Abstract The two-dimensional form of tellurium, named tellurene, holds intriguing properties for a broad range of applications. Here, the large area growth by molecular beam epitaxy of tellurium on Sb-passivated Si(111) is demonstrated. The influence of growth temperature and film thickness on the material properties was investigated. At optimized conditions, the two-dimensional growth of Te films as thin as 4 nm is established. The epilayers possess a (10 $$\bar{1}$$ 1 ¯ 0) surface orientation, with the Te chiral chains lying parallel to the surface plane. The van der Waals epitaxy occurs with the formation of a Sb2Te3 interlayer, as confirmed by transmission electron microscopy. Grazing incidence diffraction shows a discrete set of domains with in-plane rotation angles, which result in the alignment of Te lattice planes of neighbouring domains. The high hole mobility of epitaxial tellurium at room temperature is proven by Hall effect measurements. Optical spectroscopy measurements strongly support the electrical data. The thickness-dependent vibrational properties of the material were studied by Raman spectroscopy: by scaling down the film thickness, characteristic features of few-layer tellurium are observed. Hence, the present study opens the way for the integration of two-dimensional tellurium on silicon and the design of novel heterostructures of layered tellurides.

Nonvolatile control of electron spin using electric polarization offers a promising route toward energy-efficient spintronic devices. Early studies of conventional ferroelectrics, from GeTe to perovskite oxides, demonstrated that polarization switching can reversibly control spin textures and spin-to-charge conversion (SCC) in nonmagnetic materials. However, practical device implementation remains limited by polarization instabilities in ultrathin ferroelectrics and the modest efficiency of SCC. Recent advances in two-dimensional (2D) van der Waals (vdW) ferroelectrics provide new opportunities to overcome these challenges. In particular, sliding ferroelectricity enables polarization switching through interlayer displacement, offering ultralow switching barriers and reduced defect propagation while preserving the in-plane conductivity required for SCC and compatibility with atomically thin devices. In this Perspective, we discuss the evolution of ferroelectric control of spin-orbit phenomena from conventional bulk materials to emerging vdW ferroelectrics, bridging recent advances in 2D ferroelectricity with the field of spintronics. We examine polarization-controlled spin-orbit responses, including Rashba-Edelstein and spin Hall effects, and show how stacking, sliding, and twist—combined with strong spin-orbit coupling and persistent spin textures—expand the design space for ferroelectric spin-orbit (FESO) devices. Finally, we highlight opportunities offered by vdW ferroelectric altermagnets and identify the materials and device challenges that will be critical for realizing practical ferroelectric spintronic architectures.

2D semiconductors such as MoS2 offer a promising pathway for future logic and analog transistors and memories. These materials feature scalable channel size, back-end of the line compatibility, and high mobility for relatively small channel thickness approaching few atomic monolayers. An open issue for the development of mature 2D-based digital technology is the availability of both n- and p-type transistors, as well as the ability to control the transistor type in a reconfigurable way. This work presents a novel MoS2-based transistor exhibiting reconfigurable n- or p-type characteristics, namely switching from n-type to p-type and vice versa, which is attributed to ion-assisted doping from the gate dielectric layer. Extensive characterization of the device shows repeatable switching with relatively low cycle-to-cycle (C2C) and device-to-device (D2D) variability. A reconfigurable p-n junction is demonstrated via a junction-less multi-gate MoS2-based transistor. We also demonstrate various reconfigurable logic gates, including a complementary metal-oxide-semiconductor (CMOS) inverter, a fully n-type inverter and an XNOR logic gate based on MoS2 transistors, showcasing the generality and flexibility of channel reconfiguration for logic circuit applications. These results underscore the strong potential of reconfigurable MoS2 transistors for ultra-scaled, reconfigurable logic circuits.

Spin polarimetry of low-energy electron beams is of considerable importance for a wide range of applications. However, an efficient method for two-dimensional, quantitative spin mapping is still lacking as state-of-art detectors rely on the sequential measurement of the spin polarization at individual points in energy and momentum space. In this work, we exploit the spin-dependent transmission of electrons through ultrathin magnetic layers embedded in a suspended matrix of a few graphene layers, fabricated in the form of micrometric magnetic freestanding membranes with an overall thickness below 10 nm, allowing significant transmission of low-energy electrons. We systematically investigate the role of deposition process, number of graphene layers, and magnetic materials with both in-plane and out-of-plane magnetization. We end up with optimized fabrication conditions for producing highly reliable elastic membranes with energy-dependent transmittivity suitable for spin filtering. We also present an analytical model that describes the detection of the spin polarization of an electron beam and outlines the experimental conditions under which such measurements can be performed using suspended magnetic membranes. This research paves the way for the development of spin filters that can be seamlessly integrated into existing detection systems, enabling spin-, angle-, and energy-resolved photoemission experiments as add-on functionality.

