Structural and electrical characterization of doped graphene and carbon nanotube networks

Graphene, a two-dimensional sp2-hybridized network of carbon atoms has received a remarkable cornucopia of new physics and served as a unique model system, due particularly to its electronic properties, which could have interesting applications in electronic, spintronic or quantum devices. The first part of the thesis describes the modulation of graphene¿s structural and electrical properties with various kinds of doping; such as deep ultraviolet irradiation in ambient atmosphere, deep ultraviolet light irradiation in different gaseous environments, and electron beam irradiation. We have fabricated graphene (exfoliated and chemical vapor deposition grown graphene) field effect transistors using photolithography and electron beam lithography and characterized with AFM, Raman spectroscopy and transport measurement using low noise standard lock-in amplifier technique. We have explored how the ultraviolet light exposure tunes the electrical properties of graphene in an ambient atmosphere, confirmed by the shift of Dirac point position towards positive gate voltage, revealing p-type doping for graphene without degradation of mobility. We found that the doping is stable for a time scale of months. This method became more useful when half the graphene device was exposed by ultraviolet light, while the other half part was covered by a mask to make a sharp p-n junction. The doping effect became more prominent and controllable when it was made in an oxygen environment. The most interesting phenomena were observed when doped graphene was restored to a pristine state using ultraviolet light irradiation in a nitrogen environment. Furthermore, we have investigated the doping tunability with ultraviolet light irradiation on mechanically exfoliated single-, bi-, and trilayer graphenes without significantly degrading its charge carrier mobility. In a further study, the structural deformation of graphene was investigated by irradiation of an electron beam. The graphene structure changes its phase in various stages, where graphene transforms gradually from a crystalline to a nanocrystalline form and after a certain irradiation time into an amorphous form. This irradiation effect acts as an n-type dopant for graphene. In this case, mobility decreases with the gradual increase of irradiation dose, which implies the formation of localized states. The second part of the thesis describes carbon nanotube networks as flexible and transparent electrodes for electronic devices, particularly for high frequency applications. The observed results show that at low frequencies, the impedance increases as the density of nanotube networks decreases, as expected. Both the real and imaginary parts of impedance (measured up to 20 GHz) abruptly decrease as the frequency increases over the cut-off frequency. The cut-off frequency not only depends on the carbon nanotube density of the network, but also on the sample geometry. The Nyquist diagram suggests a simple equivalent circuit composed of a parallel combination of a resistor and a capacitor. The experimental results are in line with calculations made by electrochemical spectroscopy simulations. The results show that the electrical behavior is mostly determined by the contact resistance between the nanotubes, which are in a completely disordered distribution in the network. We show that carbon nanotube flexible conducting films, which may be transparent, could be competitive for some applications, such as displays, photovoltaic solar cells or selective sensors.El grafè, considerat com una xarxa bidimensional d’àtoms de carboni units per enllaços híbrids sp2, és un tema de recerca molt prolífer en els últims anys, com a model de sòlid bidimensional, i molt particularment degut a les seves propietats electròniques, que poden tenir aplicacions interessants en dispositius electrònics, spintrònics o quàntics. La primera part de la Tesi descriu la modificació de les propietats estructurals i elèctriques del grafè utilitzant diferents mètodes per a dopar-lo: radiació ultraviolada d’alta energia (DUV) en atmosfera ambient, DUV en diferents gasos tals com oxigen o nitrogen, o irradiant amb un feix d’electrons (e-beam). Hem fabricat transistors d’efecte de camp (FET) amb grafè (exfoliat a partir del grafit, o bé obtingut per deposició química en fase vapor, CVD) utilitzant fotolitografia i e-beam litografia, i els hem caracteritzat mitjançant AFM, espectroscòpia Raman i mesures de transport elèctric, per a les que hem utilitzat la tècnica d’amplificació de baix soroll, el lock-in. Hem investigat com l’exposició a la llum ultraviolada en atmosfera ambient, modula les propietats elèctriques del grafè, de manera que la posició del punt de Dirac es desplaça cap a tensions de porta positives, cosa que implica dopatge de tipus-p, sense que hi hagi degradació de la mobilitat. El dopatge és estable al menys durant mesos. Amb el mateix mètode, quan només la meitat del dispositiu és exposat a la radiació ultraviolada mentre l’altre meitat és recobert per una màscara metàl·lica, hem obtingut una unió p-n. L’efecte de dopatge és més important i controlable, quan és fet en atmosfera d’oxigen. L’efecte més interessant que hem observat és la reversibilitat, quan el grafè dopat retorna al seu estat primitiu, en ser irradiat amb llum ultraviolada en atmosfera de nitrogen. També hem investigat el dopatge amb llum ultraviolada del grafè exfoliat mecànicament, de una, dues o tres capes, observant que es produeix sense una degradació significativa de la mobilitat dels portadors de càrrega. Posteriorment hem estudiat la deformació estructural del grafè quan és irradiat amb un feix d’electrons. Hem observat canvis estructurals en diferents etapes: el grafè evoluciona gradualment, a partir de la forma cristal·lina, cap a una fase d’estructura nanocristal·lina i finalment, després d’una certa dosi de irradiació, presenta una estructura amorfa. L’efecte d’ irradiar el grafè amb electrons actua com a dopant tipus-n, però en aquest cas la mobilitat decreix en incrementar la dosi, això implica que hi ha formació d’estats localitzats. La segona part de la Tesi tracta de capes primes de nanotubs de carboni, com a elèctrodes flexibles i transparents per a dispositius electrònics, en particular per aplicacions d’alta freqüència. Els resultats obtinguts mostren que, a baixes freqüències, la impedància augmenta en disminuir la densitat de nanotubs, tal com cal esperar. Tan la part real com la part imaginària de la impedància (mesurada fins a 20 GHz) decreixen abruptament en augmentar la freqüència més enllà de la freqüència de tall. La freqüència de tall no depèn únicament de la densitat de nanotubs en la capa, sinó també de la geometria de la mostra. El diagrama de Nyquist es pot interpretar amb un circuit equivalent consistent simplement en una resistència i un condensador en paral·lel. Els resultats experimentals s’ajusten bé a les simulacions fetes per espectroscòpia d’impedàncies (EIS). Els resultats posen en evidència que el comportament elèctric queda majoritàriament determinat per la resistència de contacte entre els nanotubs, que formen la xarxa amb una distribució totalment desordenada. Hem vist que capes primes de nanotubs de carboni conductores i flexibles, que poden ser també transparents, poden ser competitives en diferents aplicacions, com ara pantalles, cel·les solars fotovoltaiques o sensors selectiu

