1,721,034 research outputs found
Wrinkling evolution of a growing bubble: the wonders of petal-like patterns in amorphous silicon membranes
No full textA large-area amorphous silicon (a-Si) membrane on an oxidized wafer (SiO2/Si) is detached from the substrate by dissolving the sandwiched oxide layer using hydrofluoric acid solution (HF/H2O). Due to the atomic disorder in the structure of a-Si, the rate of molecular diffusion inside the a-Si film and etching of the oxide layer is not uniform over the film; thus, certain over-susceptible spots for etchant infiltration starts to locally detach. Using an in situ optical microscope, initially the detached region is observed to be buckled as a circular dome-shaped protuberance, which then forms wrinkles around the rim of the a-Si bubble. Around the rim, the deformation pattern was strongly dependant on the thickness h of the film, where the number of facets in the engendered petal-like patterns decreased with the increasing h. The tension-induced wrinkling in a-Si membranes was analytically and semi-quantitatively examined, and we conclude that the formation of peripheral corrugation is primarily due to the upward stretching force exerted by the underlying droplet composed of etchant and etching byproducts. The understanding of the elastic instability in ultrathin membranes could be extended to direct measurement of the fundamental properties in mechanically inferior systems.
Transport Gap in Dual-Gated Graphene Bilayers Using Oxides as Dielectrics
No full textGraphene bilayers in Bernal stacking exhibit a transverse electric (E) field-dependent band gap, which can be used to increase the channel resistivity and enable higher on/off ratio devices. We provide a systematic investigation of transport characteristics in dual-gated graphene bilayer devices as a function of density and E field and at temperatures from room temperature down to 0.3 K. The sample conductivity shows finite threshold voltages along the electron and hole branches, which increase as the E field increases, similar to a gapped semiconductor. We extract the transport gap as a function of E field and discuss the impact of disorder. In addition, we show that beyond the threshold, the bilayer conductivity shows a highly linear dependence on density, which is largely insensitive to the applied E field and the temperature.
Insulin modulates the frequency of Ca2+ oscillations in mouse pancreatic islets
Get PDFPancreatic islets can adapt to oscillatory glucose to produce synchronous insulin pulses. Can islets adapt to other oscillatory stimuli, specifically insulin? To answer this question, we stimulated islets with pulses of exogenous insulin and measured their Ca2+ oscillations. We observed that sufficiently high insulin (>500 nM) with an optimal pulse period (similar to 4 min) could make islets to produce synchronous Ca2+ oscillations. Glucose and insulin, which are key stimulatory factors of islets, modulate islet Ca2+ oscillations differently. Glucose increases the active-to-silent ratio of phases, whereas insulin increases the period of the oscillation. To examine the dual modulation, we adopted a phase oscillator model that incorporated the phase and frequency modulations. This mathematical model showed that out-of-phase oscillations of glucose and insulin were more effective at synchronizing islet Ca2+ oscillations than in-phase stimuli. This finding suggests that a phase shift in glucose and insulin oscillations can enhance inter-islet synchronization.111Ysciescopu
HfO2/HfOxNy/HfO2 Gate Dielectric Fabricated by In Situ Oxidation of Plasma-Enhanced Atomic Layer Deposition HfN Middle Layer
No full textBy using H-2 plasma as a reactant with tetrakis(dimethylamino)hafnium precursor during plasma-enhanced atomic layer deposition, we deposited the HfOxNy layer between HfO2 layers. The 5 nm thick HfO2/HfOxNy/HfO2 (HfONO) trilayer gate oxide shows reduced capacitance equivalent oxide thickness (congruent to 1.25 nm) than that (congruent to 1.40 nm) of the HfO2 film with the same thickness due to the contribution of nitrogen incorporation to the high dielectric constant. The HfONO film utilizing H-2 plasma shows lower values of interface trap density (D-it), trapped positive charge density (Delta N-p), and gate leakage currents than the HfO2 layer with the same thickness while maintaining comparable hysteresis (< 30 mV). The results can be attributed to the presence of N-H bonds, which can reduce localized states below the conduction band and prevent the conduction-band lowering, and decrement of N-N and N-O bonds, which contribute to trap density, confirmed by the combination of X-ray photoelectron spectroscopy and near-edge X-ray absorption fine-structure analyses.
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