Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 415
Filtrar
Mais filtros

Tipo de documento
Intervalo de ano de publicação
1.
Public Health ; 225: 343-352, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-37979311

RESUMO

INTRODUCTION: The COVID-19 pandemic has prompted governments internationally to consider strengthening their public health systems. To support the work of Ireland's Public Health Reform Expert Advisory Group, the Health Information and Quality Authority, an independent governmental agency, was asked to describe the lessons learnt regarding the public health response to COVID-19 internationally and the applicability of this response for future pandemic preparedness. METHODS: Semi-structured interviews with key public health representatives from nine countries were conducted. Interviews were conducted in March and April 2022 remotely via Zoom and were recorded. Notes were taken by two researchers, and a thematic analysis undertaken. RESULTS: Lessons learnt from the COVID-19 pandemic related to three main themes: 1) setting policy; 2) delivering public health interventions; and 3) providing effective communication. Real-time surveillance, evidence synthesis, and cross-sectoral collaboration were reported as essential for policy setting; it was noted that having these functions established prior to the pandemic would lead to a more efficient implementation in a health emergency. Delivering public health interventions such as testing, contact tracing, and vaccination were key to limiting and or mitigating the spread of the SARS-CoV-2 virus. However, a number of challenges were highlighted such as staff capacity and burnout, delays in vaccination procurement, and reduced delivery of regular healthcare services. Clear, consistent, and regular communication of the scientific evidence was key to engaging citizens with mitigation strategies. However, these communication strategies had to compete with an infodemic of information being circulated, particularly through social media. CONCLUSIONS: Overall, functions relating to policy setting, public health interventions, and communication are key to pandemic response. Ideally, these should be established in the preparedness phase so that they can be rapidly scaled-up during a pandemic.


Assuntos
COVID-19 , Humanos , COVID-19/epidemiologia , COVID-19/prevenção & controle , SARS-CoV-2 , Pandemias/prevenção & controle , Reforma dos Serviços de Saúde , Saúde Pública
2.
J Cutan Pathol ; 49(4): 408-411, 2022 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-34841567

RESUMO

A 72-year-old male presented with scarring alopecia on the scalp vertex, multiple crusted plaques on the hairline, and a history of vesicular eruption on the face. The scalp showed crusted plaques with loss of follicular ostia. No follicular pustules or compound follicles were present. An initial transverse scalp biopsy showed perifollicular neutrophils, lymphocytes, and plasma cells along with dermal fibrosis. Focal epidermal/dermal and follicular/adventitial dermal clefts were apparent but were thought to be secondary to fibrosis, and the biopsy result was interpreted to represent a neutrophil-mediated cicatricial alopecia. Concurrently, direct immunofluorescence (DIF) analysis showed linear junctional deposition of IgG and C3. A repeat scalp biopsy revealed more prominent epidermal/dermal clefts, fibrosis, mixed infiltrate with neutrophils, lymphocytes, histiocytes, and plasma cells, as well as prominent follicular/adventitial dermal clefts with perifollicular neutrophils. Given the combination of clefts, perijunctional neutrophils, and positive DIF findings, it became clear that this eruption represented the Brunsting-Perry variant of cicatricial pemphigoid. Here, we illustrated that a neutrophil-rich form of cicatricial pemphigoid can masquerade as a neutrophil-mediated scarring alopecia. In evaluating a specimen suspected to be a neutrophil-mediated scarring alopecia, one should be alert to the presence of subepidermal and perifollicular clefting, and consider cicatricial pemphigoid.


Assuntos
Alopecia/patologia , Neutrófilos/patologia , Penfigoide Mucomembranoso Benigno/patologia , Idoso , Humanos , Masculino
3.
Anaesthesia ; 76(8): 1031-1041, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-33899214

