Quantum Efficiency Measurement and Modeling of Silicon Sensors Optimized for Soft X-ray Detection.

Hybrid pixel detectors have become indispensable at synchrotron and X-ray free-electron laser facilities thanks to their large dynamic range, high frame rate, low noise, and large area. However, at energies below 3 keV, the detector performance is often limited because of the poor quantum efficiency of the sensor and the difficulty in achieving single-photon resolution due to the low signal-to-noise ratio. In this paper, we address the quantum efficiency of silicon sensors by refining the design of the entrance window, mainly by passivating the silicon surface and optimizing the dopant profile of the n+ region. We present the measurement of the quantum efficiency in the soft X-ray energy range for silicon sensors with several process variations in the fabrication of planar sensors with thin entrance windows. The quantum efficiency for 250 eV photons is increased from almost 0.5% for a standard sensor to up to 62% as a consequence of these developments, comparable to the quantum efficiency of backside-illuminated scientific CMOS sensors. Finally, we discuss the influence of the various process parameters on quantum efficiency and present a strategy for further improvement.

Nonorthogonal Multireference Wave Function Description of Triplet-Triplet Energy Transfer Couplings.

In this study, the use of self-consistent field quasi-diabats is investigated for calculation of triplet energy transfer diabatic coupling elements. It is proposed that self-consistent field quasi-diabats are particularly useful for studying energy transfer (EnT) processes because orbital relaxation in response to changes in electron configuration is implicitly built into the model. The conceptual model that is developed allows for the simultaneous evaluation of direct and charge-transfer mechanisms to establish the importance of the different possible EnT mechanisms. The method's performance is evaluated using two model systems: the ethylene dimer and ethylene with the methaniminium cation. While states that mediate the charge-transfer mechanism were found to be higher in energy than the states involved in the direct mechanism, the coupling elements that control the kinetics were found to be significantly larger in the charge-transfer mechanism. Subsequently, we discuss the advantage of the approach in the context of practical difficulties with the use of established approaches.

Photoproduct formation in coenzyme B12-dependent CarH photoreceptor via a triplet pathway.

CarH is a cobalamin-based photoreceptor which has attracted significant interest due to its complex mechanism involving its organometallic coenzyme-B12 chromophore. While several experimental and computational studies have sought to understand CarH's mechanism of action, there are still many aspects of the mechanism which remain unclear. While light is needed to activate the Co-C5' bond, it is not entirely clear whether reaction pathway involves singlet or triplet diradical states. A recent experimental study implicated triplet pathway and importance of intersystem crossing (ISC) as a viable mechanistic route for photoproduct formation in CarH. Herein, a combined quantum mechanics/molecular mechanics approach (QM/MM) was used to explore the involvement of triplet states in CarH. Two possibilities were explored. The first possibility involved photo-induced homolytic cleavage of the Co-C5' where the radical pair (RP) would deactivate to a triplet state (T0) on the ground state potential energy surface (PES). However, a pathway for the formation of the photoproduct, 4',5'-anhydroadenosine (anhAdo), on the triplet ground state PES was not energetically feasible. The second possibility involved exploring a manifold of low-lying triplet excited states computed using TD-DFT within the QM/MM framework. Viable crossings of triplet excited states with singlet excited states were identified using semiclassical Landau-Zener theory and the effectiveness of spin-orbit coupling by El-Sayed rules. Several candidates along both the Co-NIm potential energy curve (PEC) and Co-C5'/Co-NIm PES were identified, which appear to corroborate experimental findings and implicate the possible role of triplet states in CarH.

Roadmap for the exposé of radiation flows (Xflows) experiment on NIF.

