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An Introduction to

NanoWires

And Their Applications
Amir Dindar
Shoeb Roman
University of South Alabama
Electrical engin...
An Introduction to Nanowires and their applications

Introduction

• Bottom-up assembled nanoscale electronics
could hold ...
An Introduction to Nanowires and their applications

Introduction

• 1D nanostructures represent the smallest
dimension st...
An Introduction to Nanowires and their applications

Introduction

Single-walled NTs have been used to fabricate
field eff...
An Introduction to Nanowires and their applications

Introduction

Advantages of Nanowires:
• NW devices can be assembled ...
An Introduction to Nanowires and their applications

Introduction

• Semiconductor NWs have been assembled
into a series o...
An Introduction to Nanowires and their applications

Introduction

• Diameter of nanowires range from a single atom to a f...
An Introduction to Nanowires and their applications

Building Blocks Synthesis

Different techniques can be generally grou...
An Introduction to Nanowires and their applications
Building Blocks Synthesis,

Spontaneous Growth

General Idea:
• Anisot...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Evaporation condensation

• Referred to as Vapor-...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Evaporation condensation

(Picture from: “Nanostr...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Evaporation condensation

Mesoporous, single-crys...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Evaporation condensation

Picture : Measuring the...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Evaporation condensation

Ultra-narrow ZnO nanobe...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Dissolution condensation

• Differs from Evaporat...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Vapor Liquid Solid Growth (VLS)

General Idea:
A ...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Vapor Liquid Solid Growth (VLS)

Growth species i...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Vapor Liquid Solid Growth (VLS)

Picture : “A Non...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Vapor Liquid Solid Growth (VLS)

TEM and selected...
An Introduction to Nanowires and their applications
Spontaneous Growth,

Vapor Liquid Solid Growth (VLS)

Z-contrast scann...
An Introduction to Nanowires and their applications

Template Base synthesis

General Idea:
• This is the very general met...
An Introduction to Nanowires and their applications

Template Base synthesis

• Electrochemical Deposition
– Negative temp...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

Negative Templat...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

• The diameter o...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

A porous Templat...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

75 nm

210nm

na...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

Advantages
• The...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

Three typical st...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

stage I
Picture:...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

stage II
Picture...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

stage III
Pictur...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

•To have freely ...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

Positive Templat...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

DNA based templa...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrochemical Deposition

DNA based templa...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrophoretic Deposition
Differs from elec...
An Introduction to Nanowires and their applications
Template Base synthesis,

Electrophoretic Deposition

Method:
•over th...
An Introduction to Nanowires and their applications
Template Base synthesis,

Surface Step-Edge Templates

General Idea
•A...
An Introduction to Nanowires and their applications

Properties and Application of Nanowires

Nanowires are promising mate...
An Introduction to Nanowires and their applications

Properties and Application of Nanowires

Different Nanowires
We can c...
An Introduction to Nanowires and their applications

Properties and Application of Nanowires

The changes in properties ar...
An Introduction to Nanowires and their applications
Properties and Application of Nanowires,

Magnetic Properties
•

Actua...
An Introduction to Nanowires and their applications

Properties and Application of Nanowires,

Optical properties
• Contro...
An Introduction to Nanowires and their applications

NanoElectronic Applications of nanowires

The most important applicat...
An Introduction to Nanowires and their applications

NanoElectronic Applications of nanowires

Sensing Devices

A structur...
An Introduction to Nanowires and their applications
NanoElectronic Applications of nanowires,

Quantum wire Transistor

Re...
An Introduction to Nanowires and their applications
NanoElectronic Applications of nanowires,

Single Electron Memory

•Si...
An Introduction to Nanowires and their applications
NanoElectronic Applications of nanowires,

Metal Semiconductor Junctio...
An Introduction to Nanowires and their applications
NanoElectronic Applications of nanowires,

Metal Semiconductor Junctio...
An Introduction to Nanowires and their applications
NanoElectronic Applications of nanowires,

