Molecules are emerging as new benchmark for metrology and fundamental physics research, driving the demand for spectroscopic techniques combining high sensitivity and resolution. Photoacoustic spectroscopy has proven to combine high sensitivity with appealing features like compactness, wavelength-independent and background-free detection. To date, photoacoustic sensing has mostly been focused on high-pressure applied trace-gas analysis, while accessing the low-pressure regime has been considered not compatible with efficient acoustic wave propagation. However, sensing gas samples at low pressure is the key to get access to high-resolution spectroscopy. Here, we demonstrate that sub-Doppler saturation spectroscopy can be performed on low-pressure trace gases in a cavity-enhanced photoacoustic sensor with mW-level mid-infrared radiation. Moreover, we show that the same setup can be operated at higher pressure, enabling trace-gas detection with 5 parts-per-billion sensitivity with a laser power as low as 35 microwatts. This allows to extend the unique advantages of the photoacoustic technique to metrology and fundamental physics and provides the mid-infrared with a cost-effective, flexible tool combining high sensitivity and resolution.

In the vast panorama of optical-based detection strategies, photoacoustic spectroscopy is particularly suitable for its versatility, high sensitivity, and scalability potential. In cantilever-enhanced photoacoustic sensors, the interferometric readout of the membrane oscillation guarantees exceptional signal-to-noise ratio, often at the expense of limited compactness. In this work, we propose a novel approach combining cantilever-enhanced photoacoustic trace-gas excitation with self-mixing interferometry for absorption signal readout. The sensor performance has been compared in terms of detection sensitivity and stability over time to that achieved with a more complex state-of-the-art readout system using a bulky balanced Michelson interferometer. Both sensors, operated with the same excitation laser emitting at 4.57µm and addressing the same target N2O line, demonstrated the same spectroscopic results in terms of signal-to-noise ratio of the acquired spectra and the same minimum detection limit of 90 parts-per-billion at tens of seconds integration time. The self-mixing readout benefits from a much reduced size, paving the way for future system downsizing and easier integration while maintaining high-sensitivity detection levels. Moreover, the intrinsic wavelength independence of photoacoustic spectroscopy, together with the broad-spectral adaptability of self-mixing readout, allows, in principle, a wide wavelength-tailorability of the sensor.

In this work we present to our knowledge the most precise measurement of the Be-7 electron capture decay half-life in a host material. A silicon carbide sample with similar to 8.62 x 10(9 7)Be atoms was measured for 83.5 d on an ultra-low background high purity Ge detector located deep underground in the Laboratori Nazionali del Gran Sasso, Italy. The result obtained for the decay half-life is T-1/2 = 53.284 +/- 0.016 d, which corresponds to an uncertainty of 0.3 parts per thousand. Thanks to the high sensitivity achieved, this measurement is paving the way to further investigations on this process aiming to understand how environmental conditions may affect the decay half-life.

Among high-performing trace-gas sensing technology, photoacoustic spectroscopy (PAS) has proven to be a promising and widely used technique, mostly because of its unique advantages. Among them, the zero-background detection, the high versatility in the choice of the excitation source, and the possibility of interrogating gaseous samples in very reduced volumes are worth mentioning. The key component of a PAS sensor is the spectrophone, which is responsible for the transduction of the acoustic wave into a measurable signal and whose properties determine the sensor's performance. In the search for novel and highly-performing spectrophones, a novel configuration combining a custom-made racket-shaped silicon-based Micro-Electro-Mechanical system (MEMS) cantilever with an easy-to-build acoustic resonator, made by a dual-tube configuration, is presented. The new configuration was tested for trace-gas sensing in a simple single-pass configuration, demonstrating a final detection sensitivity of 0.34ppb at around 20 seconds of averaging time for N2(O) trace-molecule detection.

