Atomic-level polarization reversal in sliding ferroelectric semiconductors.

Intriguing "slidetronics" has been reported in van der Waals (vdW) layered non-centrosymmetric materials and newly-emerging artificially-tuned twisted moiré superlattices, but correlative experiments that spatially track the interlayer sliding dynamics at atomic-level remain elusive. Here, we address the decisive challenge to in-situ trace the atomic-level interlayer sliding and the induced polarization reversal in vdW-layered yttrium-doped γ-InSe, step by step and atom by atom. We directly observe the real-time interlayer sliding by a 1/3-unit cell along the armchair direction, corresponding to vertical polarization reversal. The sliding driven only by low energetic electron-beam illumination suggests rather low switching barriers. Additionally, we propose a new sliding mechanism that supports the observed reversal pathway, i.e., two bilayer units slide towards each other simultaneously. Our insights into the polarization reversal via the atomic-scale interlayer sliding provide a momentous initial progress for the ongoing and future research on sliding ferroelectrics towards non-volatile storages or ferroelectric field-effect transistors.

Structural insights into histone exchange by human SRCAP complex.

Histone variant H2A.Z is found at promoters and regulates transcription. The ATP-dependent chromatin remodeler SRCAP complex (SRCAP-C) promotes the replacement of canonical histone H2A-H2B dimer with H2A.Z-H2B dimer. Here, we determined structures of human SRCAP-C bound to H2A-containing nucleosome at near-atomic resolution. The SRCAP subunit integrates a 6-subunit actin-related protein (ARP) module and an ATPase-containing motor module. The ATPase-associated ARP module encircles half of the nucleosome along the DNA and may restrain net DNA translocation, a unique feature of SRCAP-C. The motor module adopts distinct nucleosome binding modes in the apo (nucleotide-free), ADP-bound, and ADP-BeFx-bound states, suggesting that ATPase-driven movement destabilizes H2A-H2B by unwrapping the entry DNA and pulls H2A-H2B out of nucleosome through the ZNHIT1 subunit. Structure-guided chromatin immunoprecipitation sequencing analysis confirmed the requirement of H2A-contacting ZNHIT1 in maintaining H2A.Z occupancy on the genome. Our study provides structural insights into the mechanism of H2A-H2A.Z exchange mediated by SRCAP-C.

Anisotropy and thermal properties in GeTe semiconductor by Raman analysis.

Low-symmetric GeTe semiconductors have attracted wide-ranging attention due to their excellent optical and thermal properties, but only a few research studies are available on their in-plane optical anisotropic nature that is crucial for their applications in optoelectronic and thermoelectric devices. Here, we investigate the optical interactions of anisotropy in GeTe using polarization-resolved Raman spectroscopy and first-principles calculations. After determining both armchair and zigzag directions in GeTe crystals by transmission electron microscopy, we found that the Raman intensity of the two main vibrational modes had a strong in-plane anisotropic nature; the one at ∼88.1 cm-1 can be used to determine the crystal orientation, and the other at ∼124.6 cm-1 can reveal a series of temperature-dependent phase transitions. These results provide a general approach for the investigation of the anisotropy of light-matter interactions in low-symmetric layered materials, benefiting the design and application of optoelectronic, anisotropic thermoelectric, and phase-transition memory devices based on bulk GeTe.

Abnormal vibrational anisotropy and thermal properties of a two-dimensional GeAs semiconductor.

Anisotropy in a crystal structure plays a striking role in determining the optical, electrical and thermal properties of the condensed matter. Here, we investigated in-plane vibrational anisotropy in a two-dimensional (2D) van der Waals (vdW)-layered GeAs narrow-gap semiconductor by combining microstructural characterization and polarization Raman spectroscopy. Interestingly, not only the intensities but also the Raman shifts in all modes evolved periodically with different symmetries as the polarization angle changed continuously, which could be well-analyzed using the Raman tensors and further interpreted from the phonon dispersion relations. More importantly, the temperature-dependent Raman intensities of the Raman modes in the range from 83 K to 823 K gave a thermal-related uniform constant, based on which key parameters, including the thermal expansion coefficient, Grüneisen constant and quasi-particle lifetime, could be directly derived, which were in line with the calculated predictions. This investigation provides a comprehensive understanding of structure-dependent optical anisotropy in 2D vdW-layered GeAs and suggests a new idea for exploring the thermal properties of related materials using temperature-dependent Raman spectroscopy.

Sliding ferroelectricity in van der Waals layered γ-InSe semiconductor.

