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ZnO (Zinc oxide). by Alexander Glavtchev. Why is ZnO interesting?. Widely used: medicinal purposes (colds, rashes, antiseptics, sunscreen lotions) used in manufacturing of rubber as rubber cure (or as filler) pigment for paints and coatings

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ZnO (Zinc oxide)

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Zno zinc oxide l.jpg

ZnO (Zinc oxide)

by

Alexander Glavtchev


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Why is ZnO interesting?

Widely used:

  • medicinal purposes (colds, rashes, antiseptics, sunscreen lotions)

  • used in manufacturing of rubber as rubber cure (or as filler)

  • pigment for paints and coatings

  • in electronics, used mainly in laser diodes, LED’s, transparent thin film coatings, and various piezoelectrics

    Bright future:

  • shows promising signs in the field of nanotechnology, UV detecors, nanoscale detectors and actuators

  • direct bandgap semiconductor that could replace silicon as the main substrate in chip manufacturing (if it can be easily/cheaply p-doped)

  • dual semiconductor and piezoelectric properties!!


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Properties

Melting Point: 1975 °C

High electron mobility: >100cm2/Vs

High exciton binding energy: ~60meV (electron-hole binding energy)

Direct bandgap: 3.3eV


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Piezoelectric Properties

The output amplitude is related to the input signal by:

Lithium niobate (LiNbO3) and Lithium tantalate (LiTaO3) are currently two very-widely used piezoelectric crystals due to their high piezoelectric strain coefficients.


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Piezoelectric Properties

  • Can produce voltage output from applied stress (strain), or produce stress when voltage is applied.

  • Nanobelts and various nanoscale features of ZnO give higher piezoelectric constants (likely due to less dislocations and the impurity-free single-crystalline structures).

  • Piezoelectrics used in: sensors (acoustic and electronic, as pickups in electric guitars, detection/generation of sonar waves, etc.); actuators (high-precision motors, loudspeakers, atomic force microscope probe control); possible future use in vibration and noise reduction (housing, automobiles).


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Semiconductor Properties

  • Zinc oxide is a direct wide-bandgap semiconductor (~3.3-3.4eV).

  • Allows for efficient photon emission, as in LED’s or laser diodes (rather than phonon emission with energy loss and heat generation).

  • Can easily be n-doped with aluminum, indium, or extra zinc.

  • Possesses high electron mobility and photoconductivity – can help speed up currents in semiconductor devices.

    Drawbacks:

  • p-doping is currently very difficult and inefficient and has prevented mass manufacturing of ZnO-based wafers.

  • High-purity ZnO grown on substrates other than sapphire has been challenging.


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Nano-Structures

  • Zinc oxide shows great potential for nanoscale electro-mechanical fabrication.

  • Highly-symmetric, singly-crystalline nanoneedles, nanowires, nanobelts, nanorings, nanohelixes, nanocombs, etc.

  • Hexagonal (wurtzite) structure helps lattice-matching and controlled growth.

  • Positive Zn surfaces and negative O surfaces create electric dipoles that facilitate polarization growth along certain directions and planes under applied voltage and temperature.


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Nano-Structures


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Summary

  • ZnO displays dual semiconductor and piezoelectric properties.

  • Used in laser diodes and LED’s.

  • Potential to be used as a wide-bandgap semiconductor.

  • Widely used in many other fields (medicine, farming, pigments).

  • Zinc oxide nanostructure growth is heavily researched presently.

  • The substance likely has the largest variety of nanostructures (and their associated properties) among all known materials.

  • It’s hexagonal lattice can easily match catalysts’ lattice structure and facilitate controlled growth patterns.

  • Structures like nanowires, nanobelts and nanorings are of great interest in photonics research, optoelectronics, nanotechnology, and biomedicine.


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Sources

  • Nanoarchitectures of semiconducting and piezoelectric zinc oxide. JOURNAL OF APPLIED PHYSICS 97, 044304 s2005d

  • Piezoelectric Characterization of Individual Zinc Oxide Nanobelt Probed by Piezoresponse Force Microscope. Nano Lett.,Vol. 4, No. 4, 2004

  • Nanostructures of zinc oxide. Zhong Lin Wang. Materials Today, June 2004.

  • Photonic band structure of ZnO photonic crystal slab laser. JOURNAL OF APPLIED PHYSICS 98, 103102 2005

  • Deformation-Free Single-Crystal Nanohelixes of Polar Nanowires. Nano Lett.,Vol. 4, No. 7, 2004

  • Zinc oxide hexagram whiskers. APPLIED PHYSICS LETTERS 88, 093101 2006

  • Zinc Oxide Nanostructures: Growth, Properties and Applications. J. Phys.: Condens. Matter16 (2004) R829–R858

  • Nitrogen doped zinc oxide thin film.http://repositories.cdlib.org/lbnl/LBNL-54116, 2003

  • www.wikipedia.com


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