Tag: graphene

BESSY II: Heterostructures for Spintronics

BESSY II: Heterostructures for Spintronics

Spintronic devices work with spin textures caused by quantum-physical interactions. A Spanish-German collaboration has now studied graphene-cobalt-iridium heterostructures at BESSY II. The results show how two desired quantum-physical effects reinforce each other in these heterostructures. This could lead to new spintronic devices based on these materials.

Spintronics uses the spins of electrons to perform logic operations or store information. Ideally, spintronic devices could operate faster and more energy-efficiently than conventional semiconductor devices. However, it is still difficult to create and manipulate spin textures in materials.

Graphene for Spintronics

Graphene, a two-dimensional honeycomb structure build by carbon atoms, is considered an interesting candidate for spintronic applications. Graphene is typically deposited on a thin film of heavy metal. At the interface between graphene and heavy metal, a strong spin-orbit coupling develops, which gives rise to different quantum effects, including a spin-orbit splitting of energy levels (Rashba effect) and a canting in the alignment of spins (Dzyaloshinskii-Moriya interaction). Especially the spin canting effect is needed to stabilise vortex-like spin textures, known as skyrmions, which are particularly suitable for spintronics.

Plus Cobalt Monolayers

Now, however, a Spanish-German team has shown that these effects are significantly enhanced when a few monolayers of the ferromagnetic element cobalt are inserted between the graphene and the heavy metal (here: iridium). The samples were grown on insulating substrates which is a necessary prerequisite for the implementation of multifunctional spintronic devices exploiting these effects.

Read more on HZB website

Image: Symbolic illustration of a graphene layer on a microchip. In combination with a heavy-metal thin film and ferromagnetic monolayers, graphene could enable spintronic devices.

Credit: Dall-E/arö

From Theory to Confidence: Building Trust in Twistronics Models

From Theory to Confidence: Building Trust in Twistronics Models

A UK collaboration explored the transformative impact of twist angles on the electronic structure of 2D materials

A single sheet of graphene, composed of a single layer of carbon atoms in a hexagonal pattern, is a semimetal. However, adding a second sheet of graphene, twisted at a slight angle to the first, can give rise to very different electronic properties, depending on the angle. At the ‘magic’ angle of about 1.1°, for example, a twisted bilayer sheet of graphene is a superconductor. The same effect is seen in other 2D materials, giving rise to a new field of study – twistronics – seeking to both understand and exploit the relationship between twist angles and novel electronic properties. In work recently published in Nano Letters, researchers from the University of Warwick and the National Graphene Institute at the University of Manchester used spatially-resolved angle-resolved photoemission spectroscopy (ARPES) on Diamond’s I05 beamline to study the twist-dependent band structure of twisted-bilayer, monolayer-on-bilayer, and double-bilayer graphene. Their results show good agreement between experimental measurements and theoretical simulations, confirming that the models can be used to explore the electronic band structure and emergent transport and optical properties of twisted-few-layer graphenes. 

Prof Neil Wilson at the University of Warwick opens by noting that;

Twistronics is a new concept in 2D materials, in condensed matter physics. When you have two atomically thin layers next to each other, their properties depend on the twist angle between them. This happens because of changes to the electronic structure, and there has been a huge amount of research on twistronics – putting two layers together at different twist angles and seeing what happens to the optical properties and electrical properties. You’re working with two very small pieces of 2D material stacked on top of each other, typically only a few micrometres across, which is fine for optical measurements and electrical transport measurements. However, that makes it extremely challenging to study the electronic structure directly.

To get a good look at the electronic structure of these exciting materials, Prof Wilson’s group at the University of Warwick worked with researchers from the National Graphene Institute and Diamond’s I05 beamline. Prof Roman Gorbachev’s group at the National Graphene Institute is a world leader in fabricating these complex samples.

Senior Beamline Scientist Matthew Watson explains;

Angle-resolved ARPES allows us to measure directly the electronic structure of the 2D materials. It allows us to determine both the energy and momentum of the electrons within the material, which gives us directly the electronic structure which underpins the optical properties and the transport properties. And the I05 nano-branch endstation delivers spatially-resolved ARPES from ultra-small spots, on the micrometre length scales we have in these 2D samples.