Metal Nanowire

SEM microgr...
An Introduction to Nanowires and their applications
NanoElectronic Applications of nanowires,

Hierarchical Assembly Nanow...
An Introduction to Nanowires and their applications

Hierarchical Assembly Nanowires,

Electrical Field-Directed Assembly
...
An Introduction to Nanowires and their applications
Hierarchical Assembly Nanowires,
Electrical Field-Directed Assembly

E...
An Introduction to Nanowires and their applications

Hierarchical Assembly Nanowires,

Fluidic Flow-Directed Assembly

•NW...
An Introduction to Nanowires and their applications

Hierarchical Assembly Nanowires,

Fluidic Flow-Directed Assembly

Flu...
An Introduction to Nanowires and their applications

Nanoelectronic application of Nanowires,

Crossed Nanowire devices

T...
An Introduction to Nanowires and their applications

Nanoelectronic application of Nanowires,

Crossed Nanowire devices

(...
An Introduction to Nanowires and their applications

Nanoelectronic application of Nanowires,

Crossed Nanowire devices

S...
An Introduction to Nanowires and their applications

Nanoelectronic application of Nanowires,

Crossed Nanowire devices

S...
An Introduction to Nanowires and their applications

Nanoelectronic application of Nanowires,

Crossed Nanowire devices

S...
An Introduction to Nanowires and their applications

Hierarchical Assembly Nanowires,

Nanoscale Logic Gates and Computati...
An Introduction to Nanowires and their applications

Hierarchical Assembly Nanowires,

Nanoscale Logic Gates
and Computati...
An Introduction to Nanowires and their applications

