Phase Conductance of BiFeO[sub.3] Film Wang, Yufeng; Zhou, Peng; Fetisov, Leonid ...
Sensors (Basel, Switzerland),
11/2023, Volume:
23, Issue:
22
Journal Article
Peer reviewed
In this work, the local conductance of the tetragonal-like (T-like) and rhombohedral-like (R-like) phases of epitaxial BiFeOsub.3 film is systematically studied via conductive atomic force ...microscopy. At higher tip voltage, there is a mutual transition between the T-like and R-like phases, which could be attributed to the strain relaxation in the T-like phase induced by electric poling, as well as local polarization switching. The T-like phase exhibits a higher conductance, which is related to the lower interface potential barrier between the tip and film surface. Reversible low- and high-current states in the T-like phase can be tuned by polarization switching. These results will be helpful for designing novel nanoelectronic devices, such as voltage and strain sensors.
Gasdermin‐D (GSDMD), a member of the gasdermin protein family, mediates pyroptosis in human and murine cells. Cleaved by inflammatory caspases, GSDMD inserts its N‐terminal domain (GSDMDNterm) into ...cellular membranes and assembles large oligomeric complexes permeabilizing the membrane. So far, the mechanisms of GSDMDNterm insertion, oligomerization, and pore formation are poorly understood. Here, we apply high‐resolution (≤ 2 nm) atomic force microscopy (AFM) to describe how GSDMDNterm inserts and assembles in membranes. We observe GSDMDNterm inserting into a variety of lipid compositions, among which phosphatidylinositide (PI(4,5)P2) increases and cholesterol reduces insertion. Once inserted, GSDMDNterm assembles arc‐, slit‐, and ring‐shaped oligomers, each of which being able to form transmembrane pores. This assembly and pore formation process is independent on whether GSDMD has been cleaved by caspase‐1, caspase‐4, or caspase‐5. Using time‐lapse AFM, we monitor how GSDMDNterm assembles into arc‐shaped oligomers that can transform into larger slit‐shaped and finally into stable ring‐shaped oligomers. Our observations translate into a mechanistic model of GSDMDNterm transmembrane pore assembly, which is likely shared within the gasdermin protein family.
Synopsis
Gasdermin‐D, which mediates pyroptosis in human and murine cells, is directly observed inserting into lipid membranes and assembling arc‐, slit‐ and ring‐shaped oligomers. The observations translate into a mechanistic model of gasdermin‐D assembling transmembrane lytic pores.
High‐resolution time‐lapse imaging of gasdermin‐D pore formation.
Gasdermin‐D assembles arc‐, slit‐ and ring‐shaped oligomers.
Arc‐ and slit‐shaped pores transform into stable ring‐shaped pores.
Phosphatidylinositide (PI(4,5)P2) increases gasdermin‐D pore formation.
Cholesterol reduces gasdermin‐D pore formation.
High‐resolution atomic force microscopy shows how a pyroptosis‐mediating gasdermin protein inserts into lipid membranes and assembles arc‐, slit‐ and ring‐shaped oligomers.
•Several subsurface imaging methods based on mechanical sensing were compared.•Maximum detectable buried depth was evaluated quantitatively.•Depth limit from high to low is contact resonance, bimodal ...and harmonic AFM.•Sensitivity to local mechanical properties was analyzed numerically.
Several subsurface imaging methods based on atomic force microscopy (AFM) linear nanomechanical mapping, namely contact resonance (CR), bimodal and harmonic AFMs, are investigated and compared. Their respective subsurface detection capability is estimated and evaluated on a model specimen, which is prepared by embedding SiO2 microparticles in a PDMS elastomer. The measured CR frequency, bimodal and harmonic amplitudes are related to local mechanical properties by analyzing cantilever dynamics and further linked to subsurface depths of the particles by finite element analysis. The maximum detectable depths are obtained from the apparent particle diameters in subsurface image channels via employing a simple geometrical model. Under common experimental settings, results demonstrate that the depth limits reach up to about 812 nm, 212 nm and 127 nm for CR, bimodal and harmonic AFM modes, respectively. The depth sensitivity can be tuned and optimized by using either different cantilever eigenmodes in CR-AFM or spectroscopy analysis in bimodal and harmonic AFMs. The three imaging methods have their own suitable application situations. The comparisons can advance a further step into understanding the subsurface image contrast via AFM mechanical sensing.
