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1.
Nutr Metab Cardiovasc Dis ; 31(9): 2669-2677, 2021 08 26.
Artigo em Inglês | MEDLINE | ID: mdl-34362638

RESUMO

BACKGROUND AND AIMS: High-density lipoprotein cholesterol (HDL-C) concentration and variability are both important factors of cardiovascular disease (CVD) and mortality. We aimed to explore the associations of HDL-C and longitudinal change in HDL-C with risk of mortality. METHODS AND RESULTS: We recruited a total of 69,163 participants aged ≥40 years and had medical examination records of HDL-C during 2010-2014 from the Yinzhou District, Ningbo, China. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards regression models. We observed a non-linear association of HDL-C with risks of non-accidental and CVD mortality. Compared with the moderate concentration group (1.4-1.6 mmol/L), HDL-C <1 mmol/L was associated with a higher risk of non-accidental mortality (HR: 1.13 (95% CI: 1.01-1.27)) and both HDL-C <1 mmol/L and ≥2 mmol/L were associated with a higher risk of CVD mortality (HRs: 1.23 (95% CI: 1.01-1.50) and 1.37 (95% CI: 1.03-1.82), respectively). Compared with the stable group ([-0.1, +0.1 mmol/L]), a large decrease ([-0.5, -0.3 mmol/L]) and very large decrease (<-0.5 mmol/L) in HDL-C were associated with a higher risk of non-accidental mortality (HRs: 1.40 (95% CI: 1.21-1.63) and 1.78 (95% CI: 1.44-2.20), respectively). Similar results were observed for CVD mortality and cancer mortality. CONCLUSION: Extremely low or high HDL-C and a large decrease or very large decrease in HDL-C were associated with a higher risk of cause-specific mortality. Monitoring of HDL-C may have utility in identifying individuals at higher risk of mortality.


Assuntos
HDL-Colesterol/sangue , Dislipidemias/mortalidade , Hipercolesterolemia/mortalidade , Adulto , Idoso , Biomarcadores/sangue , China/epidemiologia , Dislipidemias/sangue , Dislipidemias/diagnóstico , Feminino , Humanos , Hipercolesterolemia/sangue , Hipercolesterolemia/diagnóstico , Masculino , Pessoa de Meia-Idade , Prognóstico , Estudos Retrospectivos , Medição de Risco , Fatores de Risco , Fatores de Tempo
2.
Endocrine ; 73(3): 563-572, 2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-33990892

RESUMO

BACKGROUND AND AIMS: Although low-density lipoprotein cholesterol (LDL-C) has been considered as a risk factor of atherosclerotic cardiovascular disease, limited studies can be available to evaluate the association of LDL-C with risk of mortality in the general population. This study aimed to examine the association of LDL-C level with risk of mortality using a propensity-score weighting method in a Chinese population, based on the health examination data. METHODS: We performed a retrospective cohort study with 65,517 participants aged 40 years or older in Ningbo city, Zhejiang. LDL-C levels were categorized as five groups according to the Chinese dyslipidemia guidelines in adults. To minimize potential biases resulting from a complex array of covariates, we implemented a generalized boosted model to generate propensity-score weights on covariates. Then, we used Cox proportional hazard regression models with all-cause and cause-specific mortality as the dependent variables to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs). RESULTS: During the 439,186.5 person years of follow-up, 2403 deaths occurred. Compared with the median LDL-C group (100-130 mg/dL), subjects with extremely low LDL-C levels (group 1) had a higher risk of deaths from all-cause (HR = 2.53, 95% CI:1.80-3.53), CVD (HR = 1.84, 95% CI: 1.28-2.61), ischemic stroke (HR = 2.29, 95% CI:1.32-3.94), hemorrhagic stroke (HR = 3.49, 95% CI: 1.57-7.85), and cancer (HR = 2.12, 95% CI: 1.04-4.31) while the corresponding HRs in LDL-C group 2 were relatively lower than that in group 1. CONCLUSIONS: Low LDL-C levels were associated with an increased risk of all-cause, CVD, ischemic stroke, hemorrhagic stroke, and cancer mortality in the Chinese population.


