Advanced Physics Research最新文献

Recent discovery of ultrathick MoSi₂N₄(MoN)_n monolayers open up an exciting platform to engineer two-dimensional (2D) material properties via intercalation architecture. In this study, a series of ultrathick MA₂N₄(M'N) monolayers (M, M' = Mo, W; A = Si, Ge) is computationally investigated under both homolayer and heterolayer intercalation architectures, in which the same and different species of transition metal nitride inner core sublayer are intercalated by outer passivating nitride sublayers, respectively. The MA₂N₄(M'N) are stable metallic monolayers with excellent mechanical strength. Intriguingly, the metallic states around Fermi level are localized within the inner core sublayer. Carrier conduction mediated by electronic states around the Fermi level is thus spatially insulated from the external environment by the native outer nitride sublayers, suggesting the potential of MA₂N₄(M'N) in back-end-of-line metal interconnect applications. N and Si (or Ge) vacancy defects at the outer sublayers create ‘punch through’ states around the Fermi level that bridges the carrier conduction in the inner core sublayer and the outer environment, forming an electrical contact akin to the ‘via' structures of metal interconnects. It is further shown that MoSi₂N₄(MoN) can serve as a quasi-Ohmic contact to 2D WSe₂. These findings reveal the potential of ultrathick MA₂N₄(MN) monolayers in interconnect and metal contact applications.

The control of heat conduction through the manipulation of phonons in solids is of fundamental interest and can be exploited in applications for thermoelectric conversion. In this context, the advent of novel semiconductor nanomaterials with high surface-to-volume ratio, e.g. nanowires, offer exciting perspectives, leading to significant leaps forwarding the efficiency of solid-state thermoelectric converters after decades of stagnation. Beyond the high aspect ratio, the nanowire geometry offers unprecedented possibilities of materials combination and crystal phase engineering not achievable with 2D counterparts. In this work, the growth of long (up to 100 repetitions) wurtzite InAs/InP superlattice nanowires with homogeneous segment thicknesses is reported, with control down to the single digit of nanometer. By means of Raman scattering experiments, clear modifications of the phonon dispersion in superlattice nanowires are found, where both InAs-like and InP-like modes are present. The experimentally measured modes are well reproduced by density functional perturbation theory calculations. Remarkably, it is found that the phonon frequencies can be tuned by the superlattice periodicity, opening exciting perspectives for phonon engineering and thermoelectric applications.

Density functional theory is used in the current study to thoroughly examine the physical properties of perovskites made of halide RbGeF₃ under a variety of hydrostatic pressure ranges between 0 and 50 GPa. This research seeks to reduce the electronic bandgap of RbGeF₃ under pressure to enhance the optical properties and evaluate the compounds' decency for usage in optoelectronic and electrical uses. The precision of the structural characteristics is relatively high, and they fit well with published earlier research. A higher interaction between atoms is also a result of the large drop in lattice characteristics and link length. Pressurization reveals the ionic and covalent characteristics of the bonds between Rb-F and Ge-F, respectively. Both the conductivity and the optical absorbance vary noticeably when hydrostatic pressure is applied. A zero bandgap finally arises via pressure-induced bandgap shrinkage, improving conductivity and electromagnetic absorption. Based on their optical properties, the materials being studied could be used in a variety of visible and ultraviolet optoelectronic devices. External pressure increases the anisotropy and ductility of the aforementioned perovskites, hence influencing their mechanical behavior. This study describes the changes in physical characteristics brought on by applied stress and offers a thorough examination of those changes.

Magnetic insulators, especially Y₃Fe₅O₁₂ (YIG), are considered promising candidates for spin-based device applications due to their ultralow damping, high spin injection efficiency, and long-distance spin propagation. However, these intriguing features are widely studied based on crystallization YIG films. Pure spin phenomena, like spin transport in YIG films with structural evolution, remain unclear. Herein, pure spin transportation is systematically investigated in the sandwich structure formed by YIG, the inserted layer-nominal YIG (n-YIG) with a varied crystalline structure and heavy metal Platinum (Pt). By applying ferromagnetic resonance (FMR)-driven inverse spin Hall effect (ISHE) measurement, the detected ISHE voltage signal presented a strong correlation with the thickness of n-YIG and its crystalline phase. A significant increasement in spin transportation is obtained for the crystallized n-YIG via a high-temperature annealing. These results demonstrate that pure spin current is transported availably in the structural evolution of YIG films. Furthermore, the element-specific X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectra on the n-YIG films showed a distinction for the crystallized n-YIG which indicates that the spin propagation is correlated to its magnetic order. These findings are instructive for low-dissipation spin-based devices.