Read more on Diamond website

Image: Electronic structures of twisted double bilayer graphene at large (left) and “magic” (centre) twist angles, showing the emergence of a flat band at the top, which is at the heart of the various phenomena that emerge in this system. Data measured at I05 at Diamond and reported in Nunn et al.

Credit: Matthew Watson

Single-spin flat bands in monolayer graphene

Single-spin flat bands in monolayer graphene

In the rapidly evolving landscape of electronic materials and devices, the integration of two-dimensional materials, graphene in particular, with magnetic elements has emerged as a promising frontier. The ability to engineer spin-dependent electronic properties not only expands the horizons of spintronics but also holds the potential to revolutionize a wide array of electronic applications. From ultra-fast data processing to energy-efficient memory storage and beyond, the synergistic interplay between graphene and magnetic layers opens new routes for device miniaturization, aiming at reduced power consumption and enhanced performance.

Along these lines, the realization of topological electronic flattened bands near or at the Fermi level represents a promising avenue for the emergence of exotic electronic and magnetic states. One of the key attributes of flat bands is their facile electrical tunability, allowing for the exploration of correlated phases such as unconventional superconductivity, quantum states, and insulating topological states, all within two-dimensional platforms and without the need for an applied magnetic field.

An alternative approach to generate flat bands in graphene involves exploiting the Spin-Orbit Coupling (SOC) effect induced by the proximity to magnetic and/or heavy-metal layers. Monolayer graphene (Gr) interfaced with 3d-ferromagnetic and 4f-materials presents compelling technological prospects, bridging the realms of spintronics, ultra-fast graphene-based electronics, and photonics. While Gr/3d-ferromagnetic systems exhibit strong hybridization, impacting the electronic properties of graphene, Gr/4f-ferromagnetic interfaces demonstrate a weak interaction that preserves graphene’s electronic structure.

Read more on Elettra website

Image:  Landscape of the structural and electronic properties upon Eu intercalation in Gr/Co(0001). LEED patterns acquired at a kinetic energy of 69 eV (a, d), 2D momentum maps at the Fermi level (b, e) and ARPES energy vs. momentum maps (c, f) acquired at the K point of the first Brillouin zone for Gr/Co and Gr/Eu/Co, respectively.

Enigmatic Dirac fermions in graphene

Enigmatic Dirac fermions in graphene

Since the discovery of graphene more than 15 years ago, research on graphene-based systems has grown exponentially. Graphene exhibits unique physical properties, for instance, the presence of massless Dirac fermions in a lattice of stronger covalent bonds and frequency-independent optical conductivity, which may help to realize exotic fundamental science and advanced technologies.

So far, graphene has been grown on a multitude of substrates exhibiting interesting properties. In some cases, the graphene layer has minimal link with the substrate. Experiments have revealed enigmatic properties of the Dirac fermions near the band crossing, called Dirac point, at the K point of the Brillouin zone. For example, Angle-Resolved PhotoEmission Spectroscopy (ARPES) data of graphene grown on SiC, shown in Fig. 1a, exhibit large momentum independent intensities near Dirac point as if the top and bottom of the Dirac cone are shifted away from each other. Some studies interpreted these results as a gapped Dirac cone with anomalous in-gap intensities as schematically shown in Fig. 1b. The presence of electron correlation renormalizes the dispersion as shown by red lines. Other proposals involve plasmaron bands where plasmon excitations in addition to photoexcitation of electrons leads to a shifted Dirac cone. The shifted and the pristine Dirac cones appear as a diamond shaped structure around the Dirac point as shown in Fig. 1c.

In order to address this enigmatic scenario, A. Pramanik, S. Thakur and colleagues from India, Italy and Germany performed a detailed polarization dependent ARPES investigation at the BaDElPh beamline at Elettra. Each branch of the Dirac cone was probed selectively using s– and p-polarized synchrotron light. The spectra shown in Fig. 2a,b reveal clearly dispersive bands near the Dirac point.

