Raman thermometry is a powerful technique for sub-microscale thermal measurements on semiconductor-based devices, provided that the active region remains accessible and is not obscured by metallization. Since pure metals do not exhibit Raman scattering, traditional Raman thermometry becomes ineffective in such cases. To overcome this limitation, we propose the use of atomically thin Two-Dimensional materials as local temperature sensors. These materials generate Raman spectra at the nanoscale, enabling highly precise absolute surface temperature measurements. In this study, we investigate the feasibility and effectiveness of this approach by applying it to power devices, including a calibrated gold resistor and an SiC Junction Barrier Schottky (JBS) diode. We assess the processing challenges and measurement reliability of 2D materials for thermal characterization. To validate our findings, we complement Raman thermometry with thermoreflectance measurements, which are well suited for metallized surfaces. For example, on the serpentine resistor, Raman thermometry applied to the 2D material yielded a thermal resistance of 22.099 °C/W, while thermoreflectance on the metallic surface measured 21.898 °C/W. This close agreement suggests good thermal conductance at the metal/2D material interface. The results demonstrate the potential of integrating 2D materials as effective nanoscale temperature probes, offering new insights into thermal management strategies for advanced electronic components. Additionally, thermal simulations are conducted to further analyze the thermal response of these devices under operational conditions. Furthermore, we investigate two 2D material integration methods, transfer and direct growth, and evaluate them through measured thermal resistances for the SiC JBS diode, highlighting the influence of the deposition technique on thermal performance.

The crystallographic orientation of anisotropic 2D materials plays a crucial role in their physical properties and device performance. However, standard orientation techniques such as transmission electron microscopy (TEM) or X‐ray diffraction can be complex and less accessible for routine characterization. Herein, the orientation of black phosphorus (BP) from bulk crystals to thin layers is investigated using angle‐resolved polarized Raman spectroscopy with a single‐wavelength (514 nm) Raman setup. By incorporating thickness‐dependent interference effects and anisotropic optical indices, this approach provides a reliable framework for orientation determination across different BP thicknesses. The method is validated through direct orientation measurements using TEM and electron backscattering diffraction, confirming its applicability to both thick and ultrathin samples. Given its simplicity and compatibility with widely available Raman setups, this approach offers a practical solution for characterizing BP orientation without requiring advanced structural characterization techniques.

Over the past decade, MRAMs developments have focused on improving magnetic tunnel junctions while using magnetic electrodes with fixed properties as spin sources. Interestingly, 2D semiconductors offer interface tailoring opportunities for spin valve devices, with many atomically thin materials now available. However, integrating them with oxidation-prone spintronics materials remains a challenge. Here, spin devices are fabricated and evaluated with large-scale MoS2 directly grown on a monocrystalline ferromagnetic spin source. While most spin transport experiments with 2D semiconductors focus on their isolated dielectric properties, the presented approach unlocks an additional spin manipulation opportunity from MoS2 hybridization with ferromagnetic electrodes. The experimental results show a substantial tunnel magnetoresistance (TMR) value of over 65%, an order of magnitude higher than previously observed for exfoliated 2D semiconductor-based devices. A non-monotonic dependence of the spin signal on the applied bias, including a sign reversal, is also uncovered, which is attributed to the modulation of the MoS2 band structure by the ferromagnetic electrode. Ab initio calculations support these findings by illustrating how the MoS2 band structure evolves upon hybridization, introducing a pronounced exchange-induced spin splitting and resulting in an unusual bimodal spin response. This study demonstrates the unique spin manipulation opportunities offered by 2D semiconductors unlocked by direct integration.

Discovering an efficient spintronic semiconductor workhorse with dual host capabilities as a channel and spin valve barrier remains one of the most elusive endeavors toward the development of spin-logic circuits. Graphene paved the way for two-dimensional (2D) materials, yet engineering a controlled band gap in it remains a challenge. Black phosphorus (BP) was recently unveiled as a potential candidate in the realm of 2D semiconductors, with carrier mobilities among the largest reported for a 2D material and a low spin-orbit coupling reminiscent of graphene. Although promising spin transport properties have already been reported, their potential for tunneling and spin injection remains uncharted. Here, we unveil an unknown spin transport mechanism spin-split in k-space and report on corresponding high magnetoresistance spin signals up to 500% in BP based spin valves. Those findings are analyzed and discussed in light of a first-principles theoretical investigation showing BP's potential for spin filtering beyond its expected role of spin transport channel. This strongly supports BP's vision as an outstanding platform for spintronics, as it could become a versatile workhorse yet unavailable with any other semiconductor.

