Summary (Elective) TUe (6E12X0) Nanomaterials:Chemistry and Fabrication Full Revision Notes
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Module
6E12X0 Nanomaterials (6E12X0)
Institution
Technische Universiteit Eindhoven (TUE)
This is a complete summary for the course " Nanomaterials: Chemistry and Fabrication" at TUe (Eindhoven University of Technology). The course code is 6E12X0.
,Contents INDEX Page number
-C1. An Introduction to Nanochemistry Concepts 3
-C2. Bottom Up and Supramolecular Chemistry 10
-C3. Top Down 17
-C4. Molecular Machines 28
-C5. Gold 34
-C6. Inorganic Oxides-Silica 42
-C7. Iron Oxide 52
-C8. Polymers-PDMS 59
-C9. Analytical Methods for Nanochemistry 68
-C10. Semiconductors 77
-C11. Carbon 88
-C12. Nano-safety Challenges 98
2
, An Introduction to Nanochemistry Concepts
Recap Chemistry:
Basics:
Atom consists of nucleus (protons and neutrons) surrounded by electrons. An
element is defined by the number of protons in the nucleus and a compound
consists in different type of atoms. Molecules are formed from two or more
atoms held together by chemical forces (bond). An ion is an atom with net
positive/negative charge
Quantum numbers:
• n = principal quantum number (1,2,3,4,etc.) and determines energy of
orbital which increases with increasing n.
• l = angular quantum number (0, n-1) and determines shape (number of
angular nodes) of orbital and subshell.
• ml = magnetic quantum number, for a given value of l there are 2l+1
values of ml. It determines the orbital orientation.
• ms = spin quantum number and determines electron spin (+1/2 for
spin=up and -1/2 for spin-down)
Electronegativity: is the ability of an atom in a compound/molecule to attract
electrons to itself in a chemical bond (shared electrons between two or more
atoms). Electronegativity increases to the right in the periodic table and gives
rise to polarity/polar bonds.
Covalent bonds: Consist of shared electrons between non-metal atoms of
which the orbital overlap with each other.
Ionic bond: Is formed by an electrostatic force of attraction between positive
and negative ions, a metal and non-metal atom.
Metallic bond: Occurs between metal atoms that have few electrons
compared to all accessible orbitals.
Metal Properties: High conductivity because of free electron flow that can
generate current. Ductile because local bonds can break and reform
somewhere else in the metal.
3
,Hydrogen Bonding:
Hydrogen bond is a weak bond formed by the interaction between a positively
charged hydrogen atom in a polarized bond, a bond donor (N-H/O-H) and a
negatively charged atom, hydrogen acceptor (N/O without a hydrogen atom
but has free electron pair that can be shared).
Ionic materials: high melting points/hard but brittle/dissolve easily in
water/good electricity conductor.
Single covalent bond: Is sigma bond that is formed by the overlap of two s
orbitals, formed between two adjacent p orbitals.
Pi bond: Is formed by the side-to-side overlap between two parallel p orbitals,
forming two areas of electron density above and below the molecule
Double bond = sigma + pi bond
Triple bond = sigma + 2 pi bonds
Pi bonds are weaker than sigma bonds (less energy required to break pi bond)
Reactions:
Synthesis (A + B → AB), decomposition (AB → A + B), single or double
displacement reaction, precipitation (liquid medium to solid), acid-base
reaction and redox reaction (reduction/oxidation where electron gain =
oxidation).
Nanotechnology:
Nanotechnology entails to materials in the length scale of 1-100 nanometre
range at atomic, molecular or macromolecular level. Nanomaterials have novel
functions and properties because of their small and/or intermediate size, and
you can control and manipulate them on atomic scale.
4
,Top-down approach: Converting large material to smaller pieces such as a bulk
metal to powder.
Bottom-up approach: Consists in manipulating atoms and forming clusters
with larger size.
Interface: A surface that separates much larger volumes of dissimilar
substance (between 2 different materials such as liquid-solid, solid-solid or
liquid-liquid).
There is a common approximation in physics and chemistry which is the
absence of interfaces. However, for materials in the nanometre range the
interface can’t be ignored as smaller nanocrystal diameter increases the
percentage of surface atoms.
Dangling bonds: these bonds occur at a surface when atoms have unfilled
outer orbital (valence) shells. Corners, kinks, and edges increases the density of
dangling bonds.
Surface energy: It is roughly equal to surface density of dangling bonds
multiplied by the energy of the bond. It quantifies the disruption of
intermolecular bonds that occur when a surface is created. Depends on the
shape, roughness and chemical compositions. A higher surface energy makes a
material less stable and hence, more reactive.
