interfaces – Lightsources.org

Nano-opto-electronics with Soapstone

2018/10/032018/10/23

Research shows potential of combining mineral with graphene for the design of new devices.

The development of electronic devices in the nanometric scale depends on the search for materials that have appropriate characteristics, and that are also efficient and inexpensive. This is the case of graphene, a material formed by a single layer of carbon atoms obtained from graphite. Graphene is a conductor with excellent optical and electrical properties that can be easily altered by the incidence of electric fields or light.

In addition, several other interesting structural, electronic and optical properties can be obtained by combining graphene with other materials. These new properties arise due to changes in the electronic structure in the interface of different materials when they are brought into contact. In this scenario, the search for new materials and ways of combining them becomes a natural trend.

Image: DOI: 10.1021/acsphotonics.7b01017

Berkeley Lab researchers receive DOE Early Career Research Awards

2018/06/212018/07/04

Six scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) have been selected by the U.S. Department of Energy’s (DOE’s) Office of Science to receive significant funding for research through its Early Career Research Program.

The program, now in its ninth year, is designed to bolster the nation’s scientific workforce by providing support to exceptional researchers during the crucial early career years, when many scientists do their most formative work. The six Berkeley Lab recipients are among a total of 84 recipients selected this year, including 30 from DOE’s national laboratories. This year’s awards bring to 35 the total number of Berkeley Lab scientists who have received Early Career Research Program awards since 2010.

“We are grateful that DOE has chosen to recognize these six young Berkeley Lab scientists,” said Berkeley Lab Director Mike Witherell. “Our Lab takes very seriously the responsibility to train the next generation of scientists and engineers. Each of their proposed projects not only represents cutting-edge science but will also contribute to our understanding of the world and a sustainable future.“

The scientists are each expected to receive grants of up to $2.5 million over five years to cover year-round salary plus research expenses.

Image: Ethan Crumlin is a staff scientist at the Advanced Light Source (ALS), a DOE Office of Science User Facility at Berkeley Lab, who specializes in studies of chemistry at the interfaces between solids, liquids, and gases.

The 2018 Julian David Baumert Ph.D. Thesis Award

2018/06/212018/06/21

Maxwell Terban received the 2018 Julian Baumert Ph.D. Thesis Award at this year’s Joint CFN and NSLS-II Users’ Meeting.

Maxwell Terban, a postdoctoral researcher at the Max-Plank Institute for Solid State Research, Stuttgart, is this year’s recipient of the Julian Baumert Ph.D. Thesis Award. Terban was selected for developing new research methods, based around a technique called pair distribution function (PDF), for extracting and analyzing structural signatures from materials. His research incorporated measurements from the now-closed National Synchrotron Light Source (NSLS) and the recently opened National Synchrotron Light Source II (NSLS-II)—a U.S. Department of Energy (DOE) Office of Science User Facility located at Brookhaven National Laboratory.

Each year, the Baumert Award is given to a researcher who has recently conducted a thesis project that included measurements at NSLS or NSLS-II. The award was established in memory of Julian David Baumert, a young Brookhaven physicist who worked on x-ray studies of soft-matter interfaces at NSLS.

Terban holds a bachelor’s degree in chemical engineering from the University of Massachusetts, Amherst, and a master’s degree in materials science and engineering from Columbia University. He graduated with a Ph.D. in materials science and engineering from Columbia University in 2018, and completed his doctoral dissertation under the guidance of Simon Billinge, a professor of materials science and engineering and applied physics and mathematics at Columbia.

Image: Maxwell Terban, a postdoctoral researcher at the Max-Plank Institute for Solid State Research, Stuttgart, is this year’s recipient of the Julian Baumert Ph.D. Thesis Award.

High coherence and intensity at FERMI enables new X-ray interfacial probe

2018/02/052018/03/14

Interfaces are involved in a wide range of systems and have significant implications in many fields of scientific and technological advancement, often determining device performance or chemical reactivity. Vital examples include solar cells, protein folding, and computer chips. A class of commonly used surface science techniques are comprised of even-ordered nonlinear spectroscopies (i.e., second harmonic and sum frequency generation) which exhibit no response in centrosymmetric media due to symmetry constraints.As a result, they have been widely used at optical wavelengths to explore physical and chemical properties of interfaces, where centrosymmetry is broken. Extending this to x-ray wavelengths would effectively combine the element specificity and spectral sensitivity of x-ray spectroscopy with the rigorous interfacial/surface specificity of optical even-ordered nonlinear spectroscopies. Unfortunately, at hard x-ray energies (x-ray wavelength order of the spacing between atoms) these even-ordered nonlinear spectroscopies are effectively bulk probes, as each individual atom breaks inversion symmetry. As soft x-ray wavelengths fall in between the UV and hard x-ray regimes, there has been uncertainty regarding the interface specificity of soft x-ray second harmonic generation.