RESUMO

Neuro-inflammation may be important in the pathogenesis of postoperative delirium following hip fracture surgery. Studies have suggested a potential role for steroids in reducing postoperative delirium; however, the potential efficacy and safety of pre-operative high-dose dexamethasone in this specific population is largely unknown. Conducting such a study could be challenging, considering the multidisciplinary team involvement and the emergency nature of the surgery. The aim of this study was to assess feasibility and effectiveness of dexamethasone given as early as possible following hospital admission for hip fracture, to inform whether a full-scale trial is warranted. This single-centre, randomised, double-blind, placebo-controlled study randomly allocated 79 participants undergoing hip fracture surgery to dexamethasone 20 mg or placebo pre-operatively. Eligibility and recruitment rates, timing of the intervention and adverse events were recorded. Incidence and severity of postoperative delirium were assessed using the 4AT delirium screening tool and the Memorial Delirium Assessment Scale. Postoperative pain, length of stay and mortality were also assessed. The eligibility rate for inclusion was 178/527 (34%), and 57/178 (32%) of eligible patients presented to hospital when no researcher was available (e.g. after-hours, weekends, public holidays). Recruitment was limited mainly by ethical limitations (not including patients with impaired cognition) and lack of weekend staffing. Median (IQR [range]) time from emergency department admission to drug administration was 13.3 (5.9-17.6 [1.8-139.6]) hours. There was a significant difference in delirium severity scores, favouring the dexamethasone group: median (IQR [range]) 5 (3-6 [3-7]) vs. 9 (6-13 [5-14]) in the placebo group, with the probability of superiority effect size being 0.89, p = 0.010. Delirium incidence did not differ between groups: 6/40 (15%) in the dexamethasone group vs. 9/39 (23%) in the placebo group, relative risk (95%CI) 0.65 (0.22-1.65), p = 0.360). A larger randomised controlled trial is feasible and ideally this should include people with existing cognitive impairment, seven days-a-week cover and a multicentre design.


Assuntos
Dexametasona/uso terapêutico , Delírio do Despertar/prevenção & controle , Avaliação Geriátrica/métodos , Glucocorticoides/uso terapêutico , Fraturas do Quadril/cirurgia , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Método Duplo-Cego , Estudos de Viabilidade , Feminino , Humanos , Masculino , Resultado do Tratamento
4.
BMC Geriatr ; 20(1): 247, 2020 07 17.
Artigo em Inglês | MEDLINE | ID: mdl-32680465

RESUMO

BACKGROUND: There is increasing interest among older people in moving into retirement villages (RVs), an attractive option for those seeking a supportive community as they age, while still maintaining independence. Currently in New Zealand there is limited knowledge of the medical, service supports, social status and needs of RV residents. The objective of this study is to explore RV facilities and services, the health and functional status of RV residents, prospectively study their healthcare trajectories and to implement a multidisciplinary team intervention to potentially decrease dependency and impact healthcare utilization. METHODS: All RVs located in two large district health boards in Auckland, New Zealand were eligible to participate. This three-year project comprised three phases: The survey phase provided a description of RVs, residents' characteristics and health and functional status. RV managers completed a survey of size, facilities and recreational and healthcare services provided in the village. Residents were surveyed to establish reasons for entry to the village and underwent a Gerontology Nurse Specialist (GNS) assessment providing details of demographics, social engagement, health and functional status. The cohort study phase examines residents' healthcare trajectories and adverse outcomes, over three years. The final phase is a randomised controlled trial of a multidisciplinary team intervention aimed to improve health outcomes for more vulnerable residents. Residents who triggered potential unmet health needs during the assessment in the survey phase were randomised to intervention or usual care groups. Multidisciplinary team meetings included the resident and support person, a geriatrician or gerontology nurse practitioner, GNS, pharmacist and General Practitioner. The primary outcome of the randomised controlled trial will be first acute hospitalization. Secondary outcomes include all acute hospitalizations, long-term care admissions, and all-cause mortality. DISCUSSION: This paper describes the study protocol of this complex study. The study aims to inform policies and practices around health care services for residents in retirement villages. The results of this trial are expected early 2020 with publication subsequently. TRIAL REGISTRATION: Australia and New Zealand Clinical Trials Registry: ACTRN12616000685415 . Registered 25.5.2016. Universal Trial Number (UTN): U111-1173-6083.


