photoemission – Lightsources.org

Advancing Polarization-Sensitive Photodetection: The Potential of Naturally Anisotropic Tin Monochalcogenides

2025/04/072025/05/02

A team of scientists from Wrocław University of Science and Technology, in cooperation with researchers from the URANOS beamline, conducted a series of experiments on layered semiconductors SnS and SnSe using photoemission spectroscopy. Their investigation revealed characteristic features of the electronic band structure, which influence the optical properties of these materials and their potential for near-infrared polarization-sensitive photodetectors.

Polarization-sensitive photodetectors play a crucial role in detecting changes in light polarization, which has applications ranging from liquid crystal technology to biological studies. Existing designs rely on complex optical components, but this study demonstrates that the natural anisotropy of tin monochalcogenides can significantly simplify device construction. This could lead to more efficient and compact photodetectors with polarization resolution.

The unique properties of SnS and SnSe stem from their distorted orthorhombic crystal structure, which introduces directionality in electronic band dispersion. This, in turn, affects their optical characteristics, enabling selective absorption of polarized light. The study also highlights the impact of lone electron pairs on the energy levels of these materials (determining parameters such as work function and ionization potential), which is crucial for the design of heterostructures and metal contacts. Compared to black phosphorus (BP), another anisotropic vdW crystal, SnS and SnSe offer superior stability in ambient conditions, making them more practical for real-world applications.

Read more on SOLARIS website

ALBA initiates new beamline

2022/03/022022/03/02

3Sbar (Surface Structure and Spectroscopy at 1 bar) is the name of the next ALBA beamline that will be extremely useful to provide answers to environment protection. 3Sbar is a unique instrument that will provide unprecedented insight on the understanding of fundamental processes in catalytic reactions. The project, funded by the Recovery, Transformation and Resilience Plan within the framework of the NextGenerationEU, will enter operation in 2026.

The 3Sbar project has been chosen as ALBA 14th beamline. It will allow simultaneous photoemission experiments at 1 bar gas pressures and surface X ray diffraction. The electronic and atomic structures will be both probed during surface chemical reactions and catalytic operando reactions. The products of the reactions will also be analysed by gas phase photoemission.

This new beamline will be key to understand the correlation between chemical reactions and structural changes at atmospheric pressures, which represents a big step ahead for fundamental research in surface chemistry and catalysis. It will allow to get a deep insight in the basic processes determining the efficiencies of catalysts under industrial operating pressures.

3Sbar will be extremely useful to provide answers to environmental protection, challenges such as CO2 reduction, the wastewater treatment, development of environmentally friendly industrial catalytic processes or recycling of greenhouse gases.

The beamline, adaptable to many different sample environments, will serve a wide community of users at a national and international level, from academy and industrial worlds.

Its estimated cost is 9 million euros, which have been granted by the Ministry of Science and Innovation through the European Recovery and Resilience Facility within the NextGenerationEU Programme. It covers the construction and staff positions needed for designing and operating this new beamline. Two new job positions are open now. The detailed design of the beamline starts now, the construction is expected to finish in 2025 and the instrument will be in operation by 2026.

Read more on the ALBA website

Life in synchrotron radiation research

2021/12/012021/12/02

Including the day an earthquake interrupted my beam time!

Today’s #LightSourceSelfie is brought to you by Ro-Ya Liu, Assistant Research Scientist at NSRRC, operators of the Taiwan Light Source and the Taiwan Photon Source. Ro-Ya’s research area is focused on probing the electronic structure of novel materials by using angle resolved photoemission spectroscopy. She was inspired by her Master’s supervisor whose eyes shone as he presented his new data on the quantum well state of ultra-high silver thin film. Ro-Ya wanted to experience this spark and purpose in life. After a shaky first experiment (literally shaky due to an Earthquake!), Ro-Ya has done just that during a career that has already involved working at the Taiwan Light Source, the Photon Factory, Spring 8, HiSOR, Elettra, the Advanced Light Source and Diamond Light Source. Ro-Ya is still learning from colleagues including beamline engineers and users coming to conduct experiments at the Taiwan Light Source. Their deep knowledge helps Ro-Ya in her beamline manager role. She is looking to dig deep to acquire this knowledge and continue to find great purpose in her life in synchrotron radiation research.

A new tool in attosecond science

2020/11/272020/11/30

Measuring Angle-Resolved Phases in Photoemission

Photoionization is one of the earliest observations whose explanation led to the establishment of quantum mechanics. The process is fully described by few mathematical quantities—the probability amplitudes—that are of central interest in understanding the electronic structure of matter and its theoretical foundations. Probability amplitudes are complex numbers, which are described by a magnitude and a phase. Phase information (which can be equivalently expressed as a time, i.e., a fraction of the period of the light wave causing ionization) is lost in most measurements.

An international research team from Japan, Germany, Russia, Austria, Hungary, and the local team at the FERMI free-electron laser, combined two-color XUV photoelectron spectroscopy with real-time ab initio simulations to measure phase differences with a precision of few attoseconds. The measurements, in excellent agreement with calculations, revealed a significant anisotropy with the angle of observation of the outgoing photoelectron, particularly when the frequency of the light is nearly resonant with a transition in the atom.

