Fabrication and electrical integration of robust carbon nanotube micropillars by self-directed elastocapillary densification

Vertically aligned carbon nanotube (CNT) 'forest' microstructures fabricated by chemical vapor deposition (CVD) using patterned catalyst films typically have a low CNT density per unit area. As a result, CNT forests have poor bulk properties and are too fragile for integration with microfabrication processing. We introduce a new self-directed capillary densification method where a liquid is controllably condensed onto and evaporated from the CNT forests. Compared to prior approaches, where the substrate with CNTs is immersed in a liquid, our condensation approach gives significantly more uniform structures and enables precise control of the CNT packing density. We present a set of design rules and parametric studies of CNT micropillar densification by self-directed capillary action, and show that self-directed capillary densification enhances Young's modulus and electrical conductivity of CNT micropillars by more than three orders of magnitude. Owing to the outstanding properties of CNTs, this scalable process will be useful for the integration of CNTs as a functional material in microfabricated devices for mechanical, electrical, thermal and biomedical applications. © 2011 IOP Publishing Ltd.

Tailoring GaAs, InAs, and InGaAs nanowires for optoelectronic device applications

GaAs, InAs, and InGaAs nanowires each exhibit significant potential to drive new applications in electronic and optoelectronic devices. Nevertheless, the development of these devices depends on our ability to fabricate these nanowires with tight control over critical properties, such as nanowire morphology, orientation, crystal structure, and chemical composition. Although GaAs and InAs are related material systems, GaAs and InAs nanowires exhibit very different growth behaviors. An understanding of these growth behaviors is imperative if high-quality ternary InGaAs nanowires are to be realized. This report examines GaAs, InAs, and InGaAs nanowires, and how their growth may be tailored to achieve desirable material properties. GaAs and InAs nanowire growth are compared, with a view toward the growth of high-quality InGaAs nanowires with device-accessible properties. © 2011 IEEE.

III-V semiconductor nanowires for optoelectronic device applications

Semiconductor nanowires have recently emerged as a new class of materials with significant potential to reveal new fundamental physics and to propel new applications in quantum electronic and optoelectronic devices. Semiconductor nanowires show exceptional promise as nanostructured materials for exploring physics in reduced dimensions and in complex geometries, as well as in one-dimensional nanowire devices. They are compatible with existing semiconductor technologies and can be tailored into unique axial and radial heterostructures. In this contribution we review the recent efforts of our international collaboration which have resulted in significant advances in the growth of exceptionally high quality IIIV nanowires and nanowire heterostructures, and major developments in understanding the electronic energy landscapes of these nanowires and the dynamics of carriers in these nanowires using photoluminescence, time-resolved photoluminescence and terahertz conductivity spectroscopy. © 2011 Elsevier Ltd. All rights reserved.

III-V compound semiconductor nanowires for optoelectronic device applications

GaAs and InP based III-V compound semiconductor nanowires were grown epitaxially on GaAs (or Si) (111)B and InP (111)B substrates, respectively, by metalorganic chemical vapor deposition using Au nanoparticles as catalyst. In this paper, we will give an overview of nanowire research activities in our group. In particular, the effects of growth parameters on the crystal structure and optical properties of various nanowires were studied in detail. We have successfully obtained defect-free GaAs nanowires with nearly intrinsic exciton lifetime and vertical straight nanowires on Si (111)B substrates. The crystal structure of InP nanowires, i.e., WZ or ZB, can also be engineered by carefully controlling the V/III ratio and catalyst size. © 2011 World Scientific Publishing Company.

Nanowires for optoelectronic device applications

GaAs and InP based nanowires were grown epitaxially on GaAs or InP (111)B substrates by metalorganic chemical vapor deposition using Au nanoparticles as catalyst. In this paper, we will give an overview of nanowire research activities in our group. In particular, the effects of growth parameters for GaAs and InP nanowires on the crystal quality were studied in detail. We demonstrated the ability to obtain defect-free GaAs nanowires via either two-temperature procedure, or by controlling V/III ratio or growth rate. The crystal structure of InP nanowires, ie, WZ or ZB, can also be engineered by just controlling the V/III ratio. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

Epitaxy of III-V semiconductor nanowires towards optoelectronic devices

GaAs and InP based nanowires were grown epitaxially on GaAs or InP (111)B substrates by MOCVD via VLS mechanism. In this paper, I will give an overview of nanowire research activities in our group. © 2009 IEEE.