Assuntos
Doenças Cardiovasculares , Adulto , China/epidemiologia , HDL-Colesterol , LDL-Colesterol , Estudos de Coortes , Humanos , Estudos Retrospectivos , Fatores de Risco
3.
Int J Qual Health Care ; 33(2)2021 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-33909042

RESUMO

OBJECTIVE: Unprecedented rigorous public health measures were implemented during the coronavirus disease 2019 (COVID-19) epidemic, but it is still unclear how the intervention influenced hospital visits for different types of diseases. We aimed to evaluate the impact of the intervention on hospital visits in Yinzhou District, Ningbo, Zhejiang province, China. METHODS: We conducted an interrupted time-series analysis from 1 January 2017 to 6 September 2020 based on the Yinzhou Health Information System in Ningbo, Zhejiang province. The beginning of the intervention was on 23 January 2020, and thus, there were 160 weeks before the intervention and 32 weeks after the implementation of the intervention. Level changes between expected and observed hospital visits in the post-intervention period were estimated using quasi-Poisson regression models. RESULTS: Compared with the expected level, there was an estimated decrease of -22.60% (95% confidence interval (CI): -27.53%, -17.36%) in the observed total hospital visits following the intervention. Observed hospital visits for diseases of the respiratory system were found to be decreased dramatically (-62.25%; 95% CI: -65.62%, -58.60%). However, observed hospital visits for certain diseases were estimated to be increased, including diseases of the nervous system (+11.17%; 95% CI: +3.21%, +19.74%); diseases of pregnancy, childbirth and the puerperium (+27.01%; 95% CI: +17.89%, +36.85%); certain conditions originating in the perinatal period (+45.05%; 95% CI: +30.24%, +61.56%); and congenital malformation deformations and chromosomal abnormalities (+35.50%; 95% CI: +21.24%, +51.45%). CONCLUSIONS: Our findings provided scientific evidence that cause-specific hospital visits evolve differently following the intervention during the COVID-19 epidemic.


Assuntos
COVID-19 , Hospitais/estatística & dados numéricos , COVID-19/epidemiologia , China/epidemiologia , Feminino , Humanos , Análise de Séries Temporais Interrompida , Pandemias , Gravidez , SARS-CoV-2
4.
CMAJ ; 193(15): E538-E539, 2021 04 12.
Artigo em Francês | MEDLINE | ID: mdl-33846209
6.
Sex Transm Infect ; 2020 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-33219164

RESUMO

OBJECTIVES: Co-infection of syphilis and HIV remains hard to manage and its morbidity shows a rising tendency. Syphilis has been associated with increased risk of HIV acquisition in high-risk groups, especially in men who have sex with men (MSM). This systematic review and meta-analysis estimates the effect of syphilis infection on subsequent HIV acquisition, and assesses its difference between MSM and other high-risk populations. METHODS: Five electronic databases were searched for literature published to 21 September 2019 without language restrictions. Longitudinal studies that enrolled key populations to compare the incidence of HIV with and without syphilis exposure were included. We used a random-effects model to estimate the effect of syphilis infection on HIV acquisition among high-risk populations, which include MSM, sex workers, serodiscordant couples, people who inject drugs and attendees of STD clinics. RESULTS: A total of 17 cohorts and 5 case-control studies involving 65 232 participants were included. HIV incidence showed a two-time increase after syphilis exposure, compared with a control group (relative risk (RR) 2.67 (95% CI 2.05 to 3.47); p<0.05 for prevalence; RR 3.21 (95% CI 2.26 to 4.57); p=0.419 for incidence). No significant differences were observed between MSM and other high-risk groups in syphilis infection prevalence (RR 2.60 (95% CI 1.78 to 3.80); p<0.05 vs RR, 2.98 (95% CI 2.15 to 4.14); p<0.05; ratio of relative risk 0.76 (95% CI 0.49 to 1.17)). CONCLUSIONS: Syphilis infection increases the risk of HIV acquisition in high-risk populations. There is no evidence to suggest MSM are at greater risk than other high-risk populations. Prompt diagnosis, timely treatment, preventive interventions against syphilis infection would be a worthwhile investment for reducing HIV incidence. Strategies to combat stigma and discrimination targeted at MSM are pragmatically needed.