The goal of the Xflows experimental campaign is to study the radiation flow on the National Ignition Facility (NIF) reproducing the sensitivity of the temperature (±8 eV, ±23 µm) and density (±11 mg/cc) measurements of the COAX platform [Johns et al., High Energy Density Phys. 39, 100939 (2021); Fryer et al., High Energy Density Phys. 35, 100738 (2020); and Coffing et al., Phys. Plasmas 29, 083302 (2022)]. This new platform will enable future astrophysical experiments involving supernova shock breakout, such as Radishock (Johns et al., Laboratory for Laser Energetics Annual Report 338, 2020) on OMEGA-60 [Boehly et al., Rev. Sci. Instrum. 66, 508 (1995)], and stochastic media (such as XFOL on OMEGA). Greater energy and larger physical scale on NIF [Moses et al., Eur. Phys. J. D 44, 215 (2007)] will enable a greater travel distance of radiation flow, higher density, and more manufacturable foams and enable exploration of a greater range of radiation behavior than achievable in the prior OMEGA experiments. This publication will describe the baseline configuration for the Xflows experimental campaign and the roadmap to achieve its primary objectives.

Internalizing and Externalizing Disorder Levels among Adolescents: Data from Poland.

This article concerns internalizing and externalizing behaviors among Polish adolescents attending primary schools in a medium-sized city in Poland. The aim of the study was to examine the levels of select problem behaviors (i.e., depression, withdrawal, somatic complaints, aggressive behaviors, delinquent behaviors, thought problems, and internalizing and externalizing disorders) in early adolescence. Another important aim was to establish the ranges of the norm and deviation which would indicate the need for intervention aimed at internalizing and externalizing disorders in the sample. The relationships between variables such as age, gender, and school achievement (grade average) and the groups of problem behaviors and externalizing and internalizing disorders were also examined. To diagnose the occurrence of internalizing and externalizing behaviors, a sample of 550 students (55.3% girls, 46.7% boys) were measured using the Youth Self-Report (YSR) questionnaire. The results showed statistically significant differences in internalizing and externalizing behaviors between boys and girls. Girls achieved higher scores on most of the YSR scales, including internalizing and externalizing disorders, as well as on the total score. The student subgroup scores were also differentiated in terms of age and their average grades. The results also have practical implications; namely, the need for obligatory screening tests of students' emotional states; encouraging preventive measures in schools, including diagnosis and psychological support in the context of depression; monitoring aggressive behaviors and social problems, both in boys and girls; and implementing universal, selective, and indicated prevention through complex, empirically validated educational-therapeutic programs.

Mild-to-moderate COVID-19 does not predispose to the development of autoimmune rheumatic diseases or autoimmune-based thrombosis.

An infection with severe acute respiratory syndrome coronavirus (SARS-CoV-2) may have a significant impact on the human immune system. Interactions between the virus and defence mechanisms may promote the development of autoimmune processes which manifest as antinuclear antibody (ANA) synthesis. Since many different viruses are suspected to take part in the pathogenesis of different systemic autoimmune rheumatic diseases (SARDs), we examined whether coronavirus disease 2019 convalescents who suffer from mild to moderate disease have a higher risk of developing ANA and anti-ß2-glicoprotein I IgG antibodies (ß2 GPI). In a retrospective study, we examined 294 adults among volunteer blood donors divided into convalescents (N = 215) and healthy controls (N = 79). For ANA detection, we used line-blotting, a type of indirect immunofluorescence assay (IF), to determine antigenic specificity and ELISA for ß2 GPI. We found a lower incidence of ANA in convalescents than in healthy controls, with the majority of these antibodies directed to antigens with no known clinical significance. Additionally, no participants were positive for ß2 GPI in either group. Our results show that COVID-19 with mild to moderate symptoms in the generally healthy population does not induce the development of ANA or anti-ß2 GPI antibodies for at least 6 months following the disease.

Novel fabrication tools for dynamic compression targets with engineered voids using photolithography methods.

Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets' geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling.

Mild-to-Moderate COVID-19 Convalescents May Present Pro-Longed Endothelium Injury.

