PowerPoint Presentation

Synthesis of Polymer Nanowires1OutlineIntroductionWhy Nanowires?Synthesis TechniquesAdvantagesApplicationsChallenges

2Introduction1D nanostructures can also exhibit critical device function, and thus can be exploited as both the wiring and device elements in future architectures for functional nanosystemsDiameter of nanowires range from a single atom to a few hundreds of nanometersLength varies from a few atoms to many micronsDifferent name of nanowires in literature: Whiskers, fibers Nanowires Nanorods NanoContacts3Why Nanowires?Single-walled NTs have been used to fabricate field effect transistors, diodes, and logic circuits. Problems with Nanotubes to made devices:Difficulties to control whether building blocks are semiconducting or metallic Difficulties in manipulating individual NTs

4Synthesis TechniquesSpontaneous growth:Evaporation condensationDissolution condensationVapor-Liquid-Solid growth (VLS)Stress induced re-crystallizationTemplate-based synthesis:Electrochemical depositionElectrophoretic depositionColloid dispersion, melt, or solution fillingConversion with chemical reactionElectro-spinningLithography (top-down)

5Evaporation CondensationReferred to as Vapor-Solid (VS) technique.

Nanowires and nanorods grown by this method are commonly single crystals with fewer imperfections

The formation of nanowires or nanorods is due to the anisotropic growth.

The general idea is that the different facets in a crystal have different growth rates

There is no control on the direction of growth of nanowire in this method 6Contd..

Mesoporous, single-crystal ZnO nanowires.7Vapour Liquid Solid Growth (VLS)General Idea:A second phase material, commonly referred to as catalyst, is introduces to direct and confine the crystal growth on a specific orientation and within a confined area.Catalyst forms a liquid droplet by itself Acts as a trap for growth species The growth species is evaporated first and then diffuses and dissolves into a liquid dropletIt precipitates at the interface between the substrate and the liquid8

Growth species in the catalyst droplets subsequently precipitates at the growth surface resulting in the one-directional growth VLS9

A Non-Traditional Vapor-Liquid-Solid Method for Bulk Synthesis of Semiconductor Nanowires http://www.cvd.louisville.edu/Publications/recentpublications/proceedings_mrs_fall2001.pdfVLS10Template Base SynthesisThis is the very general method

Use in fabrication of nanorods, nanowires, and nanotubes of polymers, metals, semiconductors, and oxides.

Some porous membrane with nano-size channels (pores) are used as templates from conduct the growing of nanowires

Pore size ranging from 10 nm to 100 mm can be achieved. 11

The diameter of the nanowires is determined by the geometrical constraint of the pores

Fabrication of suitable templates is clearly a critical first step Contd..12

A porous TemplateNanowire arrayContd..13Template Base SynthesisUse wire-like nanostructures, such as DNA and carbon nanotubes as templatesDNA is an excellent choice as a template to fabricate nanowires because its diameter is ~2 nm and its length and sequence can be precisely controlledNanowires are formed on the outer surface of the templatesDiameter of the nanowires is not restricted by the template sizes and can be controlled by adjusting the amount of materials deposited on the templatesRemoving the templates after deposition, wire-like and tube-like structures can be formed14DNA Based TemplateFix a DNA strand between two electrical contactsExposed to a solution containing some ionsIons bind to DNA and are then form some nanoparticles decorating along the DNA chain

15Advantages NW devices can be assembled in a rational and predictable because:Nanowires can be precisely controlled during synthesis, chemical composition, diameter, Length,doping/electronic propertiesReliable methods exist for their parallel assemblyIt is possible to combine distinct NW building blocks in ways not possible in conventional electronics.16ApplicationsThe most important application of nanowires in nanoelectronics is using them as junctions or as multi-segment nanowires or crossed nanodevices.

Potential application of nanowires is in: very dense logic dense memory optoelectronics sensing devices 17AdvancementSingle electron memory cells consume extremely low power and can be realized

Important components of such a device are a silicon nanowire as a channel, a silicon nanodot as a storage node, and a silicon nanogate as a control gate

To realize these memory devices, narrow Si NWs need to be generated18These polymers are electrochemically or chemically polymerized from corresponding monomers using an oxidizing agent (Martin, 1994). This process is composed of simple steps: 1) Fill nanopores of the membrane with monomers, 2) Polymerize the monomers inside the nanopores, and3)Remove the nanopore template to obtain pure polymers.In some cases, polymer nanowires can be destroyed or damaged because the template removal process entails harsh conditions. AAO, one of the most widely used nano templates.