We present a Raman study of Ar+-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G ...peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.
Abstract Background Major Depressive Disorder (MDD) is a leading cause of the disease burden for women of childbearing age, but the burden of MDD attributable to perinatal depression is not yet ...known. There has been little effort to date to systematically review available literature and produce global estimates of prevalence and incidence of perinatal depression. Enhanced understanding will help to guide resource allocation for screening and treatment. Methods A systematic literature review using the databases PsycINFO and PubMed returned 140 usable prevalence estimates from 96 studies. A random-effects meta-regression was performed to determine sources of heterogeneity in prevalence estimates between studies and to guide a subsequent random-effects meta-analysis. Results The meta-regression explained 31.1% of the variance in prevalence reported between studies. Adjusting for the effects of all other variables in the model, prevalence derived using symptom scales was significantly higher than prevalence derived using diagnostic instruments (odds ratio OR 1.6, 95% confidence interval CI 1.3–2.0). Additionally, prevalence was significantly higher in women from low and middle income countries compared to women from high income countries (OR 1.8, 95% CI 1.4–2.2). The overall pooled prevalence was 11.9% of women during the perinatal period (95% CI 11.4–12.5). There were insufficient data to calculate pooled incidence. Limitations Studies in low income countries were especially scarce in this review, demonstrating a need for more epidemiological research in those regions. Conclusions Perinatal depression appears to impose a higher burden on women in low- and middle-income countries. This review contributes significantly to the epidemiological literature on the disorder.
The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental ...stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential lies in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultrawideband tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light-emitting devices to touch screens, photodetectors and ultrafast lasers. Here we review the state-of-the-art in this emerging field.
Although graphite is known as one of the most chemically inert materials, we have found that graphene, a single atomic plane of graphite, can react with atomic hydrogen, which transforms this highly ...conductive zero-overlap semimetal into an insulator. Transmission electron microscopy reveals that the obtained graphene derivative (graphane) is crystalline and retains the hexagonal lattice, but its period becomes markedly shorter than that of graphene. The reaction with hydrogen is reversible, so that the original metallic state, the lattice spacing, and even the quantum Hall effect can be restored by annealing. Our work illustrates the concept of graphene as a robust atomic-scale scaffold on the basis of which new two-dimensional crystals with designed electronic and other properties can be created by attaching other atoms and molecules.
We detect electroluminescence in single layer molybdenum disulfide (MoS2) field-effect transistors built on transparent glass substrates. By comparing the absorption, photoluminescence, and ...electroluminescence of the same MoS2 layer, we find that they all involve the same excited state at 1.8 eV. The electroluminescence has pronounced threshold behavior and is localized at the contacts. The results show that single layer MoS2, a direct band gap semiconductor, could be promising for novel optoelectronic devices, such as two-dimensional light detectors and emitters.
Heterostructures formed by stacking layered materials require atomically clean interfaces. However, contaminants are usually trapped between the layers, aggregating into randomly located blisters, ...incompatible with scalable fabrication processes. Here we report a process to remove blisters from fully formed heterostructures. Our method is over an order of magnitude faster than those previously reported and allows multiple interfaces to be cleaned simultaneously. We fabricate blister-free regions of graphene encapsulated in hexagonal boron nitride with an area ~ 5000 μm
, achieving mobilities up to 180,000 cm
V
s
at room temperature, and 1.8 × 10
cm
V
s
at 9 K. We also assemble heterostructures using graphene intentionally exposed to polymers and solvents. After cleaning, these samples reach similar mobilities. This demonstrates that exposure of graphene to process-related contaminants is compatible with the realization of high mobility samples, paving the way to the development of wafer-scale processes for the integration of layered materials in (opto)electronic devices.
Nonalcoholic fatty liver disease is the most prevalent chronic liver disease in Western countries; it can progress to nonalcoholic steatohepatitis (NASH), cirrhosis and hepatocarcinoma. The ...importance of gut-liver-adipose tissue axis has become evident and treatments targeting gut microbiota may improve inflammatory and metabolic parameters in NASH patients. In a randomized, controlled clinical trial, involving 50 biopsy-proven NASH patients, we investigated the effects of synbiotic supplementation on metabolic parameters, hepatic steatosis, intestinal permeability, small intestinal bacterial overgrowth (SIBO) and lipopolysaccharide (LPS) serum levels. Patients were separated into two groups receiving Lactobacillus reuteri with guar gum and inulin for three months and healthy balanced nutritional counseling versus nutritional counseling alone. Before and after the intervention we assessed steatosis by magnetic resonance imaging, intestinal permeability by lactulose/mannitol urinary excretion and SIBO by glucose breath testing. NASH patients presented high gut permeability, but low prevalence of SIBO. After the intervention, only the synbiotic group presented a reduction in steatosis, lost weight, diminished BMI and waist circumference measurement. Synbiotic did not improve intestinal permeability or LPS levels. We concluded that synbiotic supplementation associated with nutritional counseling seems superior to nutritional counseling alone for NASH treatment as it attenuates steatosis and may help to achieve weight loss.
Screen-printed electrochemical sensing platforms, due to their scales of economy and high reproducibility, can provide a useful approach to translate laboratory-based electrochemistry into the field. ...An important factor when utilising screen-printed electrodes (SPEs) is the determination of their real electrochemical surface area, which allows for the benchmarking of these SPEs and is an important parameter in quality control. In this paper, we consider the use of cyclic voltammetry and chronocoulometry to allow for the determination of the real electrochemical area of screen-printed electrochemical sensing platforms, highlighting to experimentalists the various parameters that need to be diligently considered and controlled in order to obtain useful measurements of the real electroactive area.
The combination of plasmonic nanoparticles and graphene enhances the responsivity and spectral selectivity of graphene-based photodetectors. However, the small area of the metal–graphene junction, ...where the induced electron–hole pairs separate, limits the photoactive region to submicron length scales. Here, we couple graphene with a plasmonic grating and exploit the resulting surface plasmon polaritons to deliver the collected photons to the junction region of a metal–graphene–metal photodetector. This gives a 400% enhancement of responsivity and a 1000% increase in photoactive length, combined with tunable spectral selectivity. The interference between surface plasmon polaritons and the incident wave introduces new functionalities, such as light flux attraction or repulsion from the contact edges, enabling the tailored design of the photodetector’s spectral response. This architecture can also be used for surface plasmon biosensing with direct-electric-redout, eliminating the need of bulky optics.
The unique optoelectronic properties of graphene make it an ideal platform for a variety of photonic applications, including fast photodetectors, transparent electrodes in displays and photovoltaic ...modules, optical modulators, plasmonic devices, microcavities, and ultra-fast lasers. Owing to its high carrier mobility, gapless spectrum and frequency-independent absorption, graphene is a very promising material for the development of detectors and modulators operating in the terahertz region of the electromagnetic spectrum (wavelengths in the hundreds of micrometres), still severely lacking in terms of solid-state devices. Here we demonstrate terahertz detectors based on antenna-coupled graphene field-effect transistors. These exploit the nonlinear response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature operation at 0.3 THz, showing that our devices can already be used in realistic settings, enabling large-area, fast imaging of macroscopic samples.
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