Ultrashort laser pulses have proven to be invaluable tools for studying the out of equilibrium magnetic properties of matter [1]. Significant interest has been directed toward understanding the temporal evolution and manipulation of the magnetization vector $\vec{M}$ in ferromagnets. Pump-probe schemes have been extensively employed in the last twenty years to detect the impulsive changes in $\vec{M}$ induced by light and to track its dynamics with femtosecond resolution [2]. However, relatively few studies have explored the spatial dependence of light-induced demagnetization. These studies have predominantly utilized either point-scanning techniques [3] or a combination of polarization optics and CCD cameras [4]. In this work, we leverage the capabilities of a self-referencing ultrafast holographic microscope [5], [6] to image the spatio-temporal dynamics of the light-induced demagnetization in a Pt/CoFeB/MgO structure with 100-fs and sub-μm resolution.

Cu-substituted Ni ferrite systems are produced following a hydrothermal synthetic route carried out at relatively mild conditions (i.e., below 200°C). Different degrees of substitution were investigated, ranging from bare Ni ferrite to a complete Cu-substituted system (by replacing 100% of Ni with Cu). Morphological and structural characterisations point out that the introduction of Cu in the Ni ferrite (below 50% substitution) causes a gradual reduction of the average diameter of the ferrite polyhedral nanoparticles maintaining the Ni ferrite structure. At higher content of Cu, instead, the morphology evolves toward the co-presence of iron oxides (magnetite and hematite) and copper oxide (tenorite), without the formation of bare Cu ferrite. The partially substituted Ni ferrite nanomaterials exhibit a mostly superparamagnetic behaviour in all samples, registering a reduction of the values of magnetisation saturation by increasing the Cu content. Transmission Mössbauer spectroscopy performed on these nanomaterials evidenced a gradual lowering of the Fe fraction occupying the octahedral sites and a consequent increment of the Fe fraction in the tetrahedral sites. Quantitative analysis confirms the gradual reduction of the Ni content within the ferrite samples, coupled with the opposite increment of the Cu content, whereas the Fe content is lower in the case of Ni75-Cu25 sample. This particular behaviour can be associated with the influence of Cu substitution in the Ni ferrite structure, with preferential replacement of Fe from the octahedral B-sites toward the tetrahedral A-sites.

Surface Plasmon Polaritons (SPPs) in Au thin films are nowadays intensively exploited for sensing applications that leverage the strong optical field confinement at the metal/dielectric interface and the easy functionalization of the Au surface. Moreover, Au thin films represent one of the common starting points for the top-down nanofabrication of plasmonic nanostructures supporting localized resonances. In this framework, strategies for the growth of high-quality Au films on transparent substrates are crucial and not yet fully established. In this study, we exploit MgO(001) substrates for the growth of thin (about 45 nm) Au films, also including an additional buffer layer of Fe. We successfully demonstrate Au samples with reduced roughness and presenting Low-Energy Electron Diffraction (LEED) features, indicating a high degree of crystalline ordering. This is supported by the experimental evidence of an increased (by almost a factor of 3) propagation length compared to a reference Au sample grown on standard glass slides, which is however still significantly lower than the one expected from first principles.

The possibility to engineer (GeTe)m (Sb2 Te3 )n phase-change materials to co-host ferroelectricity is extremely attractive. The combination of these functionalities holds great technological impact, potentially enabling the design of novel multifunctional devices. Here an experimental and theoretical study of epitaxial (GeTe)m (Sb2 Te3 )n with GeTe-rich composition is presented. These layered films feature a tunable distribution of (GeTe)m (Sb2 Te3 )1 blocks of different sizes. Breakthrough evidence of ferroelectric displacement in thick (GeTe)m (Sb2 Te3 )1 lamellae is provided. The density functional theory calculations suggest the formation of a tilted (GeTe)m slab sandwiched in GeTe-rich blocks. That is, the net ferroelectric polarization is confined almost in-plane, representing an unprecedented case between 2D and bulk ferroelectric materials. The ferroelectric behavior is confirmed by piezoresponse force microscopy and electroresistive measurements. The resilience of the quasi van der Waals character of the films, regardless of their composition, is also demonstrated. Hence, the material developed hereby gathers in a unique 2D platform the phase-change and ferroelectric switching properties, paving the way for the conception of innovative device architectures.

