Ultra-violet semiconductor lasers have numerous applications for optical storage, biochemistry, sterilization or optical interconnects. However the usual design of deep UV-emitting ridge lasers relies on complex buffer layers or expensive substrates for the growth of the nitride heterostructures [1]. Moreover microlaser and nanophotonic devices with integrated sources require an alternative approach compatible with thin waveguides.In this work we demonstrate a series of nitride-on-silicon microdisk lasers covering a broad spectral range, from the blue (=470 nm) to the deep ultra-violet (=275nm), and operating at room temperature. They rely on the controlled growth of thin AlN buffer layers on silicon substrates, followed by the growth of GaN/AlN or InGaN/GaN multiple quantum wells (MQWs) with a high radiative efficiency up to T=300K. We exploit the possibility to under-etch selectively the silicon substrate in order to form nitride membranes for photonic resonators; this has allowed many demonstrations of microdisk and photonic crystal cavities with quality factors larger than 1000, ranging from the mid-IR [2] to the near-UV spectral range [3,4], now expanding to the UV-C [5].Following the demonstration of a UV-C microlaser operating atat 275 nm and at room temperature [5], the figure 1 presents the emission characteristics of a series of nitride-on-silicon microdisks with different active layers grown on a thin AlN buffer layer. Their whispering gallery modes are probed under continuous wave excitation at 266 nm with a 15 µm laser spot (Figure 1.b); the photoluminescence is collected from the edge of the microdisks. The chosen microdisk diameters in panel (b) are 5-6 µm in order to properly exhibit the modes, except for the 3 µm microdisk emitting at 275 nm. In all cases, the sharpest peaks are observed in the low energy tail of the PL spectrum where the absorption of the active layer is limited. The measured Q factors exceed 1000, and reach 4000 in the best resonators. The lasing operation is obtained under pulsed quasi-resonant optical pumping (266nm, 400ps pulses) with a threshold excitation density ranging from 2 to 40 nJ/pulse (Figure 1.a). The dependence of the lasing threshold will be discussed.In the UV-B and UV-C spectral ranges, these demonstrations underline the interest of simple binary GaN/AlN MQWs, grown on a thin AlN buffer on a silicon substrate, in order to obtain efficient active layers providing optical gain up to room temperature. The microdisk lasing in the visible spectral range, based on more mature InGaN/GaN MQWs, proves the versatility of the nitride-on-silicon photonic platform, that can embed a broad range of integrated sources.

Bacteria, a few μm in length, have the feature to store the genome in a subvolume of the cell without membrane. The bacterial cell cycle relies on a series of essential processes such as DNA replication, transcription and segregation. The mechanisms driving segregation of the genome are still unclear, mainly because the processes overlap in time and take place in the same cellular compartment. The active ParABS partition system is the only type known on chromosomes and is prevalent on low-copy number plasmids,namely the F-plasmid involved in bacterial resistance to antibiotics. ParABS is composed of three components: the proteins ParA and ParB, respectively a molecular motor (ATPase) and a binding protein, and parS, a sequence of specific binding sites. We describe the organization and architecture of the partition complex. Our model is supported by experimental data from ChIP-sequencing (LMGM, Toulouse) and super resolution microscopy techniques (CBS, Montpellier).

We present experimental and theoretical results for the transport of ions and molecules inside carbon nanotubes.

We model the ParABS system, which is a bacterial DNA Segregation Apparatus.

We present a modeling study of the electrical conductivity of charged nanopores.

Nous présentons les activités en 2016 du Projet intégré « ADN et Génomes » du LabEx NUMEV.

Nous développons une approche de modélisation pluridisciplinaire, de type génomique physique, dans le but de comprendre les mécanismes de la dynamique active des complexes intracellulaires protéines-ADN bactériens. Son but est d’unifier quantitativement, sur la base de méthodes de physique statistique, l’information provenant des expériences de séquençage à haut débit avec les données de l’imagerie moderne de super-résolution.