Assuntos
Invenções , Aposentadoria , Idoso , Idoso de 80 Anos ou mais , Austrália , Estudos de Coortes , Humanos , Nova Zelândia/epidemiologia , Inquéritos e Questionários
5.
Tech Coloproctol ; 23(8): 713-721, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31396759

RESUMO

BACKGROUND: Older age has long been linked to risk of diverticulitis, but the epidemiology is seldom described for a national population. The aim of this study was to investigate age- and gender differences in incidence, temporal trends, lifetime risk and prevalence related to acute diverticulitis hospitalisations in New Zealand. METHODS: Records of all hospitalisations with diverticulitis the primary diagnosis were obtained from the Ministry of Health for the period 2000-2015. The first acute diverticulitis admission recorded for an individual was taken as an incident event; all others were classified as recurrent. Trends in age- and sex-specific and age-standardised incidence rates are described, and lifetime risk and prevalence estimated. RESULTS: Over the 16 years from 2000 to 2015, 37,234 acute hospitalisations for diverticulitis were recorded in 28,329 people aged 30 + years (median = 66 years). Rates of incident hospitalisations rose with age, from 5/10,000 person-years at age 50-54 years to 19/10,000py by age 80-84 years. Rates for women were lower than men before age 55 years, but higher thereafter. Age-standardised rates rose 0.2/10,000py annually, but approximately doubled among men aged < 50 years. Lifetime risk was estimated at over 5%, with the prevalence pool rising to over 1.5% of the population aged 30+ in 2030. CONCLUSIONS: Rapid increases in diverticulitis admissions among young men since 2000 correspond with increases reported elsewhere but remain unexplained; notably young women follow similar trends 5-10 years later. Increasing incidence, combined with population ageing, adds urgency to explain diverticular formation, to understand factors that trigger or provoke their inflammation/infection, and to clarify treatment and (self-)management pathways.


Assuntos
Fatores Etários , Doenças Diverticulares/epidemiologia , Diverticulite/epidemiologia , Hospitalização/tendências , Fatores Sexuais , Doença Aguda/epidemiologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Incidência , Masculino , Pessoa de Meia-Idade , Nova Zelândia/epidemiologia , Prevalência
10.
Surgeon ; 15(3): 139-146, 2017 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-26283303

RESUMO

INTRODUCTION: Pulmonary complications are a significant cause of morbidity, mortality and increased hospital stay following complex abdominal surgery. We investigated whether postoperative early aerobic activity with a pedal exerciser reduced respiratory morbidity and length of stay and improved pulmonary function. METHODS: A prospective case-control study on 30 cases and 30 case matched controls aged 18 years or more who underwent major surgery was conducted. Controls were case-mix matched prospectively from a similar general surgical service not utilising postoperative exercising. Thirty consecutive cases were started on a twice-daily aerobic exercise program with pedal exerciser post-operatively day 2 or from when sitting independently. Primary outcome measures were respiratory tract infection (RTI), deep vein thrombosis (DVT) or pulmonary embolus (PE). Secondary outcome measure was subjective breathlessness and Length of Stay (LOS) postoperatively. RESULTS: The rate of RTI was only 16.6% in the exercise group and 43.3% in the control group (P = 0.024). None of the cases or controls suffered from a DVT or PE. Median postoperative length of stay in the control group was 11 ± 7.5 days whereas in the cases it was 8.5 ± 5.00 days (P = 0.049). The Borg subjective breathlessness score in the cases group showed a decline in the subjective breathlessness on postoperative day 4 (P = 0.002). CONCLUSIONS: Early aerobic activity with a pedal exerciser halves the rate of postoperative RTI and postoperative hospital stay after complex abdominal surgery. Subjective breathlessness was also reduced with the use of pedal exerciser, signifying potential to improve exercise endurance in the postoperative patient.


Assuntos
Terapia por Exercício/métodos , Cuidados Pós-Operatórios/métodos , Complicações Pós-Operatórias/prevenção & controle , Infecções Respiratórias/prevenção & controle , Procedimentos Cirúrgicos Operatórios/efeitos adversos , Estudos de Casos e Controles , Feminino , Seguimentos , Humanos , Irlanda/epidemiologia , Tempo de Internação/tendências , Masculino , Pessoa de Meia-Idade , Morbidade/tendências , Complicações Pós-Operatórias/epidemiologia , Estudos Prospectivos , Infecções Respiratórias/epidemiologia , Fatores de Risco
11.
Ir Med J ; 110(7): 618, 2017 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-29169000