Growth, structural and optical properties of III-V nanowires for optoelectronic applications

We investigate the growth of III-V nanowires by MOCVD and the structural and optical properties of these nanowires. Binary and ternary nanowires of GaAs, InAs, InP, AlGaAs and InGaAs are achieved. We discuss the nucleation and growth issues involved in fabricating high quality nanowires suitable for device applications. We have fabricated and characterised a variety of axial and radial heterostructures including GaAs/InGaAs superlattices, and GaAs/AlGaAs core-shell and core-multishell nanowires. © 2007 IEEE.

Framework for integration of informal waste management sector with the formal sector in Pakistan.

Historically, waste pickers around the globe have utilised urban solid waste as a principal source of livelihood. Formal waste management sectors usually perceive the informal waste collection/recycling networks as backward, unhygienic and generally incompatible with modern waste management systems. It is proposed here that through careful planning and administration, these seemingly troublesome informal networks can be integrated into formal waste management systems in developing countries, providing mutual benefits. A theoretical framework for integration based on a case study in Lahore, Pakistan, is presented. The proposed solution suggests that the municipal authority should draw up and agree on a formal work contract with the group of waste pickers already operating in the area. The proposed system is assessed using the integration radar framework to classify and analyse possible intervention points between the sectors. The integration of the informal waste workers with the formal waste management sector is not a one dimensional or single step process. An ideal solution might aim for a balanced focus on all four categories of intervention, although this may be influenced by local conditions. Not all the positive benefits will be immediately apparent, but it is expected that as the acceptance of such projects increases over time, the informal recycling economy will financially supplement the formal system in many ways.

Modelling of free-space optoelectronic switching with MPLS for storage area networks (SANs)

Low-cost optical switches based on SLMs have conventionally been considered unsuitable for packet switching due to slow reconfiguration time. In this paper, we demonstrate that the constraint of SLM reconfiguration time in a hybrid three-stage electronic/optical switching node architecture can be compensated through the utilization of MPLS label switching mechanism to achieve the best performance for SAN applications. © 2012 SEE.

Integration of silicon plasmonic schottky photodetector for on chip signal tapping at telecom wavelengths

We experimentally demonstrate the use of an on-chip integrated Schottky plasmonic detector for testing, monitoring and tapping signals in plasmonic and photonic devices. Theoretical model and measurement of external and integrated devices will be presented. © OSA 2013.

Integration of silicon plasmonic schottky photodetector for on chip signal tapping at telecom wavelengths

We experimentally demonstrate the use of an on-chip integrated Schottky plasmonic detector for testing, monitoring and tapping signals in plasmonic and photonic devices. Theoretical model and measurement of external and integrated devices will be presented. © OSA 2013.

Integration of silicon plasmonic schottky photodetector for on chip signal tapping at telecom wavelengths

We experimentally demonstrate the use of an on-chip integrated Schottky plasmonic detector for testing, monitoring and tapping signals in plasmonic and photonic devices. Theoretical model and measurement of external and integrated devices will be presented. © OSA 2013.

Fabrication and integration of horizontally aligned carbon nanotube C60 films for UV sensors

Carbon nanotubes (CNTs) are promising for microsystems applications, yet few techniques effectively enable integration of CNTs with precise control of placement and alignment of the CNTs at sufficiently high densities necessary for compelling mechanical or electrical performance. This paper explores new methods for scalable integration of dense, horizontally aligned (HA) CNTs with patterned electrodes. Our technique involves the synthesis of vertically aligned (VA) CNTs directly on a conductive underlayer and subsequent mechanical transformation into HA-CNTs, thus making electrical contact between two electrodes. We compare elasto-capillary folding and mechanical rolling as methods for transforming VA-CNTs, which lead to distinctly different HA-CNT morphologies and potentially impact material and device properties. As an example application of this novel CNT morphology, we investigate fabrication of electrically addressable CNT-C60 hybrid thin films that we previously demonstrated as photodetectors. We synthesize these assemblies by crystallizing C60 from dispersion on HA-CNT thin-film scaffoldings. HA-CNTs fabricated by rolling result in relatively low packing density, so C 60 crystals embed inside the HA-CNT matrix during synthesis. On the other hand, C60 crystallization is restricted to near the surface of HA-CNT films made by the elasto-capillary process. © 2013 IEEE.

Electro-optic integration of liquid crystal cladding switch with multimode passive polymer waveguides on PCB

Optical switching functionality is demonstrated in PCB integrated multimode passive polymer waveguides using a localised liquid-crystal cladding structure. Waveguide switching contrast of 15 dB is achieved with only 0.5 dB of on-state excess loss. © 2009 OSA.