Intrinsic Stress Research Articles

5142 Pheochromocytoma In The ICU- Hiding In Plain Sight

Abstract Disclosure: N. Chandrashekar: None. B. Arafah: None. Introduction: Pheochromocytomas are catecholamine-secreting tumors that are rare but dangerous and occur in <0.2% of patients with hypertension. Case: A 28 year old female with a 10 year history of hypertension and invasive stage 2b cervical cancer s/p chemoradiation presented to the hospital with circulatory shock from Takutsubo cardiomyopathy requiring intubation, vasopressors, CVVH, and ECMO. The endocrinology service was consulted due to a highly vascular, 3.6 cm, ∼23 Hounsfield units right adrenal mass evidenced on CT abdomen done months prior to admission. There were elevations in plasma normetanephrine to 15 nmol/L (ref <0.90 nmol/L), plasma metanephrine to 1.5 nmol/L (ref <0.50 nmol/L), urinary metanephrine to 565 ug/24-hours (ref 36 - 209 ug/24-hr), and urinary normetanephrine to 2580 ug/24-hr (ref 95 - 449 ug/24-hr). With her acute illness and recent use of vasopressors and quetiapine, these labs could not be accurately interpreted, and outpatient follow up was recommended. She was discharged home on metoprolol and hydralazine for hypertension management by her primary team. She was re-admitted to the CICU 2 days later for hypertensive emergency with flash pulmonary edema. With further questioning, she endorsed longstanding hypertension with episodes of headaches, palpitations, and vomiting. Her cancer therapy related menopause caused frequent nighttime hot flashes while inpatient. These episodes precipitated witnessed symptoms of catecholamine release with severe hypertension and palpitations. It was noted during her hospitalization that her symptoms were controlled during the day with frequent escape during the night despite continuous alpha and subsequent beta blockade every 6 hrs. Estrogen therapy would have been beneficial, however given a recent DVT, this was avoided and instead megestrol acetate and venlafaxine were used. With these additions, her adrenergic spells completely resolved. She then underwent a right adrenalectomy and had no significant fluctuations in her BP intraoperatively with complete resolutions of symptoms postoperatively. The pathology revealed a right 2.7 cm pheochromocytoma with no local invasion or distant metastasis. Conclusion: This is a case of pheochromocytoma crisis with cardiogenic shock followed by subsequent hypertensive emergency in the setting of inappropriate beta-blocker use. Confounders like vasopressors (increases catecholamines), intrinsic stress of critical illness (increases catecholamines), and quetiapine use (can increase normetanephrine levels) make it difficult to analyze labs. In these cases, a thorough history and imaging are key to establishing a diagnosis and initiating life-saving treatment. Another unique feature of this case is the control of the patient’s triggering menopausal hot flashes with megace and venlafaxine to preempt adrenergic spells during her admission. Presentation: 6/2/2024

Dual scalable osteogenic microtissue engineering via GelMA microsphere-inspired mechanical training and autonomous assembling of dental pulp stem cell

Large bone tissue defects present a significant clinical challenge due to the lack of stem cells and an osteogenic microenvironment, leading to fibrotic healing and impaired bone regeneration. Microsphere-based cell-on three-dimensional (3D) culture systems show great promise for constructing osteogenic microtissues. However, the underlying mechanisms require further investigation. In this study, we propose a simple, scalable framework for highly efficient osteogenic microtissue construction, utilizing gelatin methacryloyl (GelMA) microspheres and dental pulp stem cells (DPSCs). The GelMA microspheres provide an extensive, scalable 3D framework for the autonomous adhesion, migration, and proliferation of DPSCs. Within the enormous 3D space created by the microspheres, DPSCs anchor to the microspheres and neighboring cells, inducing intrinsic tensile stress and simulating a mechanical force akin to “rock climbing training”. Transcriptomic sequencing results reveal that the 3D spatial and mechanical microenvironment modulates biological processes involved in cell adhesion, extracellular matrix organization, and the positive regulation of cell migration. Further investigations demonstrate that triggering the FAK/YAP pathway mediate mechanical driven differentiation of DPSCs into the osteoblastic lineage in the excellent osteogenic microtissues. Moreover, this simple scalable 3D framework strategy is expected to enable the efficient and large-scale preparation of stem cell-based microtissues.

