Magnetoelectric dual-particulate composites with wasp-waisted magnetic response for broadband energy harvesting

International audienceDual-particulate composites of cobalt ferrite dispersed in a fully dense PZT matrix are produced by quite-fast sintering of mechanically activated powders. By high-energy milling of the powders a bi-modal grain size distribution, with octahedral nano-grains and larger grains grown by multiple parallel twinning, are achieved in the final microstructure. The material display a "wasp-waisted" magnetic response as a consequence of the two main CoFe2O4 grain populations and can be exploited for broadband energy harvesting or field sensors. After poling under 5 kV/mm, a maximum d(33) of 30 pC/N was achieved. This value is an order of magnitude lower than that of bulk PZT. Nevertheless, a magnetoelectric coefficient of 1.74 mV cm(-1) Oe(-1) is obtained, which suggests the high potentiality of these materials, since this value is higher than that shown by magnetoelectric composites with similar composition and connectivity reported in literature. This is so for a partially poled material and thus, magnetoelectric coefficients should be significantly increased by improving the poling process

Strain characterization in SiGe epitaxial samples by Tip Enhanced Raman Spectroscopy

The progressive downsizing of semiconductors is driving information processing technology into a broader spectrum of new applications and capabilities. Strained silicon has become one of the best solutions for integrated circuits thanks to the advantages in terms of miniaturization. Indeed, a biaxial tensile stress applied to the silicon in the channel region of a MOSFET increases the mobility of carriers. This stress can be imposed by doping the silicon underneath with germanium, causing a mismatch between the lattice constant thus improving the electrons’ mobility [1]. Over the years, there has been an increasing need, especially in the industrial sector, to develop faster and non-destructive characterization techniques to monitor strain during the manufacturing phases of semiconductor devices. Currently, Tip-Enhanced Raman Spectroscopy (TERS) is one of most powerful methods for strain characterization, as it is a non-contact and non-destructive technique with a lateral resolution of a few nanometers and the capability of analyzing and collecting signals from the most superficial layer of a sample. The enhanced field is strongly restricted to the surface plasmons region, just a few nanometers deep [2], thanks to the simultaneous use of a nanometric tip of an Atomic Force Microscope (AFM) and a laser from a Raman spectrometer [3]. The analyzed sample was provided by CEA-Leti (Laboratoire d'électronique des technologies de l'information, Grenoble) and consists of a (001) silicon substrate where an epitaxial layer of Si0.7Ge0.3 with thickness of 17 nm is grown following several patterns. The AFM probe employed is characterized by an innovative coating which enables its implementation in the clean room for in-line characterization. TERS is used to map the variation in the position of the silicon peak in the local Raman spectrum (≈520.5 cm-1) along the sample pattern in order to identify the strain profile with a resolution of a few nanometers. The results confirm that TERS represents a powerful tool in monitoring the quality of production lines in the semiconductor industry and currently provides the best resolution among the Raman techniques for the strain characterization. References [1] P. Dobrosz et all, Surface and Coatings Technology, 2005, 200, 1755–1760. [2] F. Shao, R. Zenobi, Analytical and Bioanalytical Chemistry, 2019, 411, 37–61. [3] N.Hayazawa et al., Nanosensing Materials Devices, and Systems III, 2007, Proc. of SPIE Vol. 6769, 67690P

Challenges - real time nano characterization related technlogieeS

The project CHALLENGES – Real-time nano-CHAracterization reLatEd techNoloGiEeS – aims to develop innovative Non-Destructive Techniques (NDTs) for reliable inline multiscale measurements down to the nanoscale, and fully compatible with different factory environments. The developed metrology technologies will enable the increase of speed, resolution, sensitivity, spectral range and compatibility within different nano-related production environments, finally improving products performance, quality and reliability, with the consequent bosting of competitiveness. The CHALLENGES’s innovation will be developed exploiting the plasmonic enhancement of optical signals. It will provide a non-destructive approach based on the use of multipurpose nano-optical techniques to enable a reliable real-time nano-scale characterization in the factory floor, using plasmonic enhanced Raman, InfraRed (IR) and Photoluminescence signals. CHALLENGES is focused on broadening the scope of AFM techniques useable in semiconductor manufacturing by implementing suitable plasmonic-based technologies to bring in industrial environments the capabilities of optical spectroscopies at the nanoscale, already demonstrated at lab level. Such composite and hybrid measurement techniques will enable new applications for the already proven industrial AFM-based characterization technologies. Signal amplification by localized plasmon resonance at a sharp AFM tip will allow improving both the spatial resolution well beyond the optical diffraction limit and the local signal intensity with an improvement of the signal/noise ratio. Improvements are also expected concerning the time scale resolving capabilities. The improvement of the spatial resolution will allow to obtain nanoscale spectral maps, compatible with the size of the current electronic devices, while the improved signal-to-noise ratio will allow for a faster and reliable punctual analysis. The final goal is to develop nanoscale metrological NDTs based on SPM platforms, for doping, annealing, metal contamination, dangling bonds presence and strain measurement directly within the production lines with real-time capabilities

Controlling electrical and optical properties of zinc oxide thin films grown by thermal atomic layer deposition with oxygen gas

The preparation of ZnO thin films with controlled electrical resistivity and optical properties is often challenged by the presence of defects, such as oxygen vacancies or interstitial zinc. Here, we investigate the material properties of ZnO polycrystalline thin films prepared by thermal Atomic Layer Deposition (ALD) with the presence of molecular oxygen pulsing during the growth. By means of structural, electrical and optical characterizations, we identify key growth parameters of this unusual ALD process. Unexpectedly, the influence of oxygen molecules on the crystallography, microstructure and morphology of ZnO films is significant from hundred-nanometers to micrometer thick film. The electrical resistivity of the films grown with oxygen gas shows a dramatic increase from 3 to 4 orders of magnitude. Additionally, photoluminescence measurements reveal that deep-level emissions caused by defects located deep in the band gap can be reduced by applying an adequate pulsing of oxygen gas during the process. Finally, we conclude with a discussion about the degree of consistency between the chemical composition, the inner strain and the optical and electrical properties of the films obtained with the different thermodynamic parameters of growth. Several hypotheses are discussed in order to understand the dominance of (002) orientation in the presence of oxygen during the ALD growth process

SiGe Bandgap Tuning for High Speed Eam

International audienc

Doping porous silicon with erbium: pores filling as a method to limit the Er-clustering effects and increasing its light emission

International audienceEr clustering plays a major role in hindering sufficient optical gain in Er-doped Si materials. For porous Si, the long-standing failure to govern the clustering has been attributed to insufficient knowledge of the several, concomitant and complex processes occurring during the electrochemical Er-doping. We propose here an alternative road to solve the issue: instead of looking for an equilibrium between Er content and light emission using 1-2% Er, we propose to significantly increase the electrochemical doping level to reach the filling the porous silicon pores with luminescent Er-rich material. To better understand the intricate and superposing phenomena of this process, we exploit an original approach based on needle electron tomography, EXAFS and photoluminescence. Needle electron tomography surprisingly shows a heterogeneous distribution of Er content in the silicon thin pores that until now couldn't be revealed by the sole use of scanning electron microscopy compositional mapping. Besides, while showing that pore filling leads to enhanced photoluminescence emission, we demonstrate that the latter is originated from both erbium oxide and silicate. These results give a much deeper understanding of the photoluminescence origin down to nanoscale and could lead to novel approaches focused on noteworthy enhancement of Er-related photoluminescence in porous silico