Phonon modes and electron-phonon coupling at the FeSe/SrTiO3 interface.

The remarkable increase in superconducting transition temperature (Tc) observed at the interface of one-unit-cell FeSe films on SrTiO3 substrates (1 uc FeSe/STO)1 has attracted considerable research into the interface effects2-6. Although this high Tc is thought to be associated with electron-phonon coupling (EPC)2, the microscopic coupling mechanism and its role in the superconductivity remain elusive. Here we use momentum-selective high-resolution electron energy loss spectroscopy to atomically resolve the phonons at the FeSe/STO interface. We uncover new optical phonon modes, coupling strongly with electrons, in the energy range of 75-99 meV. These modes are characterized by out-of-plane vibrations of oxygen atoms in the interfacial double-TiOx layer and the apical oxygens in STO. Our results also demonstrate that the EPC strength and superconducting gap of 1 uc FeSe/STO are closely related to the interlayer spacing between FeSe and the TiOx terminated STO. These findings shed light on the microscopic origin of the interfacial EPC and provide insights into achieving large and consistent Tc enhancement in FeSe/STO and potentially other superconducting systems.

Ultraflat single-crystal hexagonal boron nitride for wafer-scale integration of a 2D-compatible high-κ metal gate.

Hexagonal boron nitride (hBN) has emerged as a promising protection layer for dielectric integration in the next-generation large-scale integrated electronics. Although numerous efforts have been devoted to growing single-crystal hBN film, wafer-scale ultraflat hBN has still not been achieved. Here, we report the epitaxial growth of 4 in. ultraflat single-crystal hBN on Cu0.8Ni0.2(111)/sapphire wafers. The strong coupling between hBN and Cu0.8Ni0.2(111) suppresses the formation of wrinkles and ensures the seamless stitching of parallelly aligned hBN domains, resulting in an ultraflat single-crystal hBN film on a wafer scale. Using the ultraflat hBN as a protective layer, we integrate the wafer-scale ultrathin high-κ dielectrics onto two-dimensional (2D) materials with a damage-free interface. The obtained hBN/HfO2 composite dielectric exhibits an ultralow current leakage (2.36 × 10-6 A cm-2) and an ultrathin equivalent oxide thickness of 0.52 nm, which meets the targets of the International Roadmap for Devices and Systems. Our findings pave the way to the synthesis of ultraflat 2D materials and integration of future 2D electronics.

Inferior Interfacial Superconductivity in 1 UC FeSe/SrVO3/SrTiO3 with Screened Interfacial Electron-Phonon Coupling.

Single-unit cell (1 UC) FeSe interfaced with TiOx or FeOx exhibits significantly enhanced superconductivity compared to that of bulk FeSe, with interfacial electron-phonon coupling (EPC) playing a crucial role. However, the reduced dimensionality in 1 UC FeSe, which may drive superconducting fluctuations, complicates our understanding of the enhancement mechanisms. We construct a new superconducting interface, 1 UC FeSe/SrVO3/SrTiO3. Here, the itinerant electrons of highly metallic SrVO3 films can screen all high-energy Fuchs-Kliewer phonons, including those of SrTiO3, making it the first FeSe/oxide system with screened interfacial EPC while maintaining the 1 UC FeSe thickness. Despite comparable doping levels, the heavily electron-doped 1 UC FeSe/SrVO3 exhibits a pairing temperature (Tg ∼ 48 K) lower than those of FeSe/SrTiO3 and FeSe/LaFeO3. Our findings disentangle the contributions of interfacial EPC from dimensionality in terms of enhancing Tg in FeSe/oxide interfaces, underscoring the critical importance of interfacial EPC. This FeSe/VOx interface also provides a platform for studying interfacial superconductivity.

Nickel-Catalyzed Enantioselective Alkylation of Primary Phosphines.

