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Black silicon (BSi) is a synthetic nanomaterial with high aspect ratio nano protrusions inducing several interesting properties such as a very large absorptivity of incident radiation. We have recently shown that heavily doping the BSi in volume enables to significantly enhance its mid infrared absorptivity and tune its spectral range of interest up to 20 micrometer. In the present letter, we explore the effect of surface doping on BSi radiative properties and it absorptance, in particular since surface doping enables reaching even larger dopant concentrations than volume doping but at more limited penetration depths. We considered 12 different wafers of BSi, fabricated with cryogenic plasma etching on n and p-type silicon wafers and doped using ion-implantation with different dopant types, dosages and ion beam energies leading to different dopant concentrations and profiles. The different wafers radiative properties, reflectance, transmittance and absorptance, are measured using Fourier transform infrared spectroscopy. We show that doping an n-type BSi wafer with Phosphorous with a dose of 10^17 atm/cm2 and an energy of 100 keV increases its absorptivity up to of 98% in the spectral range of 1-5 micrometer. We propose a simple phenomenological explanation of the observed results based on the dopant concentration profiles and the corresponding incident radiation penetration depth. Obtained results provide simple design rules and pave the way for using ion-implanted BSi for various applications such as solar energy harvesting, thermo-photovoltaics and infrared radiation sensing where both high absorptance and variable dopant concentration profiles are required.

In this paper, we explore the far-field radiative thermal rectification potential of common materials such as metals, dielectrics and doped semi-conductors using radiative and thermo-radiative properties extracted from literature. Ten different materials are considered. The rectification coefficient is then calculated for 44 pairs of materials; each pair can be used for the two terminals of a radiative thermal diode. A thermal bias of 200 K is considered. The choice of materials and thermal bias value is only bound by data availability in literature. Obtained results, highlight new candidate materials for far-field radiative thermal rectification. They also highlight materials where thermal rectification is not negligible and should be considered with care in heat transfer calculations when considering systems subject to a comparable thermal bias and where these materials are used. Among the materials studied, undoped Indium Arsenide (InAs) shows great promise to be employed for thermal rectification, with a thermal rectification ratio reaching 90.5% in combination with other materials. Obtained results pave the way for an optimized design of thermal radiation control and management devices such as thermal diodes.

The full architecture of an electrostatic kinetic energy harvester (KEH) based on the concept of near-limits KEH is reported. This concept refers to the conversion of kinetic energy to electric energy, from environmental vibrations of arbitrary forms, and at rates that target the physical limits set by the device's size and the input excitation characteristics. This is achieved thanks to the synthesis of particular KEH's mass dynamics, that maximize the harvested energy. Synthesizing these dynamics requires little hypotheses on the exact form of the input vibrations. In the proposed architecture, these dynamics are implemented by an adequate mechanical control which is synthesized by the electrostatic transducer. An interface circuit is proposed to carry out the necessary energy transfers between the transducer and the system's energy tank. A computation and finite-state automaton unit controls the interface circuit, based on the external input and on the system's mechanical state. The operation of the reported near-limits KEH is illustrated in simulations that demonstrate proof of concept of the proposed architecture. A figure of $68\%$ of the absolute limit of the KEH's input energy for the considered excitation is attained. This can be further improved by complete system optimization that takes into account the application constraints, the control law, the mechanical design of the transducer, the electrical interface design, and the sensing and computation blocks.

Electrostatic transducers for vibration energy scavenging have been an object to numerous studies, but are still facing major issues relating to their conditioning circuit. One of the most popular ones uses a charge pump and a flyback circuit based on a Buck DC-DC converter (Fig. 1). A commutation between the energy accumulation in the charge pump and the recharge of the buffer capacitor Cres is assured by a switch which is the major bottleneck in the energy harvester circuit. The commutation timing of the switch determines the efficiency of the energy harvesting. In previous papers [1] the switch commutates periodically with some fixed duty ratio. However, this solution is not appropriate when the environment parameters, e.g. the vibration frequency, change. We found that the switching should be ordered by the internal state of the circuit, an not by some fixed timing scenario. We presents how to find the optimal operation mode of the harvester. To validate the study, the system was modeled using a mixed VHDL-AMS - ELDO model., Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838)