Engineering topics
Deng, Yu
Publications and source records attributed to Deng, Yu.
Superionic fluoride gate dielectrics with low diffusion barrier for two-dimensional electronics
Exploration of new dielectrics with a large capacitive coupling is an essential topic in modern electronics when conventional dielectrics suffer from the leakage issue near the breakdown limit. Here, to address this looming challenge, we demonstrate that rare-earth metal fluorides with extremely low ion migration barriers can generally exhibit an excellent capacitive coupling over 20 μF cm -2 (with an equivalent oxide thickness of ~0.15 nm and a large effective dielectric constant near 30) and great compatibility with scalable device manufacturing processes. Such a static dielectric capability of superionic fluorides is exemplified by MoS 2 transistors exhibiting high on/off current ratios over 10 8 , ultralow subthreshold swing of 65 mV dec -1 and ultralow leakage current density of ~10 -6 A cm -2 . Therefore, the fluoride-gated logic inverters can achieve notably higher static voltage gain values (surpassing ~167) compared with a conventional dielectric. Furthermore, the application of fluoride gating enables the demonstration of NAND, NOR, AND and OR logic circuits with low static energy consumption. In particular, the superconductor–insulator transition at the clean-limit Bi 2 Sr 2 CaCu 2 O 8+δ can also be realized through fluoride gating. In conclusion, our findings highlight fluoride dielectrics as a pioneering platform for advanced electronic applications and for tailoring emergent electronic states in condensed matter.
Visualizing interfacial collective reaction behaviour of Li–S batteries
Benefiting from high energy density (2,600 Wh kg -1 )) and low cost, lithium-sulfur (Li-S) batteries are considered promising candidates for advanced energy-storage systems. Despite tremendous efforts in suppressing the long-standing shuttle effect of lithium polysulfides, understanding of the interfacial reactions of lithium polysulfides at the nanoscale remains elusive. This is mainly because of the limitations of in situ characterization tools in tracing the liquid-solid conversion of unstable lithium polysulfides at high temporal-spatial resolution. There is an urgent need to understand the coupled phenomena inside Li-S batteries, specifically, the dynamic distribution, aggregation, deposition and dissolution of lithium polysulfides. Here, by using in situ liquid-cell electrochemical transmission electron microscopy, we directly visualized the transformation of lithium polysulfides over electrode surfaces at the atomic scale. Notably, an unexpected gathering-induced collective charge transfer of lithium polysulfides was captured on the nanocluster active-centre-immobilized surface. It further induced an instantaneous deposition of nonequilibrium Li2S nanocrystals from the dense liquid phase of lithium polysulfides. Without mediation of active centres, the reactions followed a classical single-molecule pathway, lithium polysulfides transforming into Li 2 S 2 and Li 2 S step by step. Molecular dynamics simulations indicated that the long-range electrostatic interaction between active centres and lithium polysulfides promoted the formation of a dense phase consisting of Li + and S n 2- (2 < n ≤ 6), and the collective charge transfer in the dense phase was further verified by ab initio molecular dynamics simulations. Finally, the collective interfacial reaction pathway unveils a new transformation mechanism and deepens the fundamental understanding of Li-S batteries.
A strain-driven thermotropic phase boundary in BaTiO 3 at room temperature by cycling compression
In BaTiO 3 single crystals, we observed a strain-driven phase transition from the tetragonal phase to the tetragonal-orthorhombic phase boundary which can be introduced by slow cycling compressions (a loading of up to 0.5 GPa, strain rate of 10 -4 s -1 , and 100 cycles) at room temperature. Different from the well-known tetragonal to cubic phase transition under stress (~2 GPa), it only takes place locally around bent 90° domain walls. The inhomogeneous local stress and electrical fields as well as the mobile point defect pinning effect contribute to the phase re-entrance. Through comparison experiments by in situ synchrotron x-ray diffraction, Raman scattering, and (scanning) transmission electron microscopy, we explored the phase transition mechanism. Based on that, we developed a mechanical method to obtain well-stabilized high-density thermotropic phase boundary structures (with tetragonal, orthorhombic, and bridging monoclinic phases) in BaTiO 3 for potential applications.