BACKGROUND: The SARS-CoV-2 pandemic posed a great threat to public health, healthcare systems and the economy worldwide. It became clear that, in addition to COVID-19 and acute disease, the condition that develops after recovery may also negatively impact survivors' health and quality of life. The damage inflicted by the viral infection on endothelial cells was identified quite early on as a possible mechanism underlying the so-called post-COVID syndrome. It became an urgent matter to establish whether convalescents present chronic endothelial impairment, which could result in an increased risk of cardiovascular and thrombotic complications. METHODS: In this study, we measured the levels of CRP, ICAM-1, VCAM-1, E-selectin and syndecan-1 as markers of inflammation and endothelial injury in generally healthy convalescents selected from blood donors and compared these to a healthy control group. RESULTS: We found higher concentrations of E-selectin and a lower level of syndecan-1 in convalescents in comparison to those of the control group. CONCLUSION: Based on our results, it can be concluded that, at least 6 months after infection, there is only slight evidence of endothelial dysfunction in COVID-19 convalescents who do not suffer from other comorbidities related to endothelial impairment.

Photoproduct formation in coenzyme B12-dependent CarH via a singlet pathway.

The CarH photoreceptor exploits of the light-sensing ability of coenzyme B12 ( adenosylcobalamin = AdoCbl) to perform its catalytic function, which includes large-scale structural changes to regulate transcription. In daylight, transcription is activated in CarH via the photo-cleavage of the Co-C5' bond of coenzyme B12. Subsequently, the photoproduct, 4',5'-anhydroadenosine (anhAdo) is formed inducing dissociation of the CarH tetramer from DNA. Several experimental studies have proposed that hydridocoblamin (HCbl) may be formed in process with anhAdo. The photolytic cleavage of the Co-C5' bond of AdoCbl was previously investigated using photochemical techniques and the involvement of both singlet and triplet excited states were explored. Herein, QM/MM calculations were employed to probe (1) the photolytic processes which may involve singlet excited states, (2) the mechanism of anhAdo formation, and (3) whether HCbl is a viable intermediate in CarH. Time-dependent density functional theory (TD-DFT) calculations indicate that the mechanism of photodissociation of the Ado ligand involves the ligand field (LF) portion of the lowest singlet excited state (S1) potential energy surface (PES). This is followed by deactivation to a point on the S0 PES where the Co-C5' bond remains broken. This species corresponds to a singlet diradical intermediate. From this point, the PES for anhAdo formation was explored, using the Co-C5' and Co-C4' bond distances as active coordinates, and a local minimum representing anhAdo and HCbl formation was found. The transition state (TS) for the formation of the Co-H bond of HCbl was located and its identity was confirmed by a single imaginary frequency of i1592 cm-1. Comparisons to experimental studies and the potential role of rotation around the N-glycosidic bond of the Ado ligand were discussed.

Computational investigations of B12-dependent enzymatic reactions.

Nature employs two biologically active forms of vitamin B12, adenosylcobalamin (or coenzyme B12) and methylcobalamin, as cofactors in molecular transformations both in bacteria and mammals. Computational chemistry, guided by experimental data, has been used to explore fundamental characteristics of these enzymatic reactions. In particular, the quantum mechanics/molecular mechanics (QM/MM) method has proven to be a powerful tool in elucidating important characteristics of B12-dependent enzymatic reactions. Herein, we will present a brief tutorial in conducting QM/MM calculations for B12 enzymatic reactions. We will summarize recent contributions that target the use of QM/MM calculations in both photochemical and enzymatic reactions including AdoCbl-dependent ethanolamine ammonia lyase, glutamate mutase, and photoreceptor CarH.

Ligand-Centered Hydrogen Evolution with Ni(II) and Pd(II)DMTH.