Functional molecules derived from stereogenic phosphorus centers have important applications in the discovery of drugs and agrochemicals. They are also widely utilized as chiral ligands or organocatalysts for diverse asymmetric transformations. However, access to P-stereogenic motifs has always been regarded as a highly challenging yet desirable goal in organic synthesis. The development of general and practical methods for the stereoselective construction of synthetically versatile P(III)-stereogenic phosphines is particularly appealing but remains elusive. Herein, we describe a nickel-catalyzed asymmetric alkylation of primary phosphines with alkyl halides for the synthesis of P-stereogenic secondary phosphine-boranes with high enantioselectivity and broad substrate scope. The resulting optically active secondary phosphine-boranes allow for further stereospecific transformations, thereby establishing a modular and efficient platform for the diversity-oriented construction of P-stereogenic phosphine compounds.

Construction of a Prognostic Nomogram for Major Amputation Within 30 Days Postrevascularization in Patients With Acute Lower Limb Ischemia Based on 2D Perfusion Parameters.

PURPOSE: The purpose of the study is to develop a prediction model for major amputation (MA) within 30 days after arterial revascularization in patients with acute lower limb ischemia (ALLI) using 2-dimensional (2D) perfusion imaging parameters. MATERIALS AND METHODS: A retrospective study was performed in ALLI patients undergoing arterial revascularization between October 2015 and May 2022. Patients were randomly assigned into training and validation cohorts in a ratio of 7:3. Variables were selected using univariate and multivariate logistic regression. A nomogram for the MA risk within 30 days after arterial revascularization in ALLI patients was created. Its discrimination, calibration, and clinical effectiveness were reported. RESULTS: A total of 310 ALLI patients (326 limbs) were included. The MA rate within 30 days after arterial revascularization was 11.6%. Skin speckle, myoglobin, and time-to-peak were independent risk factors, while atrial fibrillation was a protective factor (all p<0.05). The nomogram predicted 30-day MA with satisfactory discriminative ability. The integrated discrimination improvement was 0.279 and 0.379 for the training and validation cohorts, respectively (both p<0.001). Calibration curves were close to the standard curve. The decision curve analysis demonstrated net benefits. CONCLUSION: This 2D perfusion imaging parameter-based nomogram could accurately predict the risk of MA within 30 days postrevascularization in ALLI patients. CLINICAL IMPACT: This study introduces a novel nomogram based on 2-dimensional (2D) perfusion imaging that can significantly advance the prognosis prediction in ALLI patients. By calculating the risk of major amputation within 30 days postrevascularization, this nomogram offers an accurate predictive tool and can lead to more informed decision-making on patient management. The innovative aspect of this research lies in its utilization of 2D perfusion parameters, a novel approach that enhances risk assessment accuracy in ALLI patients. This nomogram represents a significant step toward risk stratification and can guide future research for appropriate management on ALLI patients with different risk profiles.

Probing the Mechanism of Ni-Catalyzed Asymmetric Reppe Carbonylation of Cyclopropenes with CO and ROH.

There is ongoing intense interest in catalysis with the Earth-abundant metal nickel. This DFT study reveals a plausible mechanism for the first Ni-catalyzed asymmetric Reppe carbonylation of cyclopropenes with carbon monoxide and phenols/alcohols. The RO-H bond undergoes a distinct heterolytic cleavage rather than the proposed oxidative addition, transferring a proton to a nickel-bound anionic carbon atom in a stereoselective manner. This and other novel insights gained can have implications for developing new asymmetric Reppe reactions.

Distribution characteristics of intestinal flora in patients with OSAHS and the relationship between different intestinal flora and sleep disorders, hypoxemia and obesity.

