Synthesis and Characterization of Nanoparticles

7/29/2019 Synthesis and Characterization of Nanoparticles

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SYNTHESIS AND CHARACTERIZATIONOF NANOPARTICLES

Lokesh Kulkarni

Dept. of Industrial and Systems Engineering

September 11th, 2009


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OVERVIEW

Synthesis Techniques: Top-down and Bottom-up

Synthesis Processes:

i. Gold synthesis in laboratory

ii. Inert gas condensation

iii. Laser ablation process

Characterization Tools:

i. Scanning Probe Microscopy

ii. Transmission Electron Microscope

iii. Scanning Electron Microscope

Current Research 2


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Top-down processes:

- Used to manufacture conventional

products

- Newly developed techniques allow

for much smaller sizes (close to1m)

- Processes include: Milling, Grinding,

Electron beam machining

- Examples of products: Traditional

furniture, car chassis, etc.

SYNTHESIS OF NANOMATERIALS

3

Source:

Nanotechnology: An Introduction to Snthesis,

Properties and Applications by Dieter Vollath


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SYNTHESIS OF NANOMATERIALS Bottom-up Process:

- Uses atoms and molecules as building blocks of structures

- Focus of nanotechnological manufacturing processes- Examples: Chemical synthesis processes

- Because molecular chemistry dictates the structure andhence, properties of nanomaterials, it is very important to beable to control such processes

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Source:

Nanotechnology: An Introduction to Snthesis,

Properties and Applications by Dieter Vollath


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SYNTHESIS PROCESSES

Laboratory method for synthesis of gold nanoparticles:

- Chemicals: Auric salt (source of Au ions), sodium citrate (reducingagent and surfactant), deionized water (medium of reaction

- Equipment: Flask, magnetic stirrer with heating capability

- Process: See figure

- Capable of producing spherical gold nanoparticles of around 10-20

nm in diameter

- Method first developed by J. Turkevich in 1951 and later refined by

G. Frens

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Image courtesy: Chiwoo Park


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SYNTHESIS PROCESSES

Inert Gas Condensation Process:

- Components: Metal (of desired nanoparticles), inert gas, vacuumvessel, nanoparticle-collection finger, liquid nitrogen for cooling

- Process: See diagram

- Typically results in a broad particle size distribution due to randomnature of the process

- Basic IGC process leads to several variants, one variant, beingphysical vapor synthesis process

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Images adopted from Nanomaterials: An introduction to synthesis,

properties, and applications by DieterVollath


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SYNTHESIS PROCESSES

Laser Ablation Process:

- Components: precursor target (metal or non-metal), high-powerlaser, optical focusing system, carrier gas, vacuum vessel, feedingsystem for precursor target

- Process: See figure

- More versatile than physical vapor synthesis because both, metalsand non-metals can be used as targets

- Particle size depends on: i. gas pressure and ii. Laser pulse length

- Results in a broad particle size distribution

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Image adopted from Nanomaterials: An introduction to synthesis, properties, and

applications by DieterVollath


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CHARACTERIZATION OF NANOPARTICLES

What is characterization?

- Characterization refers to study of materials features such as

its composition, structure, and various properties like physical,

electrical, magnetic, etc.

Why is characterization of nanoparticles important?

- Nanoparticle properties vary significantly with size and shape

- Accurate measurement of nanoparticles size and shape is,

therefore, critical to its applications

Tools used to characterize nanoparticles

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Scanning Probe Microscopy:

- Uses some type of probe that generates an image by physically

scanning the sample surface in a raster scan pattern

- Depending on the type of microscope, several different surface

characteristics can be analyzed- Probe microscopes:

i. Atomic Force Microscope

ii. Scanning Tunneling Microscope

iii.

Near-field Scanning Optical Microscope Other microscopes:

i. Transmission Electron Microscope

ii. Scanning Electron Microscope9


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Atomic Force Microscope:

- Operation: See figure

- Modes of operation:

i. Contact mode

ii. Non-contact mode

iii. Tapping mode

- Limitations: Probe tip radius, imageprocessing speed, small image size

- Advantages: High resolution microscope(upto few nanometers), capable of

producing 3-D images, pre-treatment of

samples is not necessary, vacuum chamber

not required for some modes of operation 10

Image source: https://reader009.{domain}/reader009/html5/0409/5acb73

Image source: http://mcf.tamu.edu/images/IMG_0750.jpg/image


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Scanning Tunneling Microscope:

- Operation: Based on tunneling current,which is explained in quantum physics

- Modes of operation:

i. Constant-current

ii. Constant-distance

- Advantages: Very high image resolution(capable of seeing and manipulating

atoms), wide temperature range and

capable of operating in ultra-high

vacuum and other gas environments

- Limitations: Again, radius of curvatureof tip, extremely sensitive to ambient

vibrations11

Image source:

http://www.nisenet.org/publicbeta/articles/seeing_atoms/images/STM-

med.jpg

Image source:

http://www.almaden.ibm.com/vis/stm/imag

es/stm10.jpg


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Transmission ElectronMicroscope:

- Operation: Image is generated basedon the interaction pattern of electronsthat transmit through the specimen

- Variation: Scanning TransmissionElectron Microscope

- Advantages: Additional analysistechniques like X-ray spectrometryare possible with the STEM, high-resolution , 3-D image construction

possible but aberrant- Limitations: Needs high-vacuum

chamber, sample preparationnecessary, mostly used for 2-Dimages 12

Image source:

http://www.udel.edu/biology/Wags/histopage/illuspage/lec1/iintro9.gif


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Scanning Electron Microscope:

- Operation: Generates image by scanningthe surface of the sample in a raster

pattern, using an electron beam

-

Modes of operation:- i. Secondary electrons

- ii. Back-scattered electrons (BSE)

- iii. X-rays

- Advantages: Bulk-samples can be

observed and larger sample area can beviewed, generates photo-like images,

very high-resolution images are possible

- Disadvantages: Samples must havesurface electrical conductivity, non-

conductive samples need to be coatedwith a conductive layer

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Image source: http://www.bioimaging.dk/uploads/pics/Scanning-electron-

microscop_03.gif

Image:http://www.engineering.a

rizona.edu/news/media/i

mage/matsci_pollen.jpg


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CURRENT RESEARCH

Challenges: Accurate characterization of nanoparticles

is very critical to study their properties. Image analysis

is very tedious and current methods are not robust,

which reduces their compatibility. Faster, robust, and

more accurate methods need to be developed

Two methods:

i. Remove white areas by identifying and eliminating

those data points that correspond to a specific

threshold pixel brightness value

ii. Attempt to identify closed particle boundaries and

eliminate data points that lie within those closed

boundary and those which do not form a closed entity 14

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Synthesis and Characterization of Nanoparticles