1. Chapter 3: Nanowires
Lecture by:
Rose Farahiyan Munawar , PhD

4. Models of 3-D nanostructures made from DNA.

8. Pre-Quiz
~ Ok from the image, which one is 1-D nanostructure?

9. Nanowires
quantum wire, metallic nanowire, semiconductor nanowire, insulating nanowire, molecular nanowire, nanowire arrays, nanowire, alumina nanowire, bismuth nanowire, boron nanowire, cadmium selenide nanowire, copper nanowire, gallium nitride nanowire, gold nanowire, gallium phosphide nanowire, germanium nanowire, indium phosphide nanowire, magnesium oxide nanowire, manganese oxide nanowire, nickel nanowire, palladium nanowire, platinum nanowire, silicon nanowire, silicon carbide nanowire, silicon nitride nanowire, titanium dioxide nanowire, zinc oxide nanowire, gold microwire, silicon microwire,

10. Nanowire (Nw)
~ this is Nw, basically have a certain diameters and lengths

11. Why Nanowires?
~ so, obviously the electronic properties are the important properties for NWs

12. Why Nanowires?
The nanowires could be used, in the near future, to link tiny components into extremely small circuits. Using nanotechnology, such components could be created out of chemical compounds.

13. Advantages of NWs:
• NW devices can be assembled in a rational and predictable because:
– NWs can be precisely controlled during synthesis,
– chemical composition,
–diameter,
–length,
– doping/electronic properties
Reliable methods exist for their parallel assembly.

14. Advantages of NWs:
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 correspondingly enabled a wide range of devices and integration strategies to be pursued

15. Structure of NWs
Whiskers, fibers:1D structures ranging from several nanometers to seve ral 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.
~ Different name of nanowires in literature….

16. Structure of NWs
~ Schematic illustration of different 1D nanostructure morphologies and the terms typically used to describe them: ~ (a) nanowires (NWs), nanofibres or whiskers;
~ (b) nanorods (NRs);
~ (c) nanobelts (NBs) or nanoribbons and
~ (d) nanotubes (NTs).
~ Among these structures, the only ones restricted to a certain cross-section are NBs, which typically have one dimension of a few nanometres and a second dimension up to the range of hundreds of nm.

17. Structure of NWs
A nanowire is a nanostructure, with the diameter of the order of a nanometer (10-9 meters). Alternatively, nanowires can be defined as structures that have a thickness or diameter constrained around tens of nanometers or less and an unconstrained length.
~ Diameter of nanowires range from a single atom to a few hundreds of nanometers.
~ Length varies from a few atoms to many microns
~ Diameter 10s nanometer

18. Structure of NWs
At these scales, quantum mechanical effects are important — hence such wires are also known as "quantum wires". Presently diameters as small as 12 nanometers

19. Structure of NWs
Typical nanowires exhibit aspect ratios (length-to-width ratio) of 1000 or more. As such they are often referred to as one-dimensional (1-D) materials.

20. Nanowires Structure
The nanowires can show peculiar shapes. Single crystal formation- common crustallographic orientation along the nanowire axis Sometimes they can show noncrystalline order, assuming e.g. a pentagonal symmetry or a helicoidal (spiral) shape.

21. Helical Nanowire

22. Nanowires Structure
The lack of crystalline order is due to the fact that a nanowire is periodic only in one dimension (along its axis).
Minimal defects within wire
Minimal irregularities within nanowire.

23. Nanowires Structure
Electrons zigzag along pentagonal tubes and spiral along helicoidal tubes. Hence it can assume any order in the other directions (in plane) if this is energetically favorable. thin, brittle, can be electrically conductive, quantum effects can be important

24. Structure of NWs
Hence it can assume any order in the other direction NWs are observed spontaneously in nature.
Nanowires can be either suspended, deposited or synthesized from the elements.

25. Types of nanowires (diameter)1
Classical Nanowires 2
Quantum Nanowires
~ Regarding to size (diameter) we have two different types of nanowires:

26. Properties of NWs
Nanowires have many interesting properties that are not seen in bulk or 3-D materials.
This is because electrons in nanowires are quantum confined laterally and thus occupy energy levels that are different from the traditional continuum of energy levels or bands found in bulk materials.

27. NW Properties
Depending on what it's made from, a NW can have the properties of an insulator, a semiconductor or a metal.

28. NW Properties ~ Many different types of nanowires exist, including….
~ We can categorize different types of nanowires regarding to the materials as follows….
~ Metal nanowires are made from nickel, platinum or gold.
~ Semi-conducting wires are comprised of silicon, indium phosphide or gallium nitride
~ And insulating are made of silicon dioxide or titanium dioxide
~ To create a molecular nanowire, the process involves repeating organic or inorganic molecular units in a particular format.

