We report high-precision resistance measurements on quantum Hall resistance devices fabricated from uniform epitaxial graphene grown by propane-hydrogen chemical vapor deposition on a two-inch silicon carbide substrate. Through molecular doping, we achieve a low carrier density regime ( n s < 1.5 x 10(11) cm(-2)) combined with high mobility (mu >= 6000 cm(2) V-1 s(-1)) at low temperature. Accurate quantization of the Hall resistance is demonstrated at magnetic flux densities as low as 3.5 T, temperatures up to 8 K, and measurement currents up to 325 mu A, with relative measurement uncertainties of a few parts per billion. A stability diagram mapping dissipation as a function of temperature and current provides insight into optimal doping conditions that maximize the breakdown current. All measurements were carried out in a pulse-tube-based cryomagnetic system, enabling simplified and continuous operation of the quantum Hall resistance standard without liquid helium consumption.

Spintronic terahertz (THz) emitters have established themselves as among the most practical broadband THz sources available, yet their performance remains fundamentally limited by the spin Hall conductivity of the nonmagnetic conversion layer - a quantity that is fixed once the material is chosen. Here, we demonstrate that in PtTe_2, a type-II Dirac semimetal within the transition metal dichalcogenide family, this limitation can be circumvented by exploiting the dramatic thickness-driven electronic phase evolution of the material itself. Using molecular beam epitaxy to grow PtTe_2 films with single-monolayer precision from 1 to 20 ML, we show that the spintronic THz emission tracks the underlying electronic phase diagram directly: it is absent in the single-layer semiconducting phase, turns on sharply at the semimetal transition near 2 ML, and reaches a peak amplitude six times that of an equivalent Pt reference at 10 ML, before declining at larger thicknesses due to THz reabsorption in the increasingly metallic film. This non-monotonic behavior is inconsistent with a bulk inverse spin Hall mechanism and instead reflects a multi-channel spin-to-charge conversion process in which spin-momentum-locked topological surface states and a thickness-dependent interfacial Rashba splitting both contribute and strengthen as the type-II Dirac band structure develops. First-principles calculations of the interfacial spin accumulation reproduce the experimental trend quantitatively, confirming this physical picture. These findings introduce thickness engineering of van der Waals semimetals as a new and accessible route to optimizing spintronic THz emitters and spin-orbit torques in magnetic memories (SOT-MRAMs), with direct implications for the broader class of dimensionally tunable topological materials.

Two-dimensional transition metal dichalcogenide (TMD) interfaces offer a versatile platform for studying quantum phenomena and developing device functionalities. When distinct TMD monolayers are stacked vertically or laterally stitched, their interfaces can exhibit unique electronic band alignments, giving rise to long-lived interlayer excitons, charge transfer effects, and moiré superlattices with correlated states. Here, we demonstrate that the interface between a large variety of two different epitaxially grown TMD monolayers controls the intensity and sign of the Rashba spin splitting, which is probed using THz spintronic emission. Optimized TMD heterobilayers, such as HfSe2/PtSe2, show enhanced THz emission that surpasses the spin-to-charge conversion efficiency of bulk TMDs, confirming the presence of Rashba states with large spin splitting at the interface. By combining spin- and angle-resolved photoemission spectroscopy with density functional theory, we reveal that the electronic hybridization between the two different TMD monolayers gives rise to extended in-gap states with strong Rashba spin-orbit coupling. The choice of TMD layers enables to engineer the sign and strength of spin-to-charge conversion in van der Waals heterobilayers, enabling to build efficient and tunable THz spintronic emitters.

Zn 3 P 2 growth on graphene: triangular grain nucleation on atomic steps of graphene substrates and its growth window.

