In Situ Studies of Volatile Molecules Trapping in Zirconium Alloy-Based Non-Evaporable Getter

La demande pour le maintien du vide et l'expulsion de gaz résiduels dans les micro-cavités dans les systèmes microélectromécaniques (MEMS) et dans d’autres dispositifs micro-fabriqués a augmenté significativement lors des dernières années.. Les gaz résiduels empoisonnent souvent le vide et finissent par détériorer le fonctionnement des dispositifs. Afin de maintenir le vide dans les cavités, quelques étapes doivent être mises en oeuvre: i) une étanchéité hermétique de la cavité doit être réalisée pour éliminer les fuites de gaz; ii) un dégazage approprié du système pour déloger et libérer les gaz piégés dans les matériaux est nécessaire avant de sceller de la cavité; Et iii) si nécessaire, incorporer une bande ou une couche mince d'un alliage métallique réactif agissant comme pompe chimique pour débarrasser le système des gaz résiduels pendant le fonctionnement du dispositif. De tels alliages sont connus sous le nom de getters, formés entre autres de métaux de transition actifs tels que Zr, Ti, V et Fe qui chimisorbent spontanément les gaz actifs dans les cavités. Pour améliorer l'efficacité de l'adsorption, une variété de systèmes de matériaux ont été proposés et testés, et deux caractéristiques semblent être critiques: (1) la morphologie (aire de surface); Et (2) la composition (réactivité physique et / ou chimique). Malgré leur importance technologique, peu de choses sont connues sur les mécanismes exacts de piégeage de gaz dans les matériaux. Ce projet aborde cette question en se basant sur des études in situ pour élucider la nature des réactions entre les constituants getters et les gaz résiduels et l'effet de la température d'activation sur la composition de surface et le piégeage des molécules volatiles. Nos études ont porté sur les alliages de zirconium-cobalt-terres rares (REM) qui ont été conçus pour avoir une basse température d'activation (<350oC) compatible avec les processus de fabrication et d’intégration de certains dispositifs MEMS. Des couches minces de ces alliages ont été pulvérisées sur Si. Les films obtenus sont très poreux, ce qui est critique pour réduire la température d'activation. La microscopie électronique à balayage (SEM), la spectroscopie de photoélectrons X (XPS), la spectrométrie de masse d'ions secondaires au temps de vol (TOF-SIMS) et la détection de recul élastique en temps de vol (TOF-ERD) ont été utilisées afin d’examiner la morphologie et la composition de la surface et du matériau massique. L'évolution de la surface en fonction de la température a été analysée in situ via XPS. Ce travail propose des mécanismes détaillés expliquant la réactivité à température ambiante et à haute température du matériau avec O2, N2 et CO2.----------Abstract Recently, there has been an increasing interest in vacuum maintenance and residual gases expulsion within small cavities in microelectromechanical systems (MEMS) and advanced field emission displays. Residual gases often poison the vacuum and eventually deteriorate device and system operation. In order to maintain vacuum in cavities, there are a few steps that must be implemented: i) a hermetic sealing of the cavity should be realized to minimize gas leakage from surrounding environment; ii) proper degassing of the system before seal-off is needed to dislodge and release trapped gases within the materials; and iii) if necessary incorporating a strip or a thin film of a reactive metal alloy which acts as a chemical pump to rid the system of residual gases during the device lifetime. Such alloys are known as getters, which contain active transition metals such as Zr, Ti, V, and Fe that spontaneously chemisorb active gases within cavities. To improve the gettering efficiency, a variety of material systems have been proposed and tested, and two characteristics appear to be critical: (1) morphology (surface area); and (2) composition (physical and/or chemical reactivity). Despites their technological importance little is known about the exact mechanisms of gas trapping within the material. This project tackles this very issue by using in situ studies to investigate the nature of bonding between the getter constituents and residual gases and the effect of the activation temperature on the surface composition and volatile molecules trapping. Our studies focused on zirconium-cobalt-rare earth metal (REM) alloys which have been developed with a low activation temperature (<350oC) for MEMS devices. Thin films of these alloys were sputtered on Si. The obtained films are highly porous, which is critical to lower the activation temperature. Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), and Time of Flight Elastic Recoil Detection (TOF-ERD) are utilized to examine the morphology and composition of both bulk and surface of the alloy. The surface evolution as a function of temperature is monitored in situ via XPS. This project elucidates the room temperature and high temperature reactivity of the material with O2, N2, and CO2