Two-dimensional (2D) van-der-Waals (vdW) layered ferroelectric semiconductors are highly desired for in-memory computing and ferroelectric photovoltaics or detectors. Beneficial from the weak interlayer vdW-force, controlling the structure by interlayer twist/translation or doping is an effective strategy to manipulate the fundamental properties of 2D-vdW semiconductors, which has contributed to the newly-emerging sliding ferroelectricity. Here, we report unconventional room-temperature ferroelectricity, both out-of-plane and in-plane, in vdW-layered γ-InSe semiconductor triggered by yttrium-doping (InSe:Y). We determine an effective piezoelectric constant of ∼7.5 pm/V for InSe:Y flakes with thickness of ∼50 nm, about one order of magnitude larger than earlier reports. We directly visualize the enhanced sliding switchable polarization originating from the fantastic microstructure modifications including the stacking-faults elimination and a subtle rhombohedral distortion due to the intralayer compression and continuous interlayer pre-sliding. Our investigations provide new freedom degrees of structure manipulation for intrinsic properties in 2D-vdW-layered semiconductors to expand ferroelectric candidates for next-generation nanoelectronics.

High Energy Storage Performance of PZO/PTO Multilayers via Interface Engineering.

Antiferroelectric thin-film capacitors with ultralow remanent polarization and fast discharge speed have attracted extensive attention for energy storage applications. A multilayer heterostructure is considered to be an efficient approach to enhance the breakdown strength and improve the functionality. Here, we report a high-performance multilayer heterostructure (PbZrO3/PbTiO3)n with a maximum recoverable energy storage density of 36.4 J/cm3 due to its high electric breakdown strength (2.9 MV/cm) through the heterostructure strategy. The positive effect of interfacial blockage and the negative effect of local strain defects competitively affect the breakdown strength, showing an inflection point at n = 3. The atomic-scale characterizations reveal the underlying microstructure mechanism of the interplay between the heterointerface dislocations and the decreased energy storage performance. This work offers the potential of well-designed multilayers with high energy storage performance through heterostructure engineering.

Atomic insights into the influence of Bi doping on the optical properties of two-dimensional van der Waals layered InSe.

As a narrow-gap semiconductor, III-VI two-dimensional (2D) van der Waals layered indium selenide (InSe) has attracted a lot of attention due to excellent physical properties. For potential optoelectronic applications, the tunability of the optical property is challenging, e.g., the modulation of optical bandgap commonly by element doping. However, the deep understanding of the influence of element doping on the microstructure and the optical properties lacks of systematic investigation. In this work, by using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, we investigate the influence of Bi doping on controlling of the microstructure and optical properties of InSe single crystal in detail. The results show that Bi doping can introduce additional stacking faults in InSe single crystal, and more importantly, the atomic spacing and lattice constant of Bi-doped InSe are changed a lot as compared to that of the undoped one. Further optical characterizations including photoluminescence and transmission spectra reveal that Bi-doping can broaden the transmission wavelength range of InSe and make its optical bandgap blue-shift, which can also be physically interpreted from the doping-induced structure change. Our work expands new ideas for the optical property modulation of 2D thin-layer materials and brings new possibilities for the development of thin-layer InSe optical devices.

Microstructurally Tailored Thin ß-Ag2 Se Films toward Commercial Flexible Thermoelectrics.

Aiming to overcome both the structural and commercial limitations of flexible thermoelectric power generators, an efficient room-temperature aqueous selenization reaction that can be completed in air within less than 1 min, to directly fabricate thin ß-Ag2 Se films consisting of perfectly crystalline and large columnar grains with both in-plane randomness and out-of-plane [201] preferred orientation, is designed. A high power factor (PF) of 2590 ± 414 µW m-1 K-2 and a figure-of-merit (zT) of 1.2 ± 0.42 are obtained from a sample with a thickness of ≈1 µm. The maximum output power density of the best 4-leg thermoelectric generator sample reach 27.6 ± 1.95 and 124 ± 8.78 W m-2 at room temperature with 30 and 60 K temperature differences, respectively, which may be useful in future flexible thermoelectric devices.

FIB-Assisted Fabrication of Single Tellurium Nanotube Based High Performance Photodetector.

Nanoscale tellurium (Te) materials are promising for advanced optoelectronics owing to their outstanding photoelectrical properties. In this work, high-performance optoelectronic nanodevice based on a single tellurium nanotube (NT) was prepared by focused ion beam (FIB)-assisted technique. The individual Te NT photodetector demonstrates a high photoresponsivity of 1.65 × 104 AW-1 and a high photoconductivity gain of 5.0 × 106%, which shows great promise for further optoelectronic device applications.