Read more on the Elettra website

Image: (a) Typical ARPES spectra of graphene on SiC along the ΓKM direction of the Brillouin zone; the origin of the momentum axis is shifted to K point. Schematic of (b) anomalous region and (c) plasmaron scenario around the Dirac point. Red curved lines in (b) show bands in the presence of electron correlation. Red Dirac cone in (c) is due to plasmaron bands.

Buckyballs on gold are less exotic than graphene

Buckyballs on gold are less exotic than graphene

C60 molecules on a gold substrate appear more complex than their graphene counterparts, but have much more ordinary electronic properties. This is now shown by measurements with ARPES at BESSY II and detailed calculations.

Graphene consists of carbon atoms that crosslink in a plane to form a flat honeycomb structure. In addition to surprisingly high mechanical stability, the material has exciting electronic properties: The electrons behave like massless particles, which can be clearly demonstrated in spectrometric experiments. Measurements reveal a linear dependence of energy on momentum, namely the so-called Dirac cones – two lines that cross without a band gap – i.e. an energy difference between electrons in the conduction band and those in the valence bands.

Variants in graphene architecture

Artificial variants of graphene architecture are a hot topic in materials research right now. Instead of carbon atoms, quantum dots of silicon have been placed, ultracold atoms have been trapped in the honeycomb lattice with strong laser fields, or carbon monoxide molecules have been pushed into place on a copper surface piece by piece with a scanning tunneling microscope, where they could impart the characteristic graphene properties to the electrons of the copper. 

Artificial graphene with buckyballs?

A recent study suggested that it is infinitely easier to make artificial graphene using C60 molecules called buckyballs. Only a uniform layer of these needs to be vapor-deposited onto gold for the gold electrons to take on the special graphene properties. Measurements of photoemission spectra appeared to show a kind of Dirac cone.

Analysis of band structures at BESSY II

“That would be really quite amazing,” says Dr. Andrei Varykhalov, of HZB, who heads a photoemission and scanning tunneling microscopy group. “Because the C60 molecule is absolutely nonpolar, it was hard for us to imagine how such molecules would exert a strong influence on the electrons in the gold.” So Varykhalov and his team launched a series of measurements to test this hypothesis.

In tricky and detailed analyses, the Berlin team was able to study C60 layers on gold over a much larger energy range and for different measurement parameters. They used angle-resolved ARPES spectroscopy at BESSY II, which enables particularly precise measurements, and also analysed electron spin for some measurements.

Read more on the HZB website

Image: Using density functional theory and measurement data from spin-resolved photoemission, the team investigated the origin of the repeating Au(111) bands and resolved them as deep surface resonances. These resonances lead to an onion-like Fermi surface of Au(111).

Credit: © HZB

Investigating high temperature superconductors

Investigating high temperature superconductors

Researchers from the ARC Centre of Excellence in Future Low Energy Electronic Technologies (FLEET) used the Soft X-ray Spectroscopy beamline at the Australian Synchrotron to investigate the structure of a promising high-temperature superconductor, a calcium-doped graphene material.

The FLEET Centre has provided a detailed description of the research, published in The Chemistry of Materials, on their website.

In characterising the material, the investigators wanted to clarify where the calcium went after it was added to a sample consisting of a single layer of graphene on a silicon carbide substrate.

Measurements at the Australian Synchrotron were able to pinpoint that the calcium atoms were located, unexpectedly, near the silicon carbide surface.

Read more on the ANSTO website

Image: Dr Anton Tadich (far right) with SXR beamline team members and researchers from the FLEET Centre.

Beyond graphene: monolayer arsenene observed for the first time

Beyond graphene: monolayer arsenene observed for the first time

An article recently published in 2D Materials shows the first experimental evidence of the successful formation of arsenene, an analogue of graphene with noteworthy semiconducting properties.

This material shows a great potential for the development of new nanoelectronics. Crucial sample preparation and electron spectroscopy experiments were performed at the Bloch beamline at MAX IV.