Genome Organization and Stability in Mammalian Pre-Implantation Development

A largely stable genome is required for normal development, even as genetic change is an integral aspect of reproduction, genetic adaptation and evolution. Recent studies highlight a critical window of mammalian development with intrinsic DNA replication stress and genome instability in the first cell divisions after fertilization. Patterns of DNA replication and genome stability are established very early in mammals, alongside patterns of nuclear organization, and before the emergence of gene expression patterns, and prior to cell specification and germline formation. The study of DNA replication and genome stability in the mammalian embryo provides a unique cellular system due to the resetting of the epigenome to a totipotent state, and the de novo establishment of the patterns of nuclear organization, gene expression, DNA methylation, histone modifications and DNA replication. Understanding DNA replication and genome stability in the early mammalian embryo is relevant for studies of both normal and disease-causing genetic variation, and to uncover basic principles of genome regulation.

Incorporating Single-Copper Sites and Host Defense Peptides into a Nanoreactor for Antibacterial Therapy by Bioinspired Design

A sustainable solution to the dramatic spread of antibiotic resistance threatening public health security is the development of antibiotic-free antimicrobial substances. Inspired by natural host defense mechanisms involving amino-terminal copper−nickel binding motif (ATCUN) antimicrobial peptides (AMPs), we have designed and prepared an artificial complex (Cu@G-AMPs) incorporating single-atom Cu catalysts for antibacterial therapy. The substrate of the complex, formed from guanine doped with abundant heteroatoms, anchored single Cu atoms with a coordination number of 2 and an average bond length of 1.91Å. Interestingly, Cu@G-AMPs, exhibiting Fenton-like catalytic activity, caused the inactivation of methicillin-resistant Staphylococcus aureus (MRSA) by generating and delivering reactive oxygen species (ROS) cargo. Mechanistically, the intrinsic stress response system of MRSA underwent an irreversible collapse when Cu@G-AMPs initiated its offensive program associated with non-specific targets. Furthermore, Cu@G-AMPs, which inherited the immunomodulatory properties of AMPs, sequentially carried out the functions of pulling edge closure, stabilizing granulation tissue, promoting collagen fiber proliferation, alleviating inflammation, and promoting neovascularization in wound areas infected by MRSA. Our results show that Cu@G-AMPs will provide a new perspective on untangling the complex regulatory networks that resistant bacteria have cultivated to deactivate commercial antibiotics.

Stress-relieved hollow porous carbon nanoring structures anchored with ZnCo2O4 nanoparticles towards super stable lithium storage

Stress-induced structural mechanical instability is a common occurrence in the electrode material during electrochemical cycling, especially for composite material systems. The structural mechanics engineering of nanocomposites comprising electrochemical active materials and carbon with novel structures holds great promise in addressing this issue. However, conventional carbonaceous materials often encounter challenges in long-term durability and high specific capacity stemming from their intrinsic uneven stress distribution and few active sites. Herein, finite element analysis reveals that the ring-like structure effectively mitigates stress concentration from expansion and possesses high packing density, outperforming traditional nanosphere and nanocube architectures. Accordingly, nanocomposites consisting of hollow porous nanostructured N-doped carbon nanorings (N-CNRs) anchored with bimetallic ZnCo2O4 nanoparticles are designed, which exhibit an extraordinary cycling performance for lithium storage with 96.4 % capacity retention following 1000 cycles and an impressively low storage degradation rate of 0.00357 % per cycle, as well as displaying an excellent specific capacity (1218 mA h/g at 0.1 A g−1) and outstanding rate performance (565 mA h/g at 5.0 A g−1). The well-engineered design nanocomposite features the synergistic effect of electrochemically active ZnCo2O4 nanoparticles integrated with structurally stable carbon nanorings for enhanced electrochemical performance.