7.
Nat Commun ; 11(1): 5974, 2020 11 25.
Artigo em Inglês | MEDLINE | ID: mdl-33239627

RESUMO

The lateral parabrachial nucleus (LPBN) is known to relay noxious information to the amygdala for processing affective responses. However, it is unclear whether the LPBN actively processes neuropathic pain characterized by persistent hyperalgesia with aversive emotional responses. Here we report that neuropathic pain-like hypersensitivity induced by common peroneal nerve (CPN) ligation increases nociceptive stimulation-induced responses in glutamatergic LPBN neurons. Optogenetic activation of GABAergic LPBN neurons does not affect basal nociception, but alleviates neuropathic pain-like behavior. Optogenetic activation of glutamatergic or inhibition of GABAergic LPBN neurons induces neuropathic pain-like behavior in naïve mice. Inhibition of glutamatergic LPBN neurons alleviates both basal nociception and neuropathic pain-like hypersensitivity. Repetitive pharmacogenetic activation of glutamatergic or GABAergic LPBN neurons respectively mimics or prevents the development of CPN ligation-induced neuropathic pain-like hypersensitivity. These findings indicate that a delicate balance between excitatory and inhibitory LPBN neuronal activity governs the development and maintenance of neuropathic pain.


Assuntos
Hiperalgesia/fisiopatologia , Neuralgia/fisiopatologia , Neurônios/metabolismo , Nociceptividade/fisiologia , Núcleos Parabraquiais/fisiologia , Animais , Modelos Animais de Doenças , Agonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Agonistas GABAérgicos/farmacologia , Ácido Glutâmico/metabolismo , Humanos , Hiperalgesia/etiologia , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Camundongos , Camundongos Transgênicos , Vias Neurais/efeitos dos fármacos , Vias Neurais/fisiologia , Neuralgia/etiologia , Neurônios/efeitos dos fármacos , Optogenética , Núcleos Parabraquiais/citologia , Núcleos Parabraquiais/efeitos dos fármacos , Nervo Fibular/lesões , Nervo Fibular/fisiopatologia , Técnicas Estereotáxicas , Ácido gama-Aminobutírico/metabolismo
8.
Am J Prev Med ; 59(3): 461-468, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32417020

RESUMO

INTRODUCTION: Although numerous studies have suggested that lifestyle-related factors are associated with chronic diseases and preventable deaths, limited evidence is available for the Chinese population. METHODS: This study established a prospective cohort of >360,000 residents on the basis of the Yinzhou Health Information System in China during 2004-2017 and calculated the combined effects of lifestyle-related factors, including BMI, smoking, alcohol consumption, and physical activity, using a points system. A Cox regression model estimated the combined effects of lifestyle-related factors on total mortality, and a competing risk model estimated the combined effects on cancer and cardiovascular disease mortality. All data analyses were conducted in 2018‒2019. RESULTS: During 3,755,879 person-years of follow-up, 11,791 deaths were identified, including 4,983 from cancer and 3,143 from cardiovascular disease. Having a standard BMI, never smoking, never drinking, and engaging in physical activity more than 4 times per week had protective effects on total mortality. Overall, the risk of total and cause-specific mortality increased with the increment of risk score. Compared with subjects in the lowest quartile, the risk of total and cause-specific mortality peaked among individuals in the fourth quartile (total mortality: hazard ratio=1.87, 95% CI=1.77, 1.98; cancer mortality: hazard ratio=2.05, 95% CI=1.87, 2.25; cardiovascular disease mortality: hazard ratio=1.51, 95% CI=1.35, 1.68). Sensitivity analyses excluding individuals with follow-up <3 years did not materially change the results. CONCLUSIONS: The combined effects of lifestyle-related factors, including BMI, smoking, alcohol drinking, and physical activity, are associated with total, cancer, and cardiovascular disease mortality among the Chinese population.


Assuntos
Doenças Cardiovasculares , Estilo de Vida , Mortalidade/tendências , Consumo de Bebidas Alcoólicas/epidemiologia , Doenças Cardiovasculares/mortalidade , China/epidemiologia , Estudos de Coortes , Humanos , Modelos de Riscos Proporcionais , Estudos Prospectivos , Fatores de Risco
9.
Health Qual Life Outcomes ; 18(1): 54, 2020 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-32131839

