Mode control in vertical-cavity surface-emitting lasers by post-processing using focused ion-beaih etching

Single-mode emission is achieved in previously multimode gain-guided vertical-cavity surface-emitting lasers (VCSEL's) by localized modification of the mirror reflectivity using focused ion-beam etching. Reflectivity engineering is also demonstrated to suppress transverse mode emission in an oxide-confined device, reducing the spectral width from 1.2 nm to less than 0.5 nm.

Carbon nanotube based cathodes for microwave amplifiers

We have studied two different kinds of electron tubes using a cold field emission cathode as the electron source. This cathode is an array of vertically aligned multiwall carbon nanotubes. The first device is a triode. With this device, we demonstrated the modulation at 32 GHZ of a 1.4 A/cm2 peak current density with a 82% modulation ratio. The second device is a traveling wave tube. For this device, the objective is to test a cathode delivering a 2 A/cm 2 electron beam. ©2009 IEEE.

COMPRESSOR BLADE

A blade (2) for a compressor comprising a pressure surface (6) and a suction surface (4), wherein the suction surface (4) comprises: a discontinuity in the chord-wise curvature of an intermediate portion of the suction surface between the blade leading edge and blade trailing edge; and a slot (20) arranged along at least a portion of the blade (2) in a substantially span-wise direction, the slot (2) being disposed at or near the said change in curvature, such that when in use lower momentum fluid near the suction surface (4) is aspirated into the slot (20).

Research roadmap for green wireline access

The paper describes different research concepts of which the combination leads to an improvement of the power consumption per subscriber in a wireline access network by 10× and the energy efficiency per transferred bit by 100×. © 2012 IEEE.

Novel nanostructured carbon nanotube electron sources

In this chapter, we present a review of our continuing efforts toward the development of discrete, low-dimensional nanostructured carbon-based electron emitters. Carbon nanotubes and nanofibers, herein referred to simply as CNTs, are one-dimensional carbon allotropes formed from cylindrically rolled and nested graphene sheets, have diameters between 1 and 500 nm and lengths of up to several millimeters, and are perfect candidates for field emission (FE) applications. By virtue of their extremely strong sp2 C-C bonding, intrinsic to the graphene hexagonal lattice, CNTs have demonstrated impressive chemical inertness, unprecedented thermal stabilities, significant resistance to electromigration, and exceptionally high axial current carrying capacities, even at elevated temperatures. These near ideal cold cathode electron emitters have incredibly high electric field enhancing aspect ratios combined with virtual point sources of the order of a few nanometers in size. The correct integration and judicious development of suitable FE platforms based on these extraordinary molecules is critical and will ultimately enable enhanced technologies. This chapter will review some of the more recent platforms, devices and structures developed by our group, as well as our contributions towards the development of industry-scalable technologies for ultra-high-resolution electron microscopy, portable x-ray sources, and flexible environmental lighting technologies. © 2012 by Pan Stanford Publishing Pte. Ltd. All rights reserved.

Growth kinetics and uniform scaling-up of graphene synthesis

Chemical vapor deposition on copper is the most widely used method to synthesize graphene at large scale. However, the clear understanding of the fundamental mechanisms that govern this synthesis is lacking. Using a vertical-flow, cold-wall reactor with short gas residence time we observe the early growths to study the kinetics of chemical vapor deposition of graphene on copper foils and demonstrate uniform synthesis at wafer scale. Our results indicate that the growth is limited by the catalytic dissociative dehydrogenation on the surface and copper sublimation hinders the graphene growth. We report an activation energy of 3.1 eV for ethylene-based graphene synthesis. © The Electrochemical Society.