Prepared by:Mrs Faraziehan Senusi

PA-A11-7CNanotechnology

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 nanotechnologyNanostructures 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 glassGold – produce red stained glassSilver – 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 tunneling microscopy

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.

Atomic force microscopy

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.

Electron microscopy techniques

Fabrication• Two basic techniques for the fabrication of nanoscale entities.

1. Top-down approachesA 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.