Synergistic effects of a copper–cobalt–nitroisophthalic acid/neodymium oxide composite on the electrochemical performance of hybrid supercapacitors

Hybrid supercapacitors can produce extraordinary advances in specific power and energy to display better electrochemical performance and better cyclic stability. Amalgamating metal oxides with metal–organic frameworks endows the prepared composites with unique properties and advantageous possibilities for enhancing the electrochemical capabilities. The present study focused on the synergistic effects of the CuCo(5-NIPA)–Nd2O3 composite. Employing a half-cell configuration, we conducted a comprehensive electrochemical analysis of CuCo(5-NIPA), Nd2O3, and their composite. Owing to the best performance of the composite, the hybrid device prepared from CuCo(5-NIPA)–Nd2O3 and activated carbon demonstrated a specific capacity of 467.5 C g−1 at a scan rate of 3 mV s−1, as well as a phenomenal energy and power density of 109.68 W h kg−1 and 4507 W kg−1, respectively. Afterwards, semi-empirical techniques and models were used to investigate the capacitive and diffusive mechanisms, providing important insights into the unique properties of battery–supercapacitor hybrids. These findings highlight the enhanced performance of the CuCo(5-NIPA)–Nd2O3 composite, establishing it as a unique and intriguing candidate for applications requiring the merging of battery and supercapacitor technologies