Flexible spintronics is an emerging field of research that has received increasing attention due to the additional functionalities that are allowed (lightweight, flexibility, shape-ability, wearability) with respect to conventional rigid systems. In this work, different strategies for the fabrication of flexible spintronic devices with perpendicular magnetic anisotropy are compared, i.e., transfer-and-bonding approaches exploiting wet and dry lift-off methods, and direct deposition on flexible substrates. To evaluate the potential of the proposed strategies, Co/Pdbased giant magneto-resistive spin-valves including a synthetic antiferromagnet reference electrode were investigated. Such stacks represent a demanding model system, owing to the large number of interfaces whose quality strongly affects the overall magnetic and electric performances. The advantages and drawbacks of the different strategies are discussed to provide crucial indications for the development of flexible spintronic devices of any complexity. Based on the results, the most suitable option for achieving high-quality heterostructures on large area surfaces via direct deposition is using polyethylene naphthalate (Teonex & REG;) tapes, provided that the processing and operating temperatures are relatively low (<525 K). On the other hand, if the process requires higher temperatures, the dry lift-off method exploiting the low adhesion between an Au underlayer and the SiOx/ Si(100) substrate is the preferred alternative.

The integration of hard magnetic alloys in the form of thick films is one of the most interesting challenges for the manufacturing of energy efficient magnetic microelectromechanical systems (MEMS) [1]. With respect to current state of the art devices, whose working principle mostly relies on the exploitation of Lorentzian forces, MEMS based on permanent magnets can potentially present lower power consumption, larger displacements and stronger actuation forces. However, despite these attractive advantages, it is generally difficult to integrate thick hard magnetic layers with currently employed MEMS fabrication techniques. Electrodeposition is a technique that is compatible with MEMS fabrication and is characterized by many significant advantages: high deposition rates, no necessity of a vacuum system, low cost, possibility to deposit alloys and composites. Despite of these advantages, electrodeposition methods capable to yield the thick hard magnetic films suitable for MEMS sensors/actuators have not been successfully developed yet. The reason resides in the problems typically encountered in the deposition of hard magnetic alloys: high residual stress, presence of cracks and inadequate surface finishing. In this context, Reverse Pulse Plating (RPP) may constitute a possible solution to address the challenges of hard magnetic alloys electrodeposition [2]. This technique can significantly reduce internal stresses and hydrogen embrittlement, inhibiting thus cracks formation. In addition, it can simplify electrolyte formulation, eliminating the need of excessive amounts of additives. Finally, it can enhance magnetic properties and refine the grain structure of the deposits, resulting in better mechanical properties. In the present work, RPP of thick and crack-free layers of CoNiP and CoPtP is investigated. These two materials are between the most studied for potential MEMS applications [3, 4]. Indeed, whereas CoPtP offers high coercivities (> 3000 Oe) and excellent remanences, CoNiP represents a low cost alternative characterized by good magnetic properties (with H C up to 2000 Oe). Co-rich CoNiP and CoPtP are deposited from a chloride based acidic electrolyte [3] and from a tartrate based bath, respectively, using ultra-fast RPP. The resulting coatings, characterized by thickness up to 20 µm, are characterized to assess their morphology, phase composition and magnetic behavior. [1] N. M. Dempsey, “Hard Magnetic Materials for MEMS Applications” in: Nanoscale Magnetic Materials and Applications, Springer, Boston, MA (2009) [2] S. Pané et al., Electrochim. Acta 56, 8979-8988 (2011) [3] D. Y. Park et al., Electrochim. Acta 47, 2893-2900 (2002) [4] D. Mallick et al., J. Appl. Phys. 125, 023902 (2019)

Synthetic antiferromagnets (SAFs) have received a renewed attention in the last few years as they exhibit key features of crystal antiferromagnets (e.g., zero remanence, high robustness against external fields) while offering additional advantages, such as easy manipulation and control of magnetic configuration, and high tunability of magnetic properties. The peculiar properties of SAF are here exploited to develop magnetic microdisks with perpendicular magnetic anisotropy for biomedical applications and flexible GMR spin-valves with potential interest in many technological fields including wearable devices, soft robotics, and bio-integrated electronics.