RESUMO

BACKGROUNDS: Social Health Scale for the Elderly short version (SHSE-S) is a psychometrically sound instrument that comprehensively assesses the social health status of older adults in China. The aim of the present study was to establish continuous normative data of SHSE-S. METHODS: We conducted a multicenter cross-sectional study among 31 communities in eastern China. Older adults aged 60 years and above were invited to participate in the study. Each participant was interviewed in-person to finish a structured questionnaire. The SHES-S score was calculated and standardized for each participant. We split the sample into generation and validation datasets and compared the distribution of SHSE-S score between two datasets. Multivariable linear regression was used to assess the SHSE-S score and demographic variables. Regression-based norms were built using a four-step process. RESULTS: A total of 6089 participants (51.2% females) aged 60 years old and above (mean age = 71.3, SD = 8.0) were enrolled as the normative sample. No significant difference was found between the distribution of SHSE-S standardized score in the generation (N = 2392) and validation (N = 3697) datasets. Multivariable linear regression showed that females, higher education levels were positive indicators while aging, living alone, divorced or never married, multimorbidity were negative factors. The regression-based norm which taking demographic factors into account was established and a user-friendly worksheet was also provided to facilitate the scoring and norming of the SHSE-S. CONCLUSIONS: The population-based regression norm of SHSE-S can be a useful tool for assessing the social health status of the Chinese elderly population.


Assuntos
Qualidade de Vida/psicologia , Determinantes Sociais da Saúde/estatística & dados numéricos , Inquéritos e Questionários/normas , Idoso , Idoso de 80 Anos ou mais , China , Estudos Transversais , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Psicometria , Ajustamento Social , Apoio Social
10.
Diabetologia ; 63(1): 85-94, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31485707

RESUMO

AIMS/HYPOTHESIS: The aim of this study was to investigate the association between visit-to-visit variability in HbA1c and cognitive function decline in the elderly population. METHODS: We performed a pooled analysis of two prospective population-based cohorts (the Health Retirement Study [HRS] and the English Longitudinal Study of Ageing [ELSA]). Cognitive function, including memory and executive function, were assessed at baseline and every 2 years, while HbA1c levels were assessed at baseline and every 4 years. Visit-to-visit variability (VVV) in HbA1c was calculated using the CV, SD and variation independent of the mean (VIM) during the follow-up period. Linear mixed models were used to evaluate the association between HbA1c variability and cognitive function decline with adjustment for demographics, mean HbA1c, education, smoking, alcohol consumption, BMI, baseline hypertension, baseline diabetes status and HDL-cholesterol. RESULTS: The study enrolled 6237 participants (58.23% women, mean age 63.38 ± 8.62 years) with at least three measurements of HbA1c. The median follow-up duration was 10.56 ± 1.86 years. In the overall sample, compared with the lowest quartile of HbA1c variability, participants in the highest quartile of HbA1c variability had a significantly worse memory decline rate (-0.094 SD/year, 95% CI -0.185, -0.003) and executive function decline rate (-0.083 SD/year, 95% CI -0.125, -0.041), irrespective of mean HbA1c values over time. Among individuals without diabetes, each 1-SD increment in HbA1c CV was associated with a significantly higher rate of memory z score decline (-0.029, 95% CI -0.052, -0.005) and executive function z score decline (-0.049, 95% CI -0.079, -0.018) in the fully adjusted model. CONCLUSIONS/INTERPRETATION: We observed a significant association between long-term HbA1c variability and cognitive decline among the non-diabetic population in this study. The effect of maintaining steady glucose control on the rate of cognitive decline merits further investigation.


Assuntos
Disfunção Cognitiva/metabolismo , Hemoglobina A Glicada/metabolismo , Idoso , Consumo de Bebidas Alcoólicas/sangue , Consumo de Bebidas Alcoólicas/metabolismo , HDL-Colesterol/sangue , Disfunção Cognitiva/sangue , Feminino , Humanos , Hipertensão/sangue , Hipertensão/metabolismo , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Fumar/sangue , Fumar/metabolismo
11.
J Zhejiang Univ Sci B ; 20(11): 910-919, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31595727