Part-per-trillion level trace-molecule detection is becoming increasingly crucial fora variety of fields in our modern society, from climate change monitoring and mitigation to health studies, from industrial processes control to safety and security. The race towards more performing sensors is witnessing a rapid evolution of photoacoustic systems, whose high degree of flexibility allows them to merge their robustness and compactness to cavity-enhanced configurations, boosting their ultimate sensitivity. This work proposes an advanced configuration of a cavity-enhanced cantilever-based photo-acoustic sensor. The developed setup exploits the advantages of mid-IR detection and introduces significant novelties in the key components, namely a non-conventional silicon "racket-shaped"cantilever, a combination of a dual-tube acoustic resonator and optical cavity to enhance the photoacoustic signal, and an improved optical readout system consisting in a stabilized balanced Michelson interferometer. With a final detection sensitivity of dry N2O down to 17 parts- per-trillion for 20 s of integration time, corresponding to a Normalized Noise Equivalent Absorption coefficient equal to 5.98 x 10-11cm-1 WHz-1/2, the achieved performance is in line with the best results obtained with PAS-based sensing addressing the same target molecule. This demonstrates the wide range of yet unexplored configurations of photoacoustic systems that can be exploited towards real-time sub-ppt sensors for practical detection of trace chemicals in the air.

Versatile, ultracompact, easy-to-handle, high-sensitivity sensors are compelling tools for in situ pivotal applications, such as medical diagnostics, security and safety assessments, and environmental control. In this work, we combine photoacoustic spectroscopy and feedback interferometry, proposing a novel trace-gas sensor equipped with a self-mixing readout. This scheme demonstrates a readout sensitivity comparable to that of bulkier state-of-the-art balanced Michelson-interferometric schemes, achieving the same spectroscopic performance in terms of signal-to-noise ratio (SNR) and minimum detection limit (MDL). At the same time, the self-mixing readout benefits from a reduced size and a lower baseline, paving the way for future system downsizing and integration while offering a higher detectability for lower gas concentrations. Moreover, the intrinsic wavelength independence of both self-mixing and photoacoustic techniques allows the applicability and tailorability of the sensor to any desired spectral range.

Trace-gas sensing at parts-per-trillion level or below, has become a hot research topic impacting daily-life applications such as human health, environmental monitoring, and security control. The scientific effort together with technological progress has enabled the possibility to reach ultra-high sensitivities also with compact and robust photoacoustic-based setups, exploiting their intrinsic high degree of flexibility with the sensitivity enhancement provided by mid-IR semiconductor laser sources and high-finesse optical cavities. In this framework, we present a study of an advanced configuration for photo-acoustic trace-gas sensors, aiming at optimizing all the key components to enable a ppt detection level. Alongside exploiting a mid-infrared continuous-wave Quantum Cascade Laser as the excitation source, a Fabry-Perot optical resonator is implemented for an efficient intra-cavity power enhancement. For the acoustic-to-voltage transduction an unconventional and highly performing "racket-shaped" silicon-based Micro-Electro-Mechanical System is exploited, whose oscillations are measured via a balanced Michelson interferometric readout.

Studies on gas trace spectroscopy have intensified considerably in recent years due to the great demand for reliable sensors in the quantification of gas concentrations in various fields, including environmental monitoring, medical sensors, early fire detection, and security control. Among various approaches, photoacoustic spectroscopy (PAS) is promising due to wavelength independence, zero background, and small investigating volumes. In this context, we report the realization and implementation of a new low-frequency, spring-like Micro Electro Mechanical System (MEMS) acting as a microphone in a PAS setup. The MEMS behaviors were studied experimentally both in amplitude and frequency modulation, analyzing the figures of merit (FOM) of each approach. Finally, a long-term stability analysis is also reported to exploit the ultimate detection limits achievable with each approach.

The achievable sensitivity level of photo-acoustic trace-gas sensors essentially depends on the performances of the acoustic transducer. In this work, the mechanical response of different silicon-based micro-electro-mechanical systems (MEMS) is characterized, aiming at investigating both their mechanical properties, namely the resonance frequency and the quality factor, and the minimum detection limit (MDL) achievable when they are exploited as an acoustic-to-voltage transducer in a trace-gas photoacoustic setup. For this purpose, a 4.56µm Continuous-Wave (CW) quantum cascade laser (QCL) is used to excite a strong N2O roto-vibrational transition with a line strength of 2.14 × 10−19 cm/molecule, and the detection of MEMS oscillations is performed via an interferometric readout. As a general trend, the minimum detection limit decreases when the resonance frequency investigated increases, achieving a value of 15 parts per billion with a 3 dB cut-off lock-in bandwidth equal to 100 mHz, around 10 kHz.

