Published on February 11, 2014
NANOWIRES Msc Physics
INTRODUCTION Nanoscale electronics could hold the promise of powering future electronic devices that can outperform existing devices and open up totally new opportunities. It will require conceptually new device building blocks, scalable circuit architectures, and fundamentally different fabrication strategies.
1D nanostructures represent the smallest dimension structure that can efficiently transport electrical carriers 1D nanostructures can also exhibit critical device function, and thus can be exploited as both the wiring and device elements in future architectures for functional nanosystems In this regard, two material classes: semiconductor nanowires (NWs) carbon nanotubes (NTs) have shown particular promise
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 So, to date, device fabrication by NT largely is a random event, thus pose a significant barrier to achieving highly integrated nanocircuits
Advantages of Nanowires NW devices can be assembled in a rational and predictable because: Nanowires can be precisely controlled during synthesis, chemical composition, diameter, length, doping/electronic properties It is possible to combine distinct NW building blocks in ways not possible in conventional electronics. NWs thus represent the best-defined class of nanoscale building blocks, and this precise control over key variables has correspondingly enabled a wide range of devices and integration strategies to be pursued
WHAT ARE NANOWIRES? Nanowires are microscopic wires that have a width measured in nanometers. Typically their width ranges from forty to fifty nanometers, but their length is not so limited. Since they can be lengthened by simply attaching more wires end to end or just by growing them longer, they can be as long as desired.
Diameter of nanowires range from a single atom to a few hundreds of nanometers. Length varies from a few atoms to many microns Different name of nanowires in literature: Whiskers, fibers: 1D structures ranging from several nanometers to several hundred microns Nanowires: Wires with large aspect ratios (e.g. >20), Nanorods: Wires with small aspect ratios. NanoContacts: short wires bridged between two larger electrodes.
SYNTHESIS OF NANOWIRES Some of the recent successful synthesis of nanowires are based on the so-called vapor-liquidsolid (VLS) mechanism
VAPOR LIQUID SOLID GROWTH (VLS)
VAPOR LIQUID SOLID GROWTH (VLS) TEM and selected area diffraction image of a single crystal ZnO nanorod.(~20 nm width).
PROPERTIES AND APPLICATION OF NANOWIRES Nanowires are promising materials for many novel applications Not only because of their unique geometry, but also because they possess many unique physical properties, including : electrical magnetic optical mechanical
MAGNETIC PROPERTIES • Actually the magnetic properties of nanowires depend on the wire diameter and aspect ratio • It is possible to control the magnetic properties of the nanowires by controlling the fabrication parameters • Remanence ratio, which measures the remanence magnetization after switching off the external magnetic field • Coercivity, which is the coercive field required to demagnetize the magnet after full magnetization. • Giant Magnetoresistance (GMR)
OPTICAL PROPERTIES • Controlling the flow of optically encoded information with nanometer-scale accuracy over distances of many microns, which may find applications in future high-density optical computing. • Silicon nanowires coated with SiC show stable photoluminescence at room temperature
STRIPED NANOWIRES Striped nanowires are capable of performing more than one task along the same wire. They are striped with different materials that posses different properties, an attribute which allows different operations to be performed at the same time. This also enables devices to be more compacted because fewer wires are needed; each nanowire is serving multiple functions
WHY ARE NANOWIRES NOT BEING IMPLEMENTED? Nanowires are not being heavily manufactured because they are still in the development stage and are only produced in the laboratory. Until production has been streamlined, made easier and faster, they will not be heavily manufactured for commercial purposes. Furthermore, though they are 4 or 5 times more effective than current technology, an industry-wide technology overhaul is not cost effective at the moment
WHAT USES ARE NANOWIRES BEING DEVELOPED FOR? IBM has been doing research on forming U-shaped nanowires to create a “racetrack memory”. This method would allow IBM to create a memory system with no moving parts and far greater storage than flash memory. This U-shape is formed with closely arranged nanowires, allowing fast transmissions and increasing storage size without adding to the overall size of the device. Nanowires are also being developed for prototype sensors. These sensors will be used on gases and biological molecules
WHAT GOOD ARE NANOWIRES? Some uses of nanowires include: Data storage/transfer Batteries/generators Transistors LED’s Optoelectronic devices Biochemical sensors Heat-pumping Thermoelectric devices
CONCLUSION • • • • • • Challenges: The insufficient control of the properties of individual building blocks Low device-to-device reproducibility Lack of reliable methods for assembling and integrating building blocks into circuits Advances: Synthesis of nanoscale building blocks with precisely controlled chemical composition, physical dimension, and electronic, optical properties Some strategies for the assembly of building blocks into increasingly complex structures New nanodevice concepts that can be implemented in high yield by assembly approaches
REFERENCE Essentials of nanotechnology; Jeremy ramsdan Nanotubes& Nanowires; C N Ram Rao Nanotubes& Nanowires; Peter John Burke Wikipedia Nanowires: A Platform for Nanoscience& Nanotechnology; Charles M. Lieber
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