Flexible, transparent electrodes using carbon nanotubes

We prepare thin single-walled carbon nanotube networks on a transparent and flexible substrate with different densities, using a very simple spray method. We measure the electric impedance at different frequencies Z(f) in the frequency range of 40 Hz to 20 GHz using two different methods: a two-probe method in the range up to 110 MHz and a coaxial (Corbino) method in the range of 10 MHz to 20 GHz. We measure the optical absorption and electrical conductivity in order to optimize the conditions for obtaining optimum performance films with both high electrical conductivity and transparency. We observe a square resistance of 1 to 8.5 k[greek capital letter omega] for samples showing 65% to 85% optical transmittance, respectively. For some applications, we need flexibility and not transparency: for this purpose, we deposit a thick film of single-walled carbon nanotubes on a flexible silicone substrate by spray method from an aqueous suspension of carbon nanotubes in a surfactant (sodium dodecyl sulphate), thereby obtaining a flexible conducting electrode showing an electrical resistance as low as 200 [greek capital letter omega]/sq. When stretching up to 10% and 20%, the electrical resistance increases slightly, recovering the initial value for small elongations up to 10%. We analyze the stretched and unstretched samples by Raman spectroscopy and observe that the breathing mode on the Raman spectra is highly sensitive to stretching. The high-energy Raman modes do not change, which indicates that no defects are introduced when stretching. Using this method, flexible conducting films that may be transparent are obtained just by employing a very simple spray method and can be deposited on any type or shape of surface.Postprint (published version

Association of high immunohistochemical expression of minichromosome maintenance 3 with human oral squamous cell carcinoma—a preliminary study

Background: Oral squamous cell carcinoma (OSCC) may arise from premalignant oral lesions (PMOL) in most cases. Minichromosome maintenance 3 (MCM3) is a proliferative marker that has been investigated as a potential diagnostic biomarker in the diagnosis of oral cancer. Objectives: To evaluate the association of MCM3 expression, its clinicopathologic parameters and to identify snuff (also called naswar) as a potential risk factor for changes in MCM3 expression in PMOL and OSCC. Methodology: Immunohistochemistry (IHC) of MCM3 was performed on 32 PMOL, 32 OSCC and 16 normal controls after optimization of IHC methodology. Histoscore (0–300) was used as a scoring system and seven different cut-offs were identified for analyses. Data were analyzed using various statistical tests. Results: Among the seven cutoffs, 40% strong positive cells were found to be a better cut-off as they were associated with many pathological variables (Broder’s grade, Aneroth’s grade, and mitotic activity). The differential MCM3 expression in oral lesions (PMOL and OSCC) was statistically significant (p = 0.03). Moreover, MCM3 expression is raised with increased duration and frequency of snuff use. Conclusion: High MCM3 expression is associated with disease progression and is a potential indicator of malignant transformations from PMOL to OSCC. Moreover, the use of snuff is associated with MCM3 over-expression

Iron, copper and silver nanoparticles: green synthesis using green and black tea leaves extracts and evaluation of antibacterial, antifungal and aflatoxin B1 adsorption activity

peer-reviewedThe present study was aimed to account an eco-friendly synthesis of iron (Fe), copper (Cu) and silver (Ag) nanoparticles (NPs) using green tea and black tea leaves extracts. Synthesized NPs were characterized using SEM, FTIR, EDX and UV/Vis spectroscopy techniques. Antibacterial activity of NPs was assessed against methicillin- and vancomycin-resistance Staphylococcus aureus strains. Antifungal activity was investigated against Aspergillus flavus and A. parasiticus fungal species. Adsorbent capability with aflatoxin B1 (AFB1) was also assessed in solution. Ag-NPs showed superior antibacterial/antifungal activities and reduced the aflatoxins production in comparison to Fe-NPs and Cu-NPs. Adsorption capability of all NPs with AFB1 contamination was found in the order of Fe-NPs > Cu-NPs > Ag-NPs. The equilibrium data showed the favorability of Langmuir isotherm with the adsorption capacity (131–139 ng/mg), Cu-NPs (114–118 ng/mg) and Ag-NPs (110–115 ng/mg). Thermodynamic parameters and kinetic studies revealed that adsorption process is spontaneous, endothermic and followed the pseudo-second order. These results suggest that the synthesized NPs could be effectively utilize as an alternative antibacterial/antifungal agent against diseases caused by multiple drug resistant pathogens. In addition, these metal NPs may be utilize as a possible aflatoxins adsorbent in human food and animal feed such as rice, wheat, maize, red chillies and poultry feed

The global burden of cancer attributable to risk factors, 2010-19 : a systematic analysis for the Global Burden of Disease Study 2019

