Fonctions Optiques pour les Technologies de l’information

Abstract Traditional perovskite research has largely focused on thermodynamically stable structures, which has limited the exploration of new architectures. In 3D perovskites, compositional changes typically lead to minor structural alterations or impurities. Thermodynamically stabilized 2D perovskites have faced significant charge transport problems due to poor energy alignment and horizontal orientation. This study introduces a groundbreaking Selective Iodoplumbate Cold Casting (SICC) process, enabling the formation of kinetic products that correspond to local minima in the reaction energy landscape. Previously, there wasn't a controlled method for synthesizing kinetically stabilized perovskites. SICC, by combining simplified precursors with room-temperature crystallization, can replicate reactant compositional changes, allowing for the creation of diverse structures that were unattainable with conventional methods. The research presents a novel corrugated 2D structure using a cation known for forming 3D perovskite structures. Additionally, kinetically stabilized n=1 2D perovskite films show grain sizes equivalent to their correlation length and a mixed orientation with over 21% out-of-plane alignment. These features enhance vertical charge transport and provide a beneficial band alignment for 3D:2D heterostructures. To prove SICC's scalability, a 50 cm² 3D:2D perovskite mini-module was fabricated. This SICC-based mini-module achieved an impressive efficiency of 22.15% and a geometric fill factor of 94.36%. It also demonstrated outstanding stability, maintaining T90 for 1200 hours under MPPT conditions at 50 °C.

Time reversal of radio-frequency or microwave signals has important applications applications in telecommunications and electronic warfare. All-digital techniques are intrinsically limited in bandwidth by the speed of the converters, which necessitate the emergence of alternative analog techniques for future implementations. We demonstrate a new, to our knowledge, microwave-photonics architecture in this context, offering integration prospects. The system we propose is based on a pair of frequency-shifting loops, where the first loop transfers the input signal from the time domain into the frequency domain. In contrast, the second loop performs the opposite process, thus achieving the desired time-reversal process. The technique is particularly versatile, allowing the time reversal of signals with bandwidths of the order of tens of MHz, durations on the order of tens of microseconds, and with arbitrarily small latency. The system can also act as a temporal buffer for the reversed signal, a promising feature for photonic-based beamforming.

Установлены критерии, определяющие наборы электрофизических и конструкционных параметров температурных датчиков на основе полупроводниковых диодов (ДДТ), при которых кривые температурной чувствительности датчиков будут иметь либо максимальный температурный диапазон отклика, либо наивысшую чувствительность. Представлен новый метод самосогласованной оптимизации устройства в контексте модели диффузионного тока через резкий асимметричный р-n переход, где коэффициент идеальности предполагается равным 1. Для ДДТ на основе Si с n+-p и p+-n переходами определены предельные кривые температурного отклика (КТО) и температурные чувствительности. Экспериментально полученные метрологические характеристики ДДТ находятся в пределах, определенных предельными характеристиками.

We detail here the general principle of a self-adaptive oscillator in which the intertwined operation of a 100-m-long active optical resonator and a standard semiconductor laser mutually coupled by stimulated Brillouin scattering offers an ultimate high spectral purity. Single frequency operation of this self-adaptive photonic oscillator is achieved without any servo locking or stabilization electronics. In free running operation, this principle leads to a Lorentzian linewidth of 40 mHz and a Flicker noise linewidth of 200 Hz for 0.01 s integration time. The long-term drift of the optical frequency without absolute frequency locking is in the range of 10 MHz over hours. This principle applies to any wavelength attainable by laser diodes which opens tremendous opportunities, in particular in applications where atomic or molecular transitions require precise wavelengths.

Automation of fluorescence microscopy is a challenge for capturing rare or transient events in biology and medicine. It relies on smart devices that integrate and interpret the observed data, and react to the targeted biological event. We report on the Roboscope, a novel autonomous microscope combining sequence interruption and deep learning integration, allowing generic event-driven acquisitions. This system distinguishes itself by its adaptability to various experiments, quick capture of dynamic events, and minimal data greediness – training with less than 100 images per class. The Roboscope’s capability is demonstrated in non-synchronized cells by capturing the metaphase, a 20-minute event happening once per day or less. Conversely, double thymidine-block synchronisation, despite occurring during DNA replication, may perturb mitotic-spindle mechanics. The Roboscope’s versatility and efficiency offer significant advancements to tackle the current challenges of cell biology, spreading out advanced microscopy methods to fundamental research as well as high content screening and precision medicine.

International audience

We present the design of a mm-wave phased array antenna enabled by photonic beam steering. The mm-wave signal is generated by InP uni-traveling-carrier (UTC) photodiodes within the photonic integrated chip (PIC). The antenna array consists of four sub-arrays, each comprising two stacked patch elements. The bottom patch is shorted to create a compact element, enabling a half-wavelength spacing in the scanning plane. This configuration results in a relatively wide scanning range of +/-30° without significant sidelobe levels. The complexity of this structure lies in the heterogeneous integration of the InP chip with the antenna array and biasing network, all printed on a low-loss substrate with low relative permittivity. The proposed array exhibits a simulated peak directivity of 16 dBi and an impedance and -3 dB gain bandwidth ranging from 43.8 GHz to 58.8 GHz.

Abstract We utilize first-principles theory to investigate the role of electron-phonon interactions within a dataset of monolayer materials. Using density functional theory to describe excited state transitions and the special displacement method to describe the role of phonons, we analyze the relationship between simple physical observables and electron-phonon coupling strength. For over 100 materials, we compute the band gap renormalization due to zero-point vibrational (ZPR) motion as a measure of electron-phonon interactions and train a machine learning model based on physical parameters. We demonstrate that the strength of electron-phonon interactions is highly dependent on the band gap, dielectric constant, and degree of ionicity, all of which can be physically justified. We then apply this model to 1302 2D materials, predicting the ZPR, which for five randomly selected materials tested agree well with first-principles predictions. This work provides an approach for quantitatively predicting the ZPR as a measure of electron-phonon interactions in 2D materials.

International audience

Here, we investigate and analyze the electronic properties of ladder- and zigzag-patterned antiphase boundaries (APBs) in II-VI and III-V semiconductors based on first-principles calculations performed on ZnS and InP. From the band-structure analysis on these configurations, we evidence a direct correlation between Fermi levels positioning and the bond length in ladder-patterned APBs. The changes on the APB bond lengths and electronic properties from III-V to II-VI ladder APBs are discussed based on the charges and atoms electronegativity. We then show how the specific atomic configuration of the zigzag-patterned and ladder-patterned APBs differ from the point of view of force accommodation. As a result, ladder-patterned APBs are found to be much more sensitive to any change of stress or the chemical environment. We finally demonstrate that a small change in the APB bond length deeply modifies the band structure and optoelectronic properties of the systems (for both III-V and II-VI semiconductors), with possible $n$- and $p$-doping type inversion, thus opening the way towards APB-engineered photoelectric devices.