RESUMO

OBJECTIVE: Mental disorders of the elderly population in China deserve attention. Social health is significantly associated with depression. This study aimed to evaluate the rate of depressive symptoms and to test the relationships between social health and depressive symptoms among a large sample of community-dwelling elderly adults. METHODS: We conducted a cross-sectional study among community-dwelling adults aged 60 years or above in Zhejiang Province, China. Face-to-face interviews were used to complete a structured questionnaire for all participants. We used the Social Health Scale for the Elderly (SHSE) to evaluate social health status and used the short form of the Geriatric Depression Scale to evaluate depressive symptoms. Multivariate logistic regression was used to evaluate the association between social health status and depressive symptoms. RESULTS: Of the total of 3757 participants included, 1887 (50.23%) were female, and the mean±standard deviation (SD) age was (70.0±8.3) years. The rate of depressive symptoms was 25.92%. The social health score was higher in non-depressed participants than in depressed participants (raw score 50.7 vs. 48.3, P<0.001). Participants with "moderate" or "good" social health had a significantly lower risk of depressive symptoms than those with "poor" social health (odds ratio (OR)=0.55, 95% confidence interval (CI): 0.46-0.66 for moderate social health; OR=0.45, 95% CI: 0.35-0.60 for good social health). The association between social health and depressive symptoms was consistent across several subgroups. CONCLUSIONS: Social health is significantly inversely associated with depressive symptoms. The SHSE may serve as an efficient screener to identify those elderly adults with social health deficits, but systematic assessment to guide intervention merits further investigation.


Assuntos
Depressão/epidemiologia , Nível de Saúde , Vida Independente , Idoso , Idoso de 80 Anos ou mais , Estudos Transversais , Feminino , Humanos , Modelos Logísticos , Masculino , Pessoa de Meia-Idade
12.
Nutr Metab Cardiovasc Dis ; 29(11): 1205-1213, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31383502

RESUMO

BACKGROUND AND AIMS: The relationship between serum total cholesterol (TC) and mortality remains inconsistent. Additionally, intra-individual variability of cholesterol has been of increasing interest as a new indicator for health outcomes. We aimed to examine the association between TC and its variability and risk of mortality. METHODS AND RESULTS: We performed a retrospective cohort study with 122,645 individuals aged over 40 years in Ningbo, China. The intra-individual variability was calculated using four metrics including standard deviation, coefficient variation, variation independent of mean and average successive variability. Hazard ratios and 95% confidence intervals were estimated for the associations of baseline and variability in TC with risk of mortality by Cox proportional hazards regression models. During 591,585.3 person-years of follow-up, 4563 deaths (including 1365 from cardiovascular disease, 788 from stroke and 1514 from cancer) occurred. A U-shaped association was observed for baseline TC level and risk of total, cardiovascular and cancer mortality, with lowest mortality at 5.46 mmol/L, 5.04 mmol/L and 5.51 mmol/L, respectively. As compared with subjects with TC variability in the lowest quartile, individuals in the highest quartile had 21% higher risk of all-cause mortality (HR = 1.21, 95% CI: 1.05 to 1.40), and 41% higher risk of CVD mortality (HR = 1.41, 95%CI: 1.10 to 1.81). CONCLUSION: Both too low and too high baseline TC level were associated with higher risk of total, cardiovascular disease and cancer mortality. Variability of TC could be a risk factor of total and CVD mortality, independent of mean TC level. Future studies are needed to confirm these findings.


Assuntos
Variação Biológica Individual , Doenças Cardiovasculares/sangue , Doenças Cardiovasculares/mortalidade , Colesterol/sangue , Idoso , Biomarcadores/sangue , Doenças Cardiovasculares/diagnóstico , China/epidemiologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Neoplasias/sangue , Neoplasias/mortalidade , Prognóstico , Estudos Retrospectivos , Medição de Risco , Fatores de Risco , Fatores de Tempo
13.
J Phys Chem Lett ; 7(11): 2024-31, 2016 06 02.
Artigo em Inglês | MEDLINE | ID: mdl-27182690

RESUMO

We observe ultrafast energy transfer between bare carbon nanotubes in a thin film using two-dimensional (2D) white-light spectroscopy. Using aqueous two-phase separation, semiconducting carbon nanotubes are purified from their metallic counterparts and condensed into a 10 nm thin film with no residual surfactant. Cross peak intensities put the time scale for energy transfer at <60 fs, and 2D anisotropy measurements determine that energy transfer is most efficient between parallel nanotubes, thus favoring directional energy flow. Lifetimes are about 300 fs. Thus, these results are in sharp contrast to thin films prepared from nanotubes that are wrapped by polymers, which exhibit picosecond energy transfer and randomize the direction of energy flow. Ultrafast energy flow and directionality are exciting properties for next-generation photovoltaics, photodetectors, and other devices.


