srm university nano materials

7/30/2019 SRM University Nano Materials

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November 8, 2012 1

Dr. Alagiriswamy A A, (M.Sc, PhD, PDF)Asst. Professor (Sr. Grade),

Dept. of Physics, SRM-University,Kattankulathur campus,

Chennai

Apr.10/10

UNIT IVLecture 2

Nanomaterials/Nanotechnology


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Nanomaterials (structures/properties)Examples of nanophase materials

Some interesting challenges/goals

Outline of the presentation


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http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/


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http://www.nano.gov/html/facts/The_scale_of_things.html


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http://images.google.co.in/imgres?imgurl=http://www.wired.com/news/images/full/combo_f.jpg&imgrefurl=http://www.wired.com/news/technology/0,1282,69772,00.html&h=520&w=375&sz=38&hl=en&start=18&um=1&tbnid=XOJJNIItxlJQqM:&tbnh=131&tbnw=94&prev=/images%3Fq%3Ddefine%2Bnanotechnology%26svnum%3D10%26um%3D1%26hl%3Den%26sa%3DN


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Bulk Well Wire Dot

Bulk Well Wire Dot

Progressive generation of nanostructures

rectangular

curvilinear

:

Nanomaterials or nanophasematerials are the materials which are made of

grains that are about 100nm in diameter and

contain less than few ten thousands of atoms

Well : - e-s move only in 2DWire : - only in 1 DDots: - confined in all directions, 3D. No movement


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What is nanoscale science & engineering?

The study of materials and associated physical,biophysical and biochemical phenomena on the

scale of ~1-100 nm.

A compelling competition : -

The primary appeal of nanotechnology is the

potential to manipulate matter at

the nanoscale. This leads to the

possibility of preparing novel materials

(nanomaterials) that have specific,manipulable physical properties and

functions.


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What makes the nanoscale special?

1) High density of structures is possible with small size.

2) Physical and chemical properties can be different at the nano-scale (e.g.electronic, optical, mechanical, thermal, chemical).

3) The physical behavior of material can be different in the nano-regimebecause of the different ways physical properties scale with dimension(e.g. area vs. volume).

Prof. Richard Feynman

Theres plenty of room at the bottom


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Physical/chemical properties can changeas we approach the nano-scale

Melting point of gold particles

M. Bawendi, MIT: web.mit.edu/chemistry/nanocluster

Evident, Inc.: www.evidenttech.comK. J. Klabunde, 2001

Fluorescence of semiconductornanocrystals

By controlling nano-scale (1) composition, (2) size, and (3) shape, we can

create new materials with new properties New technologies

Decreasing crystal size


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http://www.youtube.com/watch?v=iFXTMHMtgp8&feature=relatedhttp://en.wikipedia.org/wiki/The_New_Breed_(episode)


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(ii) Magnetic propertiesNano particles of magnetic and even non magnetic solids exhibit a totally new class of

magnetic properties.Table gives an account of magnetic behavior of very small particles of various metals.Ferro magnetic and anti ferromagnetic multilayers have been found to exhibit Giant

Magneto Resistance (GMR).Small particles differ from the bulk in that these atoms will have lower

co-ordination number.From the Fig, it is inferred that the small particles are more

magnetic than the bulk material

Metal Bulk Cluster

Na, K Paramagnetic Ferromagnetic

Fe, Co, Ni Ferro magnetic Super paramagnetic

Gd, Tb Ferromagnetic Super paramagnetic

Rh Paramagnetic Ferromagnetic

Change in bulk magnetic momentversus co- ordination number
http://images.google.co.in/imgres?imgurl=http://www.wired.com/news/images/full/combo_f.jpg&imgrefurl=http://www.wired.com/news/technology/0,1282,69772,00.html&h=520&w=375&sz=38&hl=en&start=18&um=1&tbnid=XOJJNIItxlJQqM:&tbnh=131&tbnw=94&prev=/images%3Fq%3Ddefine%2Bnanotechnology%26svnum%3D10%26um%3D1%26hl%3Den%26sa%3DN


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TECHNOLOGICAL ADVANTAGES


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NANO
http://www.youtube.com/watch?v=g9UENE6JMLI&feature=relatedhttp://www.internationalcosmeceuticals.com/qsunshade.htmlhttp://www.foe.org/nano_sunscreens_guide/Sunscreen%20Guide%203.pdfhttp://www.aloette.com/Skin_Care/Anti-Aging/Ageless_Science_Anti-Aging_Systemhttp://mrsec.wisc.edu/Edetc/IPSE/educators/activities/nanoTex.htmlhttp://www.youtube.com/watch?v=g9UENE6JMLI&feature=relatedhttp://www.nano-tex.com/


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MICROWAVE SYNTHESIS OF MATERIALS


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What are microwaves ???

Microwaves are a form of electromagnetic energy.Microwaves, like all electromagnetic radiation, have an electricalcomponent as well as a magnetic component.

The microwave portion of the electromagnetic spectrum ischaracterized by wavelengths between 1 mm and 1 m, andcorresponds to frequencies between 100 and 5,000 MHz

absorb the energy, they can reflect the energy, or they can simplypass the energy

Microwave interaction with matter is characterized by apenetration depth and its frequency


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Comparison of conventional heating with microwaves

Dipole interactions occur

polar ends of a molecule tend to align themselves

1) dipole interactions

2) ionic conduction

loss tangent is the measurable quantity


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Material Synthesis

The discovery of new materials requires the development of adiversity of synthetic techniques.