29. SEM characterization of as-synthesized silicon oxide nanowires.
~ Insulating NW helical morphology with the appearance of ordinary coiled telephone cords.

30. Indium arsenide (InAs) nanowires grown by the VLS technique
~ Semiconducting NW

31. NW Properties Insulators won't carry an electric charge
While metals carry electric charges very well.
Semiconductors fall between the two, carrying a charge under the right conditions.

32. Semiconductors are most useful in making transistors for computers.
NW Properties
By arranging semiconductor wires in the proper configuration, engineers can create transistors, which either acts as a switch or an amplifier
Semiconductors are most useful in making transistors for computers.
~ The most concerns NWs is semiconductor NW

33. NW Properties 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 NWs coated with SiC show stable photoluminescence at room temperature

34. Building Blocks Synthesis

35. There is no single fabrication method for NWs
How do we make NWs?
There is no single fabrication method for NWs
All the materials (metallic, semiconductor etc) hane been grown as 2D nanomaterials (thin films) in the last three decades

36. How do we make NWs? NW fabrication is challenging
Challenging is to grow 1D NWs
Alignment is a critical first step for developing devices that use NWs

37. ~ Like the rest of nanomaterials, methods can be broadly classified as either top-down and bottom –up techniques

38. Methods Evaporation condensation Dissolution condensation
• Spontaneous growth:
Evaporation condensation
Dissolution condensation
Vapor-Liquid-Solid growth (VLS)
Stress induced re-crystallization
Electro-spinning
Solution Synthesis
~ Different techniques can be generally grouped into five categories
~ All those techniques are the well known techniques for producing NWs

39. Methods Template-based synthesis: Electrochemical deposition
Electrophoretic deposition
Colloid dispersion, melt, or solution filling
Conversion with chemical reaction
• Lithography (top-down)

40. General Idea of Spontaneous Growth
A growth driven by reduction of Gibbs free energy or chemical potential.
This can be from either recrystallization or a decrease in supersaturation.
Anisotropic growth is required → growth along a certain orientation faster than other direction.

41. General Idea of Spontaneous Growth
Crystal growth proceeds along one direction, where as there is no growth along other direction.
Uniformly sized NWs (i.e. the same diameter along the longitudinal direction of a given NW)
~ For Nw, growth occurs only along one direction, but no growth along other direction

42. Fundamentals of evaporation (dissolution)- condensation growth

43. Fundamentals of evaporation (dissolution)- condensation growth
(1) Diffusion of growth species from the bulk (such as vapor or liquid phase) to the growing surface, which, in general, is considered to proceed rapid enough and, thus, not at a rate limiting process. (2) Adsorption and desorption of growth species onto and from the growing surface. This process can be rate limiting, if the supersaturation or concentration of growth species is low. (3) Surface diffusion of adsorbed growth species. During surface diffusion, an adsorbed species may either be incorporated into a growth site, which contributes to crystal growth, or escape from the surface.

44. Fundamentals of evaporation (dissolution)- condensation growth
(4) Surface growth by irreversibly incorporating the adsorbed growth species into the crystal structure. When a sufficient supersaturation or a high concentration of growth species is present, this step will be the rate-limiting process and determines the growth rate.
(5) If by-product chemicals were generated on the surface during the growth, by-products would desorb from the growth surface, so that growth species can adsorb onto the surface and the process can continue.
(6) By-product chemicals diffuse away from the surface so as to vacate the growth sites for continuing growth.

45. Evaporation condensation
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.

46. Evaporation condensation
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

50. 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

51. E-Beam Lithography

52. Nanowires Typical Applications
in electronic, opto-electronic and devices
as additives in advanced composites
for metallic interconnects in nanoscale quantum devices
as field-emittors and as leads for biomolecular nanosensors.
also optical, sensing, solar cells, magnetic, and electronic device applications
~ There are many applications where nanowires may become important such as…

53. Applications in Electronic

54. Applications in Electronic

55. Applications in Biomedical Engineering

56. Applications in Structural, Mechanical

57. Applications in Sensors

58. Low device-to-device reproducibility
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

59. Conclusion
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

60. References
Synthesis, Characterization, and Manipulation of Helical SiO2 Nanosprings, Hai-Feng Zhang et al.
One-Dimensional Nanostructures, Sharif Hussein Sharif Zain
An Introduction to NanoWires And Their Applications, Amir Dindar and Shoeb Roman
Nanostructures, Raul J. Martin-Palma et al.

61. References Nanostructures and Nanomaterials, GuoZhong Chao
Synthesis and applications of one-dimensional Semiconductors, Sven Barth et al.
Nanomaterials, nanotechnology and design: an introduction for engineer, M. F. Ashby et al.