“In atomic and molecular physics, the phase of probability amplitudes can reveal important information about phenomena such as the concerted motion of electrons (electron correlation) in chemical reactions” says Prof. Kevin Prince from Elettra – Sincrotrone Trieste “and our work provides a new tool for attosecond science, i.e., the observation in real time of the motion of electrons inside matter.”

Read more on the ELETTRA website

Image: Scheme of the experiment: Bichromatic, linearly polarized light (red and blue waves), with momentum k_g and electric vector E_g, ionizes neon in the reaction volume. The electron wave packets (yellow and magenta waves) are emitted with electron momentum k. The averaged phase difference between wave packets created by one- and two-photon ionization depends on the emission angle. The photoelectron angular distribution depends on the relative (optical) w‑2w phase f. Lower figures: Polar plots of photoelectron intensity at E_k=16.6 eV for coherent harmonics (asymmetric, colored plot) and incoherent harmonics (symmetric, gray plot).

Credit: Reproduced from You et al., Phys. Rev. X, 10, 031070 (2020) doi: 10.1103/PhysRevX.10.031070; copyright 2020 by the Authors. The original figure has been published under a Creative Commons Attribution 4.0 International license (CC BY 4.0) http://creativecommons.org/licenses/by/4.0/

PHELIX beamline – delivery of analyzer and spin detector

2020/07/272020/08/04

On July 22, 2020, the last components of the PHELIX end station were delivered to SOLARIS. The delivery included a high-resolution hemispherical photoelectron energy analyzer and a VLEED spin detector.

The PHELIX end station will be exceptional: it will allow scientists to perform circular dichroism measurements (CD-ARPES) and provide direct insights into the spin texture of electron states (SP-ARPES) in the same UHV system and for the same sample. Both of these methods give information about the electron spin, but the interpretation of the CD-ARPES results alone can be challenging. However, the combination of these two methods has a number of advantages allowing for the better understanding of the systems, as it excludes differences in quality between samples and the risk of surface contamination when transferring the sample between experimental systems. Both of these factors significantly affect the obtained results, and the limited control over them reduces the reliability of the research. To our knowledge, the PHELIX beamline will be one of the very few facilities in the world where such combined measurements can be performed.

Read more on the SOLARIS website

The best topological conductor yet: spiraling crystal is the key to exotic discovery

2019/03/202019/03/22

X-ray research at Berkeley Lab reveals samples are a new state of matter

The realization of so-called topological materials – which exhibit exotic, defect-resistant properties and are expected to have applications in electronics, optics, quantum computing, and other fields – has opened up a new realm in materials discovery.
Several of the hotly studied topological materials to date are known as topological insulators. Their surfaces are expected to conduct electricity with very little resistance, somewhat akin to superconductors but without the need for incredibly chilly temperatures, while their interiors – the so-called “bulk” of the material – do not conduct current.
Now, a team of researchers working at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has discovered the strongest topological conductor yet, in the form of thin crystal samples that have a spiral-staircase structure. The team’s study of crystals, dubbed topological chiral crystals, is reported in the March 20 edition of the journal Nature.

Image: This illustration shows a repeated 2D patterning of a property related to electrical conductivity, known as the surface Fermi arc, in rhodium-silicon crystal samples.
Credit: Hasan Lab/Princeton University

Tuning magnetic frustration in a dipolar trident lattice

2018/02/212018/02/22

Frustrated interactions are key to a wide range of phenomena, from protein folding and magnetic memory to fundamental studies of emergent exotic states.

Geometrical frustration and “spin ice”

When bar magnets are brought together, opposite poles will attract and like poles will repel, and the magnets will arrange themselves accordingly, to minimize energy. However, if the magnets are constrained to a lattice structure where each one has just two possible orientations, some magnets could end up geometrically “frustrated,” with neither orientation being lower in energy than the other. The system becomes what’s known as a “spin ice,” analogous to water ice, which retains intrinsic randomness (residual entropy) even at absolute zero.

Systems incorporating geometrical frustration are fascinating because their hard-to-predict behavior is key to a wide range of phenomena, from protein folding and magnetic memory to the emergence of exotic states of matter. For example, the emergence of magnetic monopole–like excitations in spin ice raises the intriguing possibility of “magnetic-charge” circuitry based on currents of magnetic monopole excitations.

Image: (extract, entire image here) Magnetic scattering patterns calculated from XMCD data for various lattice parameters. While relatively sharp peaks indicative of long-range order are seen in (a) and (c), the diffuse patterns in (b) indicate highly disordered configurations.

Observation and Control of Laser-Enabled Auger Decay

2017/09/212017/10/12

When isolated atoms are electronically excited, they have two possible ways of releasing electronic energy: by radiation or by Auger decay. The Auger process, in which the decaying electron transfers its energy to another electron causing it to detach (ionization), has played an important part in modern physics, particularly surface science, because it is by far the strongest decay channel for core holes of light elements such as carbon, nitrogen, and oxygen. In some cases, the Auger process is energetically forbidden, because the energy being exchanged is not sufficient for ionization. In this case, new electronic mechanisms for deexcitation may be discovered that “borrow” energy from the surroundings. One of these is interatomic Coulombic decay (ICD) where the energy is “borrowed” from surrounding atoms. Another mechanism is laser enabled Auger Decay (LEAD), where the energy is “borrowed” from an ancillary laser field; up to now LEAD has been observed with low-energy photons, meaning that more than one photon must be absorbed to make the process possible.

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