RESUMO

Hidradenitis Suppurativa (HS) is characterized by chronic recurrent abscesses, nodules and draining sinus tracts with scar formation. Cutaneous Crohn's Disease (CD) may also present similarly. We wished to identify and describe an Irish cohort with combined HS and CD, with a view to a better recognition of clinical manifestations and understanding of the pathophysiology underlying these two overlapping conditions. Cases were identified using the HIPE Code at Tallaght Hospital from 1990-2014 and retrospective review was performed. Seven patients with both HS and CD were identified, 5(71%) female. The median age of diagnosis with both conditions was 37 years. In all cases, CD had preceded the diagnosis of HS. All patients smoked. Six had an increased BMI and 43% had additional autoimmune conditions. All patients required treatment with a TNF-alpha inhibitor for HS with 5 of 6 subjects having reduced frequency of flare ups and clinically less active HS on follow up.


Assuntos
Doença de Crohn/complicações , Hidradenite Supurativa/complicações , Adulto , Estudos de Coortes , Feminino , Hidradenite Supurativa/tratamento farmacológico , Humanos , Masculino , Projetos de Pesquisa , Estudos Retrospectivos
12.
Am J Transplant ; 16(7): 2172-80, 2016 07.
Artigo em Inglês | MEDLINE | ID: mdl-26729617

RESUMO

Lung transplant recipients are encouraged to perform self-management behaviors, including (i) monitoring health indicators, (ii) adhering to their regimen, and (iii) reporting abnormal health indicators to the transplant coordinator, yet performance is suboptimal. When hospital discharge was imminent, this two-group trial randomized 201 recipients to use either the mobile health (mHealth) intervention (n = 99) or usual care (n = 102), to compare efficacy for promoting self-management behaviors (primary outcomes) and self-care agency, rehospitalization, and mortality (secondary outcomes) at home during the first year after transplantation. The mHealth intervention group performed self-monitoring (odds ratio [OR] 5.11, 95% confidence interval [CI] 2.95-8.87, p < 0.001), adhered to medical regimen (OR 1.64, 95% CI 1.01-2.66, p = 0.046), and reported abnormal health indicators (OR 8.9, 95% CI 3.60-21.99, p < 0.001) more frequently than the usual care group. However, the two groups did not differ in rehospitalization (OR 0.78, 95% CI 0.36-1.66, p = 0.51) or mortality (hazard ratio 1.71, 0.68-4.28, p = 0.25). The positive impact of the mHealth intervention on self-management behaviors suggests that the intervention holds promise and warrants further testing.


Assuntos
Transplante de Pulmão/reabilitação , Autocuidado , Telemedicina/estatística & dados numéricos , Idoso , Feminino , Seguimentos , Comportamentos Relacionados com a Saúde , Humanos , Masculino , Adesão à Medicação , Pessoa de Meia-Idade , Prognóstico , Qualidade de Vida , Sistemas de Alerta
14.
J Am Acad Dermatol ; 73(2): 294-303, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26054431

RESUMO

Adult-onset Still disease (AOSD) is a systemic inflammatory disorder that is clinically characterized by a heterogeneous constellation of symptoms and signs. Though an evanescent eruption is the classic cutaneous finding, recent literature has highlighted atypical rashes associated with Still disease. A second emerging concept in presentations of AOSD is its association with malignancy. This review focuses on these concepts: the clinical spectrum of atypical skin manifestations and AOSD as a paraneoplastic phenomenon. PubMed-MEDLINE was screened for peer-reviewed articles describing atypical presentations of AOSD and cases associated with malignancy. Erythematous, brown or violaceous, persistent papules and plaques were the most common cutaneous finding (28/30 [93%]). Linear configurations were also rarely described. Of these patients, 81% concurrently had the typical evanescent skin eruption. There were 31 patients with associated malignancies, most commonly breast cancer and lymphoma. The diagnosis of malignancy did not precede or immediately follow a clinical presentation otherwise consistent with AOSD in a considerable subset of patients (42%). Understanding the cutaneous spectrum of AOSD and heightened awareness for its delayed association with malignancy may lead to improved recognition of cutaneous variants and reinforce the need for diagnostic evaluation and long-term follow-up for malignancy in patients with this clinical presentation.