The discovery of graphene, the single-layer carbon honeycomb material worth the Nobel Prize in Physics in 2010, surely has had a revolutionary impact on research. It triggered a whole new field of study within two-dimensional (2D) materials. However, its application in developing new 2D electronics has been hindered by its lack on an intrinsic band gap. Researchers therefore started to turn their attention to other elements in the periodic table and set their eyes on group V, to which arsenic belongs.
“The aim of the study was to show that arsenene can be formed. Our article is the first to report this”, says Roger Uhrberg, professor at Linköping University and spokesperson for the Bloch beamline at MAX IV. Arsenene, a single-layer buckled honeycomb structure of arsenic, had been previously predicted by various theoretical studies, but this is the first experimental observation that verifies its existence.

>Read more on the MAX IV website

Image: A view of the Bloch beamline at MAX IV. The Bloch beamline consists of two branchlines, and is dedicated to high resolution photoelectron spectroscopy, encompassing angle-resolved (ARPES), spin resolved (spin-ARPES) and core-level spectroscopy.

Translucency of graphene to van der Waals forces

Translucency of graphene to van der Waals forces

If in the infinitely large it is the gravitational force that determines the evolution in space and time of planets, stars and galaxies, when we focus our observation on the atomic scale other are the forces that allow materials to exist. These are forces that, like a “special glue”, allow atoms and molecules to aggregate to form living and non-living systems. Among them we find one that, although discovered 150 years ago by Johannes Diderik van der Waals (vdW), still carries with it some aspects of ambiguity. Van der Waals was the first to reveal its origin and to give a first and simple analytical description, even though it took more than a century, with the new discoveries of quantum field theory, to be able to fully understand its quantum character and its relation to the vacuum energy and Casimir force. And only in the last 30 years it has been realized how much this force pervades the natural world. One of the wonders is represented by the geckos, who use these forces to climb vertical and smooth walls thanks to the vdW forces, which are enhanced because of the multitude of hairs present in each finger of their legs. These forces are also known to affect the stability of the double helix of the DNA and are also responsible for the interactions between different groups of amino acids.
What makes the vdW force unique is the fact that it is the weakest of the inter-atomic and inter-molecular forces present in nature and therefore it remains extremely difficult to measure with great accuracy. At the same time, even the inclusion of these force in the most accurate methods of calculation has not yet found a universal solution and the different approaches used by theoretical physicists and chemists to take them into account can sometimes lead to conflicting results.

>Read more on the Elettra website

Image:   CO desorption from Gr/Ir(111). (a) Selected spectra of the uptake corresponding to θCO=0.08 ML (bottom) and 0.30 ML (top). (b) TP-XPS C 1s core level spectra showing its evolution during thermal desorption of CO from Gr/Ir(111). (c) Comparison of CO coverage evolution as a function of temperature for selected CO initial coverages. 

Control of light at the nanoscale

Control of light at the nanoscale

Research evaluates combination of graphene and hexagonal boron nitride for opto-electronic devices of the future

Photonics is the science that investigates phenomena related to light, such as its generation, transmission and detection. Its applications can be found in a wide range of technologies that directly impact our daily life: lasers used in surgery, fiber optics for data transmission, and screens of high definition TVs and smartphones. These advances are only possible by the in-depth knowledge of the interaction of light with supercompact electronic components.
The latest frontier of photonics is the production of nanoscale devices capable of transmitting information by means of light signals, called nanophotonic or optoelectronic devices. When compared to the already established electronic components, the new nanodevices will carry a greater volume of information at a faster pace.
Today, several research groups around the world are dedicated to building ultrathin photonic devices with outstanding performance. However, such development requires materials that have appropriate characteristics, besides being efficient and inexpensive.
One of the materials of interest is graphene, formed by a single layer of carbon atoms obtained from graphite. Graphene is a conductor with excellent properties that can be easily altered by applying electric fields or light. In addition, several other interesting structural, electronic and optical properties can be obtained by combining graphene with other materials. One of these combinations under study is the system formed by graphene in contact with a hexagonal boron nitride crystal (hBN), also a few molecules thick. This system allows the control of light transport on a nanometer scale.
Image: Schematics of the Graphene-hBN and the experimental analysis using infrared nanospectroscopy. Reprinted with permission from Nano Lett. 2019, 19, 2, 708-715.
Copyright 2019 American Chemical Society.
Urea susbstitutes noble metal catalysts

Urea susbstitutes noble metal catalysts

… for the photodegradation of organic polluants.

