic chemical vapor deposition was investigated by correlating atom probe tomography (APT) and off-axis electron holography. APT results revealed that high Mg concentrations promote the formation of Mg-rich clusters. This is associated with the...

The electric potential, electric field and charge density of a monolayer of MoS2 has been quantitatively measured at atomic scale resolution. This has been performed by off-axis electron holography using a double aberration-corrected transmission electron microscope operated at 80 kV and a low electron beam current density. Using this low dose rate...

Correlation between off-axis electron holography and Atom Probe Tomography (APT) provides morphological, chemical and electrical information about Mg-doping (p-type) in gallium nitride (GaN) layers that have been grown at different temperatures at a nanometric scale. APT allows access to the 3-Dimensional (3D) distribution of atoms and their chemic...

We present a comprehensive study of the performance of GaN single-nanowire photodetectors containing an axial p-n junction. The electrical contact to the p region of the diode is made by including a p+/n+ tunnel junction as cap structure, which allows the use of the same metal scheme to contact both ends of the nanowire. Single-nanowire devices pre...

Compressively strained SiGe-On-Insulator (SGOI) made by the Ge-condensation technique is used as a performance booster for ultrathin fully depleted silicon-on-insulator transistor technology. Here, we report on the evolution of the compressive strain in the SiGe film along the formation of local SGOI. For this, experimental maps of lattice strain w...

To provide a direct comparison, off-axis holography and differential phase contrast have been performed using the same microscope on the same specimens for the measurement of active dopants and piezoelectric fields. The sensitivity and spatial resolution of the two techniques have been assessed through the study of a simple silicon p-n junction obs...

In modern electronic devices, strain is used to increase carrier mobility. It is thus mandatory to know precisely the effect of doping on the lattice parameter of silicon. However, there are many experimental biases which prevent one from measuring this effect with high accuracy. For this reason, we have designed and fabricated a step-like structur...

Clever strategies have been set up and are today routinely used to generate strains of desired directions and amplitudes in the channels of CMOS transistors. Unfortunately, many of the processing steps which follow this strain engineering have a strong impact on the final strain state of these channels, sometimes even not foreseen. Here, we report...

Clever strategies have been set up and are today routinely used to generate strains of desired directions and amplitudes in the channels of CMOS transistors. Unfortunately, many of the processing steps which follow this strain engineering have a strong impact on the final strain state of these channels, sometimes even not foreseen. Here, we report...

For long time considered as detrimental, stress is now an integral feature of modern electronic devices. Indeed, correctly oriented, the resulting strains may significantly increase carrier mobility and thus boost device performance. In this context, Dark-Field Electron Holography (DFEH) was used to study the impact of some key steps of the manufac...

In this paper we discuss developments for Lorentz mode or "medium resolution" off-axis electron holography such that it is now routinely possible obtain very high sensitivity phase maps with high spatial resolution whilst maintaining a large field of view. Modifications of the usual Fourier reconstruction procedure have been used to combine series...

In modern MOS devices, sources and drains are of nanometric dimensions and highly doped (dopant concentration typically > 10 ²⁰ at.cm ⁻³ ). Measuring such dopant concentrations and visualizing their spatial extensions in silicon, although mandatory for the development of the technology, is elusive in practice. Several TEM techniques such as EELS an...

Magnetotactic bacteria (MTB) are known to produce single-domain magnetite or greigite crystals within intracellular membrane organelles and to navigate along he Earth's magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on the Earth and they represent a fundamental model of intracellular biomi...

Off‐axis electron holography can be used to measure the electrostatic and magnetic potentials in semiconductor devices with high‐sensitivity and nm‐scale resolution [1]. In this presentation we will show experimental results that have been obtained using combinations of electron holography, precession diffraction and differential phase contrast (DP...

Longtemps considérées comme néfastes, les contraintes sont devenues un des moyens principaux pour améliorer les performances des dispositifs métal-oxyde-semiconducteur (MOS). En effet, les déformations générées augmentent sensiblement la mobilité des porteurs dans le silicium. C'est dans ce cadre que j'ai étudié, par holographie électronique en cha...

In this paper we explore the benefit of combining High Resolution X-Ray Reciprocal Space Mapping (HR-RSM) and Dark-Field Electron Holography (DFEH) techniques for strain characterization of thin pMOS-like structures. We are able to simulate the measured HR-RSM from the displacement field extracted by DFEH. This is a first step developing High Resol...

We study the interplay between strain and composition during the elementary process steps which allow the fabrication of strained ultra-thin SiGe layers on insulators from a Silicon-On-Insulator (SOI) substrate by the Ge condensation technique. Strain maps with subnanometer resolution and high precision are obtained using the dark-field electron ho...

Magnetotactic bacteria (MTB) are known to produce single-domain magnetite or greigite crystals within intracellular membrane organelles, and to navigate along the Earth’s magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on Earth and they represent a fundamental model of intracellular biomine...

We study the strain characteristics of thin SiGe layers on insulator processed by the germanium condensation technique. We perform dark-field electron holography measurements and show the relation between strain and Ge content in the layers. The characteristics of the condensation process are discussed for the realization of co-integrated MOS struc...