>Read more on the FERMI webpage

Figure: (extract) Experimental Design. X-ray pulses are passed through a 2 mm iris and focused onto the graphite sample at normal incidence. The transmitted beam is then passed through a 600 nm aluminum filter and onto a spectrometer grating, spatially resolving the second harmonic signal from the fundamental. Inset: A schematic energy level diagram of the second harmonic generation process. (entire figure here)

Enhanced magnetic hybridization of a spinterface

2018/01/172018/01/24

Interfaces between organic semiconductors and ferromagnetic metals offer intriguing opportunities in the rapidly developing field of organic spintronics. Understanding and controlling the spin-polarized electronic states at the interface is the key toward a reliable exploitation of this kind of systems. It is indeed important to master and reliably reproduce the chemical reactions responsible of the spin-polarization at the interface.

Here we propose an approach consisting in the insertion of an ultrathin, two-dimensional Cr₄O₅ magnetic oxide layer at the interface between a C₆₀ fullerene organic semiconductor and a Fe(001) ferromagnetic metal to both maximize the spin polarization and to overcome the reproducibility issues usually present in case of direct interface between metallic layer and organic semiconductor.
C60 fullerene showed a greater surface diffusivity when growing on Cr₄O₅compared to the Fe(001) case. From the first stages of surface coverage, C₆₀ tends to form islands rather than isolated molecules, leading to a well-ordered growth at higher thicknesses (Figure 1, above).

>Read more on the Elettra website

Figure 1. STM image 200 x 200 nm² of the surface of a C₆₀/ Cr₄O₅/Fe(001) sample with a fullerene coverage of about 0.5 ML. The image was taken at room temperature with ΔV= 1.7 V, I = 400 pA.

Control of magnetoresistance in spin valves

2018/01/162018/01/24

Molecules, due to their wide-ranging chemical functionalities that can be tailored on demand, are becoming increasingly attractive components for applications in materials science and solid-state physics. Remarkable progress has been made in the fields of molecular-based electronics and optoelectronics, with devices such as organic field-effect transistors and light emitting diodes. As for spintronics, a nascent field which aims to use the spin of the electron for information processing, molecules are proposed to be an efficient medium to host spin-polarized carriers, due to their weak spin relaxation mechanisms. While relatively long spin lifetimes are measured in molecular devices, the most promising route toward device functionalization is to use the chemical versatility of molecules to achieve a deterministic control and manipulation of the electron spin.

Spin-polarized hybrid states induced by the interaction of the first molecular monolayers on ferromagnetic substrates are expected to govern the spin polarization at the molecule–metal interface, leading to changes in the sign and magnitude of the magnetoresistance in spin-valve devices. The formation of spin-polarized hybrid states has been determined by spin-polarized spectroscopy methods and principle-proven in nanosized molecular junctions, but not yet verified and implemented in large area functional device architectures.

>Read more on the ALBA website

Image: Magnetoresistance (top) and X-ray spectroscopy (bottom) measurements, evidencing the control of the magnetoresistance sign and amplitude by engineering spin valves with NaDyClq/NiFe and NaDyClq/Co interfaces, and their corresponding interfacial molecule-metal hybridization states.

Ferromagnetism Emerges to Alleviate Polar Mismatch

2017/12/042018/01/17

Alchemists dreamed of turning boring, base metals into exotic, noble metals. Although such dreams were never realized, scientists today can induce unexpected properties at the interface between two materials—including properties not present in either parent material. For example, researchers have discovered that if they combine SrTiO3 (a dielectric and paramagnetic material) together with LaMnO3 (an insulating and antiferromagnetic material) in just the right way, they can induce an insulating ferromagnetic state at the interface.

Multi-orbital charge transfer at highly oriented organic/metal interfaces

2017/11/212018/01/16

Organic-based device performances have been rapidly improving in the last years, making them suitable for large-scale industrial applications, involving photo-voltaic cells, light emission systems and building of larger flexible electronics. In parallel, basic research has intensively been focused on the chemical and physical properties of semiconducting π-conjugated organic molecules, as they appear to be promising for organic-based device construction. In particular, in controlling the charge injection on such devices, a predominant role is played by the molecule-substrate interaction. Charge transfer at the molecule-metal interface strongly affects the overall physical and magnetic properties of the system, and ultimately, the device performance.
Read more on the Elettra website.