Assuntos
Luz , Nanotubos de Carbono/química , Tamanho da Partícula , Análise Espectral
14.
Nat Commun ; 6: 6732, 2015 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-25865487

RESUMO

Thin film networks of highly purified semiconducting carbon nanotubes (CNTs) are being explored for energy harvesting and optoelectronic devices because of their exceptional transport and optical properties. The nanotubes in these films are in close contact, which permits energy to flow through the films, although the pathways and mechanisms for energy transfer are largely unknown. Here we use a broadband continuum to collect femtosecond two-dimensional white-light spectra. The continuum spans 500 to 1,300 nm, resolving energy transfer between all combinations of bandgap (S1) and higher (S2) transitions. We observe ultrafast energy redistribution on the S2 states, non-Förster energy transfer on the S1 states and anti-correlated energy levels. The two-dimensional spectra reveal competing pathways for energy transfer, with S2 excitons taking routes depending on the bandgap separation, whereas S1 excitons relax independent of the bandgap. These observations provide a basis for understanding and ultimately controlling the photophysics of energy flow in CNT-based devices.

15.
Nanoscale ; 7(14): 6093-103, 2015 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-25771959

RESUMO

Recent studies have qualitatively shown that the oxidative stability of monolayer graphene integrated on oxides is relatively poor. Here, the evolution, kinetics, and energetics of this degradation are quantified. Specifically, the deterioration of graphene on SiO2 is studied in grain interiors and at grain boundaries in ambient air, dry air and nitrogen between 473 and 673 K, using spatially and temporally resolved in situ Raman spectroscopy in addition to electron microscopy and charge transport measurements. The grain interiors of chemical vapor deposition (CVD) grown graphene monolayers oxidize with an activation energy of 0.63 ± 0.05 eV in ambient air (15,000 ppm H2O). This energy increases to 1.85 ± 0.17 eV in dry air, whereas degradation is immeasurable in nitrogen and for multilayers even in ambient air. Gasification at grain boundaries in a CVD monolayer proceeds at a rate of (1.08 ± 0.02) × 10(-1) nm s(-1) at 673 K with an activation energy E(A) = 1.14 ± 0.10 eV in ambient air. The more facile degradation of the monolayer grain interiors in ambient air indicates the role of the substrate in decreasing the stability against oxidation. The electrical transport mobility decays with an activation rate similar to that of grain interiors. These results can be used to quantitatively predict graphene oxidation and gasification on SiO2 in different environments and temperatures.

16.
ACS Nano ; 8(11): 11614-21, 2014 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-25383880

RESUMO

Challenges in eliminating metallic from semiconducting single-walled carbon nanotubes (SWCNTs) and in controlling their alignment have limited the development of high-performance SWCNT-based field-effect transistors (FETs). We recently pioneered an approach for depositing aligned arrays of ultra-high-purity semiconducting SWCNTs, isolated using polyfluorene derivatives, called dose-controlled floating evaporative self-assembly. Here, we tailor FETs fabricated from these arrays to achieve on-conductance (G(on)) per width and an on-off ratio (G(on)/G(off)) of 261 µS/µm and 2 × 10(5), respectively, for a channel length (L(ch)) of 240 nm and 116 µS/µm and 1 × 10(6), respectively, for an L(ch) of 1 µm. We demonstrate 1400× greater G(on)/G(off) than SWCNT FETs fabricated by other methods, at comparable G(on) per width of ∼250 µS/µm and 30-100× greater G(on) per width at comparable G(on)/G(off) of 10(5)-10(7). The average G(on) per tube reaches 5.7 ± 1.4 µS at a packing density of 35 tubes/µm for L(ch) in the range 160-240 nm, limited by contact resistance. These gains highlight the promise of using ultra-high-purity semiconducting SWCNTs with controlled alignment for next-generation semiconductor electronics.