Assuntos
Síndromes Paraneoplásicas/diagnóstico , Síndromes Paraneoplásicas/epidemiologia , Doença de Still de Início Tardio/epidemiologia , Doença de Still de Início Tardio/patologia , Adulto , Biópsia por Agulha , Comorbidade , Feminino , Seguimentos , Humanos , Imuno-Histoquímica , Incidência , Masculino , Prurido/diagnóstico , Prurido/epidemiologia , Recidiva , Medição de Risco , Índice de Gravidade de Doença , Doença de Still de Início Tardio/diagnóstico
15.
Hum Reprod ; 29(6): 1313-9, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24706002

RESUMO

STUDY QUESTION: What was the clinical and economic impact of universal coverage of IVF in Quebec, Canada, during the first calendar year of implementation of the public IVF programme? SUMMARY ANSWER: Universal coverage of IVF increased access to IVF treatment, decreased the multiple pregnancy rate and decreased the cost per live birth, despite increased costs per cycle. WHAT IS KNOWN ALREADY: Public funding of IVF assures equality of access to IVF and decreases multiple pregnancies resulting from this treatment. Public IVF programmes usually mandate a predominant SET policy, the most effective approach for reducing the incidence of multiple pregnancies. STUDY DESIGN, SIZE, DURATION: This prospective comparative cohort study involved 7364 IVF cycles performed in Quebec during 2009 and 2011 and included an economic analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: IVF cycles performed in the five centres offering IVF treatment in Quebec during 2009, before implementation of the public IVF programme, were compared with cycles performed at the same centres during 2011, the first full calendar year following implementation of the programme. Data were obtained from the Canadian Assisted Reproductive Technologies Register (CARTR). Comparisons were made between the two periods in terms of utilization, pregnancy rates, multiple pregnancy rates and costs. MAIN RESULTS AND THE ROLE OF CHANCE: The number of IVF cycles performed in Quebec increased by 192% after the new policy was implemented. Elective single-embryo transfer was performed in 1.6% of the cycles during Period I (2009), and increased to 31.6% during Period II (2011) (P < 0.001). Although the clinical pregnancy rate per embryo transfer was lower in 2011 than in 2009 (24.9 versus 39.9%, P < 0.001), the multiple pregnancy rate was greatly reduced (6.4 versus 29.4%, P < 0.001). The public IVF programme increased government costs per IVF treatment cycle from CAD$3730 to CAD$4759. Despite increased costs per cycle, the efficiency defined by the cost per live birth, which factored in downstream health costs up to 1 year post delivery, decreased from CAD$49 517 to CAD$43 362 per baby conceived by either fresh and frozen cycles. LIMITATIONS, REASONS FOR CAUTION: The costs described in the economic model are likely an underestimate as they do not factor in many of the long-term costs that can occur after 1 year of age. The information collected in the Canadian ART register precludes the calculation of cumulative pregnancy rates. WIDER IMPLICATIONS OF THE FINDINGS: Our study confirms that the implementation of a public IVF programme favouring eSET not only sharply decreases the incidence of multiple pregnancy, but also reduces the cost per live birth. STUDY FUNDING/COMPETING INTEREST(S): M.P.V. holds a fellowship award from the Canadian Institutes of Health Research (CIHR). The economic analysis performed by M.P.C. was supported by an unrestricted grant from Ferring Pharmaceutical.


Assuntos
Fertilização in vitro/economia , Gravidez Múltipla/estatística & dados numéricos , Transferência de Embrião Único/economia , Cobertura Universal do Seguro de Saúde/economia , Adulto , Feminino , Humanos , Incidência , Gravidez , Taxa de Gravidez , Estudos Prospectivos , Quebeque , Transferência de Embrião Único/métodos
16.
Reprod Biomed Online ; 28(2): 239-45, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24365025