Image: (a) STM image including two Ni-TPP domains, labeled with A and B, respectively. STM image parameters: Vb = −1.5 V, It = 0.2 nA, image size 15 × 20 nm2, measured at 4.3 K. (b) . Proposed adsorption model for Ni-TPP/Cu(100), side view. (c) Valence band photoemission spectra of clean Cu(100) and Ni-TPP/Cu(100) acquired at 26 eV photon energy. (d) PDOS onto molecular orbitals for the Ni-TPP/Cu(100) system. The energy position of the corresponding gas-phase molecular orbitals, aligned with respect to the vacuum level, is indicated with colored bars on the top axis. (e) Comparison between μ-ARPES measured patterns (left) and the correspondent calculated |FT|2 of the molecular orbitals (right).

Emergent magnetism at transition-metal-nanocarbon interfaces

2017/08/282017/10/09

Researchers have shed light on the origin of the magnetism arising at carbon/non-magnetic 3d,5d metal interfaces

These results may allow the manipulation of spin ordering at metallic surfaces using electro-optical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices.

Interfaces are key in solid state and quantum physics, controlling many fundamental properties and enabling emergent interfacial, bi-dimensional like phenomena. Therefore they offer potential opportunities for designing hybrid materials that profit from promising combinatory effects.

In particular, the fine-tuning of spin polarization at metallo–organic interfaces opens a realm of possibilities, from the direct applications in molecular spintronics and thin-film magnetism to biomedical imaging or quantum computing. This interaction at the interface can control the spin polarization in magnetic field sensors, generate magnetization spin-filtering effects in non-magnetic electrodes or even give rise to magnetic ordering when non-magnetic elements such as diamagnetic copper or paramagnetic manganese are put in contact with carbon/fullerenes at such interfaces.

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Liquid-phase chemistry: Graphene nanobubbles

2017/04/072017/10/09

X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Absorption Spectroscopy (XAS) provide unique knowledge on the electronic structure and chemical properties of materials.

Unfortunately this information is scarce when investigating solid/liquid interfaces, chemical or photochemical reactions in ambient conditions because of the short electron inelastic mean free path (IMFP) that requires a vacuum environment, which poses serious limitation on the application of XPS and XAS to samples operating in atmosphere or in the presence of a solvent. One promising approach to enable the use of conventional electron spectroscopies is the use of thin membrane, such as graphene (Gr), which is transparent to both X-ray photons and photoelectrons. For these purposes, this work proposes an innovative system based on sealed Gr nanobubbles (GNBs) on a titanium dioxide TiO₂ (100) rutile single crystal filled with the solution of interest during the fabrication stage (Figure 1a).

The formation of irregularly shaped vesicles with an average height of 6 nm and lateral size of a few hundreds of nanometers was proved by using a multi-technique approach involving Atomic Force Microscopy (AFM, see Figure 1b,c,d), Raman (Figure 1e) and synchrotron radiation spectroscopies (Figure 2), which have unequivocally demonstrated the presence of water inside the GNBs and the transition to a flat Gr layer after water evaporation by thermal heating up to 350 °C in ultra high vacuum (UHV).

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Chemistry at the protein-mineral interface

2017/03/272017/10/09

The nucleation site of iron mineral in human L ferritin revealed by anomalous -ray diffraction

Iron ions have crucial functions in every living organism being essential for cellular respiration, DNA synthesis, detoxification of exogenous compounds, just to provide a few examples. However, the redox properties of iron ions can also cause the occurrence of deleterious free-radicals. For these reasons, when unnecessary, iron must be kept in appropriate forms unable to cause damage. Nature evolved a special protein cage, called ferritin, consisting of 24 subunits arranged to form a hollow sphere with an internal diameter of about 80 Å where mineralized iron is stored, generally under the form of insoluble ferric oxides.

In mammals, two types of subunits build-up the 24-mer ferritins: the ‘heavy’ (H) and the ‘light’ (L). These subunits differ not only in molecular weight (21.2 kDa for H and 20.0 kDa for L) but, mainly, in function. The H subunit is able to catalyze the rapid oxidation of Fe²⁺ to Fe³⁺ followed by transfer in the storage cavity. On the contrary, the L-chain does not possess catalytic activity, but it is still able to mineralize ferric ions upon spontaneous oxidation by dioxygen of captured Fe²⁺. Despite the intensive research on ferritin chemistry, the mechanisms of iron oxidation and storage to form mineral nanoparticles inside the ferritin cavity are still to be fully established.

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