COVID-19 in hospitalized infants aged under 3 months: multi-center experiences across Turkey

To investigate coronavirus disease 2019 (COVID-19) in infants aged 0 to 3 months because there is currently a significant gap in the literature on the subject. A cross-sectional study was conducted with the involvement of 19 medical centers across Turkey and 570 infants. The majority of the patients were male (58.2%), and the three most common symptoms were fever (78.2%), cough (44.6%), and feeding intolerance (39.9%). The results showed that a small percentage of infants had positive blood (0.9%) or urine cultures (10.2%). Most infants presented with fever (78.2%). Children without underlying conditions (UCs) had mostly a complicated respiratory course and a normal chest radiography. Significant more positive urine culture rates were observed in infants with fever. A higher incidence of respiratory support requirements and abnormal chest findings were seen in infants with chronic conditions. These infants also had a longer hospital stay than those without chronic conditions.  Conclusions: Our study discloses the clinical observations and accompanying bacterial infections found in infants aged under 3 months with COVID-19. These findings can shed light on COVID-19 in infancy for physicians because there is limited clinical evidence available. What is Known: • COVID-19 in infants and older children has been seen more mildly than in adults. • The most common symptoms of COVID-19 in infants are fever and cough, as in older children and adults. COVID-19 should be one of the differential diagnoses in infants with fever. What is New: • Although most infants under three months had fever, the clinical course was uneventful and respiratory complications were rarely observed in healthy children. • Infants with underlying conditions had more frequent respiratory support and abnormal chest radiography and stayed longer in the hospital.

Exploring the biointerfaces: ab initio investigation of nano-montmorillonite clay, and its interaction with unnatural amino acids

We investigated the interaction between biomimetic Fe and Mg co-doped montmorillonite nanoclay and eleven unnatural amino acids. Employing three different functionals (PBE-GGA, PBE-GGA + U, and HSE06), we examined the clay's structural, electronic, and magnetic properties. Our results revealed the necessity of using PBE-GGA + U with U ≥ 4 eV to accurately describe key clay properties. We identified amino acids that strongly interacted with the clay surface, with steric orientation playing a crucial role in facilitating binding. Our DFT calculations highlighted significant electrostatic interactions between the amino acids and the clay slab, with the amino group's predominant role in this interaction. These findings hold promise for designing amino acids for clay-amino acid systems, leading to innovative bio-material composites for various applications. Additionally, our ab-initio molecular dynamics simulations confirmed the stability of clay-amino acid systems under ambient conditions, and the introduction of an implicit water solvent enhanced the binding energy of amino acids on the clay surface.

A snapshot of pediatric inpatients and outpatients with COVID-19: a point prevalence study from Turkey

This multi-center point prevalence study evaluated children who were diagnosed as having coronavirus disease 2019 (COVID-19). On February 2nd, 2022, inpatients and outpatients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were included in the study from 12 cities and 24 centers in Turkey. Of 8605 patients on February 2nd, 2022, in participating centers, 706 (8.2%) had COVID-19. The median age of the 706 patients was 92.50 months, 53.4% were female, and 76.7% were inpatients. The three most common symptoms of the patients with COVID-19 were fever (56.6%), cough (41.3%), and fatigue (27.5%). The three most common underlying chronic diseases (UCDs) were asthma (3.4%), neurologic disorders (3.3%), and obesity (2.6%). The SARS-CoV-2-related pneumoniae rate was 10.7%. The COVID-19 vaccination rate was 12.5% in all patients. Among patients aged over 12 years with access to the vaccine given by the Republic of Turkey Ministry of Health, the vaccination rate was 38.7%. Patients with UCDs presented with dyspnea and pneumoniae more frequently than those without UCDs (p < 0.001 for both). The rates of fever, diarrhea, and pneumoniae were higher in patients without COVID-19 vaccinations (p = 0.001, p = 0.012, and p = 0.027).  Conclusion: To lessen the effects of the disease, all eligible children should receive the COVID-19 vaccine. The illness may specifically endanger children with UCDs. What is Known: • Children with COVID-19 mainly present with fever and cough, as in adults. • COVID-19 may specifically threaten children with underlying chronic diseases. What is New: • Children with obesity have a higher vaccination rate against COVID-19 than children without obesity. • Among unvaccinated children, fever and pneumoniae might be seen at a higher ratio than among vaccinated children.