Direct imaging of short-range order and its impact on deformation in Ti-6Al
Chemical short-range order (SRO) within a nominally single-phase solid solution is known to affect the mechanical properties of alloys. While SRO has been indirectly related to deformation, direct observation of the SRO domain structure, and its effects on deformation mechanisms at the nanoscale, has remained elusive. Here, we report the direct observation of SRO in relation to deformation using energy-filtered imaging in a transmission electron microscope (TEM). The diffraction contrast is enhanced by reducing the inelastically scattered electrons, revealing subnanometer SRO-enhanced domains. The destruction of these domains by dislocation planar slip is observed after ex situ and in situ TEM mechanical testing. These results confirm the impact of SRO in Ti-Al alloys on the scale of angstroms. The direct confirmation of SRO in relationship to dislocation plasticity in metals can provide insight into how the mechanical behavior of concentrated solid solutions by the material’s thermal history.
Functional Materials Under Stress: In Situ TEM Observations of Structural Evolution
The operating conditions of functional materials usually involve varying stress fields, resulting in structural changes, whether intentional or undesirable. Complex multiscale microstructures including defects, domains, and new phases, can be induced by mechanical loading in functional materials, providing fundamental insight into the deformation process of the involved materials. On the other hand, these microstructures, if induced in a controllable fashion, can be used to tune the functional properties or to enhance certain performance. In situ nanomechanical tests conducted in scanning/transmission electron microscopes (STEM/TEM) provide a critical tool for understanding the microstructural evolution in functional materials. In our study, select results on a variety of functional material systems in the field are presented, with a brief introduction into some newly developed multichannel experimental capabilities to demonstrate the impact of these techniques.
Minimized lithium trapping by isovalent isomorphism for high initial Coulombic efficiency of silicon anodes
Silicon demonstrates great potential as a next-generation lithium ion battery anode because of high capacity and elemental abundance. However, the issue of low initial Coulombic efficiency needs to be addressed to enable large-scale applications. There are mainly two mechanisms for this lithium loss in the first cycle: the formation of the solid electrolyte interphase and lithium trapping in the electrode. The former has been heavily investigated while the latter has been largely neglected. Here, through both theoretical calculation and experimental study, we demonstrate that by introducing Ge substitution in Si with fine compositional control, the energy barrier of lithium diffusion will be greatly reduced because of the lattice expansion. This effect of isovalent isomorphism significantly reduces the Li trapping by ~70% and improves the initial Coulombic efficiency to over 90%. We expect that various systems of battery materials can benefit from this mechanism for fine-tuning their electrochemical behaviors.
Hierarchically-structured large superelastic deformation in ferroelastic-ferroelectrics
Large superelastic deformation in ferroelastic-ferroelectrics (FMs) is a complex phenomenon involving multiple mechanisms operating simultaneously. Understanding how these mechanisms contribute corporately is critical to apply this useful property to the intrinsically brittle FMs, which can therefore display both excellent functional and mechanical performance. Here, we have directly observed and quantitatively analyzed in situ in a transmission electron microscope the three main mechanisms of twinning domain, phase transformation and mobile point defect contributing to extremely large superelastic deformation in single-crystal BaTiO 3 (5.0% strain) and Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (10.1% strain). Finally, our results reveal the hierarchical origin of large recoverable strain in “brittle” FMs.