Microstructure and fracture behaviour of biomimetic Al2O3-ZrO2 composite with 2-levels of structural hierarchy

We report new class of natural nacre-like alumina toughened by zirconia fabricated by the simple two-step approach of unidirectional freeze-casting and spark plasma sintering. The biomimetic alumina-zirconia with a relative density of more than 98 % was achieved by consolidating at temperature of 1300–1425 °C with 50 MPa pressure. The resultant microstructure consists of two levels of structural hierarchy, i.e. level-1: bulk lamellar brick phase (alumina platelets) and level-2: mortar phase (yttria stabilized tetragonal zirconia polycrystals). The increase in volume fraction of zirconia (in tetragonal form) from 0 to 15 vol% was effective in progressively reducing the size of alumina platelets from 12 to 9 μm, and significantly improved the flexural strength of the composite by 60 % (from 172 to 270 MPa). By optimizing the hierarchical architecture from micro to macroscopic level, the structural performance of our synthetic nacre, where strength and toughness of 270 MPa and 13.5 MPa√m respectively are superior to that of natural nacre and many other engineering materials (illustrated in the form of Ashby map). The exceptional damage resistance is rationalized by both intrinsic (stress induced tetragonal to monoclinic phase transformation of zirconia) and extrinsic (crack deflection, crack branching and bridging, multiple cracking, platelets interlocking) toughening mechanisms. For 15 vol% ZrO2 composition, the contribution of intrinsic and extrinsic toughness was quantitatively evaluated as 0.9 ± 0.03 and 4.3 ± 0.07 MPa√m respectively (with experimentally measured toughness at crack initiation as 5.2 ± 0.2 MPa√m).

The emerging roles of UFMylation in the modulation of immune responses.

Post-translational modification is a rite of passage for cellular functional proteins and ultimately regulate almost all aspects of life. Ubiquitin-fold modifier 1 (UFM1) system represents a newly identified ubiquitin-like modification system with indispensable biological functions, and the underlying biological mechanisms remain largely undiscovered. The field has recently experienced a rapid growth of research revealing that UFMylation directly or indirectly regulates multiple immune processes. Here, we summarised important advances that how UFMylation system responds to intrinsic and extrinsic stresses under certain physiological or pathological conditions and safeguards immune homeostasis, providing novel perspectives into the regulatory framework and functions of UFMylation system, and its therapeutic applications in human diseases.

The effect of replication protein A inhibition and post-translational modification on ATR kinase signaling

The ATR kinase responds to elevated levels of single-stranded DNA (ssDNA) to activate the G2/M checkpoint, regulate origin utilization, preserve fork stability, and allow DNA repair to ensure genome integrity. The intrinsic replication stress in cancer cells makes this pathway an attractive therapeutic target. The ssDNA that drives ATR signaling is sensed by the ssDNA-binding protein replication protein A (RPA), which acts as a platform for ATRIP recruitment and subsequent ATR activation by TopBP1. We have developed chemical RPA inhibitors (RPAi) that block RPA-ssDNA interactions (RPA-DBi) and RPA protein–protein interactions (RPA-PPIi); both activities are required for ATR activation. Here, we biochemically reconstitute the ATR kinase signaling pathway and demonstrate that RPA-DBi and RPA-PPIi abrogate ATR-dependent phosphorylation of target proteins with selectivity advantages over active site ATR inhibitors. We demonstrate that RPA post-translational modifications (PTMs) impact ATR kinase activation but do not alter sensitivity to RPAi. Specifically, phosphorylation of RPA32 and TopBP1 stimulate, while RPA70 acetylation does not affect ATR phosphorylation of target proteins. Collectively, this work reveals the RPAi mechanism of action to inhibit ATR signaling that can be regulated by RPA PTMs and offers insight into the anti-cancer activity of ATR pathway-targeted cancer therapeutics.

Effects of DNA Methylation of HPA-Axis Genes of F1 Juvenile Induced by Maternal Density Stress on Behavior and Immune Traits in Root Voles (Microtus oeconomus)-A Field Experiment.