Clinical, Genetic, and Outcome Characteristics of Pediatric Patients with Primary Hemophagocytic Lymphohistiocytosis

Objectİive:

In this study, we sought to describe the clinical, laboratory, and genetic characteristics of patients diagnosed with primary hemophagocytic lymphohistiocytosis. Thus, we aimed to evaluate the early diagnosis and appropriate treatment options for pediatric hemophagocytic lymphohistiocytosis patients.

Materials and Methods:

Medical records of 9 patients diagnosed with primary hemophagocytic lymphohistiocytosis between November 2013 and December 2019 were analyzed retrospectively. Clinical, genetic, and laboratory characteristics, family histories, initial complaints, physical examination findings, age at diagnosis, treatment choices, and clinical follow-up of all patients were investigated.

Results:

The mean age at diagnosis was 11 months (range: 1.5 months to 17 years). Genetic analysis was performed in all patients, and a disease-related mutation was detected in 8 (89%) of them. Among clinical features, 6 (66%) patients had fever, 5 (56%) had splenomegaly, 4 (44%) had lymphadenopathy, 4 (44%) had skin rash, and 4 (44%) had neurological findings. Hemophagocytosis was observed in the bone marrow samples of 6 (66%) patients. Disease remission was achieved in 7 (78%) patients. Hematopoietic stem cell transplantation was performed in 7 (78%) patients.

Conclusion:

Hemophagocytic lymphohistiocytosis may present with different clinical symptoms that can cause a significant diagnostic delay. The only curative treatment option in primary hemophagocytic lymphohistiocytosis patients is hematopoietic stem cell transplantation. The chemotherapy should be started as early as possible, in order to achieve a disease remission. Patients should be referred to the appropriate bone marrow transplant center for hematopoietic stem cell transplantation as soon as they reach the disease remission.

SARS-CoV-2 infection in children with rheumatic disease: Experience of a tertiary referral center

Objectives

In this study, we present our clinical severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) experience in patients with childhood rheumatic disease during novel coronavirus-2019 (COVID-19) pandemic.

Patients and methods

A total of 87 patients (50 males, 37 females; median age: 12 years; range, 6.6 to 16 years) suspected of having COVID-19 at our pediatric rheumatology clinic between March 11th and October 15th 2020 were retrospectively analyzed. Demographic and clinical features, treatments, laboratory results, imaging findings, and clinical outcomes of the patients diagnosed with COVID-19 and/or multisystem inflammatory syndrome in children (MIS-C) were retrieved from the medical records. The diagnosis of SARS-CoV-2 infection was made based on the reverse transcriptase-polymerase chain reaction test.

Results

The most common rheumatic diseases were juvenile idiopathic arthritis and familial Mediterranean fever (35.6% and 34.5%, respectively). Twenty-six of these patients were treated with biological disease-modifying anti-rheumatic drugs. SARS-CoV-2 infection was tested as positive in 84 (96.5%) patients. Also, 51 (58.6%) patients had an epidemiological contact to a person with COVID-19. Eighteen patients met the clinical criteria and diagnosed with MIS-C. The COVID-19 outbreak also caused exacerbation of systemic disease in 56 children due to medication cessation, postponed drug switch, or recurrent viral infection.

Conclusion

Children with rheumatic disease do not appear to present a higher risk of severe COVID-19. The immunosuppressive treatments can be adjusted in case of infection; otherwise, it is not recommended to interrupt the treatments. Physicians should be cautious about the hyperinflammatory syndrome associated with COVID-19 in rheumatic children, which may be severe in this group of patients and may be confused with primary diseases.

Determination of Resistance Levels Against Thiamethoxam in house fly (Musca domestica L.) Populations in Antalya

OBJECTIVE

Many fly species belonging to the genus Musca (Diptera: Muscidae) play a significant role in the transmission of pathogens like bacteria, fungi, and parasites. Among the species of this genus, the house fly Musca domestica L. is well-known. This study aimed to determine the level of insecticide resistance against thiamethoxam in house fly populations collected from the Kemer, Serik, Döşemealtı, Kepez, and Konyaaltı districts of Antalya.