Despite their partial ionic nature, many layered diatomic crystals avoid internal electric polarization by forming a centrosymmetric lattice at their optimal van-der-Waals stacking. Here, we report a ...stable ferroelectric order emerging at the interface between two naturally-grown flakes of hexagonal-boron-nitride, which are stacked together in a metastable non-centrosymmetric parallel orientation. We observe alternating domains of inverted normal polarization, caused by a lateral shift of one lattice site between the domains. Reversible polarization switching coupled to lateral sliding is achieved by scanning a biased tip above the surface. Our calculations trace the origin of the phenomenon to a subtle interplay between charge redistribution and ionic displacement, and provide intuitive insights to explore the interfacial polarization and its unique "slidetronics" switching mechanism.
Crack resistance performance by oxidation must be considered in rubber product development because cracks are the starting point for fracture. When rubber is stretched extensively, mechanical ...stresses can break apart its molecular chains, generating radicals and promoting mechanochemical oxidation. This reaction is one of the causes of cracking. However, it is not fully understood how cracks are formed in vulcanized rubber with an inhomogeneous crosslinking structure. Atomic force microscopy (AFM) nanomechanics has been utilized to observe vulcanized butadiene rubber in an elongated state. It was shown that crack generation is related to mechanochemical oxidation, and that the cracks could be clearly visualized as stress-concentrated regions at the nanoscale. Additionally, crack formation is accelerated with increasing elongation of the rubber. This demonstrates that AFM nanomechanics is an effective tool for observation of the generation of cracks associated with mechanochemical oxidation in rubber materials.
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•Crack generation was investigated using atomic force microscopy (AFM) nanomechanics.•Cracks were generated from stress-concentrated regions in the nanoscale.•Elongation and oxygen in the air cause crack generation.•Crack generation was accelerated with an increasing elongation ratio.
Perovskite MAPbBr.sub.3 (MA = CH.sub.3NH.sub.3.sup.+) single crystals were grown via the anti-solvent vapor-assisted crystallization method. The crystal growth process was optimized by adjusting the ...solution concentration and diluting the anti-solvent. The maximum size of the obtained crystal was 9 x 9 x 3 mm.sup.3. It shows that the MAPbBr.sub.3 single crystal is a cubic structure, the space group is Pm Formula omittedm, and the lattice constant is 0.59062 nm. Furthermore, its energy band gap is approximately 2.23 eV. The atomic force microscopy results demonstrated that the growth process of MAPbBr.sub.3 single crystal followed the defect step growth mechanism, which was controlled by the screw dislocations within the crystal. Based on the curling growth of a screw dislocation on the crystal surface, a spiral step was formed. After the step was rotated around the entire mesa, a higher step was generated. Repeatedly, the step growth of screw dislocation within the crystal came into being. Besides, some small pits were also observed on (100) plane of the MAPbBr.sub.3 crystal. These pits hindered the movement of steps and affected the lattice arrangement around them, causing the structural mismatch and more defects within the crystals.
In this work, a titanium oxide buffer layer was explored as a possible buffer electron transporting layer (ETL) with iodine-tin-based perovskite material for enhancement of a thin-film lead-free ...perovskite solar cell. The open-circuit voltage of the device was used as an indicator for the interface energy barrier's change with the thickness of the TiOsub.2. The buffer and photoabsorbing layers were deposited by vacuum reactive sputtering and a low-temperature ion-assisted process from a confocal sintered source, respectively, allowing precise tuning of the film properties and reproducibility of the solar cell behavior. The surface roughness of the buffer layers was investigated by atomic force microscopy and together with the measured absorbance spectra conclusions about the optical losses in the device were made. It was found that the highest voltage was generated from the structure with 75 nm-thick ETL. The electrical behavior of the cell with this buffer layer was additionally studied by impedance measurements. Small interface capacitance and contact resistance were obtained and considered suitable for photodetector fabrication. The practical applicability of the structure with a dual function of self-powered photodetection was demonstrated by the measurement of the response time.
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