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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
7/29/2019 Synthesis and Characterization of Nanoparticles
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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
4
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
5
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
6
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
7
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
8
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CHARACTERIZATION OF NANOPARTICLES
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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CHARACTERIZATION OF NANOPARTICLES
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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CHARACTERIZATION OF NANOPARTICLES
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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CHARACTERIZATION OF NANOPARTICLES
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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CHARACTERIZATION OF NANOPARTICLES
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
13
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