METHODS

Adult house flies were collected using sweep nets from livestock farms between June and November 2017. The collected flies were transported in fine muslin cages within 4-6 hours. The F3 generation of the flies was used for determining the resistance levels. In this study, at least four application doses of thiamethoxam were used for determining lethal doses (LD) and knock down times (KT). To determine KT, the flies were examined for 1 h at 5 min intervals and the affected flies were recorded. All toxicity tests were repeated thrice in the flies, including those in the control group. After 24 h, the number of dead flies was recorded and the percentage mortalities and knock down rates were compared and analyzed using the SPSS analysis program. LD₅₀ and KT₅₀ values were determined using a probit analysis program. Resistance factor was calculated by dividing the determined LD₅₀ value by the standard World Health Organization sensitive reference LD₅₀ value.

RESULTS

In this study, very high resistance levels against thiamethoxam were observed in flies sampled from all locations in Antalya.

CONCLUSION

To prevent and reduce resistance development in house flies, integrated pest control methods should be applied.

Stability of adsorption of Mg and Na on sulfur-functionalized MXenes

Two-dimensional materials composed of transition metal carbides and nitrides (MXenes) are poised to revolutionize energy conversion and storage. In this work, we used density functional theory (DFT) to investigate the adsorption of Mg and Na adatoms on five M₂CS₂ monolayers (where M = Mo, Nb, Ti, V, and Zr) for battery applications. We assessed the stability of the adatom (i.e. Na and Mg)-monolayer systems by calculating adsorption and formation energies, as well as voltages as a function of surface coverage. For instance, we found that Mo₂CS₂ cannot support a full layer of Na nor even a single Mg atom. Na and Mg exhibit the strongest binding on Zr₂CS₂, followed by Ti₂CS₂, Nb₂CS₂ and V₂CS₂. Using the nudged elastic band method (NEB), we computed promising diffusion barriers for both dilute and nearly full ion surface coverage cases. In the dilute ion adsorption case, a single Mg and Na atom on Ti₂CS₂ experience ∼0.47 eV and ∼0.10 eV diffusion barriers between the lowest energy sites, respectively. For a nearly full surface coverage, a Na ion moving on Ti₂CS₂ experiences a ∼0.33 eV energy barrier, implying a concentration-dependent diffusion barrier. Our molecular dynamics results indicate that the three (one) layers (layer) of the Mg (Na) ion on both surfaces of Ti₂CS₂ remain stable at T = 300 K. While, according to voltage calculations, Zr₂CS₂ can store Na up to three atomic layers, our MD simulations predict that the outermost layers detach from the Zr₂CS₂ monolayer due to the weak interaction between Na ions and the monolayer. This suggests that MD simulations are essential to confirm the stability of an ion-electrode system - an insight that is mostly absent in previous studies.

SARS-CoV-2 seropositivity among pediatric health care personnel after the first peak of the pandemic: nationwide surveillance in Turkey

Background

Understanding SARS-CoV-2 seroprevalence among health care personnel is important to explore risk factors for transmission, develop elimination strategies and form a view on the necessity and frequency of surveillance in the future.

Methods

We enrolled 4927 health care personnel working in pediatric units at 32 hospitals from 7 different regions of Turkey in a study to determine SARS Co-V-2 seroprevalence after the first peak of the COVID-19 pandemic. A point of care serologic lateral flow rapid test kit for immunoglobulin (Ig)M/IgG was used. Seroprevalence and its association with demographic characteristics and possible risk factors were analyzed.

Results

SARS-CoV-2 seropositivity prevalence in health care personnel tested was 6.1%. Seropositivity was more common among those who did not universally wear protective masks (10.6% vs 6.1%). Having a COVID-19-positive co-worker increased the likelihood of infection. The least and the most experienced personnel were more likely to be infected. Most of the seropositive health care personnel (68.0%) did not suspect that they had previously had COVID-19.

Conclusions

Health surveillance for health care personnel involving routine point-of-care nucleic acid testing and monitoring personal protective equipment adherence are suggested as important strategies to protect health care personnel from COVID-19 and reduce nosocomial SARS-CoV-2 transmission.