CONCLUSION

Challenges:
•The insufficient control of the properties o...
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  1. 1. An Introduction to NanoWires And Their Applications Amir Dindar Shoeb Roman University of South Alabama Electrical engineering department
  2. 2. An Introduction to Nanowires and their applications Introduction • Bottom-up assembled 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. • Central to the bottom-up approach are the nanoscale building blocks. University Of South Alabama, EE Department
  3. 3. An Introduction to Nanowires and their applications Introduction • 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 University Of South Alabama, EE Department
  4. 4. An Introduction to Nanowires and their applications Introduction 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 So, to date, device fabrication by NT largely is a random event, thus pose a significant barrier to achieving highly integrated nanocircuits. University Of South Alabama, EE Department
  5. 5. An Introduction to Nanowires and their applications Introduction 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 • Reliable methods exist for their parallel assembly. • 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 University Of South Alabama, EE Department
  6. 6. An Introduction to Nanowires and their applications Introduction • Semiconductor NWs have been assembled into a series of electronic electronics devices: – crossed NW p-n diodes, – crossed NW-FETs, – nanoscale logic gates and computation circuits, – optoelectronic devices • More general applications: – Interconnects for nano electronics – Magnetic devices – Chemical and biological sensors – Biological labels University Of South Alabama, EE Department
  7. 7. An Introduction to Nanowires and their applications Introduction • 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. • Regarding to size (diameter) we have two different types of nanowires: – Classical nanowires – Quantum nanowires University Of South Alabama, EE Department
  8. 8. An Introduction to Nanowires and their applications Building Blocks Synthesis Different techniques can be generally grouped into four categories: • Spontaneous growth: – Evaporation condensation – Dissolution condensation – Vapor-Liquid-Solid growth (VLS) – Stress induced re-crystallization • Template-based synthesis: – Electrochemical deposition – Electrophoretic deposition – Colloid dispersion, melt, or solution filling – Conversion with chemical reaction • Electro-spinning • Lithography (top-down) University Of South Alabama, EE Department
  9. 9. An Introduction to Nanowires and their applications Building Blocks Synthesis, Spontaneous Growth General Idea: • Anisotropic growth is required • Crystal growth proceeds along one direction, where as there is no growth along other direction. • Uniformly sized nanowires (i.e. the same diameter along the longitudinal direction of a given nanowire) University Of South Alabama, EE Department
  10. 10. An Introduction to Nanowires and their applications Spontaneous Growth, Evaporation condensation • Referred 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 University Of South Alabama, EE Department
  11. 11. An Introduction to Nanowires and their applications Spontaneous Growth, Evaporation condensation (Picture from: “Nanostructures of zinc oxide,” by Zhon Lin Wang, http://www.materialstoday.com/pdfs_7_6/zhang.pdf) University Of South Alabama, EE Department
  12. 12. An Introduction to Nanowires and their applications Spontaneous Growth, Evaporation condensation Mesoporous, single-crystal ZnO nanowires. (Picture from: “Nanostructures of zinc oxide,” by Zhon Lin Wang, http://www.materialstoday.com/pdfs_7_6/zhang.pdf) University Of South Alabama, EE Department
  13. 13. An Introduction to Nanowires and their applications Spontaneous Growth, Evaporation condensation Picture : Measuring the Work Function at a Nanobelt Tip and at a Nanoparticle surface, http://www.nanoscience.gatech.edu/zlwang/paper/2003/03_NL_2.pdf University Of South Alabama, EE Department
  14. 14. An Introduction to Nanowires and their applications Spontaneous Growth, Evaporation condensation Ultra-narrow ZnO nanobelts. (Picture from: “Nanostructures of zinc oxide,” by Zhon Lin Wang, http://www.materialstoday.com/pdfs_7_6/zhang.pdf) University Of South Alabama, EE Department
  15. 15. An Introduction to Nanowires and their applications Spontaneous Growth, Dissolution condensation • Differs from Evaporation-condensation • The growth species first dissolve into a solvent or a solution, and then diffuse through the solvent or solution and deposit onto the surface resulting in the growth of nanorods or nanowires. • The nanowires in this method can have a mean length of <500 nm and a mean diameter of ~60 nm University Of South Alabama, EE Department
  16. 16. An Introduction to Nanowires and their applications Spontaneous Growth, Vapor 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 droplet – It precipitates at the interface between the substrate and the liquid University Of South Alabama, EE Department