A new laser-based technique developed by the Institute of Materials Science (ICMAB-CSIC) uses urea, a common substance in the chemical industry and a low-cost alternative to noble metal co-catalyst, to enable a more efficient, one-step production of hybrid graphene-based organic-inorganic composite layers for environmental remediation, photodegradation of antibiotic contaminants from wastewater. The composition and chemical bonds of the urea-enriched thin layers were studied in detail using synchrotron light at the ALBA Synchrotron.
Human activity is increasing the amount of pollutants in water and air, as well as in all sorts of materials at home and work place. The existence of antibiotic contamination is undeniably one of the most threatening challenges to date, at a time when antibiotic-resistant bacteria has already been flagged as the next world-wide pandemic crisis.
Semiconductor photocatalysts have long been investigated for environmental remediation because they can degrade or mineralize a wide range of organic contaminants as well as pathogens. Research focuses on addressing some drawbacks that prevent their use on a large scale. On the one hand, many photocatalysts are activated only by UV radiation which represents solely a small fraction of the total available solar emission. On the other hand, the recombination of the photogenerated  electron-hole pairs that enable the decomposition of the pollutant is usually faster than the oxidation reactions that cause the degradation of organic molecules. As a consequence, noble metal co-catalysts acting as electron scavengers, such as gold or platinum, are needed in the process.

Image: Researchers Ángel Pérez  del Pino and Enikö György from the ICMAB-CSIC together with Ibraheem Yousef, scientists responsible of MIRAS beamline at ALBA.
Magnetic patterning by electron beam assisted carbon lithography

Magnetic patterning by electron beam assisted carbon lithography

The exploitation of the unique physical properties of thin films and heterostructures are opening intriguing opportunities for magnetic storage technology. These artificial materials will in fact enable novel architectures for a multitude of magnetic devices and sensors, promoting a significant improvement in storage density, functionality and efficiency. Their usage will also contribute to diminish the consumption of materials that are rare and difficult to extract, being often detrimental to the environment. With these objectives in mind, researchers are now looking with great attention at the combination of thin ferromagnetic layers with 2-dimensional crystals like graphene and transition metal dichalcogenides. Due to their layered structure, these systems exhibit very favorable magnetic properties, which can be tuned through thickness and interfacial interactions. For instance, graphene-cobalt stacks display an enhanced perpendicular magnetic anisotropy, a feature that is especially important for non-volatile memories.
The fabrication of layered materials, however, is still a very challenging process. Not only it requires atomic precision in the deposition of the various layers but also the ability to create nano or microstructures of arbitrary shape. Conventional lithography in conjunction with chemical etching permits nowadays to sculpture the matter with great accuracy, at lateral resolution close to the nanometer. Yet, this approach poses an important limitation, that is, the material can only be shaped by erosion. The ability to vary the chemical composition, by adding atoms for example, is instead very desirable for many applications. To date, this can be done by stimulating the fragmentation of suitable carrier molecules using photons or electrons. So far, various methods based on focused beam induced processing methods have been devised, which can be readily employed to deposit carbonaceous layers and metallic nanostructures. These methods, however, cannot be applied when ultra-clean, ultra-high vacuum (UHV) conditions are needed, as happens for the case of semiconductor industry.