MiR-181a contributes gefitinib resistance in non-small cell lung cancer cells by targeting GAS7
Tyrosine kinase inhibitors (TKIs) exert potent therapeutic efficacy in non-small cell lung cancers (NSCLC) harboring epidermal growth factor receptor (EGFR) activating mutations. However, a major impediment for the effective treatment is the development of drug resistance. Some evidence supports a role for miRNAs in modulating NSCLC TKIs resistance. Here we show that miR-181a is significantly up-regulated in gefitinib-resistant cells compared with gefitinib-sensitive cells. Upregulation of miR-181a caused resistance of gefitinib, whereas downregulation of miR-181a sensitized NSCLC cells to gefitinib. Furthermore, the miR-181a plasma levels were significantly increased in acquired gefitinib resistant NSCLC patients compared with the plasma levels prior to gefitinib treatment in each patient. Bioinformatics analysis and luciferase reporter assay showed that growth arrest-specific 7 (GAS7) was a direct target gene of miR-181a. A significant inverse correlation between the expression of miR-181a and GAS7 was identified in NSCLC tissues. Downregulation of GAS7 expression could antagonize gefitinib re-sensitivity in PC9GR mediated by knockdown of miR-181a via AKT/ERK pathways and epithelial-to-mesenchymal transition markers. Additionally, GAS7 expression was downregulated in a large cohort of NSCLC patients, and a high mRNA level of GAS7 was associated with improved overall survival. Collectively, our findings provide a novel basis for using miR-181a/GAS7-based therapeutic strategies to reverse gefitinib resistance in NSCLC.
Engineering microorganisms to increase ethanol production by metabolic redirection
The present invention provides for the manipulation of carbon flux in a recombinant host cell to increase the formation of desirable products. The invention relates to cellulose-digesting organisms that have been genetically modified to allow the production of ethanol at a high yield by redirecting carbon flux at key steps of central metabolism.
MiR-509-5p suppresses the proliferation, migration, and invasion of non-small cell lung cancer by targeting YWHAG
Dysregulation of microRNAs (miRNAs) expression is prevalent in human malignancy development and progression. As previously reported, miR-509-5p has been identified as a tumor suppressor in various cancers, but its role and functional mechanism in non-small lung cancer (NSCLC) remains unknown. In the present study, we found that miR-509-5p was significantly downregulated in NSCLC tissues and cell lines using Quantitative real-time PCR (qRT-PCR). In addition, overexpression of miR-509-5p markedly inhibited the proliferation, migration, invasion and phosphorylation of Akt of NSCLC cells. Moreover, we identified tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein gamma (YWHAG) as a direct target of miR-509-5p. Knockdown of YWHAG mimicked the inhibitory effects of miR-509-5p on NSCLC cells for proliferation and motility. Finally, the negative correlation between miR-509-5p and YWHAG expression in NSCLC specimens was demonstrated. Taken together, our present study revealed the tumor suppressive role of miR-509-5p in NSCLC by targeting YWHAG, suggesting that miR-509-5p/YWHAG axis might be considered as a novel and potential target for clinical diagnosis and therapeutics of NSCLC. - Highlights: • The tumor suppressive role of miRNA-509-5p in non-small cell lung cancer is revealed. • MiR-509-5p exerts its influence on NSCLC cells by targeting YWHAG. • MiR-509-5p inhibits the phosphorylation of Akt in NSCLC cells. • MiR-509-5p can be deemed as a potential diagnostic and therapeutic target for NSCLC.
Continuous-wave and actively Q-switched resonantly dual-end-pumped Er : YAG ceramic laser emitting at 1.6 μm
We demonstrate a continuous-wave (cw) and actively Q-switched Er : YAG ceramic laser resonantly dual-end-pumped by a 1532 nm fibre-coupled laser diode. A maximum cw output power of 1.48 W at 1645.3 nm is obtained at an absorbed pump power of 12.72 W, corresponding to a slope efficiency of 19.2%. In the Q-switched regime the maximum pulse energy of 0.84 mJ is reached at a pulse repetition rate of 100 Hz, pulse duration of 48.03 ns and absorbed pump power of 10.51 W. (lasers)
Single-frequency, injection-seeded Er:YAG laser based on a bow-tie ring slave resonator
A diode pumped, injection-seeded Q-switched Er:YAG laser at 1645.2 nm is demonstrated. A single frequency Er:YAG monolithic nonplanar ring oscillator (NPRO) laser emitting at 1645.24 nm with a maximum output power of 500 mW is used as a seed laser. The seed laser output is injected into a bow-tie slave laser, obtaining stable single-frequency Q-switched operation of the Er:YAG laser. The maximum single-frequency Q-switched Er:YAG laser output energy is 2.9 mJ at 100 Hz with a pulse duration of 160 ns. (lasers)