The literature shows that maternal stress can influence behavior and immune function in F1. Yet, most studies on these are from the laboratory, and replicated studies on the mechanisms by which maternal stress drives individual characteristics are still not fully understood in wild animals. We manipulated high- and low-density parental population density using large-scale field enclosures and examined behavior and immune traits. Within the field enclosures, we assessed anti-keyhole limpet hemocyanin immunoglobulin G (anti-KLH IgG) level, phytohemagglutinin (PHA) responses, hematology, cytokines, the depressive and anxiety-like behaviors and prevalence and intensity of coccidial infection. We then collected brain tissue from juvenile voles born at high or low density, quantified mRNA and protein expression of corticotropin-releasing hormone (CRH) and glucocorticoid receptor gene (NR3C1) and measured DNA methylation at CpG sites in a region that was highly conserved with the prairie vole CRH and NR3C1 promoter. At high density, we found that the F1 had a lower DNA methylation level of CRH and a higher DNA methylation level of NR3C1, which resulted in an increase in the expression levels of the CRH mRNA and protein expression and further reduced the expression levels of the NR3C1 mRNA and protein expression, and ultimately led to have delayed responses to acute immobilization stress. Juvenile voles born at high density also reduced anti-KLH IgG levels and PHA responses, increased cytokines, and depressive and anxiety-like behaviors, and the effects further led to higher coccidial infection. From the perspective of population density inducing the changes in behavior and immunity at the brain level, our results showed a physiological epigenetic mechanism for population self-regulation in voles. Our results indicate that altering the prenatal intrinsic stress environment can fundamentally impact behavior and immunity by DNA methylation of HPA-axis genes and can further drive population fluctuations in wild animals.

Operando Stress Evolution in Hard Carbon Anodes – Insight into the Mechanical Degradation Induced Failure Mode in Rechargeable Sodium Ion Batteries

Microstructural instabilities in electrodes arising from cycling induced stress is a primary failure mode in rechargeable batteries. Therefore, a quantitative knowledge of the cycling induced stress evolution in rechargeable battery electrodes is important for understanding the electrode microstructural instabilities during cycling that can potentially inform the electrode design to prolong battery cycle life. The cycling induced stress in electrodes typically arises from the volume changes associated with insertion/extraction of the electroactive species in the electrode matrix. For example, operando measurement of lithiation-delithiation induced stress in graphite electrodes that typically show 10% volume change has previously resulted in useful information that correlates well with the lithiation-delithiation mechanism in graphite anodes1. The size of the shuttling-electroactive species can be taken as an indicator of the cycling induced stress magnitude that drives the electrode microstructural instabilities. In this regard, quantification of the cycling induced stress in rechargeable Na-ion battery electrodes is warranted for understanding mechanical degradation induced failure modes owing to the larger size of the electroactive species, i.e., Na ions (vs. Li-ion).Hard carbons as potential anodes in rechargeable sodium ion batteries has gained considerable attention in the recent past due to their superior Na-ion storage capability (vs. graphite that is a canonical anode in rechargeable lithium-ion batteries). However, hard carbon anodes typically show significant capacity fade that can potentially arise from cycling induced mechanical degradation of the anodes. Operando stress measurements coupled with comprehensive electrode microstructural characterization will provide valuable insights in this context. Here we report on the operando stress evolution in hard carbon anodes in rechargeable sodium ion batteries as probed by Multiple Optical-beam Sensing (MOS) technique that basically involves monitoring the spacings among a group of laser spot (Fig. 1). Preliminary measurements have shown that the stress correlates with the potential with a maximum around 12 MPa in compression during sodiation and tensile stress of ~ 2MPa during desodiation. Operando stress measurements are performed in hard carbon anodes in two different electrode configurations – typical composite anodes (with binder and conductive agents) and hard carbon thin film anodes (without binder and conductive agents). The thin film configuration is considered to evaluate intrinsic stress response in hard carbon anodes in absence of any secondary phase. A comparison of operando stress response in these two types of hard carbon anodes along with comprehensive electrode microstructural characterization will be presented. Additionally, attempts will be made to shed light on the current debate in the mechanism of sodium storage in hard carbon anodes by comparing operando stress response of hard carbons from multiple sources along with their structural characterization (Raman, XPS, surface area etc.). V. A. Sethuraman, N. Van Winkle, D. P. Abraham, A. F. Bower, and P. R. Guduru, Journal of Power Sources, 206, 334–342 (2012). Figure 1

Fabrication of ultra-high-Q Ta2O5 microdisks by photolithography-assisted chemo-mechanical etching