500-period epitaxial Ge/Si0.18Ge0.82 multi-quantum wells on silicon

Ge/SiGe multi-quantum well heterostructures are highly sought-after for silicon-integrated optoelectronic devices operating in the broad range of the electromagnetic spectrum covering infrared to terahertz wavelengths. However, the epitaxial growth of these heterostructures at a thickness of a few microns has been a challenging task due the lattice mismatch and its associated instabilities resulting from the formation of growth defects. To elucidates these limits, we outline herein a process for the strain-balanced growth on silicon of 11.1 nm/21.5 nm Ge/Si0.18Ge0.82 superlattices (SLs) with a total thickness of 16 {\mu}m corresponding to 500 periods. Composition, thickness, and interface width are preserved across the entire SL heterostructure, which is an indication of limited Si-Ge intermixing. High crystallinity and low defect density are obtained in the Ge/Si0.18Ge0.82 layers, however, the dislocation pile up at the interface with the growth substate induces micrometer-longs cracks on the surface. This eventually leads to significant layer tilt in the strain-balanced SL and in the formation of millimeter-long, free-standing flakes. These results confirm the local uniformity of structural properties and highlight the critical importance of threading dislocations in shaping the wafer-level stability of thick multi-quantum well heterostructures required to implement effective silicon-compatible Ge/SiGe photonic devices

Temperature-Dependent <i>in Situ</i> Studies of Volatile Molecule Trapping in Low-Temperature-Activated Zr Alloy-Based Getters

The activation process and the gettering mechanisms of Zr–Co-rare earth metal alloy getters were investigated. The evolution of the surface composition prior to and upon exposure to volatile molecules (O₂, N₂, CO₂) was monitored <i>in situ</i> using X-ray photoelectron spectroscopy under annealing conditions compatible with low processing temperature regimes. The thermally activated process of surface oxygen diffusion into the bulk was elucidated and found to involve an activation energy of 0.21 ± 0.02 eV in the 200–350 °C temperature range. This activation process was also found to reversibly transform ZrO₂ into Zr­(OH)₂ through the interaction with thermally desorbed hydrogen. Carbidic species form upon annealing at 250 °C via the interaction with an adventitious carbon layer on the surface, which results in the decrease in the number of surface sites available for subsequent gettering. <i>In situ</i> studies of the material reactivity with high purity O₂, N₂, and CO₂ were also investigated. O₂ was found to saturate the surface after single exposure, while CO₂ dissociates into CO and O^–, where O^– is incorporated deeper in the material and CO forms an ad-layer on the surface of the getter. N₂ was found to weakly interact with the partially activated surface and to form ZrN only upon annealing the sample to 350 °C indicating the poor reactivity of the material with N₂ at room temperature. The results display the importance of ridding systems of residual gases, especially N₂, by properly degassing the system prior to sealing to minimize and/or eliminate trapped gases within devices during operation

Epidemiology and clinical characteristics of viral infections in hospitalized children and adolescents with cancer in Lebanon.