Comprehensive Study of Lithium Adsorption and Diffusion on Janus Mo/WXY (X, Y = S, Se, Te) Using First-Principles and Machine Learning Approaches

The structural asymmetry of two-dimensional (2D) Janus transition-metal dichalcogenides (TMDs) produces internal dipole moments that result in interesting electronic properties. These properties differ from the regular (symmetric) TMD structures that the Janus structures are derived from. In this study, we, first, examine adsorption and diffusion of a single Li atom on regular MX₂ and Janus MXY (M = Mo, W; XY = S, Se, Te) TMD structures at various concentrations using first-principles calculations within density functional theory. Lithium adsorption energy and mobility differ on the top and bottom sides of each Janus material. The correlation between Li adsorption energy, charge transfer, and bond lengths at different coverage densities is carefully examined. To gain more physical insight and prepare for future investigations into regular TMD and Janus materials, we applied a supervised machine learning (ML) model that uses clusterwise linear regression to predict the adsorption energies of Li on top of 2D TMDs. We developed a universal representation with a few descriptors that take into account the intrinsic dipole moment and the electronic structure of regular and Janus 2D layers, the side where the adsorption takes place, and the concentration dependence of adatom doping. This representation can easily be generalized to be used for other impurities and 2D layer combinations, including alloys as well. At last, we focus on analyzing these structures as possible anodes in battery applications. We conducted Li diffusion, open-circuit voltage, and storage capacity simulations. We report that lithium atoms are found to easily migrate between transition-metal (Mo, W) top sites for each considered case, and in these respects, many of the examined Janus materials are comparable or superior to graphene and regular TMDs. In addition, we report that the side with higher electronegative chalcogen atoms is suitable for Li adsorption and only MoSSe and MoSeTe can be suitable for full coverage of Li atoms on the surface. Bilayer Li adsorption was hindered due to negative open-circuit voltage. Bilayer Janus structures are better suited for battery applications due to less volumetric expansion/contraction during the discharge/charge process and having higher storage capacity. Janus monolayers undergo a transition from semiconducting to metallic upon adsorption of a single Li ion, which would improve anode conductivity. The results imply that the examined Janus structures should perform well as electrodes in Li-ion batteries.

First-principles discovery of stable two-dimensional materials with high-level piezoelectric response

The rational design of two-dimensional (2D) piezoelectric materials has recently garnered great interest due to their increasing use in technological applications, including sensor technology, actuating devices, energy harvesting, and medical applications. Several materials possessing high piezoelectric response have been reported so far, but a high-throughput first-principles approach to estimate the piezoelectric potential of layered materials has not been performed yet. In this study, we systematically investigated the piezoelectric (e11,d11) and elastic (C11and C12) properties of 128 thermodynamically stable 2D semiconductor materials by employing first-principle methods. Our high-throughput approach demonstrates that the materials containing Group-V elements produce significantly high piezoelectric strain constants,d11> 40 pm V-1, and 49 of the materials considered have thee11coefficient higher than MoS2insomuch as BrSSb has one of the largestd11with a value of 373.0 pm V-1. Moreover, we established a simple empirical model in order to estimate thed11coefficients by utilizing the relative ionic motion in the unit cell and the polarizability of the individual elements in the compounds.

Testicular dysgenesis syndrome and phthalate exposure: A review of literature

Endocrine disruptors are chemicals that interfere with the body's endocrine system and cause adverse effects in biological systems. Phthalates are a group of man-made chemicals which are mainly used as plasticizers and classified as endocrine disruptors. They are also used in cosmetic and personal care products as color or smell fixators. Moreover, phthalates are present in inks, adhesives, sealants, automobile parts, tools, toys, carpets, medical tubing and blood storage bags, and food packages. Pathological condition known as "testicular dysgenesis syndrome" (TDS) or "phthalate syndrome" is usually linked to phthalate exposure and is coined to describe the rise in alterations in reproductive health in men, such as reduced semen quality (decrease in sperm counts, sperm motility and increase in abnormal sperms), hypospadias, cryptorchidism, reduced anogenital distance and early-life testicular cancer. Phthalates are suggested to cause direct effect on gonadal and non-gonadal tissues, impair the differentiation and morphogenesis of seminiferous tubules and accessory sex organs and testicular cells (both Sertoli and Leydig cells), alter estradiol and/or testosterone levels, decrease insulin-like 3 (INSL3) peptide production, impair spermatogenesis and lead to epigenetic alterations, all of which may lead to TDS. This review will mainly focus on phthalates as causes of TDS and their mechanisms of action.