>Read more on the Elettra website

Figure 1.  (left) Scheme of the protocol for printing chemo-magnetic patterns in ultrathin Co on Re(0001). (a) The film is exposed to CO at room temperature. The irradiation with a focused electron beam (yellow) stimulates the dissociation of the molecule, which results in the accumulation of atomic carbon on the surface. (b) Subsequently, the sample is annealed above 170 °C to desorb molecularly adsorbed CO from the non-irradiated surface regions. (c) LEEM image of an e-beam irradiated disk. Disk diameter: 1 μm; Co thickness: 4 atomic layers; irradiation energy: 50 eV; CO dose: 9.75 L; (d) Intensity profile across the orange line in the LEEM image in (c) and fit using a step function convoluted with a Gaussian of full width at half-maximum of 30 nm. The dashed blue lines indicate the 15–85% distance between minimum and maximum intensity. (e) XMCD-PEEM image of the same region at the Co L3 edge. (f) Intensity profiles across the blue and orange dashed lines in the XMCD-PEEM image in (e). The magnetic stripes indicate out-of-plane magnetic anisotropy. The stripe period is 120 nm. Adapted with permission from [1].
Copyright (2018) American Chemical Society.

Towards upscaling the production of graphene nanoribbons for electronics

Towards upscaling the production of graphene nanoribbons for electronics

Two-dimensional sheets of graphene in the form of ribbons a few tens of nanometers across have unique properties that are highly interesting for use in future electronics.

Researchers have now for the first time fully characterised nanoribbons grown in both the two possible configurations on the same wafer with a clear route towards upscaling the production.
Graphene in the form of nanoribbons show so called ballistic transport, which means that the material does not heat up when a current flow through it. This opens up an interesting path towards high speed, low power nanoelectronics. The nanoribbon form may also let graphene behave more like a semiconductor, which is the type of material found in transistors and diodes. The properties of graphene nanoribbons are closely related to the precise structure of the edges of the ribbon. Also, the symmetry of the graphene structure lets the edges take two different configurations, so called zigzag and armchair, depending on the direction of the long respective short edge of the ribbon.

See some video interviews and the entire article on the MAX IV website

Doped epitaxial graphene close to the Lifshitz transition

Doped epitaxial graphene close to the Lifshitz transition

Graphene, an sp2 bonded sheet of carbon atoms, is still attracting lots of interest almost 15 years after its discovery. Angle-resolved photoemission spectroscopy (ARPES) is a uniquely powerful method to study the electronic structure of graphene and it has been used extensively to study the coupling of electrons to lattice vibrations (phonons) in doped graphene. This electron-phonon coupling (EPC) manifests as a so-called “kink” feature in the electronic band structure probed by ARPES. What is much less explored is the effect of EPC on the phonon structure. A very accurate probe of the phonons in graphene is Raman spectroscopy.
M.G. Hell and colleagues from Germany, Italy, Indonesia, and Japan combined ARPES (carried out at the BaDelPhbeamline – see Figure 1) with low energy electron diffraction (LEED) and Raman spectroscopy (carried out at the University of Cologne in Germany) in a clever way to fully understand the coupled electron-phonon system in alkali metal doped graphene. LEED revealed ordered (1×1), (2×2), and (sqrt3xsqrt3)R30°adsorbate patterns with increasing alkali metal deposition. The ARPES analysis yielded not only the carrier concentration but also the EPC coupling constant. Ultra-High Vacuum (UHV) Raman spectra carried out using identically prepared samples with the very same carrier concentrations provided the EPC induced changes in the phonon frequencies.

>Read more on the Elettra Sincrotrone Trieste website

Image:  Top: ARPES spectra along the Γ-K-M high symmetry direction of the hexagonal Brillouin zone for Cs doped graphene/Ir(111) with increasing Cs deposition. The Dirac energy ED and the observed LEED reconstruction are also indicated. Bottom: Corresponding Fermi surfaces at the indicated charge carrier concentration. 

Graphene on the way to superconductivity

Graphene on the way to superconductivity

Scientists at HZB have found evidence that double layers of graphene have a property that may let them conduct current completely without resistance. They probed the bandstructure at BESSY II with extremely high resolution ARPES and could identify a flat area at a surprising location.

Carbon atoms have diverse possibilities to form bonds. Pure carbon can therefore occur in many forms, as diamond, graphite, as nanotubes, football molecules or as a honeycomb-net with hexagonal meshes, graphene. This exotic, strictly two-dimensional material conducts electricity excellently, but is not a superconductor. But perhaps this can be changed.

