arXiv subjects

Frederik Schiller

Publications and source records attributed to Frederik Schiller.

10 recordsLinked to original sources

arXiv2026

Galvanic intercalation of molecular cations into van der Waals materials

The intercalation of molecular species between the layers of van der Waals (vdW) crystals is a powerful approach to combine the remarkable physical properties of vdW materials with the chemical versatility of organic molecules. However, the full transformative potential of molecular intercalation remains underexplored, largely due to the lack of simple, broadly applicable methods that preserve high crystalline quality down to the few-layer limit. Here, we introduce a simple galvanic approach to intercalate different molecules into various vdW materials under ambient conditions, leveraging the low reduction potential of selected metals. We employ our method, which is particularly well-suited for the in-situ intercalation of few-layer-thick crystals, to intercalate nine vdW materials, including magnets and superconductors, with molecules ranging from conventional alkylammonium ions to metallorganic and bio-inspired chiral cations. Notably, intercalation leads to an unprecedented transition from antiferromagnetic to ferrimagnetic ordering in α-RuCl3 and to a molecule-dependent enhancement of the superconducting transition in 2H-TaS2. These results establish our approach as a versatile technique for engineering atomically thin quantum materials and heterostructures, unlocking the transformative effects of molecular intercalation.

cond-mat.mtrl-sci↗

arXiv2025

Suppressing metal molecule charge transfer with a phosphorus interlayer

Porphyrins are organic molecules that exhibit excellent opto-electronics properties, making them suitable for a variety of applications. Nevertheless, their functionality strongly depends on the surface onto which they are deposited, and on the interaction between the molecules and the substrate itself, which often leads to an undesired alteration in their electronic properties. In this study, we use a phosphorus interlayer on a Cu(110) surface as a buffer layer for the electronic decoupling of Zinc-TetraPhenylPorphyrin (ZnTPP) molecules. Using a combination of complementary techniques, such as Near Edge X-ray Absorption Fine Structure (NEXAFS), X-ray and Ultraviolet Photoemission Spectroscopy (XPS, UPS) as well as Scanning Tunneling Spectroscopy (STS) techniques, it is shown how the charge transfer from the metal, responsible for quenching the ZnTPP lowest unoccupied molecular level (LUMO) levels, is effectively prevented by the presence of a phosphorus reconstruction in between.

cond-mat.mes-hall↗

arXiv2025

Tunable magnetism in 2D organic-ion-intercalated MnPS3 via molecule-dependent vacancy generation

The magnetic properties of van der Waals materials are profoundly influenced by structural defects. The layered antiferromagnet MnPS3 offers a unique opportunity to explore defect-related magnetism, as Mn2+ vacancies can be generated by the intercalation of specific guest molecules. However, the effectiveness of this process in atomically thin flakes and the extent of the magnetic tunability remain unclear. Here, we show that the magnetic properties of MnPS3 can be tailored through the intercalation of different guest molecules. Notably, the insertion of four alkylammonium ions introduces different populations of Mn2+ vacancies, leading to a transition from the pristine antiferromagnetic state to more complex magnetic textures, including a ferrimagnetic state displaying a magnetic saturation of 1 uB/atom. Moreover, we show that the intercalation of few-nm-thick flakes also leads to the emergence of a ferrimagnetic response. This in-flake intercalation, which can be monitored in real time using optical microscopy, can be interrupted before completion, generating lateral heterostructures between pristine and intercalated areas. This approach opens the way to the use of partial intercalation to define regions with distinct magnetic properties within a single flake.