Education of Healthcare Personnel Working with Pediatric Patients During COVID-19 Pandemic within the Framework of Infection Control

Objective: In the early stages of any epidemic caused by new emerging pathogens healthcare personnel is subject to a great risk. Pandemic caused by SARS-CoV-2, proved to be no exception. Many healthcare workers died in the early stages of pandemic due to inadequate precautions and insufficient protection. It is essential to protect and maintain the safety of healthcare personnel for the confinement of pandemic as well as continuity of qualified healthcare services which is already under strain. Educating healthcare personnel on appropiate use of personal protective equipment (PPE) is as essential as procuring them. Material and Methods: A survey is conducted on 4927 healthcare personnel working solely with pediatric patients from 32 different centers. Education given on PPE usage were questioned and analyzed depending on age, sex, occupation and region. Results: Among four thousand nine hundred twelve healthcare personnel from 32 different centers 91% (n= 4457) received education on PPE usage. Of those who received education only 36% was given both theoretical and applied education. Although there was no differences among different occupation groups, receiving education depended on regions. Conclusion: It is essential to educate healthcare personnel appropiately nationwidely for the continuity of qualified healthcare services during the pandemic.

COVID-19 Pandemisinde Enfeksiyon Kontrol Çalışmaları Çerçevesinde Çocuk Hastalarla Çalışan Sağlık Personeli Eğitimi

Objective: In the early stages of any epidemic caused by new emerging pathogens healthcare personnel is subject to a great risk. Pandemic caused by SARS-CoV-2, proved to be no exception. Many healthcare workers died in the early stages of pandemic due to inadequate precautions and insufficient protection. It is essential to protect and maintain the safety of healthcare personnel for the confinement of pandemic as well as continuity of qualified healthcare services which is already under strain. Educating healthcare personnel on appropiate use of personal protective equipment (PPE) is as essential as procuring them. Material and Methods: A survey is conducted on 4927 healthcare personnel working solely with pediatric patients from 32 different centers. Education given on PPE usage were questioned and analyzed depending on age, sex, occupation and region. Results: Among four thousand nine hundred twelve healthcare personnel from 32 different centers 91% (n= 4457) received education on PPE usage. Of those who received education only 36% was given both theoretical and applied education. Although there was no differences among different occupation groups, receiving education depended on regions. Conclusion: It is essential to educate healthcare personnel appropiately nationwidely for the continuity of qualified healthcare services during the pandemic.

Engineering magnetic anisotropy and exchange couplings in double transition metal MXenes via surface defects

Two-dimensional (2D) materials have been experimentally proven to manifest almost all types of material properties observed in bulk materials. However, 2D magnetism was elusive until recently. In this work, we used an approach that synergistically uses density functional theory, and Monte Carlo methods to investigate the magnetic and electronic properties of magnetic double transition metal MXene alloys (Hf₂MnC₂O₂and Hf₂VC₂O₂) by exploiting realistic surface terminations via creating surface defects including oxygen vacancies and H adatoms. We found that introducing surface oxygen vacancies or hydrogen adatoms is able to modify the electronic structures, magnetic anisotropies, and exchange couplings. Depending on the defect concentration, a ferromagnetic half-metallic state can be realized for both Hf₂VC₂O₂and Hf₂MnC₂O₂. Bare Hf₂VC₂O₂exhibits easy-axis anisotropy, whereas bare Hf₂MnC₂O₂exhibits easy-plane anisotropy; however, defects can change the latter to easy-axis anisotropy, which is preferable for spintronics applications. The considered defects were found to modify the magnetic anisotropy by as much as 300%. Defects also produce an inhomogeneous pattern of exchange couplings, which can further enhance the Curie temperature. In particular, Hf₂MnC₂O₂H_0.22was predicted to have a Curie temperature of about 171 K due to a combination of easy-axis anisotropy and a connected network of enhanced exchange couplings. Our calculations suggest a route toward engineering exchange couplings and magnetic anisotropy to improve magnetic properties.

Revealing the Formation Energy-Exfoliation Energy-Structure Correlation of MAB Phases Using Machine Learning and DFT