OBJECTIVE: To investigate the distribution characteristics of intestinal flora in patients with obstructive sleep apnoea hypopnea syndrome (OSAHS) of different severities and the relationship between different intestinal flora and sleep structure disorder, hypoxemia and obesity. METHODS: A total of 25 healthy volunteers and 80 patients with OSAHS were enrolled in this study. The control group was healthy, and the experimental group comprised patients with OSAHS. The apnoea-hypopnea index (AHI), minimum saturation of peripheral oxygen (SpO2min), mean saturation of peripheral oxygen, body mass index, maximum apnoea time and other indicators were collected in clinical practice. The patients with OSAHS were divided into 20 mild and 42 moderate OSAHS cases, as well as 18 patients with severe OSAHS according to the AHI classification. Bioinformatics-related statistics were analysed using the QIIME2 software, and clinical data were analysed with the SPSS 22.0 software. RESULTS: The changes in microbial alpha diversity in the intestinal flora of patients with OSAHS showed that richness, diversity and evenness decreased, but the beta diversity did not change significantly. The Thermus Anoxybacillus, Anaerofustis, Blautia, Sediminibacterium, Ralstonia, Pelomonas, Ochrobactrum, Thermus Sediminibacterium, Ralstonia, Coccidia, Cyanobacteria, Anoxic bacilli and Anaerobes were negatively correlated with AHI (r = -0.38, -0.36, -0.35, -0.33, -0.31, -0.29, -0.22, -0.18) and positively correlated with SpO2min (r =0.38, 0.2, 0.25, 0.22, 0.24, 0.11, 0.23, 0.15). CONCLUSION: Some bacteria showed a significant correlation with clinical sleep monitoring data, which provides a possibility for the assessment of disease risk, but the mechanisms of their actions in the intestinal tract are not clear at present. Further research and observations are needed.

Catalytic Asymmetric Construction of C- and Si-Stereogenic Silacyclopentanes via Hydrosilylation of Arylmethylenecyclopropanes.

Silacycles have exhibited significant potential for application in the fields of medicinal chemistry, agrochemistry, and materials science. Accordingly, the development of effective methods for synthesizing these compounds has attracted increasing attention. Here, we report an efficient Cu-catalyzed enantioselective hydrosilylation of arylmethylenecyclopropanes with hydrosilanes, that allows the rapid assembly of various enantioenriched carbon- and silicon-stereogenic silacyclopentanes in good yields with excellent enantioselectivities and diastereoselectivities under mild conditions. Further stereospecific transformation of the Si-H bond on the chiral silicon center expands the diversity of these C- and Si-stereogenic silacyclopentanes.

Synthesizing Cr-Based Two-Dimensional Conjugated Metal-Organic Framework Through On-Surface Substitution Reaction.

A single-layer Cr3 (HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) conjugated metal-organic framework (c-MOF) is synthesized under ultrahigh vacuum conditions by substituting Cr for Ni in Ni3 (HITP)2 template. As revealed by low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy, while codeposition of Cr atoms and 2,3,6,7,10,11-hexaaminotriphenylene precursors produces irregular branches, crystalline Cr3 (HITP)2 frameworks are obtained by depositing Cr atoms to the Ni3 (HITP)2 templates. The density functional theory calculations reveal that the binding energy between Cr and HITP ligands is much higher than that for Ni, which hampers the growth of crystalline Cr3 (HITP)2 frameworks through direct coordination assembly but makes the substitution reaction energetically favorable. This work demonstrates a new strategy to prepare high-quality early-transition-metal-based c-MOFs under ultrahigh vacuum conditions.

Direct Observation of Topological Phonons in Graphene.

Phonons, as the most fundamental emergent bosons in condensed matter systems, play an essential role in the thermal, mechanical, and electronic properties of crystalline materials. Recently, the concept of topology has been introduced to phonon systems, and the nontrivial topological states also exist in phonons due to the constraint by the crystal symmetry of the space group. Although the classification of various topological phonons has been enriched theoretically, experimental studies were limited to several three-dimensional (3D) single crystals with inelastic x-ray or neutron scatterings. The experimental evidence of topological phonons in two-dimensional (2D) materials is absent. Here, using high-resolution electron energy loss spectroscopy following our theoretical predictions, we directly map out the phonon spectra of the atomically thin graphene in the entire 2D Brillouin zone, and observe two nodal-ring phonons and four Dirac phonons. The closed loops of nodal-ring phonons and the conical structure of Dirac phonons in 2D momentum space are clearly revealed by our measurements, in nice agreement with our theoretical calculations. The ability of 3D mapping (2D momentum space and energy space) of phonon spectra opens up a new avenue to the systematic identification of the topological phononic states. Our work lays a solid foundation for potential applications of topological phonons in superconductivity, dynamic instability, and phonon diode.

