1. Introduction
Spontaneously distorted nematic states have been theoretically predicted long ago for bent-shaped mesogens [1-3]. Recent experiments [4] confirmed the existence of the twist-bend nematic phase, NTB, with short-pitch heliconical precession of the director n. Another predicted state [3], the splay-bend nematic, NSB, with n oscillating in a plane, is still elusive. However, a recent birefringence study [5] suggested NSB structure of the defect wall separating two NTB domains with opposite chiralities.
2. Twist-bend to splay-bend transition under strong electric field
Here we investigate the NTB state of the bent-shaped dimer CB7CB under strong a.c. electric field, (E ~10 V/µm) parallel to the helix axis. This in-plane field is applied in a 2 µm cell using two ITO electrodes (Fig.1). Crossing the N- NTB transition under field, we observe in the interelectrode region slightly lower transition temperature and much stronger birefringence than that reported in the NTB phase [5], suggesting an electric-field induced NTB – NSB transition.
3. Conclusion
A strong electric field applied to the NTB phase induces a transition to the splay-bend nematic phase, instead to the usual uniform nematic N. We explain this in the framework of the elastic-instability model [3] of the NTB and NSB phases by taking into account the strong biaxiality of the bent-shape nematic.
References
[1]R. B. Meyer, in Molecular Fluids, edited by R. Balian and G. Weill (Gordon and Breach, New York 1976), pp. 273
[2]V. L. Lorman and B. Mettout, Phys. Rev. Lett. 82, 940 (1999).
[3]I. Dozov, EPL (Europhysics Letters) 56, 247 (2001).
[4]M. Cestari, S. Diez-Berart, D. A. Dunmur, A. Ferrarini, M. R. de la Fuente, D. J. B. Jackson, D. O. Lopez, G. R. Luckhurst, M. A. Perez-Jubindo, R. M. Richardson, J. Salud, B. A. Timimi and H. Zimmermann, Physical Review E 84, 031704 (2011).
[5]C. Meyer, G. R. Luckhurst and I. Dozov, Journal of Materials Chemistry C 3, 318 (2015).

Midwave infrared (MWIR) InAs/GaSb superlattice (SL) photodiode with a dopant-free p–n junction was fabricated by molecular beam epitaxy on GaSb substrate. Depending on the thickness ratio between InAs and GaSb layers in the SL period, the residual background carriers of this adjustable material can be either n-type or p-type. Using this flexibility in residual doping of the SL material, the p–n junction of the device is made with different non-intentionally doped (nid) SL structures. The SL photodiode processed shows a cut-off wavelength at 4.65 μm at 77 K, residual carrier concentration equal to 1.75 × 1015 cm−3, dark current density as low as 2.8 × 10−8 A/cm2 at 50 mV reverse bias and R0A product as high as 2 × 106 Ω cm2. The results obtained demonstrate the possibility to fabricate a SL pin photodiode without intentional doping the pn junction.

We propose an holographic microscopy reconstruction method, which propagates the hologram, in the object half space, in the vicinity of the object. The calibration yields reconstructions with an undistorted reconstruction grid i.e. with orthogonal $x$, $y$ and $z$ axis and constant pixels pitch. The method is validated with an USAF target imaged by a $\times$60 microscope objective, whose holograms are recorded and reconstructed for different USAF locations along the longitudinal axis: -75 to +75 $\mu$m. Since the reconstruction numerical phase mask, the reference phase curvature and MO form an afocal device, the reconstruction can be interpreted as occurring equivalently in the object or in image half space.

We have investigated the active motion of self-propelled colloids confined at the air–water interface and explored the possibility of enhancing the directional motion of self-propelled Janus colloids by slowing down their rotational diffusion. The two dimensional motion of micron-sized silica–platinum Janus colloids has been experimentally measured by particle tracking video-microscopy at increasing concentrations of the catalytic fuel, i.e. H2O2. Compared to the motion in the bulk, a dramatic enhancement of both the persistence length of trajectories and the speed has been observed. The interplay of colloid self-propulsion, due to an asymmetric catalytic reaction occurring on the colloid, surface properties and interfacial frictions controls the enhancement of the directional movement. The slowing down of the rotational diffusion at the interface, also measured experimentally, plays a pivotal role in the control and enhancement of active motion.

Nanophotonics is an emerging field where researchers look for potential application of carbon nanotubes (SWNT) in the framework of silicon photonics technology, due to SWNT ability to emit, modulate and detect light in the wavelength range of silicon transparency. In this field of nanotube photonics, a first milestone was to couple light emission from SWNT into silicon waveguides [1]. Current researches focus on coupling SWNT with optical cavities, either for enhancing nanotube photoluminescence (PL) or nonlinear optical phenomena, at the nanoscale. Several works focused on the integration of carbon nanotubes with photonic cavities built on silicon-on-insulator (SOI) substrate, which is the preferential platform for photonic applications. Such work included coupling nanotubes with microdisk resonators[2], nanobeam cavity[3] or photonic crystal cavities[4]. However, these kinds of cavities could not be easily coupled to silicon waveguides, and were addressed using out-of-the-plane μ-PL configuration, hindering subsequent integration into more complex photonic devices. Building up on our previous work[5], we propose to couple carbon nanotube PL with silicon microring resonators in a fully integrated configuration, with an access waveguide[6]. PL coupled to microring mode could be collected from the access waveguide, with efficient rejection on non-resonant photons. Emission quality factor up to 8000 were observed. Moreover, this design allow for collinear excitation of SWNT through the access waveguide, leading to efficient excitation and collection of SWNT PL at different wavelength. Compare to previous designs, the requirement of an external laser source for out-of-the-plane SWNT excitation is lifted, underlining the pertinence of this approach for realistic carbon nanotube based photonic devices.

1D hybrid nano-systems are elaborated with photo-active pi-conjugated molecules (quathertiophene and phathlocyanine) encapsulated into the hollow core of single-walled carbon nanotubes. We evidence that the supramolecular organizations of confined oligothiophenes (from 1 to 3 chains into a nanotube section) depend on the nanocontainer size. The physical interactions can switch from molecule-molecule to molecule-nanotube interactions depending on the tube diameter. In addition, permanent and photo-induced electron transfers are evidenced from the confined molecules to the nanotubes. The supramolecular organization of MPc molecules is shown to be a 1D-phase for which the angle between the molecule ring and the nanotubes axis is close to 32°. Confined MPc molecules display Raman spectra hardly altered with respect to the bulk phase, suggesting a rather weak interaction with the tubes.