17.
ACS Nano ; 8(6): 5383-94, 2014 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-24806792

RESUMO

We utilize femtosecond transient absorption spectroscopy to study dynamics of photoexcitation migration in films of semiconducting single-wall carbon nanotubes. Films of nanotubes in close contact enable energy migration such as needed in photovoltaic and electroluminescent devices. Two types of films composed of nanotube fibers are utilized in this study: densely packed and very porous. By comparing exciton kinetics in these films, we characterize excitation transfer between carbon nanotubes inside fibers versus between fibers. We find that intrafiber transfer takes place in both types of films, whereas interfiber transfer is greatly suppressed in the porous one. Using films with different nanotube composition, we are able to test several models of exciton transfer. The data are inconsistent with models that rely on through-space interfiber energy transfer. A model that fits the experimental results postulates that interfiber transfer occurs only at intersections between fibers, and the excitons reach the intersections by diffusing along the long-axis of the tubes. We find that time constants for the inter- and intrafiber transfers are 0.2-0.4 and 7 ps, respectively. In total, hopping between fibers accounts for about 60% of all exciton downhill transfer prior to 4 ps in the dense film. The results are discussed with regards to transmission electron micrographs of the films. This study provides a rigorous analysis of the photophysics in this new class of promising materials for photovoltaics and other technologies.

18.
Small ; 10(16): 3299-306, 2014 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-24719253

RESUMO

Using a novel two-step fabrication scheme, we create highly semiconducting-enriched single-walled carbon nanotube (sSWNT) bulk heterojunctions (BHJs) by first creating highly porous interconnected sSWNT aerogels (sSWNT-AEROs), followed by back-filling the pores with [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM). We demonstrate sSWNT-AERO structures with density as low as 2.5 mg cm(-3), porosity as high as 99.8%, and diameter of sSWNT fibers ≤ 10 nm. Upon spin coating with PC(71)BM, the resulting sSWNT-AERO-PC(71)BM nanocomposites exhibit highly quenched sSWNT photoluminescence, which is attributed to the large interfacial area between the sSWNT and PC(71)BM phases, and an appropriate sSWNT fiber diameter that matches the inter-sSWNT exciton migration length. Employing the sSWNT-AERO-PC(71)BM BHJ structure, we report optimized solar cells with a power conversion efficiency of 1.7%, which is exceptional among polymer-like solar cells in which sSWNTs are designed to replace either the polymer or fullerene component. A fairly balanced photocurrent is achieved with 36% peak external quantum efficiency (EQE) in the visible and 19% peak EQE in the near-infrared where sSWNTs serve as electron donors and photoabsorbers. Our results prove the effectiveness of this new method in controlling the sSWNT morphology in BHJ structures, suggesting a promising route towards highly efficient sSWNT photoabsorbing solar cells.

19.
Nano Lett ; 14(2): 682-6, 2014 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-24382263

RESUMO

Field-effect transistors (FETs) that are stretchable up to 50% without appreciable degradation in performance are demonstrated. The FETs are based on buckled thin films of polyfluorene-wrapped semiconducting single-walled carbon nanotubes (CNTs) as the channel, a flexible ion gel as the dielectric, and buckled metal films as electrodes. The buckling of the CNT film enables the high degree of stretchability while the flexible nature of the ion gel allows it to maintain a high quality interface with the CNTs during stretching. An excellent on/off ratio of >10(4), a field-effect mobility of 10 cm(2) · V(-1) · s(-1), and a low operating voltage of <2 V are achieved over repeated mechanical cycling, with further strain accommodation possible. Deformable FETs are expected to facilitate new technologies like stretchable displays, conformal devices, and electronic skins.

20.
Nano Lett ; 13(4): 1495-501, 2013 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-23464618

RESUMO

Carbon nanotubes are a promising means of capturing photons for use in solar cell devices. We time-resolved the photoexcitation dynamics of coupled, bandgap-selected, semiconducting carbon nanotubes in thin films tailored for photovoltaics. Using transient absorption spectroscopy and anisotropy measurements, we found that the photoexcitation evolves by two mechanisms with a fast and long-range component followed by a slow and short-range component. Within 300 fs of optical excitation, 20% of nanotubes transfer their photoexcitation over 5-10 nm into nearby nanotube fibers. After 3 ps, 70% of the photoexcitation resides on the smallest bandgap nanotubes. After this ultrafast process, the photoexcitation continues to transfer on a ~10 ps time scale but to predominantly aligned tubes. Ultimately the photoexcitation hops twice on average between fibers. These results are important for understanding the flow of energy and charge in coupled nanotube materials and light-harvesting devices.


Assuntos
Nanotubos de Carbono/química , Pontos Quânticos/química , Energia Solar , Fótons
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