Nowadays, the scientific community and industry are increasingly pressed to provide solutions for developing compact and highly-performing trace-gas sensors for several applications of crucial importance, such as environmental monitoring or medical diagnostics. In this context, this work describes a novel configuration, making use of a mid-IR spectrophone combining the compactness of a photo-acoustic setup, a non-conventional micro-electro-mechanical (MEMS) acousto-to-voltage transducer, and the sensitivity enhancement given by a cost-effective and easy-to-build dual-tube resonator configuration. In the optimal condition of sample pressure, the system developed in this work can achieve a minimum detection limit (MDL) equal to 0.34 ppb when averaging up to 10 s. Compared with previous literature of single-pass photoacoustic-based sensors for N2O, this corresponds to a significant improvement both for the achieved normalized noise equivalent absorption coefficient (NNEA) equal to 1.41 × 10−9 cm−1WHz−1/2, and for a Noise-Equivalent-Concentration (NEC) of 1 ppb obtained at 1 s of averaging time.

We present our most recent results on trace-gas detection with an intracavity cantilever-enhanced photoacoustic sensor. A full performance analysis is performed using a standard cantilever, and preliminary results exploiting alternative configurations are discussed.

The race towards compact and robust sensors able to detect extremely low concentrations of molecules in the air plays an important role in our modern society, impacting sectors such as energy production, environmental monitoring, transportation, agriculture, safety, and security. During the last decade, optical detection with ultra-high sensitivity, down to the part-per-quadrillion level, was demonstrated with cavity-ring down techniques [1], enabling laser sensors to enter areas such as archaeology (radiocarbon dating), climate change monitoring, bio-fuel control, contaminant assessment for the semiconductor industry and so on. More recently, photoacoustic sensors based on quartz tuning forks and silicon cantilevers have shown great potential in achieving a sensitivity at the level of the techniques mentioned above, especially when combined with narrow-linewidth mid-infrared lasers and high-finesse optical cavities [2]–[5]. Besides the extremely high sensitivity, such sensors have unique characteristics of robustness, record dynamic range, and compact size, which make them particularly attractive for in-field applications.

Emerging wide bandgap semiconductor devices such as the ones built with SiC have the potential to revolutionize the power electronics industry through faster switching speeds, lower losses, and higher blocking voltages, which are superior to standard silicon-based devices. Besides the widely used 4H-SiC, the cubic polytype 3C-SiC, with 2.3 eV band gap, has interesting features such as possibility to be grown on a silicon substrate, a reduced density of states at the SiC/SiO2 interface, and a higher channel mobility—characteristics that are ideal for its incorporation in metal oxide semiconductor field effect transistors. However, realization of defect free bulk 3C-SiC wafers is very challenging and p+ doping and activation mechanisms using ion implantation followed by thermal annealing are not well-known. Within the framework of the European R D project CHALLENGE, we studied ion implantation of Aluminum on bulk 3C-SiC as well on EPI grown 3C-SiC on Si performed by furnace and/or laser anneal. For 3C-SiC on Si, results using long furnace anneal at temperature < 1400 °C as well as laser anneal are presented. For bulk 3C-SiC, higher temperature anneals (1650 to 1800 °C) are studied. SIMS, ECV, -and TLM characterization methods have been used to study the chemical and active dopant profiles as well as sheet resistance and contact resistance. Demonstration of a fully implanted PiN vertical Diode on Bulk 3C-SiC is then presented.