cond-mat.mtrl-sci↗

arXiv2025

Atomically thin silver films for enhanced nanoscale nonlinear optics

The inherently weak nonlinear optical response of bulk materials remains a fundamental limitation in advancing photonic technologies. Nanophotonics addresses this challenge by tailoring the size and morphology of nanostructures to manipulate the optical near field, thus modulating the nonlinear response. Here, we explore a complementary strategy based on engineering the electronic band structure in the mesoscopic regime to enhance optical nonlinearities. Specifically, we demonstrate an increase in second-harmonic generation (SHG) from crystalline silver films as their thickness is reduced down to just a few atomic monolayers. Operating at the boundary between bulk and two-dimensional systems, these ultra-thin films exhibit a pronounced enhancement of SHG with decreasing thickness. This enhancement stems from quantum confinement effects that modify the interaction between electronic states and incident light, which we explain based on quantum-mechanical calculation. Our atomically-thin crystalline silver films provide a new means to overcome the small interaction volumes inherent to nanophotonic platforms, enabling efficient nanoscale nonlinear optics with potential applications in photonics, sensing, and quantum technologies.

physics.optics↗

arXiv2025

Formation and protection of an Eu-Ir surface compound below hexagonal boron nitride

Europium (Eu) intercalation below hexagonal boron nitride (hBN) on an Ir(111) substrate at various Eu coverages is investigated. The structural and electronic properties were examined using low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), x-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES). Depending on the deposition temperature, different superstructures, (5 $\times$ $M$), (5 $\times$ 2), and ($ \sqrt{3}$ $\times$ $\sqrt{3})R30^{\circ}$ with respect to the Ir substrate were identified by LEED. The (5 $\times$ $M$) superstructure ($M$ $>$ 2), at 0.1 monolayer (ML), preserved the hBN/Ir Moir{é} pattern and exhibited a unidirectional ordering of Eu atoms. At higher coverage of 0.26 ML, a (5 $\times$ 2) superstructure emerged, where excess Eu atoms diffused into the bulk and were analyzed as Eu in a tri-valent state. At the highest preparation temperature with a one-third ML Eu, the formation of a ($\sqrt{3}$ $\times$ $\sqrt{3})R30^{\circ}$ superstructure indicates the presence of a EuIr$_{2}$ surface alloy beneath the hBN layer, with di-valent Eu atoms suggesting potential ferromagnetic properties. Air exposure was used to evaluate the protection of the hBN layer, and the results indicate that the EuIr$_{2}$ surface alloy was partially protected. However, the hBN layer remained intact by intercalation and air exposure, as confirmed by ARPES analysis.

cond-mat.mtrl-sci↗

arXiv2024

The role of rare-earth atoms in the anisotropy and antiferromagnetic exchange coupling at a hybrid metal-organic interface

Magnetic anisotropy and magnetic exchange interactions are crucial parameters that characterize the hybrid metal-organic interface, key component of an organic spintronic device. We show that the incorporation of 4$f$ RE atoms to hybrid metal-organic interfaces of CuPc/REAu$_2$ type (RE= Gd, Ho) constitutes a feasible approach towards on-demand magnetic properties and functionalities. The GdAu$_2$ and HoAu$_2$ substrates differ in their magnetic anisotropy behavior. Remarkably, the HoAu$_2$ surface boosts the inherent out-of-plane anisotropy of CuPc, owing to the match between the anisotropy axis of substrate and molecule. Furthermore, the presence of RE atoms leads to a spontaneous antiferromagnetic (AFM) exchange coupling at the interface, induced by the 3$d$-4$f$ superexchange interaction between the unpaired 3$d$ electron of CuPc and the 4$f$ electrons of the RE atoms. We show that 4$f$ RE atoms with unquenched quantum orbital momentum ($L$), as it is the case of Ho, induce an anisotropic interfacial exchange coupling.

cond-mat.mtrl-sci↗

arXiv2024

Percolating Superconductivity in Air-Stable Organic-Ion Intercalated MoS2

When doped into a certain range of charge carrier concentrations, MoS2 departs from its pristine semiconducting character to become a strongly correlated material characterized by exotic phenomena such as charge density waves or superconductivity. However, the required doping levels are typically achieved using ionic-liquid gating or air-sensitive alkali-ion intercalation, which are not compatible with standard device fabrication processes. Here, we report on the emergence of superconductivity and a charge density wave phase in air-stable organic cation intercalated MoS2 crystals. By selecting two different molecular guests, we show that these correlated electronic phases depend dramatically on the intercalated cation, demonstrating the potential of organic ion intercalation to finely tune the properties of 2D materials. Moreover, we find that a fully developed zero-resistance state is not reached in few-nm-thick flakes, indicating the presence of three-dimensional superconductive paths which are severed by the mechanical exfoliation. We ascribe this behavior to an inhomogeneous charge carrier distribution, which we probe at the nanoscale using scanning near-field optical microscopy. Our results establish organic-ion intercalated MoS2 as a platform to study the emergence and modulation of correlated electronic phases.