MAB phases became popular as ultrahigh-temperature materials with high damage tolerance and excellent electrical conductivity. MAB is used to exfoliate two-dimensional (2D) transition-metal borides (MBenes), which are promising materials for developing next-generation nanodevices. In this report, we explore the correlation between the formation energy, exfoliation energy, and structural factors of MAB phases with orthorhombic and hexagonal crystal symmetries using density functional theory (DFT) and machine learning. For this, we developed three different machine learning models based on the support vector machine, deep neural network, and random forest regressor to study the stability of the MAB phases by calculating their formation energies. Our support vector machine and deep neural network models are capable of predicting the formation energies with mean absolute errors less than 0.1 eV/atom. MAB phases with the chemical formulas, MAB, M₂AB₂, and M₃AB₄, where M = Nb, Mn, Ti, W, V, Sc, Cr, Hf, Mo, Zr, Ta, and Fe, and A = group III-A elements (Al, Ga, In and Tl), were investigated to find out the formation energy and their structure correlation. We demonstrated that the stability of a MAB phase for a given transition-metal decreases when the A element changes from Al to Tl. DFT revealed that M-A and B-A bond strength strongly correlates with the stability of MAB phases. In addition, the exfoliation possibility of 2D MBenes becomes higher when the A element changes from Al to Tl because of weakening of M-A and B-A bonds.

Hemophagocytic Lymphohistiocytosis Related to Tuberculosis Disease

Hemophagocytic lymphohistiocytosis (HLH) is a rare, albeit potentially fatal, condition in which fever, hepatosplenomegaly, and cytopenia predominate the clinical picture. Although it may be primary, it may also develop secondary to various etiologies. Herein, we aimed to report a patient who was diagnosed with pulmonary tuberculosis, developed fever and cytopenia during follow-up, and received immunomodulatory therapy together with antituberculosis therapy for the diagnosis of HLH. Sequencing of PRF1 showed heterozygous mutation. Although primary HLH has been detected in infants and children, genetic mutation of genes should be considered a differential diagnosis of HLH even in the adolescent.

How to cite this article

Erdoğan S, Çakır D, Bozkurt T, Karakayalı B, Kalın S, Koç B, et al. Hemophagocytic Lymphohistiocytosis Related to Tuberculosis Disease. Indian J Crit Care Med 2020;24(1):63-65.

The Effect of Flexible Lightwand and Ultrasonography Combination on Complications of the Percutaneous Dilatational Tracheostomy Procedure

The aim of this study was to evaluate the effect of the flexible lightwand and ultrasonography (USG) combination on reducing the complications in percutaneous dilatational tracheostomy (PDT) opened with the forceps dilatation method. A retrospective examination was made of 138 patients between January 2014 and December 2018. Before starting to process, the anatomic structures of the patients were visualized with USG and the tracheostomy area was marked. Sedation and local anesthesia were applied to patients before the procedure, then the percutaneous tracheostomy was performed using the Griggs technique after confirmation of the tracheostomy localization defined with USG using the transillumination method with a flexible lightwand within an endotracheal tube. Complications that developed associated with the procedure were recorded. The mean age of the patients was 59.1±22.0 years and the mean length of stay in the intensive care unit was 42.3±35.5 days (range, 11-207 days). Overall, complications developed in 22 (15.6%) patients, of which 10.7% were early complications (1.4% related to the tube, 5.8% minor and 3.5% major complications). Tube- related complications were seen to develop in two patients. In the evaluation of the early minor complications, the most frequently seen complication was minor bleeding in 5.8% of the patients. No major vessel bleeding was determined in any patient in the early or late period. Of the late complications, the infection was seen to develop in four (2.8%) patients and stenosis in three (2.1%). The combination of flexible lightwand and USG in the PDT procedure minimized tube-related complications and contributed to the prevention of bleeding complications.

Alkali Metal Intercalation in MXene/Graphene Heterostructures: A New Platform for Ion Battery Applications

The adsorption and diffusion of Na, K, and Ca atoms on MXene/graphene heterostructures of MXene systems Sc₂C(OH)₂, Ti₂CO₂, and V₂CO₂ are systematically investigated by using first-principles methods. We found that alkali metal intercalation is energetically favorable and thermally stable for Ti₂CO₂/graphene and V₂CO₂/graphene heterostructures but not for Sc₂C(OH)₂. Diffusion kinetics calculations showed the advantage of MXene/graphene heterostructures over sole MXene systems as the energy barriers are halved for the considered alkali metals. Low energy barriers are found for Na and K ions, which are promising for fast charge/discharge rates. Calculated voltage profiles reveal that estimated high capacities can be fully achieved for Na ion in V₂CO₂/graphene and Ti₂CO₂/graphene heterostructures. Our results indicate that Ti₂CO₂/graphene and V₂CO₂/graphene electrode materials are very promising for Na ion battery applications. The former could be exploited for low voltage applications while the latter will be more appropriate for higher voltages.