A complicated option for superconductivity
In April 2018, a group at MIT, USA, showed that it is possible to generate a form of superconductivity in a system of two layers of graphene under very specific conditions: To do this, the two hexagonal nets must be twisted against each other by exactly the magic angle of 1.1°. Under this condition a flat band forms in the electronic structure. The preparation of samples from two layers of graphene with such an exactly adjusted twist is complex, and not suitable for mass production. Nevertheless, the study has attracted a lot of attention among experts.

>Read more on the BESSY II at HZB website

Image: The data show that In the case of the two-layer graphene, a flat part of bandstructure only 200 milli-electron volts below the Fermi energy. Credit: HZB

Golden nanoglue completes the wonder material

Golden nanoglue completes the wonder material

Modern microelectronics relies on semiconductors and their metal electrodes. High-performance device functionality demands high transistor density within a single chip, which soon will reach the physical limits of bulk materials. Alternatives have been found in atomically thin materials, e.g. graphene and its semiconductive inorganic relatives.

MoS2 (molybdenum disulphide) is the representative inorganic layered crystal with properties similar to those of graphene. To be useful in applications, it must be joined to the metallic electrodes to enable charge flow between the metals and semiconductive (M/S) counterparts. In a recent study, scientists from University of Oulu, Finland have demonstrated the success of joining MoS2 to Ni (nickel) particles by using gold (Au) nanoglue as a buffer material. Through in-house observations and the first-principles calculations, the semiconductor and metal can be bridged either by the crystallized gold nanoparticles, or by the newly formed MoS2-Au-Ni ternary alloy.
A metallic contact is formed, leading to enhanced electron mobility crossing the M/S interface.

>Read more on the MAX IV Laboratory website

Image: representation of gold nanoglue joining molybdenum disulphide and nickel. 

Towards oxide-integrated epitaxial graphene-based spin-orbitronics

Towards oxide-integrated epitaxial graphene-based spin-orbitronics

An international team of researchers from IMDEA Nanociencia and Complutense and Autónoma universities in Madrid, the Institut Néel in Grenoble and the ALBA Synchrotron in Barcelona has elucidated a new property of Graphene/Ferromagnetic interfaces: the existence of a sizable magnetic unidirectional interaction, technically a Dzyaloshinskii–Moriya Interaction of Rashba origin, which is responsible for establishing a chiral character to magnetic domain wall structures.

A major challenge for future spintronics is to develop suitable spin transport channels with long spin lifetime and propagation length. Graphene can meet these requirements, even at room temperature. On the other side, taking advantage of the fast motion of chiral textures, that is, Néel-type domain walls and magnetic skyrmions, can satisfy the demands for high-density data storage, low power consumption, and high processing speed. The integration of graphene as an efficient spin transport channel in the chiral domain walls technology depends on the ability to fabricate graphene-based perpendicular magnetic anisotropy (PMA) systems with tailored interfacial SOC.

Studies on graphene-based magnetic systems are not abundant and, typically, make use of metallic single crystals as substrates which jeopardize the exploration of their transport properties (since the current is drained by the substrate). To solve this challenge, the IMDEA Nanociencia leading team succeeded to fabricate high-quality epitaxial asymmetric gr/Co/Pt(111) structures grown on (111)-oriented oxide substrates. The quality of the interfaces was checked by low-energy electron diffraction and also by advanced high-resolution transmission microscopy at the Universidad Complutense de Madrid (UCM) microscopy centre and resonant X-ray specular reflectivity at BOREAS beamline at ALBA (see fig.1). The magnetic anisotropy and properties were investigated by magneto-optical Kerr magnetometry in IMDEA and Universidad Autónoma de Madrid (UAM) and complemented with element resolved XMCD magnetometry also at BOREAS beamline. Finally, the chirality of the magnetic domain walls was analysed using a customized magneto-optical Kerr effect microscope and pulse field electronics in collaboration with the team at Institut Néel in Grenoble.

>Read more on the ALBA website