Background Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. Methods The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk-outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. Findings Globally, in 2019, the risk factors included in this analysis accounted for 4.45 million (95% uncertainty interval 4.01-4.94) deaths and 105 million (95.0-116) DALYs for both sexes combined, representing 44.4% (41.3-48.4) of all cancer deaths and 42.0% (39.1-45.6) of all DALYs. There were 2.88 million (2.60-3.18) risk-attributable cancer deaths in males (50.6% [47.8-54.1] of all male cancer deaths) and 1.58 million (1.36-1.84) risk-attributable cancer deaths in females (36.3% [32.5-41.3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20.4% (12.6-28.4) and DALYs by 16.8% (8.8-25.0), with the greatest percentage increase in metabolic risks (34.7% [27.9-42.8] and 33.3% [25.8-42.0]). Interpretation The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.Peer reviewe

The global burden of adolescent and young adult cancer in 2019 : a systematic analysis for the Global Burden of Disease Study 2019

Background In estimating the global burden of cancer, adolescents and young adults with cancer are often overlooked, despite being a distinct subgroup with unique epidemiology, clinical care needs, and societal impact. Comprehensive estimates of the global cancer burden in adolescents and young adults (aged 15-39 years) are lacking. To address this gap, we analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019, with a focus on the outcome of disability-adjusted life-years (DALYs), to inform global cancer control measures in adolescents and young adults. Methods Using the GBD 2019 methodology, international mortality data were collected from vital registration systems, verbal autopsies, and population-based cancer registry inputs modelled with mortality-to-incidence ratios (MIRs). Incidence was computed with mortality estimates and corresponding MIRs. Prevalence estimates were calculated using modelled survival and multiplied by disability weights to obtain years lived with disability (YLDs). Years of life lost (YLLs) were calculated as age-specific cancer deaths multiplied by the standard life expectancy at the age of death. The main outcome was DALYs (the sum of YLLs and YLDs). Estimates were presented globally and by Socio-demographic Index (SDI) quintiles (countries ranked and divided into five equal SDI groups), and all estimates were presented with corresponding 95% uncertainty intervals (UIs). For this analysis, we used the age range of 15-39 years to define adolescents and young adults. Findings There were 1.19 million (95% UI 1.11-1.28) incident cancer cases and 396 000 (370 000-425 000) deaths due to cancer among people aged 15-39 years worldwide in 2019. The highest age-standardised incidence rates occurred in high SDI (59.6 [54.5-65.7] per 100 000 person-years) and high-middle SDI countries (53.2 [48.8-57.9] per 100 000 person-years), while the highest age-standardised mortality rates were in low-middle SDI (14.2 [12.9-15.6] per 100 000 person-years) and middle SDI (13.6 [12.6-14.8] per 100 000 person-years) countries. In 2019, adolescent and young adult cancers contributed 23.5 million (21.9-25.2) DALYs to the global burden of disease, of which 2.7% (1.9-3.6) came from YLDs and 97.3% (96.4-98.1) from YLLs. Cancer was the fourth leading cause of death and tenth leading cause of DALYs in adolescents and young adults globally. Interpretation Adolescent and young adult cancers contributed substantially to the overall adolescent and young adult disease burden globally in 2019. These results provide new insights into the distribution and magnitude of the adolescent and young adult cancer burden around the world. With notable differences observed across SDI settings, these estimates can inform global and country-level cancer control efforts. Copyright (C) 2021 The Author(s). Published by Elsevier Ltd.Peer reviewe

Global age-sex-specific mortality, life expectancy, and population estimates in 204 countries and territories and 811 subnational locations, 1950–2021, and the impact of the COVID-19 pandemic: a comprehensive demographic analysis for the Global Burden of Disease Study 2021