Van der Waals heterostructures are set as strong contenders for post-CMOS quantum materials engineering. A major step for their systematic exploration and exploitation of technological component demonstrators resides in their eased large-scale design. In this direction, the growth of artificial van der Waals 2D superlattices is presented here such as (MoS2/WS2)(n), (WS2/WSe2)(n), and (MoS2/WSe2)(n) with unit cells repetitions reaching n > 10. The fabrication of these materials is enabled by a fully automated in-situ pulsed laser deposition (PLD) tool. This approach provides cm(2) scale homogeneous superlattices with on-demand material parameters tailoring (layer number, order, and composition). The process is rapid and simple compared to manual pickup exfoliation methods or to sequential transfers of single layers grown by techniques such as chemical vapor deposition, allowing a large repetition of the unit cells in a "mille-feuille" cake configuration. The computational exploration of this family of superlattice materials sheds light on the potential for optoelectronic property design by shaping the band-structure landscape while taking into account the influential effects induced by proximity. Overall, this large-area approach is proposed as an entry point for the systematic design of complex van der Waals heterostructures.

High-TC cuprate superconductors' growth conditions and their incompatibility with some of the most standard nanofabrication approaches make their large-scale integration with 2D materials (such as graphene, transition metal dichalcogenides, and other Van der Waals materials) much more difficult than for conventional, metallic superconductors. Here, we address this challenge and develop an approach based on pulsed laser deposition that allows the growth of the 2D semiconductor MoS2 on the archetypal high-TC superconductor YBa2Cu3O7−x. This yields functional heterostructures in which the individual constituents' properties are preserved and that show superconducting coupling across their interface. The developed approach paves the way for large-scale 2D semiconductor co-integration with high-TC superconductors toward the study and leverage of the superconducting proximity effect in hybrid devices.

Black phosphorus (BP) stands out from other two-dimensional (2D) materials by the wide amplitude of the band-gap energy (Eg) that sweeps an optical window from visible to infrared wavelengths, depending on the layer thickness. This singularity made optical and excitonic properties of BP difficult to map. Here we report a comprehensive study of the intrinsic (i.e., measured at 4 K) optical properties of 79 passivated BP flakes obtained by mechanical exfoliation of thickness ranging from 4 to 700 nm. By following single- or multistamp exfoliation protocols and by combining micro-Raman and photoluminescence experiments, we demonstrate that the exfoliation step induces line like defects which open radiative recombination paths alternative to those of the crystalline bulk and that actually dominate the emission process. We also show that the evolution of the photoluminescence energy versus thickness follows an inverse square law. We relate this to a quantum well model whose validity is discussed and justified at intermediate thickness. Finally, we report that the emission energy of BP slabs placed in different 2D heterostructures is not significantly modulated by the dielectric environment.

Raman thermometry is well-suited for thermal measurements on semiconductor-based devices when the active area is accessible. To improve the technique, we develop the use of 2D materials as local sensors at the nanoscale for a very precise absolute surface temperature measurement. In this paper, we show the performances and limitations for the application on power devices.

L'introduction des systèmes 2D en spintronique a été à l'origine de plusieurs découvertes majeures et de phénomènes originaux. Ce chapitre passe en revue les avancées et applications dans ce domaine, comme l'effet Rashba-Edelstein inverse, le transport de spin dans les matériaux 2D et leur intégration dans les jonctions tunnel magnétiques, les mémoires magnétiques à accès aléatoire et les propriétés de spin des isolants topologiques.