Assessment of Knee Menisci in Healthy Adults Using Shear Wave Elastography.

OBJECTIVES: The aim of this study was to explore the application value of shear wave elastography in healthy adults with knee meniscus. METHODS: One hundred adult subjects who underwent health checkups at our hospital from December 2022 to February 2023 were selected as research participants. Shear wave elastography was used to evaluate the periphery of the lateral and medial meniscus in both knees. To assess the mean differences in Young's modulus values between male and female groups, a one-way analysis of variance (ANOVA) and independent samples t-test were conducted. In addition, a Pearson correlation coefficient test was used to analyze the correlation between the elastic values of the meniscus and age, height, weight, and body mass index (BMI). RESULTS: There were no significant differences in elastic values between the lateral meniscus of the left and right sides or between the medial meniscus of the left and right sides within the same gender group (P > .05). Stiffness values of the medial meniscus were higher in each gender group than those of the lateral meniscus (P < .01). Additionally, males demonstrated higher stiffness values than females (P < .01). As age increased, the Young's modulus of the meniscus increased significantly (r > .75, P < .01). CONCLUSION: Shear wave elastography can serve as an adjunctive tool to aid in the assessment of knee meniscal elasticity.

Dramatic Plasmon Response to the Charge-Density-Wave Gap Development in 1T-TiSe_{2}.

1T-TiSe_{2} is one of the most studied charge density wave (CDW) systems, not only because of its peculiar properties related to the CDW transition, but also due to its status as a promising candidate of exciton insulator signaled by the proposed plasmon softening at the CDW wave vector. Using high-resolution electron energy loss spectroscopy, we report a systematic study of the temperature-dependent plasmon behaviors of 1T-TiSe_{2}. We unambiguously resolve the plasmon from phonon modes, revealing the existence of Landau damping to the plasmon at finite momentums, which does not support the plasmon softening picture for exciton condensation. Moreover, we discover that the plasmon lifetime at zero momentum responds dramatically to the band gap evolution associated with the CDW transition. The interband transitions near the Fermi energy in the normal phase are demonstrated to serve as a strong damping channel of plasmons, while such a channel in the CDW phase is suppressed due to the CDW gap opening, which results in the dramatic tunability of the plasmon in semimetals or small-gap semiconductors.

Hepatic arterial infusion chemotherapy and sequential ablation treatment in large hepatocellular carcinoma.

AIM: To investigate the individualized survival benefit of hepatic arterial infusion chemotherapy (HAIC) and sequential ablation treatment in large hepatocellular carcinoma (HCC) patients. METHODS: Between February 2016 and December 2020, a total of 228 HCC patients (diameter > 5 cm) who underwent HAIC alone (HAIC group, n = 135) or HAIC and sequential ablation (HAIC-ablation group, n = 93) treatment were reviewed. We applied the inverse probability of treatment weighting (IPTW) to adjust for potential bias of two treatment groups. The overall survival (OS) and progression-free survival (PFS) were compared with Kaplan-Meier curves. The Cox regression model was used to identify independent prognostic factors. And a prediction nomogram based on these independent prognostic factors was built, aiming to make probabilistic survival predictions and estimate personalized ablation benefits. RESULTS: After a median follow-up of 17.9 months, HCC patients in the HAIC-ablation group have longer significantly OS and PFS than those in the HAIC alone group (median OS: 22.2 months vs. 14.5 months; median PFS: 8.5 months vs. 4.6 months; both, p < 0.001). The IPTW-adjusted analysis revealed similar findings (both, p < 0.001). Tumor size, tumor number, and treatment modality were identified as independent prognostic factors for OS. The nomogram based on these factors showed favorable discrimination and well calibration. CONCLUSIONS: HAIC and sequential ablation provided significant survival benefits in patients with large HCC. The nomogram could help predict individual survival probabilities and estimate personalized sequential ablation benefits.