In this study, we report a pair of electrocatalysts for the hydrogen evolution reaction (HER) based on the noninnocent ligand diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-pyridinehydrazone) (H2DMTH, H2L1). The neutral complexes NiL1 and PdL1 were synthesized and characterized by spectroscopic and electrochemical methods. The complexes contain a non-coordinating, basic hydrazino nitrogen that is protonated during the HER. The pKa of this nitrogen was determined by spectrophotometric titration in acetonitrile to be 12.71 for NiL1 and 13.03 for PdL1. Cyclic voltammograms of both NiL1 and PdL1 in acetonitrile exhibit diffusion-controlled, reversible ligand-centered events at -1.83 and -1.79 V (vs ferrocenium/ferrocene) for NiL1 and PdL1, respectively. A quasi-reversible, ligand-centered event is observed at -2.43 and -2.34 V for NiL1 and PdL1, respectively. The HER activity in acetonitrile was evaluated using a series of neutral and cationic acids for each catalyst. Kinetic isotope effect (KIE) studies suggest that the precatalytic event observed is associated with a proton-coupled electron transfer step. The highest turnover frequency values observed were 6150 s-1 at an overpotential of 0.74 V for NiL1 and 8280 s-1 at an overpotential of 0.44 V for PdL1. Density functional theory (DFT) computations suggest both complexes follow a ligand-centered HER mechanism where the metals remain in the +2 oxidation state.

Photolytic properties of B12-dependent enzymes: A theoretical perspective.

The biologically active vitamin B12 derivates, methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), are ubiquitous organometallic cofactors. In addition to their key roles in enzymatic catalysis, B12 cofactors have complex photolytic properties which have been the target of experimental and theoretical studies. With the recent discovery of B12-dependent photoreceptors, there is an increased need to elucidate the underlying photochemical mechanisms of these systems. This book chapter summarizes the photolytic properties of MeCbl- and AdoCbl-dependent enzymes with particular emphasis on the effect of the environment of the cofactor on the excited state processes. These systems include isolated MeCbl and AdoCbl as well as the enzymes, ethanolamine ammonia-lyase (EAL), glutamate mutase (GLM), methionine synthase (MetH), and photoreceptor CarH. Central to determining the photodissociation mechanism of each system is the analysis of the lowest singlet excited state (S1) potential energy surface (PES). Time-dependent density functional theory (TD-DFT), employing BP86/TZVPP, is widely used to construct such PESs. Regardless of the environment, the topology of the S1 PES of AdoCbl or MeCbl is marked by characteristic features, namely the metal-to-ligand charge transfer (MLCT) and ligand field (LF) regions. Conversely, the relative energetics of these electronic states are affected by the environment. Applications and outlooks for Cbl photochemistry are also discussed.

Aerobic photolysis of methylcobalamin: unraveling the photoreaction mechanism.

The photo-reactivity of cobalamins (Cbls) is influenced by the nature of axial ligands and the cofactor's environment. While the biologically active forms of Cbls with alkyl axial ligands, such as methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), are considered to be photolytically active, in contrast, the non-alkyl Cbls are photostable. In addition to these, the photolytic properties of Cbls can also be modulated in the presence of molecular oxygen, i.e., under aerobic conditions. Herein, the photoreaction of the MeCbl in the presence of oxygen has been explored using density functional theory (DFT) and time-dependent DFT (TD-DFT). The first stage of the aerobic photoreaction is the activation of the Co-C bond and the formation of the ligand field (LF) electronic state through the displacement of axial bonds. Once the photoreaction reaches the LF excited state, three processes can occur: namely the formation of OO-CH3 through the reaction of CH3 with molecular oxygen, de-activation of the {Im⋯[CoII(corrin)]⋯CH3}+ sub-system from the LF electronic state by changing the electronic configuration from (dyz)1(dz2)2 to (dyz)2(dz2)1 and the formation of the deactivation complex (DC) complex via the recombination of OO-CH3 species with the de-excited [CoII(corrin)] system. In the proposed mechanism, the deactivation of the [CoII(corrin)] subsystem may coexist with the formation of OO-CH3, followed by immediate relaxation of the subsystems in the ground state. Moreover, the formation of the OO-CH3 species followed by the formation of the {[CoIII(corrin)]-OO-CH3}+ complex stabilizes the system compared to the reactant complex.

Indium-Based Micro-Bump Array Fabrication Technology with Added Pre-Reflow Wet Etching and Annealing.