A crystallographically heterogeneous moire interface of hexagonal graphene (Gr) and a tetragonal L1(0)-FePd alloy is bonded via van der Waals (vdW) forces. Robust interfacial perpendicular magnetic anisotropy was discovered at the L1(0)-FePd side of the Gr/L1(0)-FePd heterogeneous interface (H. Naganuma et al. ACS Nano, 2022, 16, 4139). This study focuses on the Gr side of the Gr/L1(0)-FePd interface. X-ray absorption spectroscopy measurements of Gr from two different angles demonstrated that in addition to the pi* orbital peak being observed at a glance incident angle (theta(A) = 30 degrees), it was also observed at a nominal incident (NI) angle (theta(A) = 90 degrees). The appearance of the pi* peak at NI is attributed to the wavy Gr and strong bonding of the chemisorption-type vdW force. The densities of states of p(x), p(y), and pz from first-principles calculations indicate another reason for the pi* peak at NI. The p(z) orbital of C twists into the x-y plane owing to its chemical bond with Fe or perturbation of the Fe ion to the C orbital. This twisted p(z) orbital appears near the Fermi level. Thus, the p* peak at NI can be interpreted to appear owing to three reasons: (i) the wavy Gr, (ii) the twisted pz orbital near the Fermi level, and (iii) the chemisorption-type vdW force. The X-ray magnetic circular dichroism of the C K-edge and first-principles calculations revealed that wavy Gr has a spin magnetic moment of 0.018 mu(B)/C atoms but no orbital magnetic moment.

The discovery of graphene has opened novel exciting opportunities in terms of functionalities and performances for spintronics devices. To date, it is mainly graphene properties for efficient in-plane spin transport which have been put forward. [1] We will present here experimental results concerning integration of graphene and other 2D Materials in vertical Magnetic Tunnel Junctions (MTJ), with strong technological potential. [2]We will show that a thin graphene passivation layer, directly integrated by low temperature catalyzed chemical vapor deposition (CVD), [3] allows to preserve a highly surface sensitive spin current polarizer/analyzer behavior. Characterizations of complete spin valves making use of graphene grown by CVD will be presented. The graphene layer prevents the oxidation of ferromagnets, unlocking in turn the exploration of spin filtering phenomena at graphene/ferromagnet interfaces, [4] as well as the introduction of novel ambient/wet processes for spintronics such as atomic layer deposition (ALD) and electro-grafting. [5] We will discuss the measured experimental spin signals in light of bulk band structure spin filtering effect as usually observed with MgO, but also highlight the role of interfacial hybridization (a.k.a. spinterface) for spin selection with ab-initio calculations in support. [6] The interfacial hybridization potential for spintronics will be underlined by the discussion of graphene/insulating FM based MTJ devices towards gated 2D spin sources. [7] We will further discuss the various observed spin filtering effects by analyzing results with other 2D materials (such as h-BN and ${\mathrm {WS}}_{2}$) integrated in MTJ devices. [8] Finally, we will expand the discussion to a novel pulsed laser deposition (PLD) approach for the definition of complex van der Waals heterostructures of 2D materials in MTJs. [9] This PLD growth approach unlocks the association in heterostructure of wide families of multifunctional 2D materials, including the most delicate ones. The different presented experiments unveil promising approaches for the quantum engineering of multifunctional 2D materials heterostructures for spintronics

With the development of technologies taking advantage of emerging quantum phenomena under extreme conditions of dimensionality and temperature, the search for alternative materials and heterostructure engineering has opened up on several fronts. Here, we report the magnetotransport properties of topological-insulator/two-dimensional-ferromagnet (TI/2D-FM) heterostructures composed of Cr1+delta Te2/Bi2Te3 stacks grown by molecular-beam epitaxy. The electrical transport measurements reveal high levels of fieldlike effective torques, up to 115 mT at a current density of 107 A/cm2; the occurrence of interfacial magnetoresistance effects, such as the anisotropic interfacial magnetoresistance; and anomalies in the anomalous Hall effect. Furthermore, we report on complementary characterization with scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and superconducting quantum interference device measurements. Finally, magnetization reversal induced by current pulses is also reported. The reported results make the relevance of the TI/2D-FM interface evident and indicate the preservation of polarized surface states at the interface.

This chapter focuses on the recent advances in two-dimensional (2D) electron gas at different oxide surfaces–interfaces, the rebirth of Rashba physics, and the new paradigm that these concepts open for spintronic devices. It describes the essential aspects of spin injection and spin detection using non-local techniques. The chapter introduces spin precession measurements, which allow the determination of all the spin-transport parameters of the system, with a single properly designed device. It then provides a overview models of spin relaxation, which in the case of 2D materials, provides a rich variety of spin relaxation mechanisms. The chapter also provides a brief survey of spin transport phenomena in 2D materials, particularly in graphene, when proximitized to high spin–orbit transition metal dichalcogenides, and the emergence of anisotropic spin dynamics, spin Hall and spin galvanic effects in such heterostructures.

