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Prepared by:
Mrs Faraziehan Senusi
PA-A11-7C
Nanotechnology
Fabrication
Chapter 6
Frontier Chemistry
Nanomaterials
Reference: Inorganic Chemistry4th ed, 2006, Shriver & Atkins, Oxford
Nanoscience
Characterization
Synthesis
Nanomaterials
• Materials having critical dimension between 1-100 nm.
• Nano material is taken to be a solid material and exhibits
‘novel’ properties related to this scale.
• Novel optical properties appear in nanoparticle are being
exploited for
– Information
– Biological
– Sensing
– Energy technologies
– Example: semiconducting nanoparticle and metallic
nanoparticle
‘novel’: New or unusual in an interesting way
Nanomaterials - DNA
• Original version of nanotechnology occurred in nature, where
organisms developed an ability to manipulate light and matter
on a atomic scale to build devices that perform specific
functions, such as stored information, reproducing themselves
and moving about.
• DNA ~ ultimate nanomaterial.
• It stores information as the sequence of base pairs that are
spaced about 0.3 nm apart.
• Folded DNA molecules have an information density of more
than about 1 Tb cm-2 (1 Tb = 1012 bits), which is much greater
than achieved in most current data storage system.
Nanoscience
• Study of the properties of matter that have length
scales between 1 and 100 nm.
• Study of the new effects that arise only in materials
that exist on the nanoscale.
Nanotechnology
• Collection of procedures for manipulating matter on this
scale in order to build nanosized entities for useful
purposes.
• Study of the procedures that creates new functionalities
that are possible only by manipulating matter on the
nanometre scale.
• Photosynthesis – example of biological nanotechnology
Nanostructures are exploited to:
– absorb light
– Separate electric charge
– Shuttle proton around
– Convert solar energy into biologically useful
chemical energy
• Human have practised nanotechnology for centuries
• Example:
Gold and silver salts have been used to colour glass
Gold – produce red stained glass
Silver – produce yellow
Photosensitive nanosized particle in silver halide
emulsions used in photography
Nanosized carbon granules in the ‘carbon black’ used for
reinforcing tyres and in printer’s ink
Biomedical technology
metallic nanopigment ~ used to tag DNA and
other nanoparticles
• Began to take shape in the latter half of the
twentieth century
• Significant contribution
– Gerd Binnig and Heinrich Rohrer developed the
scanning tunneling microscope
– Scanning probe tip was used to rearrange atoms on a
surface to spell out words
– Demonstrating an ability to manipulate and characterize
nanoscale structure
Characterization
• Areas of nanomaterials, nanoscience and
nanotechnology were intimately tied in characterization
and fabrication methods.
• Great advances made in these areas would not have
occurred without the ability to characterize the
nanostructural, chemical and physical properties of
materials.
• Methods:
Scanning probe microscopy
Electron microscopy techniques
Scanning probe microscopy -
Scanning tunneling microscopy
• Scanning tunneling microscopy (STM) was the first of a series
of Scanning probe microscopy, which are techniques that allow
3D imaging of the surface of materials by using sharp and
sensitive physical probes.
• This technique use a sharply pointed probe brought into close
proximity with the specimen and construct image by scanning
the probe over the surface of the specimen
• Monitoring the spatial variation in the value of physical
parameter, such as potential difference, electric current,
magnetic field and mechanical force.
– In STM, an atomically sharp conductive tip is scanned at
about 0.3 – 10 nm above the surface.
– Uses tunnelling current from a sharp tip to image and
characterize a surface
Scanning probe microscopy -
Atomic force microscopy
• In AFM, atoms at the tip of the probe interact with the surface atoms of
the sample through intermolecular forces such as van der waals
interactions.
• The cantilever holding the probe bends up and down in response to the
forces and the extent of deflection is monitored with a reflected beam.
• Variations on AFM include:
Frictional force microscope – measures variations in the lateral forces
on the tip based on chemical variations on the surface
Magnetic force microscope – uses magnetic tip to image magnetic
structures
Electrostatic force microscope - uses tips that can sense electric fields
Scanning capacitance microscope - tip is used as an electrode in a
capacitor
• Scanning near-field optical microscopy (SNFOM)
– Combines the local interactions of a scanning probe and a specimen
with well –established methods of optical spectroscopy.
Electron microscopy techniques
• Electron beams are accelerated through 1-200kv and
electric and magnetic field are used to focus the electron
• In transmission electron microscopy (TEM) – the electron
beam passes through the thin sample being examined and
is imaged on a phosphorescent screen
– Often used for imaging electron-transparent biological
samples because it offers atomic resolution for high-
resolution metarials studies.
• In scanning electron miscroscopy (SEM) – the beam is
scanned over the object and the reflected (scattered) beam
is then imaged by the detector.
• In both microscopes, the electron probes caused the
production of X-rays with energies characteristic of the
elemental composition of the material.
Fabrication • Two basic techniques for the fabrication of nanoscale entities.
1. Top-down approaches
A macroscale (or microscale) object and to carve out
nanoscale patterns.
In this approaches, patterns are first designed on a large scale,
their lateral dimensions are reduced and then used to transfer
the nanoscales features into or onto the bulk material.
Physical interaction
• Lithography ~ method for making printed circuits
• Mechanical stamping
• Nanoscale printing
Most common approach is photolithography, the technique
used to fabricate very large scale integrated circuits having
feature dimension on the 100 nm scale
Bulk material
Thin films
Heterostructures
Litographic wires
Quantum dots
Nanocrystals
Molecular wires
Proteins
Molecules
Atoms
Top - down
1 nm
1 m
100 pm
Bottom - up
Top-down technique
starts with larger
objects that are whittled
down into nanoscale
objects
Bottom-down
technique starts with
smaller objects that are
combined into
nanoscale objects
2. Bottom – up approaches
– Build larger objects by controlling the arrangements of
their component smaller-scale objects
– Start with control over the arrangements of atoms and
molecules
– Bottom up approach to nanoscale fabrication because of
its focus on the interactions of atoms and molecules and
their arrangement into larger functional structures
Synthesis
• Methods widely used to prepare nanomaterials.
Solution based synthesis of nanoparticles
– Main techniques for nanoparticle synthesis because they have
atomically mixed and highly mobile reagents
• Allow for the incorporation of stabilizing molecule
• Widely successful in practise
• Two stages of crystallization from solution are nucleation
and growth
– Basic stages in solution chemistry are:
• Solvate the reactant species and additives
• Form stable solid nuclei from solution
• Grow the solid particles by addition of material until the
reactant species are consumed.
Vapour phase synthesis of nanoparticle
• Alternative techniques for nanoparticle synthesis
because they have atomically mixed and highly
mobile reagents
• It can be controlled by varying the condition and
also widely succesful in practice.
• It as a attractive synthesis methods for particles
when continuous operation is required or when
solution method do not produce good quality
nanoparticles.
Synthesis using frameworks, supports and substrates
Nanosized reaction vessel
• By carrying out reactions in nanoscale reaction vessels, the
ultimate dimensions of solid products are confined to the vessel
size; a reverse micelle has an aqueous core in which reactions can
occur
Physical vapour deposition
• A vapour of atoms, ions or clusters physically adsorb to the surface
and combine with other species to create a solid
• Molecular beam epitaxy (MBE) is a technique where evaporated
species from elemental charges are directed as a beam at a substrate
where growth occurs
Chemical vapour deposition
• A vapour of molecules chemically interact or decompose at or near
the substrate, where they adsorb to the surface and combine with
other species to create a solid and residual gaseous product.