BackgroundViral infections in children and adolescents with malignancy are commonly encountered and have a significant impact on morbidity and mortality. Studies and epidemiological data regarding viral infections in children with cancer in developing countries are lacking. This retrospective cohort study aims to assess the burden of viral infections in children and adolescents with cancer, by assessing prevalence, risk factors, as well as morbidity and mortality of common viruses over a period of 8 years.Methods and findingsMedical records of cancer patients treated at the Children Cancer Center of Lebanon were reviewed and 155 participants under the age of 21 were identified with at least one documented viral infection during the period from July 2009 to November 2017. This subset included 136 participants with active malignancy and 19 participants with a history of cancer who underwent hematopoietic stem cell transplantation [HSCT] and were in remission; the latter group was analyzed separately. Information regarding participant characteristics, hospital course, and complications were obtained. Associations between viral infections and certain factors were assessed. In the cohort, 64% were male, 81% were Lebanese. In participants with active malignancy, 90% received chemotherapy in the 6 months preceding the viral infection episode, 11% received radiotherapy. 51% of participants were neutropenic at the time of viral detection, and 77% were lymphopenic. 17% experienced a bacterial co-infection, and 3 experienced a viral co-infection. Among 162 viral infection episodes, clinically diagnosed skin infections, mainly herpes simplex virus type 1 and varicella-zoster virus, were the most common [44% of cases]. These were followed by laboratory-proven systemic herpes infections: cytomegalovirus [14%] and Epstein-Barr virus [6%]. Respiratory viruses: influenza and respiratory syncytial virus, accounted for 9% and 4%, respectively, whereas rotavirus represented 11% and BK virus represented 3% of cases. Acute lymphocytic leukemia was the most prevalent neoplasia [57%]. Fever was the most common presenting symptom [55%] and febrile neutropenia was the reason for admission in 24% of cases. The mean length of stay was significantly longer in participants with cytomegalovirus infections and significantly lower in rotavirus infection. Admission to the ICU occurred in 9%, complications in 8%, and mortality in 5%. Participants with viral infections post-HSCT were noted to have a significantly longer length of hospital stay compared to non-HSCT participants, with no other significant differences in clinical course and outcome. The study was limited by its retrospective nature and by the late introduction and underuse of multiplex PCR panels, which may have led to underdiagnosis of viral infections.ConclusionsViral infections were prevalent in our sample of cancer patients and may have contributed to morbidity and mortality. Newly available viral diagnostics are likely to vastly increase the number and scope of detectable viral infections in this population. Prospective studies using multiplex PCR technology with systematic testing of patients will be more helpful in defining the burden of viral infections. Furthermore, efforts at antimicrobial stewardship would benefit from the identification of viral causes of infection and limit the unnecessary use of antibiotics in the pediatric cancer population

Pancreatic surgery outcomes: multicentre prospective snapshot study in 67 countries

Background: Pancreatic surgery remains associated with high morbidity rates. Although postoperative mortality appears to have improved with specialization, the outcomes reported in the literature reflect the activity of highly specialized centres. The aim of this study was to evaluate the outcomes following pancreatic surgery worldwide.Methods: This was an international, prospective, multicentre, cross-sectional snapshot study of consecutive patients undergoing pancreatic operations worldwide in a 3-month interval in 2021. The primary outcome was postoperative mortality within 90 days of surgery. Multivariable logistic regression was used to explore relationships with Human Development Index (HDI) and other parameters.Results: A total of 4223 patients from 67 countries were analysed. A complication of any severity was detected in 68.7 percent of patients (2901 of 4223). Major complication rates (Clavien-Dindo grade at least IIIa) were 24, 18, and 27 percent, and mortality rates were 10, 5, and 5 per cent in low-to-middle-, high-, and very high-HDI countries respectively. The 90-day postoperative mortality rate was 5.4 per cent (229 of 4223) overall, but was significantly higher in the low-to-middle-HDI group (adjusted OR 2.88, 95 per cent c.i. 1.80 to 4.48). The overall failure-to-rescue rate was 21 percent; however, it was 41 per cent in low-to-middle-compared with 19 per cent in very high-HDI countries.Conclusion: Excess mortality in low-to-middle-HDI countries could be attributable to failure to rescue of patients from severe complications. The authors call for a collaborative response from international and regional associations of pancreatic surgeons to address management related to death from postoperative complications to tackle the global disparities in the outcomes of pancreatic surgery (NCT04652271; ISRCTN95140761)