Zn3P2 is a promising earth-abundant absorber for thin-film photovoltaics, yet its development is hindered by the lack of lattice-matched substrates, its incompatible thermal expansion coefficient, and a complex defect landscape. Here, we demonstrate the quasi-van der Waals epitaxy of Zn3P2 on graphene by metal-organic vapour phase epitaxy (MOVPE) and directly link the density of antiphase boundaries to optical emission modulation using correlative electron microscopy and cathodoluminescence (CL). Moreover, it is observed through CL that grain boundaries act as non-radiative sinks for excited charge carriers. The effect extends several micrometres into the grains, making grain boundaries detrimental to the applicability of Zn3P2 in read devices. Further comparison with molecular beam epitaxy grown films reveals the suppression of strain-related sub-bandgap emission in MOVPE-grown material. Overall, quasi-van der Waals epitaxy of Zn3P2 by MOVPE resulted in larger grains and improved material quality. In addition, these results directly link extended defects to recombination pathways in Zn3P2 and highlight grain-size control as a key strategy for improving earth-abundant photovoltaic absorbers.

Silicene growth on graphene has emerged as a novel method for fabricating silicon-based van der Waals heterostructures. However, the silicene flakes produced in this manner are the result of an exotic growth mode characterized by metastable nanostructures with varying degrees of deviation from equilibrium, with large two-dimensional flakes surrounded by a rim that coexist with small 3D islands, and, at large deposits, thick dendritic pyramids separated by a denuded zone. In order to rationalize and control this growth, a model is derived that revisits the dewetting thermodynamics and considers generally ignored adsorption and step-edge energies. The model is investigated using kinetic Monte-Carlo simulations and mean-field rate equations, and implemented by close inspection of microscopy images. This model perfectly reproduces the experimental outcomes, unveiling an anomalous growth mode, and provides guidelines on experimental conditions for high-quality silicene growth.

The polarity of III-nitride materials critically influences their physical properties and behavior. In this study, we identify closed polarity inversion domains (IDs) in epitaxial AlN layers grown on sapphire substrates and analyze the mechanism underlying their formation following high-temperature annealing. These IDs are defined by two distinct inversion domain boundaries (IDBs): a lower flat IDB in the c-plane (growth plane), where the polarity transitions from Al-polar to N-polar, and an upper convex IDB, which spans multiple layers and gradually restores Al-polarity. The IDs are uniformly distributed in the entire AlN epilayer thickness, and their lateral dimension varies over a wide range that goes from 50 to 300 nm, while their vertical size remains below 10 nm. A comprehensive characterization of the atomic structure and chemical composition shows that codoping with oxygen (O) and silicon (Si) is essential for the formation and stabilization of the IDs, with O promoting vacancy-impurity clusters and Si facilitating vacancy creation and impurity precipitation during cooling. Our findings highlight the critical role of impurities in polarity inversion within AlN layers, providing fundamental insights for the design of III-nitride-based electronic and optoelectronic devices, where polarity manipulation is critical.

Zn3P2, made from earth-abundant elements, is a promising candidate for thin-film solar cells but faces limitations due to difficulties in achieving n-type doping and its large lattice mismatch with commercial substrates and a high thermal expansion coefficient, causing defects and cracks. Graphene substrates can address these challenges thanks to its weak van der Waals interactions with Zn3P2 allowing for mechanical transfer of the thin film and strain-free growth. This study compares five graphene substrates for quasi-van der Waals epitaxial (q-vdWe) growth of polycrystalline Zn3P2 thin films using molecular beam epitaxy. Surface features like steps and wrinkles on graphene were identified as main nucleation sites for Zn3P2, provided the graphene has minimal point defects. The highest-quality thin films, with the largest grain sizes, were grown on H-CVD graphene on the Si-face of 6H-SiC, featuring solely terraces of atomic height. All substrates showed comparable growth windows for crystalline Zn3P2, with higher growth temperatures improving crystal quality, as indicated by enhanced photoluminescence. Cryo-cathodoluminescence measurements revealed spatially localized sub-bandgap emissions, potentially linked to localized strain fields at grain boundaries of up to ±3% as identified by cross-sectional transmission electron microscopy. This work provides insights into advantages and drawbacks of utilising q-vdWe to produce Zn3P2 thin films for solar cell applications and highlights the effects of graphene substrate choice and growth parameters on Zn3P2 film quality.