cond-mat.supr-con↗

arXiv2024

Gate-tunable spin Hall effect in an all-light-element heterostructure: graphene with copper oxide

Graphene is a light material for long-distance spin transport due to its low spin-orbit coupling, which at the same time is the main drawback to exhibit a sizeable spin Hall effect. Decoration by light atoms has been predicted to enhance the spin Hall angle in graphene while retaining a long spin diffusion length. Here, we combine a light metal oxide (oxidized Cu) with graphene to induce the spin Hall effect. Its efficiency, given by the product of the spin Hall angle and the spin diffusion length, can be tuned with the Fermi level position, exhibiting a maximum (1.8 $\pm$ 0.6 nm at 100 K) around the charge neutrality point. This all-light-element heterostructure shows a larger efficiency than conventional spin Hall materials. The gate-tunable spin Hall effect is observed up to room temperature. Our experimental demonstration provides an efficient spin-to-charge conversion system free from heavy metals and compatible with large-scale fabrication.

cond-mat.mes-hall↗

arXiv2023

Simulating high-pressure surface reactions with molecular beams

Using a reactive molecular beam with high kinetic energy ($E_{kin}$) it is possible to speed gas-surface reactions involving high activation barriers ($E_{act}$), which would require elevated pressures ($P_0$) if a random gas with a Maxwell-Boltzmann distribution is used. By simply computing the number of molecules that overcome the activation barrier in a random gas at $P_0$ and in a molecular beam at $E_{kin}$=$E_{act}$, we establish an $E_{kin}$-$P_0$ equivalence curve, through which we postulate that molecular beams are ideal tools to investigate gas-surface reactions that involve high activation energies. In particular, we foresee the use of molecular beams to simulate gas surface reactions within the industrial-range ($>$ 10 bar) using surface-sensitive Ultra-High Vacuum (UHV) techniques, such as X-ray photoemission spectroscopy (XPS). To test this idea, we revisit the oxidation of the Cu(111) surface combining O$_2$ molecular beams and XPS experiments. By tuning the kinetic energy of the O$_2$ beam in the range 0.24-1 eV we achieve the same sequence of surface oxides obtained in Ambient Pressure Photoemission (AP-XPS) experiments, in which the Cu(111) surface was exposed to a random O$_2$ gas up to 1 mbar. We observe the same surface oxidation kinetics as in the random gas, but with a much lower dose, close to the expected value derived from the equivalence curve.

cond-mat.mtrl-sci↗

arXiv2023

A ferromagnetic Eu-Pt surface compound grown below hexagonal boron nitride

One of the fundamental applications for monolayer-thick 2D materials is their use as protective layers of metal surfaces and in-situ intercalated reactive materials in ambient conditions. Here we investigate the structural, electronic, and magnetic properties, as well as the chemical stability in air of a very reactive metal, Europium, after intercalation between a hexagonal boron nitride (hBN) layer and a Pt substrate. We demonstrate that Eu intercalation leads to a hBN-covered ferromagnetic EuPt$_2$ surface alloy with divalent Eu$^{2+}$ atoms at the interface. We expose the system to ambient conditions and find a partial conservation of the di-valent signal and hence the Eu-Pt interface. The use of a curved Pt substrate allows us to explore the changes in the Eu valence state and the ambient pressure protection at different substrate planes. The interfacial EuPt$_2$ surface alloy formation remains the same, but the resistance of the protecting hBN layer to ambient conditions is reduced, likely due to a rougher surface and a more discontinuous hBN coating.

cond-mat.mtrl-sci↗