Artificial 2D van der Waals heterostructures with controllable vertical stacking and rotational orientation exhibit multifaceted electronic properties that are appealing for applications in fields ...ranging from optoelectronics to energy storage. Along with transition metal dichalcogenides and graphene, borophene has recently emerged as a promising building block for 2D devices due to its conductive nature as well as its exceptional mechanical and electronic properties. Here, it is demonstrated that the combination of the dissolution‐segregation process and chemical vapor deposition allows for the synthesis of graphene/borophene heterostructures of the highest crystalline and chemical quality, in which graphene sits on top of the borophene layer with metallic character. The formation of laterally distinct micron‐sized areas allows a comparative study of borophene, graphene, and the graphene–borophene heterostack in terms of their electronic properties and stability in a reactive environment. Whereas pristine borophene is particularly prone to oxidation, the graphene–borophene heterostack is chemically inert and enables the conservation of borophene's character even after exposure to air. This study opens up new perspectives for the scalable synthesis of graphene–borophene heterostacks with enhanced ability to preserve the metallic character and electronic properties of borophene.
Heterostructures of 2D materials host peculiar electronic, magnetic, and optical properties. In this respect, graphene is often a fundamental building block in the fabrication of efficient and long‐lasting devices. Here, a novel synthesis of a twisted graphene/borophene heterostructure is presented and its enhanced ambient stability is tested, allowingthe preservation of the metallic nature of borophene.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The ability to manipulate magnetic anisotropy is essential for magnetic sensing and storage tools. Surface carbon species offer cost‐effective alternatives to metal‐oxide and noble metal capping ...layers, inducing perpendicular magnetic anisotropy in ultrathin ferromagnetic films. Here, the different mechanisms by which the magnetism in a few‐layer‐thick Co thin film is modified upon adsorption of carbon monoxide (CO), dispersed carbon, and graphene are elucidated. Using X‐ray microscopy with chemical and magnetic sensitivity, the in‐plane to out‐of‐plane spin reorientation transition in cobalt is monitored during the accumulation of surface carbon up to the formation of graphene. Complementary magneto‐optical measurements show weak perpendicular magnetic anisotropy (PMA) at room temperature for dispersed carbon on Co, while graphene‐covered cobalt exhibits a significant out‐of‐plane coercive field. Density‐functional theory (DFT) calculations show that going from CO/Co to C/Co and to graphene/Co, the magnetocrystalline and magnetostatic anisotropies combined promote out‐of‐plane magnetization. Anisotropy energies weakly depend on carbidic species coverage. Instead, the evolution of the carbon chemical state from carbidic to graphitic is accompanied by an exponential increase in the characteristic domain size, controlled by the magnetic anisotropy energy. Beyond providing a basic understanding of the carbon‐ferromagnet interfaces, this study presents a sustainable approach to tailor magnetic anisotropy in ultrathin ferromagnetic films.
Magnetic properties of Co ultrathin films are shown to undergo dramatic changes upon surface carbon accumulation. Chemical transformation from molecular carbon monoxide to surface carbide and to a graphene layer progressively enhances the perpendicular magnetic anisotropy of Co. Calculations reveal that magnetocrystalline and magnetostatic contributions play distinctly different roles for the different carbon species.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A complex interplay between the crystal structure and the electron behavior within borophene renders this material an intriguing 2D system, with many of its electronic properties still undiscovered. ...Experimental insight into those properties is additionally hampered by the limited capabilities of the established synthesis methods, which, in turn, inhibits the realization of potential borophene applications. In this multimethod study, photoemission spectroscopies and scanning probe techniques complemented by theoretical calculations have been used to investigate the electronic characteristics of a high-coverage, single-layer borophene on the Ir(111) substrate. Our results show that the binding of borophene to Ir(111) exhibits pronounced one-dimensional modulation and transforms borophene into a nanograting. The scattering of photoelectrons from this structural grating gives rise to the replication of the electronic bands. In addition, the binding modulation is reflected in the chemical reactivity of borophene and gives rise to its inhomogeneous aging effect. Such aging is easily reset by dissolving boron atoms in iridium at high temperature, followed by their reassembly into a fresh atomically thin borophene mesh. Besides proving electron-grating capabilities of the boron monolayer, our data provide comprehensive insight into the electronic properties of epitaxial borophene which is vital for further examination of other boron systems of reduced dimensionality.
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IJS, KILJ, NUK, PNG, UL, UM
We report on a custom‐built UHV‐compatible Magneto‐Optical Kerr Effect (MOKE) magnetometer for applications in surface and materials sciences, operating in tandem with the PhotoEmission Electron ...Microscope (PEEM) endstation at the Nanospectroscopy beamline of the Elettra synchrotron. The magnetometer features a liquid‐nitrogen‐cooled electromagnet that is fully compatible with UHV operation and produces magnetic fields up to about 140 mT at the sample. Longitudinal and polar MOKE measurement geometries are realized. The magneto‐optical detection is based on polarization analysis using a photoelastic modulator. The sample manipulation system is fully compatible with that of the PEEM, making it possible to exchange samples with the beamline endstation, where complementary X‐ray imaging and spectroscopy techniques are available. The magnetometer performance is illustrated by experiments on cobalt ultra‐thin films, demonstrating close to monolayer sensitivity. The advantages of combining in situ growth, X‐ray Magnetic Circular Dichroism imaging (XMCD‐PEEM) and MOKE magnetometry into a versatile multitechnique facility are highlighted.
A UHV‐compatible MOKE magnetometer for in situ studies operating in tandem with the PEEM at the Nanospectroscopy beamline of the Elettra synchrotron.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
A complex interplay between the crystal structure and electron behavior within borophene renders this material an intriguing 2D system with many of its electronic properties still undiscovered. ...Experimental insight into those properties is additionally hampered by the limited capabilities of the established synthesis methods, which in turn inhibits the realization of potential borophene applications. In this multi-method study, photoemission spectroscopies and scanning probe techniques complemented by theoretical calculations have been used to investigate the electronic characteristics of a high-coverage, single-layer borophene on Ir(111) substrate. Our results show that the binding of borophene to Ir(111) exhibits pronounced one-dimensional modulation and transforms borophene into a nano-grating. The scattering of photoelectrons from this structural grating gives rise to the replication of electronic bands. In addition, the binding modulation is reflected in the chemical reactivity of borophene and gives rise to its inhomogeneous aging effect. Such aging is easily reset by dissolving boron atoms in iridium at high temperature followed by their reassembly into a fresh atomically-thin borophene mesh. Besides proving electron-grating capabilities of the boron monolayer, our data provides a comprehensive insight into the electronic properties of epitaxial borophene which is vital for further examination of other boron systems of reduced dimensionality.
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