Among the different methods to grow graphene on silicon carbide (SiC), the chemical vapor deposition (CVD) in a hydrogen atmosphere has several interesting features arising from the use of this gas. Despite its versatility and its ability to grow graphene with a quality allowing applications in electrical metrology, this synthesis method remains largely understudied. This work is specifically dedicated to this growth technique in conditions leading to the epitaxy of graphene on a buffer layer. We first show that hydrogen has several effects during the cooling down, possibly leading to hydrogen intercalation beneath graphene, or even to graphene etching. Then, we use a specific cooling under argon, allowing the suppression of hydrogen effects, to follow the successive phases of the graphene formation, from the nucleation of islands and ribbons to their coalescence on SiC. Finally, we demonstrate that graphene growth is, in our growth conditions, self-limited to a unique monolayer.

The growth of two-dimensional molybdenum disulphide (MoS2) layers on Gallium Nitride/Sapphire (GaN/ Al2O3) substrates using molecular beam epitaxy (MBE) growth technique has been investigated. We show that optimized conditions at a substrate temperature around 700 degrees C lead to full surface coverage of MoS2 on GaN. The growth proceeds through the initial formation of triangular-shaped MoS2 flakes/domains on the GaN surface. Raman spectroscopy and high-resolution scanning transmission electron microscopy reveal the formation at the wafer-scale of a MoS2 monolayer and few bilayers. A closer analysis of regions with two MoS2 layers reveals the coexistence of both 1 T and 1H phases, showing strong bonds between the top layer of GaN and the first MoS2 layer, and van der Waals interactions between the first and second MoS2 layers.

The integration of graphene in silicon technology using a Ge buffer layer is of high interest for both fundamental science and device applications. Various studies have investigated the growth of graphene on germanium by chemical vapor deposition, a technique that has unique advantages for applications but is hard to understand due to the interplay of interrelated and complex physicochemical mechanisms. To further understand the mechanisms of growth and the interactions between the germanium substrate and the deposited carbon atoms, we use an ultrahigh-vacuum molecular beam epitaxy chamber equipped with a carbon atomic source. The structures are characterized using scanning transmission electron microscopy and Raman spectroscopy, as well as capacitance and photocurrent spectroscopies. Our results show that the high deposition temperature yields high-quality graphene with good uniformity. Although Raman spectra reveal a prominent defect peak attributed to the underlying germanium substrate, the graphene/Ge(001) structure still exhibits promising electrical and optoelectronic properties. Notably, the observed quantum capacitance and photocurrent responses highlight its strong potential for applications in microelectronics and optoelectronics.

Purpose: The primary aim was to describe the patterns of paramacular involvement, not yet reported but that optical coherence tomography angiography can now detect in patients with sickle cell disease. The secondary aim was to search arguments concerning the physiopathogeny of paramacular involvement. Methods: This institutional cohort retrospective study was conducted in a Referral Center for Ophthalmological Rare Diseases. Follow-up included an ophthalmologic examination with optical coherent tomography and optical coherent tomography angiography. Results: One hundred and thirty-two patients with SCD were included. Typical sickle cell maculopathy was observed in temporal area in 84 eyes (40.0%) of SS patients and eight eyes (14.8%) of SC patients ( P < 0.001). Enlargement of the foveal avascular zone was observed in 10 eyes of eight SS patients. Two atypical parafoveal abnormalities were found in SS patients only. The first one consisted of macular thinning with normal vascularization in 15 eyes of 11 patients. The second atypical maculopathy was large areas of loss of vascularization without retinal thinning 10 eyes of six patients. Multivariate analysis did not show a statistically significant relation between the peripheral sickle retinopathy stage and the different type of sickle cell maculopathy ( P = 0.21). Conclusion: Those atypical sickle cell maculopathy may correspond to early forms preceding a typical sickle cell disease maculopathy (SCDM). This would point toward several physiopathogenic mechanisms. The first one included the existence of ischemia that can be related to anemia. Presence of retinal thinning without vascular involvement point out to a neurogenic mechanism.

