Controlled Generation of a p-n Junction in a Waveguide Integrated Graphene Photodetector.

With its electrically tunable light absorption and ultrafast photoresponse, graphene is a promising candidate for high-speed chip-integrated photonics. The generation mechanisms of photosignals in graphene photodetectors have been studied extensively in the past years. However, the knowledge about efficient light conversion at graphene p-n junctions has not yet been translated into high-performance devices. Here, we present a graphene photodetector integrated on a silicon slot-waveguide, acting as a dual gate to create a p-n junction in the optical absorption region of the device. While at zero bias the photothermoelectric effect is the dominant conversion process, an additional photoconductive contribution is identified in a biased configuration. Extrinsic responsivities of 35 mA/W, or 3.5 V/W, at zero bias and 76 mA/W at 300 mV bias voltage are achieved. The device exhibits a 3 dB bandwidth of 65 GHz, which is the highest value reported for a graphene-based photodetector.

Thermal Light Emission from Monolayer MoS2.

Layered transition metal dichalcogenide semiconductors, such as MoS2 and WSe2 , exhibit a range of fascinating properties and are being currently explored for a variety of electronic and optoelectronic devices. These properties include a low thermal conductivity and a large Seebeck coefficient, which make them promising for thermoelectric applications. Moreover, transition metal dichalcogenides undergo an indirect-to-direct bandgap transition when thinned down in thickness, leading to strong excitonic photo- and electroluminescence in monolayers. Here, it is demonstrated that a MoS2 monolayer sheet, freely suspended in vacuum over a distance of 150 nm, emits visible light as a result of Joule heating. Due to the poor transfer of heat to the contact electrodes, as well as the suppressed heat dissipation through the underlying substrate, the electron temperature can reach ≈1500-1600 K. The resulting narrow-band light emission from thermally populated exciton states is spatially located to an only ≈50 nm wide region in the center of the device and goes along with a negative differential electrical conductance of the channel.

Bone mineral density in partially recovered early onset anorexic patients - a follow-up investigation.

BACKGROUND AND AIMS: There still is a lack of prospective studies on bone mineral development in patients with a history of early onset Anorexia nervosa (AN). Therefore we assessed associations between bone mass accrual and clinical outcomes in a former clinical sample. In addition to an expected influence of regular physical activity and hormone replacement therapy, we explored correlations with nutritionally dependent hormones. METHODS: 3-9 years (mean 5.2 +/- 1.7) after hospital discharge, we re-investigated 52 female subjects with a history of early onset AN. By means of a standardized approach, we evaluated the general outcome of AN. Moreover, bone mineral content (BMC) and bone mineral density (BMD) as well as lean and fat mass were measured by dual-energy x-ray absorptiometry (DXA). In a substudy, we measured the serum concentrations of leptin and insulin-like growth factor-I (IGF-I). RESULTS: The general outcome of anorexia nervosa was good in 50% of the subjects (BMI >/= 17.5 kg/m2, resumption of menses). Clinical improvement was correlated with BMC and BMD accrual (chi2 = 5.62/chi2 = 6.65, p = 0.06 / p = 0.036). The duration of amenorrhea had a negative correlation with BMD (r = -.362; p < 0.01), but not with BMC. Regular physical activity tended to show a positive effect on bone recovery, but the effect of hormone replacement therapy was not significant. Using age-related standards, the post-discharge sample for the substudy presented IGF-I levels below the 5th percentile. IGF-I serum concentrations corresponded to the general outcome of AN. By contrast, leptin serum concentrations showed great variability. They correlated with BMC and current body composition parameters. CONCLUSIONS: Our results from the main study indicate a certain adaptability of bone mineral accrual which is dependent on a speedy and ongoing recovery. While leptin levels in the substudy tended to respond immediately to current nutritional status, IGF-I serum concentrations corresponded to the individual's age and general outcome of AN.