Ambipolar Graphene Field Effect Transistors by Local Metal Side Gates

We demonstrate ambipolar graphene field effect transistors individually controlled by local metal side gates. The side gated field effect can have on/off ratio comparable with that of the global back gate, and can be tuned in a large range by the back gate and/or a second side gate. We also find that the side gated field effect is significantly stronger by electrically floating the back gate compared to grounding the back gate, consistent with the finding from electrostatic simulation.Comment: 4 pages, 3 figure

Synthetic Graphene Grown by Chemical Vapor Deposition on Copper Foils

The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interests. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapour deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality comparable to exfoliated graphene. In this chapter, we review the synthesis and characterizations of graphene grown on copper foil substrates by atmospheric pressure chemical vapour deposition. We also discuss potential applications of such large scale synthetic graphene.Comment: 23 pages, 4 figure

Effect of oxygen plasma etching on graphene studied with Raman spectroscopy and electronic transport

We report a study of graphene and graphene field effect devices after exposure to a series of short pulses of oxygen plasma. We present data from Raman spectroscopy, back-gated field-effect and magneto-transport measurements. The intensity ratio between Raman "D" and "G" peaks, I(D)/I(G) (commonly used to characterize disorder in graphene) is observed to increase approximately linearly with the number (N(e)) of plasma etching pulses initially, but then decreases at higher Ne. We also discuss implications of our data for extracting graphene crystalline domain sizes from I(D)/I(G). At the highest Ne measured, the "2D" peak is found to be nearly suppressed while the "D" peak is still prominent. Electronic transport measurements in plasma-etched graphene show an up-shifting of the Dirac point, indicating hole doping. We also characterize mobility, quantum Hall states, weak localization and various scattering lengths in a moderately etched sample. Our findings are valuable for understanding the effects of plasma etching on graphene and the physics of disordered graphene through artificially generated defects.Comment: 10 pages, 5 figure

Polariton Nanophotonics using Phase Change Materials

Polaritons formed by the coupling of light and material excitations such as plasmons, phonons, or excitons enable light-matter interactions at the nanoscale beyond what is currently possible with conventional optics. Recently, significant interest has been attracted by polaritons in van der Waals materials, which could lead to applications in sensing, integrated photonic circuits and detectors. However, novel techniques are required to control the propagation of polaritons at the nanoscale and to implement the first practical devices. Here we report the experimental realization of polariton refractive and meta-optics in the mid-infrared by exploiting the properties of low-loss phonon polaritons in isotopically pure hexagonal boron nitride (hBN), which allow it to interact with the surrounding dielectric environment comprising the low-loss phase change material, Ge$_3$Sb$_2$Te$_6$ (GST). We demonstrate waveguides which confine polaritons in a 1D geometry, and refractive optical elements such as lenses and prisms for phonon polaritons in hBN, which we characterize using scanning near field optical microscopy. Furthermore, we demonstrate metalenses, which allow for polariton wavefront engineering and sub-wavelength focusing. Our method, due to its sub-diffraction and planar nature, will enable the realization of programmable miniaturized integrated optoelectronic devices, and will lay the foundation for on-demand biosensors.Comment: 15 pages, 4 figures, typos corrected in v

Intravitreal bevacizumab associated with grid laser photocoagulation in macular edema secondary to branch retinal vein occlusion

To evaluate intravitreal bevacizumab (IVB) combined with grid laser photocoagulation in macular edema (ME) secondary to branch retinal vein occlusion (BRVO). METHODS: Eight eyes (8 patients) with ME associated with BRVO with at least 3 months of evolution since symptom onset were included. All subjects underwent measurement of best-corrected visual acuity (BCVA) and imaging with spectral domain optical coherence tomography (SD-OCT) at baseline and 1, 3, 6, and 12 months. Intravitreal bevacizumab was administered at baseline and macular grid laser photocoagulation 1 month later. During follow-up, additional IVB was administered based on physician discretion if persistent or recurrent intraretinal fluid (cysts) was observed on SD-OCT. The mean BCVA and SD-OCT central subfield thickness (CST) values were determined at each time point. Fisher exact test was performed to assess differences between baseline and post-treatment BCVA and SD-OCT measurements. RESULTS: The mean baseline BCVA was 0.28+/-0.14 (mean+/-SD), and the mean CST was 479+/-137 microm. The mean BCVAs at 1, 3, 6, and 12 months were 0.47+/-0.18 (p=0.031), 0.56+/-0.50 (p=0.031), 0.65+/-0.60 (p=0.008), and 0.66+/-0.65 (p=0.016), respectively. The mean CST values at 1, 3, 6, and 12 months were 295+/-60 microm (p=0.008), 333+/-114 microm (p=0.070), 339+/-80 microm (p=0.008), and 335+/-109 microm (p=0.008). A mean 2.13 injections were administered; the second injection was administered a mean of 2.71 months after baseline. CONCLUSIONS: Combined treatment with IVB and macular grid photocoagulation provided good results and may be considered as an alternative therapy for ME in BRVO. Further studies are needed to assess these preliminary results