Tantalum pentoxide (Ta2O5) is widely recognized as a promising material platform for photonic integration. This is primarily attributed to its exceptional properties including large bandgap of 3.8 eV, broad transparency window ranging from 300 nm to 8000 nm, high nonlinear refractive index of ∼7.2 × 10−19 m2/W, low optical loss, moderate refractive index of 2.05, low intrinsic material stress, compatibility with CMOS technology, and high solubility for rare-earth ions. However, dry etching of Ta2O5 is challenging and typically results in sidewall roughness with substantial scattering losses. Here, we report on fabrication of a high-Q whispering gallery mode (WGM) microdisk with a diameter of 120 µm and a loaded Q factor of 1.92 × 106 by femtosecond laser photolithography assisted chemo-mechanical etching (PLACE) on amorphous Ta2O5 film. Thanks to the suppression of sidewall scattering, the loaded Q factor is two orders of magnitude higher than the best reported value in dispersion engineered Ta2O5 microresonators.

Multifunctional Cross-Linking Composite Binder Enables the Stable Performance of Si-Based Anodes for High-Energy-Density Lithium-Ion Batteries.

The intrinsic volumetric stress during cycling is the main obstacle for developing Si-based materials as high-energy-density lithium-ion battery anodes. Elastic binders have been demonstrated as an efficient approach to alleviate the stress of Si. Herein, we design a tough 3D hard/soft polymeric network (LPTS) using lithiated poly(acrylic acid), silk sericin, and highly branched tannic acid. Covalent cross-linking provides a robust mechanical strength to endure the large stress. The formed multiple hydrogen bonds with bonding energies between 3.46 and 25 kcal mol-1 can effectively dissipate the stress through sequential hydrogen bond disassociation. The multifunctional LPTS binder maintains the integrity of the Si-based electrodes during repeated discharging/charging. Additionally, Li+ can be transferred via a Li-conducting group (-COOLi), thereby enhancing the ionic conductivity of electrodes. Consequently, the Si/LPTS electrode exhibits an improved initial Coulombic efficiency and excellent durability over 400 cycles. Meanwhile, this binder is also suitable for Si-C anodes, enabling stable cycling at a high areal capacity >3.6 mAh cm-2 and delivering 72.2% capacity retention for the LFP||Si-C/LPTS full cell after 200 cycles. This study provides insight into developing efficient Si-based binders that are facile and low-cost for next-generation high-energy-density systems.

The Effect of Replication Protein A Inhibition and Post-Translational Modification on ATR Kinase Signaling.

The ATR kinase responds to elevated levels of single-stranded DNA (ssDNA) to activate the G2/M checkpoint, regulate origin utilization, preserve fork stability, and allow DNA repair towards ensuring genome integrity. The intrinsic replication stress in cancer cells makes this pathway an attractive therapeutic target. The ssDNA that drives ATR signaling is sensed by the ssDNA-binding protein replication protein A (RPA), which acts as a platform for ATRIP recruitment and subsequent ATR activation by TopBP1. We have developed chemical RPA inhibitors (RPAi) that block RPA-ssDNA interactions, termed RPA-DBi, and RPA protein-protein interactions, termed RPA-PPIi; both activities are required for ATR activation. Here, we employ a biochemically reconstituted ATR kinase signaling pathway and demonstrate that both RPA-DBi and RPA-PPIi abrogate ATR-dependent phosphorylation of downstream target proteins. We demonstrate that RPA post-translational modifications (PTMs) impact ATR kinase activation but do not alter sensitivity to RPAi. Specifically, phosphorylation of RPA32 and TopBP1 stimulate, while RPA70 acetylation has no effect on ATR phosphorylation of target proteins. Collectively, this work reveals the RPAi mechanism of action to inhibit ATR signaling that can be regulated by RPA PTMs and offers insight into the anti-cancer activity of ATR pathway targeted cancer therapeutics.