Lead-free piezoelectric (K, Na)NbO3 (KNN) is considered one of the promising candidates for the replacement of Pb(ZrxTi1−x)O3. Several studies underlined the issue of K and Na volatility with increasing deposition temperatures, leading to high leakage currents in thin films, which still represents a major drawback for applications. This paper shows how epitaxial growth with concomitant preferred orientation of KNN films on niobium-doped strontium titanate (Nb:STO) depends on growth temperature and substrate strain. A preferred out-of-plane polar (001) orientation of KNN is obtained at high temperatures (>600 °C), while (100) orientation is dominant for lower ones. The (001) orientation is forced out-of-plane due to the sizeable in-plane stress derived from a negative lattice mismatch of pseudo-cubic KNN with respect to the underlying cubic (001) Nb:STO substrate. Moreover, we show that K-Na deficiency and high leakage of epitaxial KNN films deposited at high temperatures are accompanied by the appearance of a pattern of orthogonal spontaneous ferroelectric domains aligned to the [100] and [010] directions of Nb:STO. This pattern, visible in secondary electron microscopy, piezoforce response microscopy, and conductive atomic force microscopy images, is uncorrelated to the surface morphology. Supported by reciprocal space mapping by x-ray diffraction, this phenomenon is interpreted as the result of strain relaxation via ferroelectric domain formation related to K-Na deficient films displaying a sizable and increasing compressive strain when grown on Nb:SrTiO3. Our findings suggest that strain engineering strategies in thin films could be used to stabilize specific configurations of piezo- and ferroelectric domains.

In the quest for ultra-low power electronic devices beyond the CMOS platform, ferroelectric Rashba semiconductors offer intriguing possibilities. After an overview of the main findings in this context, I will show that the ferroelectric polarization of epitaxial thin films of GeTe can be reliably switched by electrical gating and used to control spin-to-charge conversion by spin Hall effect. Ferroelectricity allows for efficient switching and stable state retention, while spin currents provides an effective read-out of the memory state. Doping, allowing and dimensionality can be used to tailor the properties of these compounds towards logic-in-memory devices with monolithic integrability with silicon.

Synthetic antiferromagnets with perpendicular magnetic anisotropy (PMA-SAFs) have gained growing attention for both conventional and next-generation spin-based technologies. While the progress of PMA-SAF spintronic devices on rigid substrates has been remarkable, only few examples of flexible thin-film heterostructures are reported in the literature, all containing platinum group metals (PGMs). Systems based on Co/Ni may offer additional advantages with respect to devices containing PGMs, i.e., low damping and high spin polarization. Moreover, limiting the use of PGMs may relieve the demand for critical raw materials and reduce the environmental impact of related technologies, thus contributing to the transition toward a more sustainable future. Here, we discuss for the first time the realization of Co/Ni-based PMA-SAFs on polymer tapes and exploit it to obtain flexible giant magneto-resistive spin valves (GMR-SVs) with perpendicular magnetic anisotropy. Several combinations of buffer and capping layers (i.e., Pt, Pd, and Cu/Ta) are also investigated. High-quality flexible SAFs with a fully compensated antiferromagnetic region and SVs with a sizable GMR ratio (up to 4.4%), in line with the values reported in the literature for similar systems on rigid substrates, were obtained in all cases. However, we demonstrate that PGMs allows achieving the best results when used as a buffer layer, while Cu is the best choice as a capping layer to optimize the properties of the stacks. We justify the role of buffer and capping layers in terms of different interdiffusion mechanisms occurring at the interface between the metallic layers. These results, along with the high robustness of the samples' properties against bending (up to 180°), indicate that complex and bendable Co/Ni-based heterostructures with reduced content of PGMs can be obtained on flexible tapes, allowing for the development of novel flexible and sustainable spintronic devices for applications in many fields including wearable electronics, soft robotics, and biomedicine.

Malaria remains the most important mosquito-borne infectious disease worldwide, with 229 million new cases and 409.000 deaths in 2019. The infection is caused by a protozoan parasite which attacks red blood cells by feeding on hemoglobin and transforming it into hemozoin. Despite the WHO recommendation of prompt malaria diagnosis, the quality of microscopy-based diagnosis is frequently inadequate while rapid diagnostic tests based on antigens are not quantitative and still affected by non-negligible false negative/positive results. PCR-based methods are highly performant but still not widely used in endemic areas. Here, a diagnostic tool (TMek), based on the paramagnetic properties of hemozoin nanocrystals in infected red blood cells (i-RBCs), is reported on. Exploiting the competition between gravity and magnetic forces, i-RBCs in a whole blood specimen are sorted and electrically detected in a microchip. The amplitude and time evolution of the electrical signal allow for the quantification of i-RBCs (in the range 10-105 i-RBC µL-1) and the distinction of the infection stage. A preliminary validation study on 75 patients with clinical suspect of malaria shows on-field operability, without false negative and a few false positive results. These findings indicate the potential of TMek as a quantitative, stage-selective, rapid test for malaria.