Determination of Dynamically Stable Electrenes toward Ultrafast Charging Battery Applications

Electrenes, an atomically thin form of layered electrides, are very recent members of the 2D materials family. In this work, we employed first-principle calculations to determine stable, exfoliatable, and application-promising 2D electrene materials among possible M₂X compounds, where M is a group II-A metal and X is a nonmetal element (C, N, P, As, and Sb). The promise of stable electrene compounds for battery applications is assessed via their exfoliation energy, adsorption properties, and migration energy barriers toward relevant Li, Na, K, and Ca atoms. Our calculations revealed five new stable electrene candidates in addition to previously known Ca₂N and Sr₂N. Among these seven dynamically stable electrenes, Ba₂As, Ba₂P, Ba₂Sb, Ca₂N, Sr₂N, and Sr₂P are found to be very promising for either K or Na ion batteries due to their extremely low migration energy barriers (5-16 meV), which roughly demonstrates 105 times higher mobility than graphene and two to four times higher mobility than other promising 2D materials such as MXene (Mo₂C).

In pursuit of barrierless transition metal dichalcogenides lateral heterojunctions

There is an increasing need to understand interfaces between two-dimensional materials to realize an energy efficient boundary with low contact resistance and small heat dissipation. In this respect, we investigated the impact of charge and substitutional atom doping on the electronic transport properties of the hybrid metallic-semiconducting lateral junctions, formed between metallic (1T and 1T _d ) and semiconducting (1H) phases of MoS₂ by means of first-principles and non-equilibrium Green function formalism based calculations. Our results clearly revealed the strong influence of the type of interface and crystallographic orientation of the metallic phase on the transport properties of these systems. The Schottky barrier height, which is the dominant mechanism for contact resistance, was found to be as large as 0.63 eV and 1.19 eV for holes and electrons, respectively. We found that armchair interfaces are more conductive as compared to zigzag termination due to the presence of the metallic Mo zigzag chains that are directed along the transport direction. In order to manipulate these barrier heights we investigated the influence of electron doping of the metallic part (i.e. 1T _d -MoS₂). We observed that the Fermi level of the hybrid system moves towards the conduction band of semiconducting 1H-MoS₂ due to filling of 4d-orbital of metallic MoS₂, and thus the Schottky barrier for electrons decreases considerably. Besides electron doping, we also investigated the effect of substitutional doping of metallic MoS₂ by replacing Mo atoms with either Re or Ta. Due to its valency, Re (Ta) behaves as a donor (acceptor) and reduces the Schottky barrier for electrons (holes). Since Re and Ta based transition metal dichalcogenides crystallize in either the 1T _d or 1T phase, substitutional doping with these atom favors the stabilization of the 1T _d phase of MoS₂. Co-doping of hybrid structure results in an electronic structure, which facilities easy dissociation of excitons created in the 1H part.

The influence of surface functionalization on thermal transport and thermoelectric properties of MXene monolayers

The newest members of a two-dimensional material family, involving transition metal carbides and nitrides (called MXenes), have garnered increasing attention due to their tunable electronic and thermal properties depending on the chemical composition and functionalization. This flexibility can be exploited to fabricate efficient electrochemical energy storage (batteries) and energy conversion (thermoelectric) devices. In this study, we calculated the Seebeck coefficients and lattice thermal conductivity values of oxygen terminated M2CO2 (where M = Ti, Zr, Hf, Sc) monolayer MXene crystals in two different functionalization configurations (model-II (MD-II) and model-III (MD-III)), using density functional theory and Boltzmann transport theory. We estimated the thermoelectric figure-of-merit, zT, of these materials by two different approaches, as well. First of all, we found that the structural model (i.e. adsorption site of oxygen atom on the surface of MXene) has a paramount impact on the electronic and thermoelectric properties of MXene crystals, which can be exploited to engineer the thermoelectric properties of these materials. The lattice thermal conductivity κl, Seebeck coefficient and zT values may vary by 40% depending on the structural model. The MD-III configuration always has the larger band gap, Seebeck coefficient and zT, and smaller κl as compared to the MD-II structure due to a larger band gap, highly flat valence band and reduced crystal symmetry in the former. The MD-III configuration of Ti2CO2 and Zr2CO2 has the lowest κl as compared to the same configuration of Hf2CO2 and Sc2CO2. Among all the considered structures, the MD-II configuration of Hf2CO2 has the highest κl, and Ti2CO2 and Zr2CO2 in the MD-III configuration have the lowest κl. For instance, while the band gap of the MD-II configuration of Ti2CO2 is 0.26 eV, it becomes 0.69 eV in MD-III. The zTmax value may reach up to 1.1 depending on the structural model of MXene.