Embryonic stem cells maintain high origin activity and slow forks to coordinate replication with cell cycle progression

Embryonic stem (ES) cells are pluripotent stem cells that can produce all cell types of an organism. ES cells proliferate rapidly and are thought to experience high levels of intrinsic replication stress. Here, by investigating replication fork dynamics in substages of S phase, we show that mammalian pluripotent stem cells maintain a slow fork speed and high active origin density throughout the S phase, with little sign of fork pausing. In contrast, the fork speed of non-pluripotent cells is slow at the beginning of S phase, accompanied by increased fork pausing, but thereafter fork pausing rates decline and fork speed rates accelerate in an ATR-dependent manner. Thus, replication fork dynamics within the S phase are distinct between ES and non-ES cells. Nucleoside addition can accelerate fork speed and reduce origin density. However, this causes miscoordination between the completion of DNA replication and cell cycle progression, leading to genome instability. Our study indicates that fork slowing in the pluripotent stem cells is an integral aspect of DNA replication.

Sustained high expression of NRF2 inhibits cell apoptosis in arsenite-transformed human keratinocytes

Our previous study identified that nuclear factor-erythroid-2 p45-related factor 2 (NRF2) was activated in arsenite-induced tumorigenesis. However, the underlying mechanisms of NRF2 mediating apoptosis in arsenic-induced skin carcinogenesis remain unknown. This study explored the dynamic changes in apoptosis rate and the expression of apoptosis proteins in immortalized human keratinocytes (HaCaT) malignant transformation caused by 1.0 μM NaAsO2 at passages 0, 1, 7, 14, 21, 28, and 35. The result showed that the apoptosis rate decreased. The apoptosis-related proteins cleaved-caspase-3/caspase-3 ratio decreased in the later stages (passages 21, 28, and 35). Moreover, the expression of intrinsic ER stress pathway-related CHOP, ATF4, ATF6, and the intrinsic mitochondrial pathway-related Bax protein decreased in the later stages, while Bcl-2 and Mcl-1 increased, and NRF2 protein levels also increased. The apoptosis rate increased by silencing NRF2 expression in arsenite-transformed HaCaT (T-HaCaT) cells. Meanwhile, the expression of pro-apoptotic proteins (cleaved-caspase-3/caspase-3, CHOP, Bax) and ATF4, ATF6 increased. On the contrary, antiapoptotic protein levels (Bcl-2 and Mcl-1) decreased. The ability of colony formation and migration of T-HaCaT cells decreased. In conclusion, arsenite activated NRF2 in the later stages, decreasing apoptosis characterized by inhibiting endoplasmic reticulum stress-depended and mitochondria-depended apoptosis pathway, and further promoting NaAsO2-induced HaCaT cellular malignant transformation.

Investigation of the Bending Behavior in Silicon Nanowires: A Nanomechanical Modeling Perspective

Nanowires (NWs) play a crucial role across a wide range of disciplines such as nanoelectromechanical systems, nanoelectronics and energy applications. As NWs continue to reduce in dimensions, their mechanical properties are increasingly affected by surface attributes. This study conducts a comprehensive examination of nanomechanical models utilized for interpreting large deformations in the bending response of silicon NWs. Specifically, the Heidelberg, Hudson, Zhan, SimpZP and ExtZP nanomechanical models are explored regarding their capability to predict the elastic properties of silicon NWs with varying critical dimensions and crystal orientations. Molecular dynamics simulations are employed to model silicon NWs with unreconstructed surface states. The calculation of intrinsic stresses and the methodology for quantifying surface properties, including surface stresses and surface elasticity constants, are carried out using atomistic modeling. The findings reveal significant disparities of up to 100 GPa among nanomechanical models in interpreting a singular force-deflection response obtained for a silicon NW. Inadequate consideration of surface and intrinsic effects in nanomechanical modeling of NWs leads to substantial variability in their mechanical properties. This investigation yields valuable insights into the surface characteristics of silicon NWs, thereby enhancing our understanding of the essential role played by nanomechanical models in the intricate interpretation of mechanical properties at the nanoscale.

Orchestrating Stress Responses in Multiple Sclerosis: A Role for Astrocytic IFNγ Signaling.