  17. 17. An Introduction to Nanowires and their applications Spontaneous Growth, Vapor Liquid Solid Growth (VLS) Growth species in the catalyst droplets subsequently precipitates at the growth surface resulting in the one-directional growth University Of South Alabama, EE Department
  18. 18. An Introduction to Nanowires and their applications Spontaneous Growth, Vapor Liquid Solid Growth (VLS) Picture : “A Non-Traditional Vapor-Liquid-Solid Method for Bulk Synthesis of Semiconductor Nanowires,” Shashank Sharma, and Mahendra K. Sunkara, http://www.cvd.louisville.edu/Publications/recentpublications/proceedings_mrs_fall2001.pdf University Of South Alabama, EE Department
  19. 19. An Introduction to Nanowires and their applications Spontaneous Growth, Vapor Liquid Solid Growth (VLS) TEM and selected area diffraction image of a single crystal ZnO nanorod.(~20 nm width). Pictures : “ZnO nanowire growth and devices,” Y.W. Heoa, D.P. Nortona, et al., Materials Science and Engineering R 47 (2004) 1–47 University Of South Alabama, EE Department
  20. 20. An Introduction to Nanowires and their applications Spontaneous Growth, Vapor Liquid Solid Growth (VLS) Z-contrast scanning transmission electron microscopy image of a (Zn,Mg)O nanorod with a Ag catalyst particle at the rod tip. Pictures : “ZnO nanowire growth and devices,” Y.W. Heoa, D.P. Nortona, et al., Materials Science and Engineering R 47 (2004) 1–47 University Of South Alabama, EE Department
  21. 21. An Introduction to Nanowires and their applications Template Base synthesis General Idea: • This 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. University Of South Alabama, EE Department
  22. 22. An Introduction to Nanowires and their applications Template Base synthesis • Electrochemical Deposition – Negative template – Positive template • This is a self-propagating process • This method can be understood as a special electrolysis resulting in the deposition of solid material on an electrode • Only applicable to electrically conductive materials: metals, alloys, semiconductors, and electrical conductive polymers. University Of South Alabama, EE Department
  23. 23. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition Negative Template • use prefabricated cylindrical nanopores in a solid material as templates • There are several ways to fill the nanopores to form nanowires, but the electrochemical method is a general and versatile method. • Electrodeposition often requires a metal film on one side of the freestanding membrane to serve as a working electrode on which electrodeposition takes place • If dissolve away the host solid material, freestanding nanowires are obtained. University Of South Alabama, EE Department
  24. 24. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition • The diameter of the nanowires is determined by the geometrical constraint of the pores • Fabrication of suitable templates is clearly a critical first step University Of South Alabama, EE Department
  25. 25. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition A porous Template Nanowire array Picture: “Fabrication of Polypyrrole Nanowire and Nanotube Arrays,” Fa-Liang Cheng*, Ming-Liang Zhang and Hong Wang, http://www.mdpi.net/sensors/papers/s5040245.pdf University Of South Alabama, EE Department
  26. 26. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition 75 nm 210nm nano wires grown in a 80nm template membrane after dissolution of the membrane. 100nm Picture: “Fabrication of Polypyrrole Nanowire and Nanotube Arrays,” Fa-Liang Cheng*, Ming-Liang Zhang and Hong Wang, http://www.mdpi.net/sensors/papers/s5040245.pdf University Of South Alabama, EE Department
  27. 27. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition Advantages • The ability to create highly conductive nanowires. Because electrodeposition relies on electron transfer, which is the fastest along the highest conductive path. • electrodeposited nanowires tend to be dense, continuous, and highly crystalline in contrast to other deposition methods. • the ability to control the aspect ratio of the metal nanowires by monitoring the total amount of passed charge. University Of South Alabama, EE Department
  28. 28. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition Three typical stages in electrodeposition process: stage I: corresponds to the electrodeposition of metal into the pores until they are filled up to the top surface of the membrane (stage I) Stage II: the pores are filled up with deposited metal, metal grow out of the pores and forms hemispherical caps on the membrane surface Stage III: When the hemispherical caps coalescence into a continuous film University Of South Alabama, EE Department
  29. 29. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition stage I Picture: Template Synthesis of Nanowires in Porous Polycarbonate Membranes: Electrochemistryand Morphology, http://www.phys.ens.fr/~bachtold/publication/wire-JPCB.pdf University Of South Alabama, EE Department