A distinct correlation between the vibrational and thermal transport properties of group VA monolayer crystals

The investigation of thermal transport properties of novel two-dimensional materials is crucially important in order to assess their potential to be used in future technological applications, such as thermoelectric power generation. In this respect, the lattice thermal transport properties of the monolayer structures of group VA elements (P, As, Sb, Bi, PAs, PSb, PBi, AsSb, AsBi, SbBi, P3As1, P3Sb1, P1As3, and As3Sb1) with a black phosphorus like puckered structure were systematically investigated by first-principles calculations and an iterative solution of the phonon Boltzmann transport equation. Phosphorene was found to have the highest lattice thermal conductivity, κ, due to its low average atomic mass and strong interatomic bonding character. As a matter of course, anisotropic κ was obtained for all the considered materials, owing to anisotropy in frequency values and phonon group velocities calculated for these structures. However, the determined linear correlation between the anisotropy in the κ values of P, As, and Sb is significant. The results corresponding to the studied compound structures clearly point out that thermal (electronic) conductivity of pristine monolayers might be suppressed (improved) by alloying them with the same group elements. For instance, the room temperature κ of PBi along the armchair direction was predicted to be as low as 1.5 W m-1 K-1, whereas that of P was predicted to be 21 W m-1 K-1. In spite of the apparent differences in structural and vibrational properties, we peculiarly revealed an intriguing correlation between the κ values of all the considered materials as κ = c1 + c2/m2, in particular along the zigzag direction. Furthermore, our calculations on compound structures clearly showed that the thermoelectric potential of these materials can be improved by suppressing their thermal properties. The presence of ultra-low κ values and high electrical conductivity (especially along the armchair direction) makes this class of monolayers promising candidates for thermoelectric applications.

Strain enhancement of acoustic phonon limited mobility in monolayer TiS3

Strain engineering is an effective way to tune the intrinsic properties of a material.

Realization of a p-n junction in a single layer boron-phosphide

Two-dimensional (2D) materials have attracted growing interest due to their potential use in the next generation of nanoelectronic and optoelectronic applications. On the basis of first-principles calculations based on density functional theory, we first investigate the electronic and mechanical properties of single layer boron phosphide (h-BP). Our calculations show that h-BP is a mechanically stable 2D material with a direct band gap of 0.9 eV at the K-point, promising for both electronic and optoelectronic applications. We next investigate the electron transport properties of a p-n junction constructed from single layer boron phosphide (h-BP) using the non-equilibrium Green's function formalism. The n- and p-type doping of BP are achieved by substitutional doping of B with C and P with Si, respectively. C(Si) substitutional doping creates donor (acceptor) states close to the conduction (valence) band edge of BP, which are essential to construct an efficient p-n junction. By modifying the structure and doping concentration, it is possible to tune the electronic and transport properties of the p-n junction which exhibits not only diode characteristics with a large current rectification but also negative differential resistance (NDR). The degree of NDR can be easily tuned via device engineering.

Fluorographane: a promising material for bipolar doping of MoS2

Using first principles calculations we show that one can realize vanishing n-type/p-type Schottky barrier heights when contacting MoS₂ to fluorographane.

Angle-resolved synchrotron photoemission and density functional theory on the iridium modified Si(1 1 1) surface

The physical and electronic properties of the Ir modified Si(1 1 1) surface have been investigated with the help of angle resolved photoemission spectroscopy and density functional theory. The surface consists of Ir-ring clusters that form a [Formula: see text]reconstruction. A comparison between the measured and calculated band structure of the system reveals that the dispersions of the projected bulk states and the states originating from [Formula: see text] domains are heavily modified due to Umklapp scattering from the surface Brillouin zone. Density of states calculations show that Ir-ring clusters contribute to the states in the vicinity of the Fermi level.

Doping of rhenium disulfide monolayers: a systematic first principles study

The absence of a direct-to-indirect band gap transition in ReS₂ when going from the monolayer to bulk makes it special among the other semiconducting transition metal dichalcogenides.