Enantioselective Hydroxylation of Dihydrosilanes to Si-Chiral Silanols Catalyzed by In Situ Generated Copper(II) Species.

Catalytic enantioselective hydroxylation of prochiral dihydrosilanes with water is expected to be a highly efficient way to access Si-chiral silanols, yet has remained unknown up to date. Herein, we describe a strategy for realizing this reaction: using an alkyl bromide as a single-electron transfer (SET) oxidant for invoking CuII species and chiral multidentate anionic N,N,P-ligands for effective enantiocontrol. The reaction readily provides a broad range of Si-chiral silanols with high enantioselectivity and excellent functional group compatibility. In addition, we manifest the synthetic potential by establishing two synthetic schemes for transforming the obtained products into Si-chiral compounds with high structural diversity. Our preliminary mechanistic studies support a mechanism involving SET for recruiting chiral CuII species as the active catalyst and its subsequent σ-metathesis with dihydrosilanes.

Observation of Nodal-Line Plasmons in ZrSiS.

Nodal-line semimetals (NLSMs), a large family of new topological phases of matter with continuous linear band crossing points in the momentum space, attract considerable attention. Here, we report the direct observation of plasmons originating from topological nodal-line states in a prototypical NLSM ZrSiS by high-resolution electron energy loss spectroscopy. There exist three temperature-independent plasmons with energies ranging from the near- to the mid-infrared frequencies. With first-principles calculations of a slab model, these plasmons can be ascribed to the correlations of electrons in the bulk nodal lines and their projected surface states, dubbed nodal-line plasmons. An anomalous surface plasmon has higher excitation energy than the bulk plasmon due to the larger contribution from the nodal-line projected surface states. This work reveals the novel plasmons related to the unique nodal-line states in a NLSM.

Mechanistic Insights into Formation of All-Carbon Quaternary Centers via Scandium-Catalyzed C-H Alkylation of Imidazoles with 1,1-Disubstituted Alkenes.

This density functional theory (DFT) study reveals a detailed plausible mechanism for the Sc-catalyzed C-H cycloaddition of imidazoles to 1,1-disubstituted alkenes to form all-carbon quaternary stereocenters. The Sc complex binds the imidazole substrate to enable deprotonative C2-H bond activation by the Sc-bound α-carbon to afford the active species. This complex undergoes intramolecular cyclization (C═C into Sc-imidazolyl insertion) with exo-selectivity, generating a ß-all-carbon-substituted quaternary center in the polycyclic imidazole derivative. The Sc-bound α-carbon deprotonates the imidazole C2-H bond to deliver the product and regenerate the active catalyst, which is the rate-determining step. Calculations illuminate the electronic effect of the ancillary Cp ligand on the catalyst activity and reveal the steric bias caused by using a chiral catalyst that induce the enantioselectivity. The insights can have implications for advancing rare-earth metal-catalyzed C-H functionalization of imidazoles.

Activation of Aryl Carboxylic Acids by Diboron Reagents towards Nickel-Catalyzed Direct Decarbonylative Borylation.

The Ni-catalyzed decarbonylative borylation of (hetero)aryl carboxylic acids with B2 cat2 has been achieved without recourse to any additives. This Ni-catalyzed method exhibits a broad substrate scope covering poorly reactive non-ortho-substituted (hetero)aryl carboxylic acids, and tolerates diverse functional groups including some of the groups active to Ni0 catalysts. The key to achieve this decarbonylative borylation reaction is the choice of B2 cat2 as a coupling partner that not only acts as a borylating reagent, but also chemoselectively activates aryl carboxylic acids towards oxidative addition of their C(acyl)-O bond to Ni0 catalyst via the formation of acyloxyboron compounds. A combination of experimental and computational studies reveals a detailed plausible mechanism for this reaction system, which involves a hitherto unknown concerted decarbonylation and reductive elimination step that generates the aryl boronic ester product. This mode of boron-promoted carboxylic acid activation is also applicable to other types of reactions.