Today some raw materials (RMs) have become essential in the manufacturing of common goods and technologies we use every day. Readily accessible RMs, such as rare-earth-elements, indium, neodymium, etc., are important to EU industries and allow the transition towards a low-carbon economy. With the future global resource use projected to double by 2030, addressing raw materials through the entire value chain becomes a priority as well as transferring these ideas to youngsters. “RAWsikoMaterials aroud us” is a serious videogame developed in the framework of Raw Matters Ambassadors at Schools, an European project funded by EIT RawMaterials, with the aim to offer teachers an educational tool able to increase student awareness of the current societal challenges for a sustainable innovation by using an innovative approach. RAWsiko is focused on RMs important for the EU economy but at risk of supply, their distribution in the world, their use in the modern technologies and why access to them is pivotal for European economy. The players can experience the complexity of the raw material supply that occurs behind some everyday life devices such as flat screens and lamps, but also behind the equipment for the transition to the renewable energies such as photovoltaic panels and wind turbines. RAWsiko can be a support to teach science, technology, and citizenship in a funny way by involving students from 11 to 19 years old and contributing to disseminate the issues of the European Green Deal and the Sustainable Development Goals of the United Nation Agenda 2030. Such knowledge and awareness among the younger generation is indispensable to secure sustainable success in the European raw materials sector and will help to create a new generation of people sk illed in entrepreneurship and raw materials, and respecting our Earth.

The root mean square (rms) surface roughness extracted from atomic force microscopy is widely employed to complement the characterisation of ion implantation processes in 4H-SiC. It is known that the protection of a carbon film eliminates or mitigates roughening of the SiC surface during postimplantation annealing. This study, based on a rich original data collection of Al+ ion implanted 4H-SiC samples, allows for a quantitative description of the surface morphology as a function of the annealing temperature and time and of the Al implanted concentration. With increasing thermal budget, the evolution from flat, to blurred with ripples, granular, and finally jagged surface, results in a monotonous increase in the root mean square roughness. Additional information is given by the trends of the roughness exponent and of the correlation length, extracted from the height-height correlation function, which account for the surface evolution below 1700°C and for the effect of the Al implanted concentration on the ripple size, respectively. A combination of low roughness parameter and high correlation length identify the transition from ripples to jagged morphology. LAY DESCRIPTION: Selective area doping is a key step in the fabrication of hexagonal Silicon Carbide (4H-SiC) power electronic devices. It is achieved by ion implantation followed by a high temperature postimplantation annealing to restore the lattice and electrically activate the dopants. Aluminium, the preferred p-type dopant, is electrically activated at temperature ranging between 1500°C and 2000°C. The time required to complete the activation process is longer the lower the annealing temperature, spanning between some minutes and hundreds of hours. During annealing, 4H-SiC wafers are encapsulated by a temperature-resistant carbon layer (C-cap) in order to avoid step bunching and reduce surface roughening. Nevertheless, surface modifications can occur at high temperature. For this reason, the characterisations of 4H-SiC doping processes report not only the electrical activation of the dopants, but also the root mean square surface roughness obtained at the end of the process. However, rms values can be scattered because technological parameters such as the heating system and the way to deposit and remove the C-cap can affect the final result as well as the process parameters. Furthermore, the C-cap resistance to long annealing has been proven only by electrical measurements, but the surface morphology has never been observed. This work presents a quantitative characterisation of the surface morphology of Al implanted 4H-SiC as a function of the annealing temperature, time and of the Al implanted concentration, independent of the heating system and of the C-cap technology. The produced sample collection allowed to correlate characteristic surface features with the corresponding quantities extracted from image analysis that can be more sensitive to process parameters than the sole rms. These findings can be used to enrich process optimisation tools.

The results of the first experiments for achieving the thermal equilibrium during 1300 °C annealing of 1×10 20 cm -3 ion implanted Al + in 3C-SiC are shown. X-ray diffraction, through reciprocal space maps and 2Θ scans, characterizes the 3C-SiC lattice recovery. The achievement of a ohmic behavior of Ni/Al/Ti alloy indicates the onset of a measurable electrical activation of the Al implanted layer. The Al electrical activation is qualified through the implanted layer sheet resistance.