Synthesis of Graphene on Gold

Here we report chemical vapor deposition of graphene on gold surface at ambient pressure. We studied effects of the growth temperature, pressure and cooling process on the grown graphene layers. The Raman spectroscopy of the samples reveals the essential properties of the graphene grown on gold surface. In order to characterize the electrical properties of the grown graphene layers, we have transferred them on insulating substrates and fabricated field effect transistors. Owing to distinctive properties of gold, the ability to grow graphene layers on gold surface could open new applications of graphene in electrochemistry and spectroscopy.Comment: 8 pages, 4 figure

Semi-Transparent Image Sensors for Eye-Tracking Applications

Image sensors hold a pivotal role in society due to their ability to capture vast amounts of information. Traditionally, image sensors are opaque due to light absorption in both the pixels and the read-out electronics that are stacked on top of each other. Making image sensors visibly transparent would have a far-reaching impact in numerous areas such as human-computer interfaces, smart displays, and both augmented and virtual reality. In this paper, we present the development and analysis of the first semi-transparent image sensor and its applicability as an eye-tracking device. The device consists of an 8x8 array of semi-transparent photodetectors and electrodes disposed on a fully transparent substrate. Each pixel of the array has a size of 60 x 140 {\mu}m and an optical transparency of 85-95%. Pixels have a high sensitivity, with more than 90% of them showing a noise equivalent irradiance < 10-4 W/m2 for wavelengths of 637 nm. As the semi-transparent photodetectors have a large amount of built-in gain, the opaque read-out electronics can be placed far away from the detector array to ensure maximum transparency and fill factor. Indeed, the operation and appearance of transparent image sensors present a fundamental shift in how we think about cameras and imaging, as these devices can be concealed in plain sight

Broadband Optical Modulators Based on Graphene Supercapacitors

Optical modulators are commonly used in communication and information technology to control intensity, phase, or polarization of light. Electro-optic, electroabsorption, and acousto-optic modulators based on semiconductors and compound semiconductors have been used to control the intensity of light. Because of gate tunable optical properties, graphene introduces new potentials for optical modulators. The operation wavelength of graphene-based modulators, however, is limited to infrared wavelengths due to inefficient gating schemes. Here, we report a broadband optical modulator based on graphene supercapacitors formed by graphene electrodes and electrolyte medium. The transparent supercapacitor structure allows us to modulate optical transmission over a broad range of wavelengths from 450 nm to 2 μm under ambient conditions. We also provide various device geometries including multilayer graphene electrodes and reflection type device geometries that provide modulation of 35%. The graphene supercapacitor structure together with the high-modulation efficiency can enable various active devices ranging from plasmonics to optoelectronics

Gate-Tunable Photoemission from Graphene Transistors

In this Letter, we report gate-tunable X-ray photoelectron emission from back-gated graphene transistors. The back-gated transistor geometry allows us to study photoemission from graphene layer and the dielectric substrate at various gate voltages. Application of gate voltage electrostatically dopes graphene and shifts the binding energy of photoelectrons in various ways depending on the origin and the generation mechanism(s) of the emitted electrons. The gate-induced shift of the Fermi energy of graphene alters the binding energy of the C 1s electrons, whereas the electric field of the gate electrodes shift the binding energy of core electrons emitted from the gate dielectric underneath the graphene layer. The gradual change of the local potential through depths of the gate dielectric provides quantitative electrical information about buried interfaces. Our results suggest that gate-tunable photoemission spectra with chemically specific information linked with local electrical properties opens new routes to elucidating operation of devices based especially on layered materials

Electrically controlled terahertz spatial light modulators with graphene arrays

Gate-tunable high-mobility electrons on atomically thin graphene layers provide a unique opportunity to control electromagnetic waves in a very broad spectrum. In this paper, we describe an electrically-controlled multipixel terahertz light modulators. The spatial light modulator is fabricated using two large-area graphene layers grown by chemical vapor deposition and transferred on THz transparent and flexible substrates. Room temperature ionic liquid, inserted between the graphene, provides mutual gating between the graphene layers. We used passive matrix addressing to control local charge density thus the THz transmittance. With this device configuration, we were able to obtain 5x5 arrays of graphene modulator with 65% modulation between 0.1 to 1.5 THz

Highly Proton Conductive Phosphoric Acid–Nonionic Surfactant Lyotropic Liquid Crystalline Mesophases and Application in Graphene Optical Modulators

Proton conducting gel electrolytes are very important components of clean energy devices. Phosphoric acid (PA, H₃PO₄·H₂O) is one of the best proton conductors, but needs to be incorporated into some matrix for real device applications, such as into lyotropic liquid crystalline mesophases (LLCMs). Herein, we show that PA and nonionic surfactant (NS, C₁₂H₂₅(OCH₂CH₂)₁₀OH, C₁₂E₁₀) molecules self-assemble into PANS–LLCMs and display high proton conductivity. The content of the PANS–LLCM can be as high 75% H₃PO₄·H₂O and 25% 10-lauryl ether (C₁₂H₂₅(OCH₂CH₂)₁₀OH, C₁₂E₁₀), and the mesophase follows the usual LLC trend, bicontinuous cubic (V₁)–normal hexagonal (H₁)–micelle cubic (I₁), by increasing the PA concentration in the media. The PANS–LLCMs are stable under ambient conditions, as well as at high (up to 130 °C) and low (−100 °C) temperatures with a high proton conductivity, in the range of 10^–2 to 10^–6 S/cm. The mesophase becomes a mesostructured solid with decent proton conductivity below −100 °C. The mesophase can be used in many applications as a proton-conducting media as well as a phosphate source for the synthesis of various metal phosphates. As an application, we demonstrate a graphene-based optical modulator using supercapacitor structure formed by graphene electrodes and a PANS electrolyte. A PANS–LLC electrolyte-based supercapacitor enables efficient optical modulation of graphene electrodes over a range of wavelengths, from 500 nm to 2 μm, under ambient conditions

Kinematic analysis and palaeoseismology of the Edremit Fault Zone: evidence for past earthquakes in the southern branch of the North Anatolian Fault Zone, Biga Peninsula, NW Turkey

The Edremit Fault Zone (EFZ) forms one of the southern segments of the North Anatolian Fault Zone (NAFZ) at the northern margin of the Edremit Gulf (Biga Peninsula, South Marmara Region, Turkey). Stratigraphic, structural and kinematic results indicate that basinward younging of the fault zone, in terms of a rolling-hinge mechanism, has resulted in at least three discrete Miocene to Holocene deformational phases: the oldest one (Phase 1) directly related to the inactive Kazda Detachment Fault, which was formed under N-S trending pure extension; Phase 2 is characterised by a strike-slip stress condition, probably related to the progression of the NAFZ towards the Edremit area in the Plio-Quaternary; and Phase 3 is represented by the high-angle normal faulting, which is directly interrelated with the last movement of the EFZ. Our palaeoseismic studies on the EFZ revealed the occurrence of three past surface rupture events; the first one occurred before 13178 BC, a penultimate event that may correspond to either the 160 AD or 253 AD historical earthquakes, and the youngest one can be associated with the 6 October 1944 earthquake (M-w=6.8). These palaeoseismic data indicate that there is no systematic earthquake recurrence period on the EFZ