  30. 30. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition stage II Picture: Template Synthesis of Nanowires in Porous Polycarbonate Membranes: Electrochemistryand Morphology, http://www.phys.ens.fr/~bachtold/publication/wire-JPCB.pdf University Of South Alabama, EE Department
  31. 31. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition stage III Picture: Template Synthesis of Nanowires in Porous Polycarbonate Membranes: Electrochemistryand Morphology, http://www.phys.ens.fr/~bachtold/publication/wire-JPCB.pdf University Of South Alabama, EE Department
  32. 32. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition •To have freely standing nanowires we have to remove the template hosts after forming the nanowires in the templates by dissolving away the template materials in a suitable solvent. •If want to separate the nanowires from the metal films on which the nanowire are grown, a common method is to first deposit a sacrificial metal. University Of South Alabama, EE Department
  33. 33. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition Positive Template Method •Use wire-like nanostructures, such as DNA and carbon nanotubes as templates. •Nanowires are formed on the outer surface of the templates •Diameter of the nanowires is not restricted by the template sizes and can be controlled by adjusting the amount of materials deposited on the templates •Removing the templates after deposition, wire-like and tube-like structures can be formed University Of South Alabama, EE Department
  34. 34. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition DNA based template DNA is an excellent choice as a template to fabricate nanowires because its diameter is ~2 nm and its length and sequence can be precisely controlled General procedure: Fix a DNA strand between two electrical contacts Exposed to a solution containing some ions Ions bind to DNA and are then form some nanoparticles decorating along the DNA chain University Of South Alabama, EE Department
  35. 35. An Introduction to Nanowires and their applications Template Base synthesis, Electrochemical Deposition DNA based template General procedure: •Fix a DNA strand between two electrical contacts •Exposed to a solution containing some ions •Ions bind to DNA and are then form some nanoparticles decorating along the DNA chain University Of South Alabama, EE Department
  36. 36. An Introduction to Nanowires and their applications Template Base synthesis, Electrophoretic Deposition Differs from electrochemical deposition in several aspects The deposit need not be electrically conductive Particularly for oxide nanowires: SiO2, TiO2, Bi2O3, etc. Different sizes of TiO2 nanorods grown in a membrane by sol electrophoretic deposition. Diameters: (A) 180 nm, (B) 90 nm, (C) 45 nm Picture: “A study on the growth of TiO2 nanorods using sol electrophoresis,” S. J. LIMMER, T. P. CHOU, G. Z. CAO, University of Washington, http://faculty.washington.edu/gzcao/publications/papers/31.pdf University Of South Alabama, EE Department
  37. 37. An Introduction to Nanowires and their applications Template Base synthesis, Electrophoretic Deposition Method: •over the surface of nanoparticles develops an electrical charge via some chemical techniques. This combination is typically called Counter-Ion •Upon application of an external electric filed to a system of charged nanosize particle system, the particles are set in motion in response to the electric filed •This type of motion is referred to as electrophoresis. •The rest of this technique, in general, is the same as electrochemical deposition. University Of South Alabama, EE Department
  38. 38. An Introduction to Nanowires and their applications Template Base synthesis, Surface Step-Edge Templates General Idea •Atomic-scale steps on a crystal surface can be used as templates to grow nanowires. •The method takes the advantage of the fact that deposition of many materials on the surface often starts preferentially at defect sites, such as surface step-edges. •The problem is that these nanowires can not be easily removed from the surface on which they are deposited University Of South Alabama, EE Department
  39. 39. An Introduction to Nanowires and their applications 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 University Of South Alabama, EE Department
  40. 40. An Introduction to Nanowires and their applications Properties and Application of Nanowires Different Nanowires We can categorize different types of nanowires regarding to the materials as follows: • • • • • Metal nanowires Semiconductor nanowires (Silicon nanowires) Oxide nanowires Multi-segment nanowires Semiconductor quantum wires University Of South Alabama, EE Department
  41. 41. An Introduction to Nanowires and their applications Properties and Application of Nanowires The changes in properties arise from quantum confinement. • Quantum confinement describes how the electronic and optical properties change when the sampled material is in sufficiently small amounts, typically 10 nanometers or less. • Specifically, the phenomenon results from electrons and holes being squeezed into a dimension that approaches a critical quantum measurement. University Of South Alabama, EE Department