Superconducting proximity effects in graphene have received a great deal of attention for over a decade now. This has unveiled a plethora of exotic effects linked to the specificities of graphene's electronic properties. The vast majority of the related studies are based on conventional, low-temperature superconducting metals with isotropic s-wave pairing. Here we review recent advances made on the less studied case of unconventional high-temperature superconducting cuprates. These are characterized by an anisotropic d-wave pairing, whose interplay with Dirac electrons yields very rich physics and novel proximity behaviours. We provide a theoretical analysis and summarize the experiments reported so far. These unveil hints of proximity-induced unconventional pairing and demonstrate the gate-tunable, long-range propagation of high-temperature superconducting correlations in graphene. Finally, the fundamental and technological opportunities brought by the theoretical and experimental advances are discussed, together with the interest in extending similar studies to other Dirac materials.

A crystallographically heterogeneous interface was fabricated by growing hexagonal graphene (Gr) using chemical vapor deposition (CVD) on a tetragonal FePd epitaxial film grown by magnetron sputtering. FePd was alternately arranged with Fe and Pd in the vertical direction, and the outermost surface atom was identified primarily as Fe rather than Pd. This means that FePd has a high degree of L10-ordering, and the outermost Fe bonds to the carbon of Gr at the interface. When Gr is grown by CVD, the crystal orientation of hexagonal Gr toward tetragonal L10-FePd selects an energetically stable structure based on the van der Waals (vdW) force. The atomic relationship of Gr/L10-FePd, which is an energetically stable interface, was unveiled theoretically and experimentally. The Gr armchair axis was parallel to FePd [100]L10, where Gr was under a small strain by chemical bonding. Focusing on the interatomic distance between the Gr and FePd layers, the distance was theoretically and experimentally determined to be approximately 0.2 nm. This shorter distance (≈0.2 nm) can be explained by the chemisorption-type vdW force of strong orbital hybridization, rather than the longer distance (≈0.38 nm) of the physisorption-type vdW force. Notably, depth-resolved X-ray magnetic circular dichroism analyses revealed that the orbital magnetic moment (Ml) of Fe in FePd emerged at the Gr/FePd interface (@inner FePd: Ml = 0.16 μB → @Gr/FePd interface: Ml = 0.32 μB). This interfacially enhanced Ml showed obvious anisotropy in the perpendicular direction, which contributed to interfacial perpendicular magnetic anisotropy (IPMA). Moreover, the interfacially enhanced Ml and interfacially enhanced electron density exhibited robustness. It is considered that the shortening of the interatomic distance produces a robust high electron density at the interface, resulting in a chemisorption-type vdW force and orbital hybridization. Eventually, the robust interfacial anisotropic Ml emerged at the crystallographically heterogeneous Gr/L10-FePd interface. From a practical viewpoint, IPMA is useful because it can be incorporated into the large bulk perpendicular magnetic anisotropy (PMA) of L10-FePd. A micromagnetic simulation assuming both PMA and IPMA predicted that perpendicularly magnetized magnetic tunnel junctions (p-MTJs) using Gr/L10-FePd could realize 10-year data retention in a small recording layer with a circular diameter and thickness of 10 and 2 nm, respectively. We unveiled the energetically stable atomic structure in the crystallographically heterogeneous interface, discovered the emergence of the robust IPMA, and predicted that the Gr/L10-FePd p-MTJ is significant for high-density X nm generation magnetic random-access memory (MRAM) applications.

Epitaxial clusters of chromium and chromium-vanadium oxides are studied by tunnel magneto-resistivity measurements, x-ray absorption spectrometry and circular magnetic circular dichroism. They turn out to carry a small magnetic moment that follows a super-paramagnetic behavior. The chromium ion contribution to this magnetization is mainly due to an original magnetic Cr2O3-like phase, whereas usual Cr2O3is known to be anti-ferromagnetic in the bulk. For mixed clusters, vanadium ions also contribute to the total magnetization and they are coupled to the chromium ion spins. By measuring the dichroic signal at different temperatures, we get insight into the possible spin configurations of vanadium and chromium ions: we propose that the magnetic dipoles observed in the clusters assembly could be related to ionic spins that couple at a very short range, as for instance in short one-dimensional spins chains.