Indium-based micro-bump arrays, among other things, are used for the bonding of infrared photodetectors and focal plane arrays. In this paper, several aspects of the fabrication technology of micrometer-sized indium bumps with a smooth surface morphology were investigated. The thermal evaporation of indium has been optimized to achieve ~8 µm-thick layers with a small surface roughness of Ra = 11 nm, indicating a high packing density of atoms. This ensures bump uniformity across the sample, as well as prevents oxidation inside the In columns prior to the reflow. A series of experiments to optimize indium bump fabrication technology, including a shear test of single columns, is described. A reliable, repeatable, simple, and quick approach was developed with the pre-etching of indium columns in a 10% HCl solution preceded by annealing at 120 °C in N2.

A Study of Defects in InAs/GaSb Type-II Superlattices Using High-Resolution Reciprocal Space Mapping.

In this paper, the study of defects in InAs/GaSb type-II superlattices using high-resolution an x-ray diffraction method as well as scanning (SEM) and transmission (TEM) electron microscopy is presented. The investigated superlattices had 200 (#SL200), 300 (#SL300), and 400 (#SL400) periods and were grown using molecular beam epitaxy. The growth conditions differed only in growth temperature, which was 370 °C for #SL400 and #SL200, and 390 °C for #SL300. A wings-like diffuse scattering was observed in reciprocal space maps of symmetrical (004) GaSb reflection. The micrometer-sized defect conglomerates comprised of stacking faults, and linear dislocations were revealed by the analysis of diffuse scattering intensity in combination with SEM and TEM imaging. The following defect-related parameters were obtained: (1) integrated diffuse scattering intensity of 0.1480 for #SL400, 0.1208 for #SL300, and 0.0882 for #SL200; (2) defect size: (2.5-3) µm × (2.5-3) µm -#SL400 and #SL200, (3.2-3.4) µm × (3.7-3.9) µm -#SL300; (3) defect diameter: ~1.84 µm -#SL400, ~2.45 µm -#SL300 and ~2.01 µm -#SL200; (4) defect density: 1.42 × 106 cm-2 -#SL400, 1.01 × 106 cm-2 -#SL300, 0.51 × 106 cm-2 -#SL200; (5) diameter of stacking faults: 0.14 µm and 0.13 µm for #SL400 and #SL200, 0.30 µm for #SL300.

Electronic and photolytic properties of hydridocobalamin.

Hydridocobalamin (HCbl), is a known member of the B12 family of molecules (cobalamins, Cbls) yet unlike other well-studied Cbls, little is known of the electronic and photolytic properties of this species. Interest in HCbl has increased significantly in recent years when at least three experimentally proposed mechanisms implicate HCbl as an intermediary in the photoreaction of coenzyme B12-dependent photoreceptor CarH. Specifically, cleavage of the Co-C5' bond of coenzyme B12 could lead to a ß-hydride or ß­hydrogen elimination reaction to form HCbl. HCbl is known to be a transient species where the oxidation state of the Co is variable; Co(I)-H+ ↔ Co(II)-H â†” Co(III)-H-. Further, HCbl is a very unstable with a pKa of ~1. This complicates experimental studies and to the best of our knowledge there are no available crystal structures of HCbl - either for the isolated molecule or bound to an enzyme. In this study, the electronic structure, photolytic properties, and reactivity of HCbl were explored to determine the preferred oxidation state as well as its potential role in the formation of the photoproduct in CarH. Natural bond orbital (NBO) analysis was performed to determine the oxidation state of Co in isolated HCbl. Based on the NBO analysis of HCbl, Co clearly had excess negative charge, which is in stark contrast to other alkylCbls where the Co ion is marked by significant positive charge. In sum, NBO results indicate that the CoH bond is strongly polarized and almost ionic. It can be described as protonated Co(I). In addition, DFT was used to explore the bond dissociation energy of HCbl based on homolytic cleavage of the CoH bond. TD-DFT calculations were used to compare computed electronic transitions to the experimentally determined absorption spectrum. The photoreaction of CarH was explored using an isolated model system and a pathway for hydrogen transfer was found. Finally, quantum mechanics/molecular mechanics (QM/MM) calculations were employed to investigate the formation of HCbl in CarH.