RESUMO

This study evaluated the lifetime future net tax revenues from individuals conceived after IVF relative to those naturally conceived. A model based on the method of generational accounting was developed to evaluate investments in IVF. Calculations were based on average investments paid and received from the government by an individual. All costs were discounted to their net present values and adjusted for survival. The lifetime net present value of IVF-conceived individuals was -€81,374 (the minus sign reflecting negative net present value). The lifetime net present value of IVF-conceived men and women were -€47,091 and -€123,177, respectively. The lifetime net present value of naturally conceived individuals was -€70,392; respective amounts for men and women were -€36,109 and -€112,195. The model was most sensitive to changes in the growth of healthcare costs, economic growth and the discount rate. Therefore, it is concluded that, similarly to naturally conceived individuals in the Netherlands, IVF-conceived individuals have negative discounted net tax revenue at the end of life. The analytic framework described here undervalues the incremental value of an additional birth because it only considers the fiscal consequences of life and does not take into consideration broader macroeconomic benefits. This study evaluated the lifetime future net tax revenues from individuals conceived after IVF relative those naturally conceived. A model based on the method of generational accounting to evaluate investments in IVF was used. Calculations were based on average investments paid and received from the government by an individual. The lifetime net present value of IVF-conceived individuals was -€81,374 (the minus sign reflecting negative net present value). The lifetime net present value of IVF-conceived men and women were -€47,091 and -€123,177, respectively. The lifetime net present value of naturally conceived individuals was -€70,392; respective amounts for men and women were -€36,109 and -€112,195. The model was most sensitive for changes in the growth in healthcare costs, economic growth and the discount rate. Just as naturally conceived individuals in the Netherlands, IVF-conceived individuals have negative discounted net tax revenue at the end of life. The analytic framework described here undervalues the incremental value of an additional birth because it only considers the fiscal consequences of life and does not take into consideration broader macroeconomic benefits.


Assuntos
Fertilização in vitro/estatística & dados numéricos , Modelos Econômicos , Impostos/estatística & dados numéricos , Contabilidade/métodos , Análise Custo-Benefício , Feminino , Fertilização in vitro/efeitos adversos , Humanos , Masculino , Países Baixos
17.
Artigo em Inglês | MEDLINE | ID: mdl-25108134

RESUMO

Metabolic rate and evaporative water loss are two commonly measured physiological variables. It is therefore important, especially for comparative studies, that these variables (and others) are measured under standardised conditions, of which a resting state during the inactive phase is part of the accepted criteria. Here we show how measurement duration and timing affect these criteria and impact on the estimation of basal metabolic rate (oxygen consumption and carbon dioxide production) and standard evaporative water loss of a small nocturnal rodent. Oxygen consumption, carbon dioxide production and evaporative water loss all decreased over the duration of an experiment. Random assortment of hourly values indicated that this was an animal rather than a random effect for up to 11h. Experimental start time also had a significant effect on measurement of physiological variables. A longer time period was required to achieve minimal carbon dioxide consumption and evaporative water loss when experiments commenced earlier in the day; however, experiments with earlier start times had a lower overall estimates of minimal oxygen consumption and carbon dioxide production. For this species, measurement duration of at least 8h, ideally commencing between before the inactive phase at 03:00h and 05:00h, is required to obtain minimal standard values for physiological variables. Up to 80% of recently published studies measuring basal metabolic rate and/or evaporative water loss of small nocturnal mammals may overestimate basal values due to insufficiently long measurement duration.


Assuntos
Animais Selvagens/fisiologia , Metabolismo Basal , Comportamento Animal , Ritmo Circadiano , Ratos/fisiologia , Perda Insensível de Água , Animais , Dióxido de Carbono/metabolismo , Monitorização Fisiológica/veterinária , Consumo de Oxigênio , Distribuição Aleatória , Reprodutibilidade dos Testes , Fatores de Tempo , Austrália Ocidental
20.
Nano Lett ; 12(11): 5448-54, 2012 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-23078572

RESUMO

Investigating the structure of quantized plateaus in the Hall conductance of graphene is a powerful way of probing its crystalline and electronic structure and will also help to establish whether graphene can be used as a robust standard of resistance for quantum metrology. We use low-temperature scanning gate microscopy to image the interplateau breakdown of the quantum Hall effect in an exfoliated bilayer graphene flake. Scanning gate images captured during breakdown exhibit intricate patterns where the conductance is strongly affected by the presence of the scanning probe tip. The maximum density and intensity of the tip-induced conductance perturbations occur at half-integer filling factors, midway between consecutive quantum Hall plateau, while the intensity of individual sites shows a strong dependence on tip-voltage. Our results are well-described by a model based on quantum percolation which relates the points of high responsivity to tip-induced scattering in a network of saddle points separating localized states.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA