Hafnia
Ontology highlight
ABSTRACT:
PROVIDER: PRJNA647928 | ENA |
REPOSITORIES: ENA
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Project description:Because of its compatibility with semiconductor-based technologies, hafnia (HfO2) is today's most promising ferroelectric material for applications in electronics. Yet, knowledge on the ferroic and electromechanical response properties of this all-important compound is still lacking. Interestingly, HfO2 has recently been predicted to display a negative longitudinal piezoelectric effect, which sets it apart from classic ferroelectrics (e.g., perovskite oxides like PbTiO3) and is reminiscent of the behavior of some organic compounds. The present work corroborates this behavior, by first-principles calculations and an experimental investigation of HfO2 thin films using piezoresponse force microscopy. Further, the simulations show how the chemical coordination of the active oxygen atoms is responsible for the negative longitudinal piezoelectric effect. Building on these insights, it is predicted that, by controlling the environment of such active oxygens (e.g., by means of an epitaxial strain), it is possible to change the sign of the piezoelectric response of the material.
| S-EPMC8674271 | biostudies-literature
Project description:Understanding the atomic structure of amorphous solids is important in predicting and tuning their macroscopic behavior. Here, we use a combination of high-energy X-ray diffraction, neutron diffraction, and molecular dynamics simulations to benchmark the atomic interactions in the high temperature stable liquid and low-density amorphous solid states of hafnia. The diffraction results reveal an average Hf-O coordination number of ~7 exists in both the liquid and amorphous nanoparticle forms studied. The measured pair distribution functions are compared to those generated from several simulation models in the literature. We have also performed ab initio and classical molecular dynamics simulations that show density has a strong effect on the polyhedral connectivity. The liquid shows a broad distribution of Hf-Hf interactions, while the formation of low-density amorphous nanoclusters can reproduce the sharp split peak in the Hf-Hf partial pair distribution function observed in experiment. The agglomeration of amorphous nanoparticles condensed from the gas phase is associated with the formation of both edge-sharing and corner-sharing HfO6,7 polyhedra resembling that observed in the monoclinic phase.
| S-EPMC5706237 | biostudies-literature
Project description:Memory devices with high speed and high density are highly desired to address the 'memory wall' issue. Here we demonstrated a highly scalable, three-dimensional stackable ferroelectric diode, with its rectifying polarity modulated by the polarization reversal of Hf0.5Zr0.5O2 films. By visualizing the hafnium/zirconium lattice order and oxygen lattice order with atomic-resolution spherical aberration-corrected STEM, we revealed the correlation between the spontaneous polarization of Hf0.5Zr0.5O2 film and the displacement of oxygen atom, thus unambiguously identified the non-centrosymmetric Pca21 orthorhombic phase in Hf0.5Zr0.5O2 film. We further implemented this ferroelectric diode in an 8 layers 3D array. Operation speed as high as 20?ns and robust endurance of more than 109 were demonstrated. The built-in nonlinearity of more than 100 guarantees its self-selective property that eliminates the need for external selectors to suppress the leakage current in large array. This work opens up new opportunities for future memory hierarchy evolution.
| S-EPMC7070068 | biostudies-literature
Project description:Hafnia alvei, a gram-negative bacterium, is an opportunistic pathogen associated with mixed hospital infections, bacteremia, septicemia, and respiratory diseases. Various 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo)-containing fragments different from known structures of core oligosaccharides were previously found among fractions obtained by mild acid hydrolysis of some H. alvei lipopolysaccharides (LPSs). However, the positions of these segments in the LPS structure were not known. Analysis of de-N,O-acylated LPS by nuclear magnetic resonance spectroscopy and mass spectrometry allowed the determination of the location of a Kdo-containing trisaccharide in the structure of H. alvei PCM 32 LPS. It was established that the trisaccharide {L-alpha-D-Hepp-(1-->4)-[alpha-D-Galp6OAc-(1-->7)]-alpha-Kdop-(2-->} is an integral part of the outer-core oligosaccharide of H. alvei 32 LPS. The very labile ketosidic linkage between -->4,7)-alpha-Kdop and -->2)-Glcp in the core oligosaccharide was identified. Screening for this Kdo-containing trisaccharide was performed on the group of 37 O serotypes of H. alvei LPSs using monospecific antibodies recognizing the structure. It was established that this trisaccharide is a characteristic component of the outer-core oligosaccharides of H. alvei 2, 32, 600, 1192, 1206, and 1211 LPSs. The weaker cross-reactions with LPSs of strains 974, 1188, 1198, 1204, and 1214 suggest the presence of similar structures in these LPSs, as well. Thus, we have identified new examples of endotoxins among those elucidated so far. This type of core oligosaccharide deviates from the classical scheme by the presence of the structural Kdo-containing motif in the outer-core region.
| S-EPMC2620813 | biostudies-literature
Project description:Hafnia paralvei Genome sequencing and assembly
| PRJNA481542 | ENA