University students' strategies of coping with stress during the coronavirus pandemic: Data from Poland.

The COVID-19 pandemic has changed the functioning of universities worldwide. In Poland, the transfer to online teaching was announced without prior warning, which radically changed students' daily functioning. This situation clearly showed the students' helplessness and difficulties with coping with this new, stressful situation, highlighted in many previous studies. A sudden and far-reaching change in daily functioning caused anxiety, depression, and stress in this group. Thus, from a pedagogical and psychological point of view, it is pertinent to examine the students' strategies of coping with stress caused by the COVID-19 pandemic. To this end, in 2020, a sample of Polish students was anonymously measured using the Mini-COPE questionnaire. Data was gathered from 577 students from 17 universities. The statistical analysis showed that during the coronavirus pandemic, Polish students most often used the coping strategies of: acceptance, planning, and seeking emotional support. Such factors as age, gender, and place of residence influenced the choice of specific strategies of coping with stress during the COVID-19 pandemic. The results also showed that the youngest students had the lowest coping skills. The results allow for concluding that the students' maladaptive strategies of coping with stress, especially during the pandemic, may result in long-term consequences for their psychophysiological health and academic achievements. Thus, based on the current results and on the participatory model of intervention, a support program for students is proposed which would involve psychological, organizational, and instrumental support.

Photoassisted Charge Transfer Between DMF and Substrate: Facile and Selective N,N-Dimethylamination of Fluoroarenes.

A reversible Van der Waals complex formation between the electron-deficient fluorinated aromatic ring and N,N-dimethylformamide (DMF) molecules followed by light irradiation resulted in charge transfer (CT) process. The complex was stabilized by ammonium formate and further decomposed to form the C-N bond. Control experiments revealed that the simultaneous SN Ar pathway also contributes to product formation. This methodology is mild, metal-free, and effective for the amination of a variety of substrates. The reproducibility of this methodology was also verified on gram-scale reactions. The CT states were supported by control UV/Vis spectroscopy and computational studies.

Characterization of Chromium Compensated GaAs Sensors with the Charge-Integrating JUNGFRAU Readout Chip by Means of a Highly Collimated Pencil Beam.

Chromium compensated GaAs or GaAs:Cr sensors provided by the Tomsk State University (Russia) were characterized using the low noise, charge integrating readout chip JUNGFRAU with a pixel pitch of 75 × 75 µm2 regarding its application as an X-ray detector at synchrotrons sources or FELs. Sensor properties such as dark current, resistivity, noise performance, spectral resolution capability and charge transport properties were measured and compared with results from a previous batch of GaAs:Cr sensors which were produced from wafers obtained from a different supplier. The properties of the sample from the later batch of sensors from 2017 show a resistivity of 1.69 × 109 Ω/cm, which is 47% higher compared to the previous batch from 2016. Moreover, its noise performance is 14% lower with a value of (101.65 ± 0.04) e- ENC and the resolution of a monochromatic 60 keV photo peak is significantly improved by 38% to a FWHM of 4.3%. Likely, this is due to improvements in charge collection, lower noise, and more homogeneous effective pixel size. In a previous work, a hole lifetime of 1.4 ns for GaAs:Cr sensors was determined for the sensors of the 2016 sensor batch, explaining the so-called "crater effect" which describes the occurrence of negative signals in the pixels around a pixel with a photon hit due to the missing hole contribution to the overall signal causing an incomplete signal induction. In this publication, the "crater effect" is further elaborated by measuring GaAs:Cr sensors using the sensors from 2017. The hole lifetime of these sensors was 2.5 ns. A focused photon beam was used to illuminate well defined positions along the pixels in order to corroborate the findings from the previous work and to further characterize the consequences of the "crater effect" on the detector operation.