This talk will discuss efforts to pattern and shape-reconfigure liquid metals as conductive inks for stretchable, soft, and reconfigurable electronics1. Alloys of gallium have metallic conductivity, yet have low viscosity, low toxicity, and negligible volatility. Despite the large surface tension of the metal, it can be patterned into non-spherical 2D and 3D shapes due to the presence of an ultra-thin oxide skin that forms on its surface, as shown in the image. Liquid metal is extremely soft and flows in response to stress to retain electrical continuity under extreme deformation. By embedding the metal into elastomeric or gel substrates, it is possible to form soft electrodes, stretchable antennas, and ultra-stretchable wires that maintain metallic conductivity up to ~800% strain. The resulting conductors are selfhealing. The metals can also be filled into microchannels or hollow fibers for capacitive touch sensors, and mechanically tough fibers. It is also possible to 3D print the metal for source and drain contacts for transistors and as interconnects for energy harvesters. More recently, we demonstrated that liquid metal circuits can also be used for soft, tactile logic2. Perhaps one of the more unique aspects of liquid metals is the ability to manipulate their shape for reconfigurable electronics. Electrochemistry can deposit and remove the oxide layer to manipulate the interfacial tension—a dominante force at the microscale—over an enormous range. Reductive potentials remove the oxide layer and put the metal in a state of high tension. However, oxidative potentials deposit the oxide layer on the metal and put it in a state of low tension. Experiments suggest the tension could be near zero using less than one volt. Unlike electrowetting, which can require hundreds of volts, here, the changes result due to electrochemically deposited species on the metal surface.

Lead-free piezoceramics aiming at replacing the market-dominant Pb(ZrxTi1−x)O3 have been extensively researched for more than a decade worldwide due to the toxicity of lead. In this context, (K0.5Na0.5)NbO3 (KNN) triggered the attention of the scientific community thanks to its bulk record piezoelectric coefficient combined with high critical temperature, which make it a good candidate for applications. In this paper, (001)-oriented KNN thin films grown by pulsed laser deposition on Pt(111)/TiO2/SiO2/Si substrates are investigated. We highlight the relevance of the template substrate in determining the structure of the film. Developing a suitable treatment for the Pt substrate is of great importance to film morphologic and topographic quality and to electric, ferroelectric, and piezoelectric properties. From local characterization of piezoelectric properties, we find a piezoelectric coefficient d33 of about 80 pm/V, comparable to the highest values reported for state-of-the-art undoped KNN thin films. Finally, electrical characterization of fabricated micro-capacitors allows the investigation of dielectric performance and shows remanent ferroelectric polarization over microscopic areas, thus paving the way to the integration of these KNN films in microfabricated actuator devices.

Since its birth in the 1990s, semiconductor spintronics has suffered from poor compatibility with ferromagnets as sources of spin. While the broken inversion symmetry of some semiconductors may alternatively allow for spin-charge interconversion, its control by electric fields is volatile. Ferroelectric Rashba semiconductors stand as appealing materials unifying semiconductivity, large spin-orbit coupling, and non-volatility endowed by ferroelectricity. However, their potential for spintronics has been little explored. Here, we demonstrate the non-volatile, ferroelectric control of spin-to-charge conversion at room temperature in epitaxial GeTe films. We show that ferroelectric switching by electrical gating is possible in GeTe despite its high carrier density. We reveal a spin-to-charge conversion as effective as in Pt, but whose sign is controlled by the orientation of the ferroelectric polarization. The comparison between theoretical and experimental data suggests that spin Hall effect plays a major role for switchable conversion. These results open a route towards devices combining spin-based logic and memory integrated into a silicon-compatible material.

Interfaces play a crucial role in the study of novel phenomena emerging at heterostructures comprising metals and functional oxides. In this work, we consider Cr/BaTiO3 heterostructures grown on Nb:SrTiO3 (001) substrates. Chromium thin films with 2 nm nominal thickness are deposited by molecular beam epitaxy on the BaTiO3 layer, and subsequently annealed in vacuum at temperatures ranging from 800 K to 970 K, and finally exposed to 10(-7) torr of molecular oxygen for 300 s. Highly ordered films are obtained for each of this condition, ranging from metallic Cr to insulating Cr2O3 with tetragonal structure. Quite unexpectedly, an intermediate fully ordered - case exists, with the co-presence of Cr and Cr2O3 compounds, each one with its proper crystal orientation. These results show the opportunity of controlling the metal/oxide state of crystalline Cr films grown onto the ferroelectric template BaTiO3/Nb:SrTiO3.