  42. 42. An Introduction to Nanowires and their applications Properties and Application of Nanowires, 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) In a viscous solvent, magnetic field can be used to orient the growing nanowires. University Of South Alabama, EE Department
  43. 43. An Introduction to Nanowires and their applications Properties and Application of Nanowires, 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 University Of South Alabama, EE Department
  44. 44. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires The 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 University Of South Alabama, EE Department
  45. 45. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires Sensing Devices A structure for transport measurements sensor by nanowires Pictures : “ZnO nanowire growth and devices,” Y.W. Heoa, D.P. Nortona, et al., Materials Science and Engineering R 47 (2004) 1–47 University Of South Alabama, EE Department
  46. 46. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires, Quantum wire Transistor Recent advances in formation methods allowed the fabrication of silicon quantum-wire transistors •The quantum wires have a width of 65 nm and are fully embedded in silicon dioxide. •A coulomb staircase, that is, step-like conductance versus gate voltage, was observed at temperature below 4.2 K. •Some techniques used Single electron Transistor based on a 30 nm wide Si NW, which can be operate at 77 K. The device showed clear single electron tunneling and welldefined single island and two tunnel junctions. University Of South Alabama, EE Department
  47. 47. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires, Single Electron Memory •Single electron memory cells consume extremely low power and can be realized by using the coulomb blockade effect. •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 generated. University Of South Alabama, EE Department
  48. 48. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires, Metal Semiconductor Junction •Junctions between carbon nanotubes and silicon nanowires has been done. •To fabricate NT/SiNW junctions, SiNWs are grown from the end of the NT tips. •It has a characteristic the same as metalsemiconductor Schottkey diode. University Of South Alabama, EE Department
  49. 49. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires, Metal Semiconductor Junction (Picture from: “Controlled growth and electrical properties of heterojunctions of carbon nanotubes and silicon nanowires,” Jiangtao Hu et al. , http://cmliris.harvard.edu/publications/1999/nature399_48.pdf) University Of South Alabama, EE Department
  50. 50. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires, Metal Nanowire SEM micrograph of single ZnO nanowire bridging two Al/Pt/Au Ohmic contact Pictures : “ZnO nanowire growth and devices,” Y.W. Heoa, D.P. Nortona, et al., Materials Science and Engineering R 47 (2004) 1–47 University Of South Alabama, EE Department
  51. 51. An Introduction to Nanowires and their applications NanoElectronic Applications of nanowires, Hierarchical Assembly Nanowires First: methods are needed to assemble NWs into highly integrated arrays with controlled orientation and spatial position. Second: approaches must be devised to assemble NWs on multiple length scales and to make interconnects between nano-, micro- and macroscopic worlds. In this regard, there are two promising approaches: Electrical field-directed assembly Fluidic flow-directed assembly. University Of South Alabama, EE Department
  52. 52. An Introduction to Nanowires and their applications Hierarchical Assembly Nanowires, Electrical Field-Directed Assembly •Electrical fields can be used effectively to attract and align NWs due to their highly anisotropic structures and large polarizabilities •Can also be used to position individual NWs at specific positions with controlled directionality •can be carried out in a layer-by-layer fashion to produce crossed NW junctions. Limitations •The need for conventional lithography to pattern microelectrode arrays used to produce aligning fields •The effect of fringing electric fields at the submicron length scales. University Of South Alabama, EE Department
  53. 53. An Introduction to Nanowires and their applications Hierarchical Assembly Nanowires, Electrical Field-Directed Assembly E-field-directed assembly of NWs. (a) Schematic view of E-field alignment. (b) Parallel array of NWs aligned between two parallel electrodes. (c) Spatially positioned parallel array of NWs obtained following E-field assembly. The top inset shows 15 pairs of parallel electrodes with individual NWs bridging each diametrically opposed electrode pair. (d) Crossed NW junction obtained using layer-by-layer alignment with the E-field applied in orthogonal directions in the two assembly steps. Picture: “Integrated nanoscale electronics and optoelectronics: Exploring nanoscale science and technology through semiconductor nanowires,” Yu Huang1,2,‡ and Charles M. Lieber3. Pure Appl. Chem., Vol. 76, No. 12, pp. 2051–2068, 2004. University Of South Alabama, EE Department