Microwave methods offer the opportunity to synthesize and modifythe composition, structure and morphology of materials, particularlycomposites via differential heating.

Microwave-induced plasmas (MIPs) allow any solid mixture to beheated, and can promote direct microwave heating at elevatedtemperature, greatly expanding the use of microwaves for reactionsbetween solids and gassolid mixtures.

Microwave-assisted synthesis is generally much faster, cleaner, and more economical thanthe conventional methods. A variety of materials such as carbides, nitrides, complex oxides, silicides, zeolites, apatite,etc. have been synthesized using microwaves.


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Principles of Electron Microscopy (SEM and TEM


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Electron Microscopy Techniques Electron Microscopes are scientific instruments that use a beam of highly energetic

electrons to examine objects on a very fine scale. The main advantage of Electron Microscopy is the unusual short wavelength of theelectron beams, substituted for light energy ( = h/p) The wavelengths of about 0.005 nm increases the resolving power of the instrument tofractionsTopography The surface features of an object or "how it looks", its texture; direct relation between

these features and materials properties (hardness, reflectivity...etc.)Morphology The shape and size of the particles making up the object; direct relation between thesestructures and materials properties (ductility, strength, reactivity...etc.)Composition The elements and compounds that the object is composed of and the relative amounts ofthem; direct relationship between composition and materials properties (melting point,

reactivity, hardness...etc.)Crystallographic Information. How the atoms are arranged in the object; direct relationbetween these arrangements and materials properties (conductivity, electrical properties,strength...etc.)


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Types Transmission electron microscopy, which essentially

looks through a thin slice of a specimen.

Scanning electron microscopy, which looks at the

surface of a solid object.


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Transmission Electron Microscope(TEM)

Working Concept TEM works much like a slide projector. A projector shines a beam of light through

(transmits) the slide, as the light passesthrough it is affected by the structures andobjects on the slide.

These effects result in only certain parts ofthe light beam being transmitted throughcertain parts of the slide.

This transmitted beam is then projectedonto the viewing screen, forming anenlarged image of the slide.

TEMs work the same way except that they

shine a beam of electrons (like the light)through the specimen (like the slide).

Whatever part is transmitted is projectedonto a phosphor screen for the user to see.


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The "Virtual Source" - the electron gun, produces a stream ofmonochromatic electrons.

This stream is focused to a small, thin, coherent beam by the use ofcondenser lenses 1 and 2. The first lens (usually controlled by the"spot size knob") largely determines the "spot size"; the general sizerange of the final spot that strikes the sample.

The second lens (usually controlled by the "intensity or brightnessknob" actually changes the size of the spot on the sample; changing it

from a wide dispersed spot to a pinpoint beam. The beam is restricted by the condenser aperture (usually user

selectable), knocking out high angle electrons (those far from theoptic axis, the dotted line down the center)

The beam strikes the specimen and parts of it are transmitted

Source : - Inelastically Scattered ElectronsBraggs lawKakuchi Bands: - Bands of alternating light and dark lines that are formed by inelastic scatteringinteractions that are related to atomic spacings in the specimen


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Scanning Electron Microscope (SEM)

Working Concept

SEM allows surfaces of objects to be seen intheir natural state without staining.

The specimen is put into the vacuum chamberand covered with a thin coating of gold to

increase electrical conductivity and thus forms aless blurred image.

The electron beam then sweeps across the objectbuilding an image line by line as in a TVCamera.

As electrons strike the object, they knock looseshowers of electrons that are captured by adetector to form the image.


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Specimen Interactions and utilization:Backscattered Electrons

FormationCaused by an incident electron colliding with an atom in the specimen which isnearly normal to the incident's path.The incident electron is then scattered "backward" 180 degrees.

Secondary Electrons

Source This ionized electron then leaves the atom with a very small kinetic energy (5eV)

and is then termed a "secondary electron". Each incident electron can produce several secondary electrons.Auger ElectronsSource

Caused by the de-energization of the specimen atom after a secondary electron is produced.

X-raysSource

Caused by the de-energization of the specimen atom after a secondary electron isproduced


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Advantages

The AFM has several advantages over the scanning electronmicroscope (SEM). Unlike the electron microscope which provides a two-dimensional

projection or a two-dimensional image of a sample, the AFMprovides a true three-dimensional surface profile.

Additionally, samples viewed by AFM do not require any special

treatments (such as metal/carbon coatings) that would irreversiblychange or damage the sample. While an electron microscope needs an expensive vacuum

environment for proper operation, most AFM modes can workperfectly well in ambient air or even a liquid environment.

This makes it possible to study biological macromolecules and even

living organisms. In principle, AFM can provide higher resolution than SEM. It has

been shown to give true atomic resolution in ultra-high vacuum(UHV).


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Disadvantages

A disadvantage of AFM compared with the scanning electron microscope(SEM) is the image size.

The SEM can image an area on the order of millimetres by millimetres witha depth of field on the order of millimetres.

The AFM can only image a maximum height on the order of micrometres

and a maximum scanning area of around 150 by 150 micrometres.

Another inconvenience is that at high resolution, the quality of an image islimited by the radius of curvature of the probe tip, and an incorrect choiceof tip for the required resolution can lead to image artifacts.

Slow scan and less scanner area

Artefacts/Hystersis effects or cross-talk influences the image


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