Background: Estimates of demographic metrics are crucial to assess levels and trends of population health outcomes. The profound impact of the COVID-19 pandemic on populations worldwide has underscored the need for timely estimates to understand this unprecedented event within the context of long-term population health trends. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 provides new demographic estimates for 204 countries and territories and 811 additional subnational locations from 1950 to 2021, with a particular emphasis on changes in mortality and life expectancy that occurred during the 2020–21 COVID-19 pandemic period. Methods: 22 223 data sources from vital registration, sample registration, surveys, censuses, and other sources were used to estimate mortality, with a subset of these sources used exclusively to estimate excess mortality due to the COVID-19 pandemic. 2026 data sources were used for population estimation. Additional sources were used to estimate migration; the effects of the HIV epidemic; and demographic discontinuities due to conflicts, famines, natural disasters, and pandemics, which are used as inputs for estimating mortality and population. Spatiotemporal Gaussian process regression (ST-GPR) was used to generate under-5 mortality rates, which synthesised 30 763 location-years of vital registration and sample registration data, 1365 surveys and censuses, and 80 other sources. ST-GPR was also used to estimate adult mortality (between ages 15 and 59 years) based on information from 31 642 location-years of vital registration and sample registration data, 355 surveys and censuses, and 24 other sources. Estimates of child and adult mortality rates were then used to generate life tables with a relational model life table system. For countries with large HIV epidemics, life tables were adjusted using independent estimates of HIV-specific mortality generated via an epidemiological analysis of HIV prevalence surveys, antenatal clinic serosurveillance, and other data sources. Excess mortality due to the COVID-19 pandemic in 2020 and 2021 was determined by subtracting observed all-cause mortality (adjusted for late registration and mortality anomalies) from the mortality expected in the absence of the pandemic. Expected mortality was calculated based on historical trends using an ensemble of models. In location-years where all-cause mortality data were unavailable, we estimated excess mortality rates using a regression model with covariates pertaining to the pandemic. Population size was computed using a Bayesian hierarchical cohort component model. Life expectancy was calculated using age-specific mortality rates and standard demographic methods. Uncertainty intervals (UIs) were calculated for every metric using the 25th and 975th ordered values from a 1000-draw posterior distribution. Findings: Global all-cause mortality followed two distinct patterns over the study period: age-standardised mortality rates declined between 1950 and 2019 (a 62·8% [95% UI 60·5–65·1] decline), and increased during the COVID-19 pandemic period (2020–21; 5·1% [0·9–9·6] increase). In contrast with the overall reverse in mortality trends during the pandemic period, child mortality continued to decline, with 4·66 million (3·98–5·50) global deaths in children younger than 5 years in 2021 compared with 5·21 million (4·50–6·01) in 2019. An estimated 131 million (126–137) people died globally from all causes in 2020 and 2021 combined, of which 15·9 million (14·7–17·2) were due to the COVID-19 pandemic (measured by excess mortality, which includes deaths directly due to SARS-CoV-2 infection and those indirectly due to other social, economic, or behavioural changes associated with the pandemic). Excess mortality rates exceeded 150 deaths per 100 000 population during at least one year of the pandemic in 80 countries and territories, whereas 20 nations had a negative excess mortality rate in 2020 or 2021, indicating that all-cause mortality in these countries was lower during the pandemic than expected based on historical trends. Between 1950 and 2021, global life expectancy at birth increased by 22·7 years (20·8–24·8), from 49·0 years (46·7–51·3) to 71·7 years (70·9–72·5). Global life expectancy at birth declined by 1·6 years (1·0–2·2) between 2019 and 2021, reversing historical trends. An increase in life expectancy was only observed in 32 (15·7%) of 204 countries and territories between 2019 and 2021. The global population reached 7·89 billion (7·67–8·13) people in 2021, by which time 56 of 204 countries and territories had peaked and subsequently populations have declined. The largest proportion of population growth between 2020 and 2021 was in sub-Saharan Africa (39·5% [28·4–52·7]) and south Asia (26·3% [9·0–44·7]). From 2000 to 2021, the ratio of the population aged 65 years and older to the population aged younger than 15 years increased in 188 (92·2%) of 204 nations. Interpretation: Global adult mortality rates markedly increased during the COVID-19 pandemic in 2020 and 2021, reversing past decreasing trends, while child mortality rates continued to decline, albeit more slowly than in earlier years. Although COVID-19 had a substantial impact on many demographic indicators during the first 2 years of the pandemic, overall global health progress over the 72 years evaluated has been profound, with considerable improvements in mortality and life expectancy. Additionally, we observed a deceleration of global population growth since 2017, despite steady or increasing growth in lower-income countries, combined with a continued global shift of population age structures towards older ages. These demographic changes will likely present future challenges to health systems, economies, and societies. The comprehensive demographic estimates reported here will enable researchers, policy makers, health practitioners, and other key stakeholders to better understand and address the profound changes that have occurred in the global health landscape following the first 2 years of the COVID-19 pandemic, and longer-term trends beyond the pandemic