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.

Mechanism of polarization pinning in vertical cavity surface emitting lasers using focused ion beam etching

Photoluminescence experiments have identified strain as the origin for polarization pinning in vertical cavity surface emitting lasers post-processed by focused ion beam etching. Theoretical models were applied to deduce the strain in devices. Post-annealing was used to optimize polarization pinning.

High power laser with integrated lens using focused ion beam etching

In this study, a collimating lens is introduced at the output facet of a tapered waveguide laser to compensate for the divergence of the optical mode. The collimating lens is shown to enhance the laser efficiency while simultaneously reducing the far field divergence.

Focused ion beam etching of GaN

We have investigated the use of focused ion beam (FIB) etching for the fabrication of GaN-based devices. Although work has shown that conventional reactive ion etching (RIE) is in most cases appropriate for the GaN device fabrication, the direct write facility of FIB etching - a well-established technique for optical mask repair and for IC failure analysis and repair - without the requirement for depositing an etch mask is invaluable. A gallium ion beam of about 20nm diameter was used to sputter GaN material. The etching rate depends linearly on the ion dose per area with a slope of 3.5×10 -4μm3/pC. At a current of 3nA, for example, this corresponds to an etch rate of 1.05μm3/s. Good etching qualities have been achieved with a side wall roughness significantly below 0.1μm. Changes in the roughness of the etched surface plane stay below 8nm.

Droplet Generator

A method and device for periodically perturbing the flow field within a microfluidic device to provide regular droplet formation at high speed.

Method of etching

A method of creating micro patterned devices by patterning thin films which are deposited on a substrate. A channel or channels is created on the substrate, the width being of fine enough resolution such that a flowable mask material can be drawn along the channel by capillary forces.

The dominant role of the solvent-water interface in water droplet templating of polymers

We investigate the formation of microstructured polymer networks known as Breath Figure templated structures created by the presence of water vapour over evaporating polymer solutions. We use a highly controlled experimental approach to examine this dynamic and non-equilibrium process to uniquely compare pure solvent systems with polymer solutions and demonstrate using a combination of optical microscopy, focused ion-beam milling and SEM analysis that the porous polymer microstructure is completely controlled by the interfacial forces that exist between the water droplet and the solvent until a final drying dilation of the imprints. Water droplet contact angles are the same in the presence or absence of polymer and are independent of size for droplets above 5 μm. The polymer acts a spectator that serves to trap water droplets present at the air interface, and to transfer their shape into the polymer film. For the smallest pores, however, there are unexpected variations in the contact angle with pore size that are consistent with a possible contribution from line tension at these smaller dimensions. © The Royal Society of Chemistry.

Electron-beam-induced direct etching of graphene

We present electron-beam-induced oxidation of single- and bilayer graphene devices in a low-voltage scanning electron microscope. We show that the injection of oxygen leads to targeted etching at the focal point, enabling us to pattern graphene with a resolution of better than 20 nm. Voltage-contrast imaging, in conjunction with finite-element simulations, explain the secondary-electron intensities and correlate them to the etch profile. © 2013 Elsevier Ltd. All rights reserved.

Bouncing Water Droplet on a Superhydrophobic Carbon Nanotube Array

Over the past few decades, superhydrophobic materials have attaracted a lot of interests, due to their numerous practical applications. Among various superhydrophobic materials, carbon nanotube arrays have gained enormous attentions simply because of their outstanding properties. The impact dynamic of water droplet on a superhydrophobic carbon nanotube array is shown in this fluid dynamics video.

Water droplet flow paths and droplet deposition in low pressure steam turbines

The complex three-dimensional two-phase flow in a low pressure steam turbine is investigated with comprehensive numerical flow simulations. In addition to the condensation process, which already takes place in the last stages of steam turbines, the numerical flow model is enhanced to consider the drag forces between the droplets and the vapour phase. The present paper shows the differences in the flow path of the phases and investigates the effect of an increasing droplet diameter. For the flow simulations a performance cluster is used because of the high effort for such multi-momentum two-phase flow calculations. In steam turbines the deposition of small water droplets on the stator blades or on parts of the casing is responsible for the formation of large coarse water droplets and these may cause additional dissipation as well as damage due to blade erosion. A method is presented that uses detailed CFD data to predict droplet deposition on turbine stator blades. This simulation method to detect regions of droplet deposition can help to improve the design of water removal devices. © Springer-Verlag Berlin Heidelberg 2013.