We report on the growth of a ferromagnetic cobalt electrode by atomic layer deposition (ALD) and demonstrate it as a functional spin source in complete magnetic tunnel junctions (MTJs). Using an in situ protocol, we integrate a reference tunnel barrier on top of the ALD cobalt spin source stabilizing its metallic nature and allowing further characterization. The cobalt layer, grown in mbar conditions with chemical precursors, is assessed to be metallic and ferromagnetic using both x-ray photoelectron spectroscopy and superconducting quantum interference device magnetometry measurements. Atomic force microscopy tapping and conductive tip mode analyses reveal a very flat film with low roughness (0.2 nm RMS) with a high homogeneity of surface conductivity matching the best reference samples grown by sputtering. We finally evaluate its behavior in full MTJ spin valves, using a reference spin analyzer to highlight that the ALD grown layer is, indeed, spin polarized and can act as a functional spintronics electrode. This result opens the perspective of exploiting the benefits of ALD (such as the wide area low-cost process, extreme conformality, layer by layer growth of heterostructures, area selectivity, etc.) for spintronics applications.

Hardware spiking neural networks hold the promise of realizing artificial intelligence with high energy efficiency. In this context, solid-state and scalable memristors can be used to mimic biological neuron characteristics. However, these devices show limited neuronal behaviors and have to be integrated in more complex circuits to implement the rich dynamics of biological neurons. Here we studied a NbOx memristor neuron that is capable of emulating numerous neuronal dynamics, including tonic spiking, stochastic spiking, leaky-integrate-and-fire features, spike latency, temporal integration. The device also exhibits phasic bursting, a property that has scarcely been observed and studied in solid-state nano-neurons. We show that we can reproduce and understand this particular response through simulations using non-linear dynamics. These results show that a single NbOx device is sufficient to emulate a collection of rich neuronal dynamics that paves a path forward for realizing scalable and energy-efficient neuromorphic computing paradigms.

2D materials offer the ability to expose their electronic structure to manipulations by a proximity effect. This could be harnessed to craft properties of 2D interfaces and van der Waals heterostructures in devices and quantum materials. We explore the possibility to create an artificial spin polarized electrode from graphene through proximity interaction with a ferromagnetic insulator to be used in a magnetic tunnel junction (MTJ). Ferromagnetic insulator/graphene artificial electrodes were fabricated and integrated in MTJs based on spin analyzers. Evidence of the emergence of spin polarization in proximitized graphene layers was observed through the occurrence of tunnel magnetoresistance. We deduced a spin dependent splitting of graphene's Dirac band structure (∼15 meV) induced by the proximity effect, potentially leading to full spin polarization and opening the way to gating. The extracted spin signals illustrate the potential of 2D quantum materials based on proximity effects to craft spintronics functionalities, from vertical MTJs memory cells to logic circuits.

We report on large spin-filtering effects in epitaxial graphene-based spin valves, strongly enhanced in our specific multilayer case. Our results were obtained by the effective association of chemical vapor deposited (CVD) multilayer graphene with a high quality epitaxial Ni(111) ferromagnetic spin source. We highlight that the Ni(111) spin source electrode crystallinity and metallic state are preserved and stabilized by multilayer graphene CVD growth. Complete nanometric spin valve junctions are fabricated using a local probe indentation process, and spin properties are extracted from the graphene-protected ferromagnetic electrode through the use of a reference Al2O3/Co spin analyzer. Strikingly, spin-transport measurements in these structures give rise to large negative tunnel magneto-resistance TMR = -160%, pointing to a particularly large spin polarization for the Ni(111)/Gr interface PNi/Gr, evaluated up to -98%. We then discuss an emerging physical picture of graphene-ferromagnet systems, sustained both by experimental data and ab initio calculations, intimately combining efficient spin filtering effects arising (i) from the bulk band structure of the graphene layers purifying the extracted spin direction, (ii) from the hybridization effects modulating the amplitude of spin polarized scattering states over the first few graphene layers at the interface, and (iii) from the epitaxial interfacial matching of the graphene layers with the spin-polarized Ni surface selecting well-defined spin polarized channels. Importantly, these main spin selection effects are shown to be either cooperating or competing, explaining why our transport results were not observed before. Overall, this study unveils a path to harness the full potential of low Resitance.Area (RA) graphene interfaces in efficient spin-based devices.