Multiple sclerosis (MS) is an inflammatory and neurodegenerative disease that is characterized by the infiltration of peripheral immune cells into the central nervous system (CNS), secretion of inflammatory factors, demyelination, and axonal degeneration. Inflammatory mediators such as cytokines alter cellular function and activate resident CNS cells, including astrocytes. Notably, interferon (IFN)γ is a prominent pleiotropic cytokine involved in MS that contributes to disease pathogenesis. Astrocytes are dynamic cells that respond to changes in the cellular microenvironment and are highly responsive to many cytokines, including IFNγ. Throughout the course of MS, intrinsic cell stress is initiated in response to inflammation, which can impact the pathology. It is known that cell stress is pronounced during MS; however, the specific mechanisms relating IFNγ signaling to cell stress responses in astrocytes are still under investigation. This review will highlight the current literature regarding the impact of IFNγ signaling alone and in combination with other immune mediators on astrocyte synthesis of free oxygen radicals and cell death, and cover what is understood regarding astrocytic mitochondrial dysfunction and endoplasmic reticulum stress.

Low-loss and high-index contrast ultraviolet-C free-standing waveguides made of thermal silicon oxide.

Photonics in the ultraviolet provides an avenue for key advances in biosensing, pharmaceutical research, and environmental sensing. However, despite recent progress in photonic integration, a technological solution to fabricate photonic integrated circuits (PICs) operating in the UV-C wavelength range, namely, between 200 and 280 nm, remains elusive. Filling this gap will open opportunities for new applications, particularly in healthcare. A major challenge has been to identify materials with low optical absorption loss in this wavelength range that are at the same time compatible with waveguide design and large-scale fabrication. In this work, we unveil that thermal silicon oxide (TOX) on a silicon substrate is a potential candidate for integrated photonics in the UV-C, by removing the silicon substrate under selected regions to form single-side suspended ridge waveguides. We provide design guidelines for low-loss waveguide geometries, avoiding wrinkling due to residual intrinsic stress, and experimentally demonstrate waveguides that exhibit optical propagation losses below 3 and 4 dB/cm at a wavelength of 266 nm with claddings of air and water, respectively. This result paves the way for on-chip UV-C biological sensing and imaging.

Suppression of crack formation in wafer-scale amorphous SiNx films by residual hydrogen-ligands manipulation

Plasma-Enhanced Chemical Vapor Deposition (PECVD) of amorphous silicon nitride (SiNx) thin films is a critical procedure in microelectronics serving as a surface passivation layer and dielectric barrier. However, intrinsic film stress continuously builds up along with PECVD growth, leading to film cracking. How to achieve crack-free PECVD amorphous SiNx film within a large thickness range remains a critical unresolved challenge in semiconductor industry. In this study, we revealed that high residual NH ligands from the NH3 precursor could induce excessive tensile strain at the SiNx/Si wafer interface and consequently aggravate SiNx film crack formation. With a heating pretreatment on the wafer, residual H ligands were effectively reduced to achieve homogenous chemical composition in SiNx film. As a result, the crack number declined ∼42% and the remaining crack length was substantially shorter in contrast to the original SiNx film. This work demonstrates the crucial role of residual ligands on internal strain regulation and points out a pathway to achieve crack-free PECVD SiNx films in industrial manufacturing.

On corrosion of zirconium alloy in dissolved oxygen water: The role of Cu addition

It is significantly important to improve the corrosion resistance of Zr-Sn-Nb alloys in dissolved oxygen (DO) high temperature water by compositional modification. Here, the effect of Cu addition on the corrosion behaviors of Zr-0.5Sn-0.2Nb-0.4Fe-0.2Cr alloy was studied by using an autoclave circulating water loop at 360 °C/20 MPa up to 250 days. The oxide microstructures were characterized by a combination of SEM, TEM, STEM-EELS and PED. The results showed that compared with 0Cu alloy and 0.07Cu alloy, 0.13Cu alloy shows better corrosion resistance and its final weight gain after 250 days exposure is even lower than that of commercial Zr-4 alloy. The oxides for 0.07Cu and 0.13Cu alloys show more ordered crystals, thinner oxide and less lateral cracks, and the columnar grains show a stronger {10–3} texture, compared to Cu-free counterpart. The t-Zr2Cu SPPs have oxidized in the oxygen-rich layer below the O/M interface. The Cu ions tend to diffuse towards the grain boundary of dense columnar grains and maybe strengthen the grain boundaries, avoiding the defect generation under intrinsic stress in the oxide.