  54. 54. An Introduction to Nanowires and their applications Hierarchical Assembly Nanowires, Fluidic Flow-Directed Assembly •NWs can be aligned by passing a suspension of NWs through microfluidic channel structures over a flat substrate, so all of the NWs are aligned along the flow direction. •Can be used to organize NWs into more complex crossed NW structures, which are critical for building high-density nanodevice arrays, using a layer-by-layer deposition process. University Of South Alabama, EE Department
  55. 55. An Introduction to Nanowires and their applications Hierarchical Assembly Nanowires, Fluidic Flow-Directed Assembly Fluidic flow-directed assembly of NWs. (a,b) Schematic (a) and SEM image (b) of parallel NW arrays obtained by passing a NW solution through a channel on a substrate; (c,d) Schematic (c) and SEM image (d) of crossed NW matrix obtained by orthogonally changing the flow direction in a sequential flow alignment process. (e,f) Schematic (e) and SEM image (f) of regular NW arrays obtained by flowing NW solution over a chemically patterned surface. (g,h) Parallel and crossed NW device arrays obtained with fluidic flow assembly. Picture: “Integrated nanoscale electronics and optoelectronics: Exploring nanoscale science and technology through semiconductor nanowires,” Yu Huang1,2,‡ and Charles M. Lieber3. Pure Appl. Chem., Vol. 76, No. 12, pp. 2051–2068, 2004. University Of South Alabama, EE Department
  56. 56. An Introduction to Nanowires and their applications Nanoelectronic application of Nanowires, Crossed Nanowire devices The crossed NW structure can be configured into a variety of devices, such as diodes and transistors. A p-n diode can be obtained by simply crossing p- and n-type NW. Picture: “Indium phosphide nanowires as building blocks for nanoscale electronic and optoelectronic devices,” Xiangfeng Duan, http://www.phy.cuhk.edu.hk/~jfwang/PDF/2001 Nature InP NW.pdf University Of South Alabama, EE Department
  57. 57. An Introduction to Nanowires and their applications Nanoelectronic application of Nanowires, Crossed Nanowire devices (c) Schematics illustrating the crossed NW-FET concept. (d) Gate-dependent I-V characteristics of a cNW-FET formed using a p-NW as the conducting channel and n-NW as the local gate. The red and blue curves in the inset show Isd vs. Vgate for n-NW (red) and global back (blue) gates when the Vsd is set at 1 V. The conductance modulation (>105) of the FET is much more significant with the NW gate than that with a global back gate (<10). Picture: “Integrated nanoscale electronics and optoelectronics: Exploring nanoscale science and technology through semiconductor nanowires,” Yu Huang1,2,‡ and Charles M. Lieber3. Pure Appl. Chem., Vol. 76, No. 12, pp. 2051–2068, 2004. University Of South Alabama, EE Department
  58. 58. An Introduction to Nanowires and their applications Nanoelectronic application of Nanowires, Crossed Nanowire devices SEM micrograph of ZnO nanowire Schottky diode and its I-V curve both in the dark and with UV illumination Pictures : “ZnO nanowire growth and devices,” Y.W. Heoa, D.P. Nortona, et al., Materials Science and Engineering R 47 (2004) 1–47 University Of South Alabama, EE Department
  59. 59. An Introduction to Nanowires and their applications Nanoelectronic application of Nanowires, Crossed Nanowire devices SEM micrograph of fabricated FET. Pictures : “ZnO nanowire growth and devices,” Y.W. Heoa, D.P. Nortona, et al., Materials Science and Engineering R 47 (2004) 1–47 University Of South Alabama, EE Department
  60. 60. An Introduction to Nanowires and their applications Nanoelectronic application of Nanowires, Crossed Nanowire devices SEM micrographs of ZnO MOSFET structure Pictures : “ZnO nanowire growth and devices,” Y.W. Heoa, D.P. Nortona, et al., Materials Science and Engineering R 47 (2004) 1–47 University Of South Alabama, EE Department
  61. 61. An Introduction to Nanowires and their applications Hierarchical Assembly Nanowires, Nanoscale Logic Gates and Computational Circuits •Diodes and transistors represent two basic device elements in logic gates. •Crossed NW p-n diodes and NW-FETs enable more complex circuits, such as logic gates to be produced. •A two-input logic OR gate was realized using a 2(p) by 1(n) crossed NW p-n diode array •A two-input logic AND gate can also be realized using two diodes and one NWFET •Similarly NOR gate with three NWFETs in series University Of South Alabama, EE Department
  62. 62. An Introduction to Nanowires and their applications Hierarchical Assembly Nanowires, Nanoscale Logic Gates and Computational Circuits Picture: “Integrated nanoscale electronics and optoelectronics: Exploring nanoscale science and technology through semiconductor nanowires,” Yu Huang1,2,‡ and Charles M. Lieber3. Pure Appl. Chem., Vol. 76, No. 12, pp. 2051– 2068, 2004. University Of South Alabama, EE Department
  63. 63. An Introduction to Nanowires and their applications 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 University Of South Alabama, EE Department
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