Radical Dehydroxylative Alkylation of Tertiary Alcohols by Ti Catalysis.

Deoxygenative radical C-C bond-forming reactions of alcohols are a long-standing challenge in synthetic chemistry, and the current methods rely on multistep procedures. Herein, we report a direct dehydroxylative radical alkylation reaction of tertiary alcohols. This new protocol shows the feasibility of generating tertiary carbon radicals from alcohols and offers an approach for the facile and precise construction of all-carbon quaternary centers. The reaction proceeds with a broad substrate scope of alcohols and activated alkenes. It can tolerate a wide range of electrophilic coupling partners, including allylic carboxylates, aryl and vinyl electrophiles, and primary alkyl chlorides/bromides, making the method complementary to the cross-coupling procedures. The method is highly selective for the alkylation of tertiary alcohols, leaving secondary/primary alcohols (benzyl alcohols included) and phenols intact. The synthetic utility of the method is highlighted by its 10-g-scale reaction and the late-stage modification of complex molecules. A combination of experiments and density functional theory calculations establishes a plausible mechanism implicating a tertiary carbon radical generated via Ti-catalyzed homolysis of the C-OH bond.

DFT Mechanistic Insight into the Dioxygenase-like Reactivity of a CoIII-peroxo Complex: O-O Bond Cleavage via a [1,3]-Sigmatropic Rearrangement-like Mechanism.

Dioxygen O-O bond activation is a process for oxygenases and oxidases to perform biological functions and synthetic biomimetic catalysts to carry out oxygenation reactions using molecular O2 as an oxidant. Inspired by the experimental development of a CoIII-peroxo complex (i.e., [CoIII(TBDAP)(O2)]+, TBDAP = N,N-ditert-butyl-2,11-diaza[3.3](2,6)-pyridinophane) that exhibits dioxygenase-like reactivity to activate nitriles, a density functional theory (DFT) mechanistic study has been carried out to understand how the peroxo ligand is broken to activate nitriles. The study unveils that the O-O bond cleavage takes place via conversion to a CoII-superoxo complex aided by nitrile coordination, followed by formation of a five-membered intermediate via superoxo O2 radical nucleophilic attack at the nitrile carbon. Finally, a [1,3]-sigmatropic rearrangement-like process breaks the dioxygen bond. The otherwise difficult [1,3]-sigmatropic rearrangement is enabled by the mediation of CoIII(TBDAP) which alters a concerted rearrangement to a sequential process of O-O bond cleavage and N-O bond formation. Expectedly, the unveiling of the O-O bond cleavage mechanism could offer a clue for the development of biomimetic metal oxygenation catalysts.

Enhanced Superconducting State in FeSe/SrTiO_{3} by a Dynamic Interfacial Polaron Mechanism.

The observation of substantially enhanced superconductivity of single-layer FeSe films on SrTiO_{3} has stimulated intensive research interest. At present, conclusive experimental data on the corresponding electron-boson interaction is still missing. Here we use inelastic electron scattering spectroscopy and angle resolved photoemission spectroscopy to show that the electrons in these systems are dressed by the strongly polarized lattice distortions of the SrTiO_{3}, and the indispensable nonadiabatic nature of such a coupling leads to the formation of dynamic interfacial polarons. Furthermore, the collective motion of the polarons results in a polaronic plasmon mode, which is unambiguously correlated with the surface phonons of SrTiO_{3} in the presence of the FeSe films. A microscopic model is developed showing that the interfacial polaron-polaron interaction leads to the superconductivity enhancement.