Strong Substrate Influence on Atomic Structure and Properties of Epitaxial VO₂ Thin Films

The metal–insulator transition (MIT) observed in vanadium dioxide has been a topic of great research interest for past decades, with the underlying physics yet not fully understood due to the complex electron interactions and structures involved. The ability to understand and tune the MIT behavior is of vital importance from the perspective of both underlying fundamental science as well as potential applications. In this work, scanning transmission electron microscopy (STEM) is used to investigate cross-section lamella of the VO2 films deposited using pulsed laser deposition on three substrates: c-cut sapphire, TiO2(101) and TiO2(001). Advanced STEM imaging is performed in which also the oxygen atom columns are resolved. The overall film quality and structures on atomic and nanoscale are linked to the electrical transition characteristics. Relatively poor MIT characteristics are observed on c-sapphire due to the presence of very small domains with six orientation variants, and on TiO2 (001) due to the presence of cracks induced by stress relaxation. However, the MIT on TiO2 (101) behaves favorably, despite similar stress relaxation which, however, only leads to domain boundaries but no cracks.</p

Direct epitaxial growth of polar Hf0.5 Zr0.5 O2 films on corundum

Single-phase epitaxial Hf0.5 Zr0.5 O2 films with non-centrosymmetric orthorhombic structure have been grown directly on electrode-free corundum (a-Al2 O3) substrates by pulsed laser deposition. A combination of high-resolution X-ray diffraction and X-ray absorption spectroscopy confirms the epitaxial growth of high-quality films belonging to the Pca21 space group, with 111] out-of-plane orientation. The surface of a 7-nm-thick sample exhibits an atomic step-terrace structure with a corrugation of the order of one atomic layer, as proved by atomic force microscopy. Scanning transmission electron microscopy reveals that it consists of grains with around 10 nm lateral size. The polar nature of this film has been corroborated by pyroelectric measurements. These results shed light on the mechanisms of the epitaxial stabilization of the ferroelectric phase of hafnia. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Nano-vault architecture mitigates stress in silicon-based anodes for lithium-ion batteries

Nanomaterials undergoing cyclic swelling-deswelling benefit from inner void spaces that help accommodate significant volumetric changes. Such flexibility, however, typically comes at a price of reduced mechanical stability, which leads to component deterioration and, eventually, failure. Here, we identify an optimised building block for silicon-based lithium-ion battery (LIB) anodes, fabricate it with a ligand- and effluent-free cluster beam deposition method, and investigate its robustness by atomistic computer simulations. A columnar amorphous-silicon film was grown on a tantalum-nanoparticle scaffold due to its shadowing effect. PeakForce quantitative nanomechanical mapping revealed a critical change in mechanical behaviour when columns touched forming a vaulted structure. The resulting maximisation of measured elastic modulus (similar to 120GPa) is ascribed to arch action, a well-known civil engineering concept. The vaulted nanostructure displays a sealed surface resistant to deformation that results in reduced electrode-electrolyte interface and increased Coulombic efficiency. More importantly, its vertical repetition in a double-layered aqueduct-like structure improves both the capacity retention and Coulombic efficiency of the LIB. Lithiation of anodes during cycling of lithium-ion batteries generates stresses that reduce operation lifetime. Here, a composite silicon-based anode with a nanoscale vaulted architecture shows high mechanical stability and electrochemical performance in a lithium-ion battery.Peer reviewe

The College News, 1918-05-23, Vol. 04, No. 27

Bryn Mawr College student newspaper. Merged with The Haverford News in 1968 to form the Bi-college News (with various titles from 1968 on). Published weekly (except holidays) during the academic year

The initial prodrome to bipolar affective disorder: prospective case studies.