SummaryFew studies have used validated scales to assess the intensity and determinants of fatigue, a major symptom of sickle cell disease (SCD). We aimed to assess the level of basal fatigue in adult patients with SCD, using the Functional Assessment of Chronic Illness Therapy—Fatigue (FACIT‐Fatigue) questionnaire. We prospectively included 102 stable adult outpatients with SCD over 2 months, who answered the FACIT‐Fatigue (ranging from 0 (worst imaginable fatigue) to 52 (no fatigue)) and reported on the intensity of fatigue and its impact on quality of life. The cut‐off for significant fatigue was <34. The median [IQR] FACIT‐Fatigue score was 29 [22–37], indicating moderate‐to‐severe fatigue. In a multivariate analysis, the FACIT‐Fatigue score was significantly associated with female sex, high body mass index, high level of stress, poor sleep quality, and number of previous episodes of acute chest syndrome, but not with the genotype or the haemoglobin level. Most adult patients with SCD experience significant and sometimes intense fatigue; this is probably due to several factors, including disease activity. Fatigue should be evaluated systematically during consultations and in patient education programmes and as an end‐point in therapeutic trials.

To fabricate native and monolithic full color micro-displays with a pixel pitch below 10 µm, the three primary colors should be achieved with the InGaN alloy. The prerequisite is to get an efficient red emission with thin InxGa1-xN quantum well (QW) width and an In content of 35%. However, the In content is limited to 25% when grown on GaN. A full InGaN structure combined with different types of relaxed InGaN pseudo-substrates are used to reduce the strain in the active zone. Red electroluminescence was obtained until 650 nm. Homogeneous red emitting InGaN based QWs were also demonstrated.

We investigated using a custom NGS panel of 149 genes the mutational landscape of 64 consecutive adult patients with tyrosine kinase fusion-negative hypereosinophilia (HE)/hypereosinophilic syndrome (HES) harboring features suggestive of myeloid neoplasm. At least one mutation was reported in 50/64 (78%) patients (compared to 8/44 (18%) patients with idiopathic HE/HES/HEUS used as controls; p < .001). Thirty-five patients (54%) had at least one mutation involving the JAK-STAT pathway, including STAT5B (n = 18, among which the hotspot N642H, n = 13), JAK1 (indels in exon 13, n = 5; V658F/L, n = 2), and JAK2 (V617F, n = 6; indels in exon 13, n = 2). Other previously undescribed somatic mutations were also found in JAK2, JAK1, STAT5B, and STAT5A, including three patients who shared the same STAT5A V707fs mutation and features consistent with primary polycythemia. Nearly all JAK-STAT mutations were preceded by (or associated with) myelodysplasia-related gene mutations, especially in RNA-splicing genes or chromatin modifiers. In multivariate analysis, neurologic involvement (hazard ratio [HR] 4.95 [1.87-13.13]; p = .001), anemia (HR 5.50 [2.24-13.49]; p < .001), and the presence of a high-risk mutation (as per the molecular international prognosis scoring system: HR 6.87 [2.39-19.72]; p < .001) were independently associated with impaired overall survival. While corticosteroids were ineffective in all treated JAK-STAT-mutated patients, ruxolitinib showed positive hematological responses including in STAT5A-mutated patients. These findings emphasize the usefulness of NGS for the workup of tyrosine kinase fusion-negative HE/HES patients and support the use of JAK inhibitors in this setting. Updated classifications could consider patients with JAK-STAT mutations and eosinophilia as a new "gene mutated-entity" that could be differentiated from CEL, NOS, and idiopathic HES.

AbstractFull color micro-displays with a pixel pitch of below 10 µm are needed for augmented and virtual reality applications. In the native emission approach, high efficiency Red-Green-Blue (RGB) pixels could be achieved using monolithically integrated InGaN based micro-LEDs. Here, we report the growth of high optical quality RGB InGaN/InGaN quantum wells grown on InGaN nanopyramids of diameter less than 1 µm by metal organic vapor phase epitaxy. We synthesized the nanopyramids by nanoselective area growth using an in situ patterned epitaxial graphene on SiC as an embedded mask. The RGB emission properties at different locations on the sample are dependent on the size of the InGaN nanopyramids. Advanced correlative analysis conducted on the same transmission electron microscopy lamella reveal a fully or at least nearly relaxed In0.13Ga0.87N core and very regular quantum wells emitting in the red range (620 nm) along the pyramid sidewalls with an In content up to 40%.