Fabio La Mattina

Over the last decades, the development of micro- and nanoparticle pastes (nanopastes) for sinter-bonding (sintering) has been a major research effort in the field of micro- and nanojoining, firstly of Ag-based pastes, and more recently also of Cu-based pastes. One classical application scenario is semiconductor die attach for power electronics, where sintering can provide bonds with superior temperature stability as well as thermal and electrical conductivity. A recently proposed novel application field is the use of sinter-bonding for transfer and integration of functional thin films: thin films and 2D materials can offer unique properties, e.g. for sensing, catalysis, and electronics. However, film manufacturing often requires distinct growth conditions. For subsequent film integration into a functional device, the films must be transferred and bonded to a suitable host structure. Current transfer methods often lead to film damage and/or insufficient bond qualities. In this work, we present sinter-bonding with nanopastes as a flexible and easy-to-use method to realise high-quality thin-film transfers and provide an in-depth discussion of the process steps and bonding mechanisms.

We present α-Al2O3 XAS, XES and RIXS measurements across the Al L2/L3 edges at about 79 eV excitation energy. In the emission spectra, we identify two fluorescence peaks, corresponding to electronic transitions into the 2p core hole from mixed states of Al 3s and Al 3d character, both mixed with O 2p orbitals. Even if the XAS spectrum shows more than one resonance, surprisingly only one clear RIXS signal with energy loss equal to 10.7 eV is present in the data. Nevertheless, this allows us to tentatively extract from the measured high-resolution data the linewidths for fluorescence and RIXS transitions, with the latter being almost a factor of two smaller than the former.

MXenes are 2D transition metal carbides, nitrides, and/or carbonitrides, capable of intercalation by various cations through chemical or electrochemical means. Previous research has primarily focused on intercalating alkaline and alkaline earth cations, such as Li+, K+, Na+, Mg2+ or alkylammonium cations, into Ti3C2Tx MXenes. However, the impact of intercalated transition metal (TM) ions on the electronic and electrochemical properties of MXenes remains largely unexplored. In this study, we investigated the effects of pre-intercalated Cu ions on Ti3C2Tx MXenes and vice versa to gain a comprehensive understanding of how the electronic and electrochemical properties of both intercalated TM ion and MXene host are altered. Using in-situ X-ray absorption spectroscopy (XAS), we reveal changes in the oxidation states of intercalated Cu ions and Ti atoms during charging and their corresponding role in charge storage mechanisms. Our findings show that electronic coupling between Ti3C2Tx and Cu ions results in modified electrochemical and electronic properties compared to pristine Ti3C2Tx. These insights lay the foundation for the rational design and utilization of TM ion intercalants to tailor the properties of MXenes for various electrochemical systems and beyond.

In the past 5 years, the transfer of epitaxial oxide thin films has drawn a renewed interest in the scientific community. The major challenge in this technology is to minimize the appearance of extended bulk defects such as plastic deformations, cracks, and delamination, which are induced by the transfer process to a new host substrate. In this work, a procedure for the transfer of epitaxial oxide films where a rigid bond to the final host holder is obtained via a metallic Au/Ag bonding layer is presented. Here, the transfer of SrRuO₃ (SRO) and SrRuO₃/SrTiO₃ (STO) epitaxial films grown on a water‐soluble Sr₃Al₂O₆ sacrificial layer is reported. These epitaxial films are grown on a STO substrate and transferred onto a Si host substrate. Roughness values lower than 1nm are observed for the transferred SRO membranes. Cross‐section analysis shows straight interfaces without plastic deformation of the membranes. X‐ray diffraction rocking‐curve analysis evidences that mechanical damage is minimized and the membranes remain close to their initial quality. This procedure represents an important step forward in the development of advanced technologies for membrane transfer of epitaxial oxides and superstructures.

The compound SrAl₂O₄:Eu²⁺,Dy³⁺ is currently one of the best‐performing persistent phosphors and numerous studies have been performed to understand the mechanisms involved in its afterglow process. One aspect which so far has received only limited attention is the dependence of loading curve characteristics on dopant concentrations. Herein, a detailed study of the loading curves of SrAl₂O₄:Eu²⁺,Dy³⁺ as a function of composition, sample temperature, and pump intensity is presented, completed by emission decay and quantum yield measurements. The observed emission decays can be described using the Inokuti−Hirayama equation for a Dexter energy transfer (ET) process. As the Dexter ET rate and the electron transfer rate have a similar radial dependence, the Inokuti−Hirayama equation can also describe the electron transfer process involved for the trapping process. These observations indicate that in this persistent phosphor, the trapping process is a local process; however, different types of traps appear to present different “Dexter” critical radii R₀. This electron transfer is also temperature dependent, which requires further investigations.

Nanomultilayers are complex architectures of materials stacked in sequence with layer thicknesses in the nanometer range. Their application in microelectronics is challenged by their thermal stability, conductivity, and interface reactivity, which can compromise their performance and usability. By using different materials as thermal barriers and by changing their thickness, it is possible to manipulate interfacial effects on thermal transport. In this work, we report on the thermal conductivity of Cu/W, Cu/Ta, and Cu/TaN sputter deposited nanomultilayers with different thicknesses. The resistive interfacial effects are rationalized and discussed also in relation to the structural transformation into a nano-composite upon high-temperature annealing.

The temperature and magnetic field dependence of resistivity in WO_2.9 was investigated. The variation of resistivity with temperature displayed unusual features, such as a broad maximum around 230 K and a logarithmic increase of resistivity below 16 K. In the temperature range 16–230 K, we observed metallic-like behavior with a positive temperature coefficient. The combined analysis of resistivity and magnetoresistance (MR) data shows that these unusual transport properties of WO_2.9 can be understood by considering the (bi)polaronic nature of charge carriers. In contrast to magnetization data, superconducting transition below T_c = 80 K was not detected in resistivity measurements, indicating that the superconductivity is localized in small regions that do not percolate. We found a strong increase in positive MR below 80 K. This effect is similar to that observed in underdoped cuprates, where the substantial increase of MR is attributed to superconducting fluctuations in small clusters. Therefore, the temperature dependence of MR indicates the presence of non-percolating superconducting clusters in WO_2.9 below 80 K in agreement with magnetization data.