The initial prodrome to bipolar disorder has received very little attention to date, with most of the available data only addressing the prodrome to relapse. This study presents several prospective case studies of the initial prodrome to bipolar affective disorder. Three patients are presented who developed bipolar disorder during their treatment at the Personal Assessment and Crisis Evaluation Clinic (PACE). They were prospectively interviewed over a 12-month period using standard clinical research interviews. These patients met the criteria for bipolar disorder by the end of the treatment period. Depressive symptoms were the main reason for their first clinical presentation, with mania developing at a later date. Other comorbidities were observed before they were diagnosed with bipolar disorder. The generalisability of our findings was constrained because of the small sample size. Furthermore, our findings are likely to be influenced by the intake criteria used at PACE, a clinic that primarily aims at identifying patients at risk of psychosis rather than bipolar disorder. Our study provides information about the initial prodrome to bipolar disorder, which has previously been neglected in research studies. We found there were no prodrome features that clearly distinguished between patients who go on to develop bipolar disorder and those who develop schizophrenia. We hope our prospective data will be the starting point for subsequent studies, with the aim of applying these findings to developing suitable preventative interventions for bipolar disorder

Risk factors for hospital admission in patients undergoing outpatient anterior cruciate ligament reconstruction: A national database study

© 2020 Professor P K Surendran Memorial Education Foundation Introduction: Anterior Cruciate Ligament Reconstructions (ACLR) are routinely performed in an outpatient setting with low 90-day readmission rates (2.3%); however, admissions rates in the immediate perioperative period have been previously reported as high as 13.1%. Despite the surprisingly high number of patients requiring immediate perioperative admission, there has been a lack of recent literature specifically examining the associated risk factors for admission. Methods: Using the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database, a query for patients who underwent ACLR from 2011 through 2018 was performed using Current Procedural Terminology codes. The following concomitant procedures were included: meniscectomy, meniscal repair, diagnostic arthroscopy, loose body removal, synovectomy, chondroplasty, abrasion chondroplasty, drilling for osteochondritis dissecans. Demographics including age, sex, race, body mass index (BMI) and comorbidities were collected. Perioperative factors collected were anesthesia type and operative times. Patient demographic and perioperative data were compared using Fisher\u27s exact test and Pearson\u27s chi-square test. Multivariate logistic regressions were used to calculate odds ratios (OR) and 95% confidence intervals (CI) of independent risk factors for postoperative admission. Holm-Bonferroni method yielded adjusted p-value thresholds for significance. Results: Of the 20,819 patients undergoing ACLR with and without concomitant procedures, 3.8% of patients were admitted to the hospital in the immediate postoperative period. Following multivariate regression analysis, increased odds of admission were demonstrated with the use of regional anesthesia alone (OR = 2.77, 95%CI: 2.22–3.44; p \u3c 0.001), increasing concurrent procedures (Table 1), and obesity classes II (OR = 1.62, 95%CI: 1.26–2.10; p \u3c 0.001) and III (OR = 1.81, 95%CI: 1.33–2.47; p \u3c 0.001). Subsequent subgroup analysis of the isolated ACLR procedures (N = 9,423) demonstrated a 3.3% postoperative admission rate. Multivariate regressions demonstrated increased odds of admission with regional anesthesia use only (OR = 2.62, 95%CI: 1.90–3.60; p \u3c 0.001), obesity class II (OR = 2.22, 95%CI: 1.51–3.26; p \u3c 0.001), and increasing minutes of operative time (OR = 1.01, 95%CI: 1.01–1.01; p \u3c 0.001). Table 2 demonstrates increasing rates and odds of admission with increasing operative time in hours. Conclusion: Anterior Cruciate Ligament Reconstructions are routinely performed in an outpatient setting; nevertheless, a subset of ACLR patients is admitted postoperatively. We found an increased risk of admission with the use of regional anesthesia alone, increasing concurrent procedures and obesity classes II and III. A further understanding of patient risk factors for those undergoing ACLR allows orthopedic surgeons to better develop a preoperative plan and discuss patient expectations, which will lead to more efficient resource allocation and improved patient satisfaction