2D magnetic materials offer the opportunity to study and manipulate emergent collective excitations. Among these, spin–phonon coupling is one of the most important interactions correlating charge, spin and lattice vibrations. Understanding and controlling this coupling is important for spintronics applications, control of magnons and phonon by THz radiation, and for strain-driven magnetoelastic applications. Here, a resonant mode-selective spin–phonon coupling in several magnetic 2D metal thiophosphates (NiPS₃, FePS₃, CoPS₃ and MnPS₃) through multi-excitation and temperature-dependent Raman scattering measurements is uncovered. The phonon mode, which is a Raman-active out-of-plane vibrational mode (∼250 cm⁻¹ or 7.5 THz), exhibits an asymmetric Fano lineshape where its asymmetry is proportional to the spin–phonon coupling. The measurements reveal the coupling to be the highest in NiPS₃, followed by FePS₃ and CoPS₃, and least in MnPS₃. These differences are attributed to the metal–sulfur interatomic distances, which are the lowest in NiPS₃, followed by CoPS₃, FePS₃ and MnPS₃. Finally, the spin–phonon coupling is also observed in exfoliated materials, with a slight reduction between 20 and 30% in the thinnest flakes compared to the bulk crystals.

Photoemission Electron Microscopy

In article number 2300122, Jan Vogelsang and co-workers demonstrate an attosecond interferometry experiment on zinc oxide (ZnO) surface using spatially and energetically resolved photoelectrons. Photoemission electron microscopy is combined with near-infrared pump-extreme ultraviolet probe laser spectroscopy and the instantaneous phase of an infrared field is resolved with high spatial resolution. Results show how the core level states with the low binding energy of ZnO are well suited to perform spatially resolved attosecond interferometry experiments.

Combinatorial pulsed laser deposition (C-PLD) based on segmented targets has led to new possibilities in the pace of discovery of novel advanced materials with significantly reduced deposition time and material consumption. However, fabrication of established segmented targets may be complex or not even possible for certain material combinations. In this article, two alternative C-PLD techniques based on easy-to-fabricate segmented targets are presented. One approach uses two semi-circular segments A and B with a systematic adjustable lateral shift of the target rotation axis from the target center. The other approach is based on a new target design defined by an ABA-segmentation where B is a horizontal bar between two semi-circular segments of A. Both approaches enable growth of discrete composition libraries. The concepts and important parameters are introduced and computer simulations as function of the geometric parameters are made to yield the expected thin film compositions. As proof-of-concept, the techniques are employed on the transparent, semiconducting ternary alloy zinc-tin-oxide. The simulations are in very good agreement with the experimental data. Physical properties of films grown by the demonstrated approaches are compared with those obtained by established PLD processes.

Photophysical Ion Dynamics

In article number 2300120, Konstantinos Papadopoulos, Ola Kenji Forslund, Yasmine Sassa, and co-workers conduct a muon spin relaxation (μ⁺SR) study of hybrid perovskite MAPbX₃ (X=Br, Cl) single crystals with and without illumination. The experimental and simulation results demonstrate an increase in organic molecule fluctuations under illumination, depending on the choice of the halide ion. These effects are correlated with the structural transformations and long carrier lifetimes observed in perovskite solar cells.

Layered SnAs-based Zintl compounds exhibit a distinctive electronic structure, igniting extensive research efforts in areas of superconductivity, topological insulators, and quantum magnetism. In this paper, the crystal structures and electronic properties of the Zintl compound SrSn₂As₂ upon compression are systematically investigated. Pressure-induced superconductivity is observed in SrSn₂As₂ with a nonmonotonic evolution of superconducting transition temperature T_c. Theoretical calculations together with high-pressure synchrotron X-ray diffraction and Raman spectroscopy have identified that SrSn₂As₂ undergoes a structural transformation from a rhombohedral R$$m phase to the monoclinic C2/m phase. Beyond 28.3 GPa, T_c is suppressed due to a reduction of the density of state (DOS) at the Fermi level. The discovery of pressure-induced superconductivity, accompanied by structural transitions in SrSn₂As₂, greatly expands the physical properties of layered SnAs-based compounds and provides new ground states upon compression.