Surface pressure: It’s the pressure that is generated on a surface by its surface
energy and it increases with increasing surface curvature.
5
,Laplace Law: A mathematical relation between the surface pressure of a
sphere and its radius and surface energy. It is calculated by the formula below.
Size of nanoparticles can be controlled by the length of synthesis reaction,
different optical/fluorescent properties.
Shape is also important as rodlike shape gives for example 2 absorption bands,
while a sphere would only show 1 absorption band.
There is a stronger size-dependent effect when the length is smaller.
Top-down approach (solid state engineering):
Creates smaller features from a larger material from photo-lithography by
cutting and trimming the material.
Photo-lithography:
A patterning method that employs a photomask which allows light to pass
through a pre-patterned master to replicate the pattern of the master in a
photosensitive substrate (for example, photoresist ) at a reduced length scale.
6
,Bottom-up approach (synthetic chemistry):
Starts from smaller atoms to create a nanomaterial. You start from smallest
components and assemble your desired structure from the ground up.
Self-assembly: Is the spontaneous self-organization of objects to the minimal
free energy of overall system, difficult to control size and always contains
defects.
It can be either dynamic or static self-assembly.
Static self-assembly: Is determined by the state of minimal free energy in a
confined system that energy can neither enter or leave.
Static self-assembly is often seen as a cheap way of fabricating complex
structures, using natural forces.
Dynamic self-assembly: self-assembly out of equilibrium conditions where the
state of minimal free energy is determined by the flux of energy in and out of
the system.
Dynamic self-assembly is aiming at developing adaptive systems. Systems
which adapt to the environment, systems which learn and that can be turned
off by removing the power input.
Co-assembly: a self-assembly process where two or more different
components self-assemble and form a complex structure where the two are
usually segregated and not entirely mixed.
Templating: the use of an existing material of a certain shape as a mold to
create a negative reproduction of in a new material.
Defects:
Point defects: occur in a lattice when an atom is missing, misplaced, or
different from what is should be. Doping creates point effects for a good cause.
Line defects: occur in a lattice when the position of an entire string of atoms in
the lattice is misplaced. This defect is responsible for plastic deformation for
example.
Planar defects: occur in a lattice when a whole plane of atoms is missing or
misplaced.
7
,Grain boundaries: interfaces between misaligned crystalline grains within a
polycrystalline material. Responsible for diffusion properties like ionic
conductivity.
Doping: creating point defects that allow electronic charge to be conducted.
The number and type of defects essentially determine the different properties
of a nanomaterial. Defects are caused and created by different growth of
nucleation sites
Bio-nano interface:
Examples:
- Use luminescent nanocrystals to track the movement of proteins or
cells.
- Attach specific molecules to the surface of my nanostructures so that
they bind with specific tissues.
Stimuli-responsive materials: materials that change their properties (colour,
shape) in response to external stimuli (light, pH).
Drug delivery: when a therapeutic drug is brought by a carrier to a specific site
in the body where it is needed to effect treatment.
The three main fields in Bio-Nano:
- Bio Analytics
- Targeting (imaging, treatment, delivery)
- Regeneration (tissue, organs, bone, cells)
The three directions in research:
- Imaging
- Treatment
- Delivery
Active targeting: Attaching a targeting vector to the nanostructures which
would specifically attach to the target.
Passive targeting: Using the leakiness of tumours ‘vessels to segregate
nanoscopic probes into the malignant tissue.
8
,Present chemical challenges to the bionanochemist:
- Be biodegradable and non-toxic
- Degrade if possible at the same rate at which the tissues are
regenerating
Regenerative medicine can reduce price of healthcare.
9
, Bottom Up and Supramolecular Chemistry
Supramolecular chemistry involves investigating new molecular systems in
which the most important feature is that the components are held together
reversibly by intermolecular forces (not covalent bonds).
Supramolecular synthesis is thermodynamically controlled.
Complementarity (Lock and Key):
The lock is the host/receptor/antibody and it is complementary to the key,
which is the guest/substrate/metal), both sterically and electronically.
Complementarity occurs in enzymes for example.
Proteins: Primary structure (amino acid residues), secondary structure (alpha-
helix) and tertiary structure (3D amino acid folding leading to folded
polypeptide chain). Finally, the quaternary structure of a protein can be for
example haemoglobin, which has four polypeptide chains. Each polypeptide
chain is a subunit that constitutes the quaternary structure of a protein.
The most important example of complementarity is the base pairing in the
DNA double helix.
DNA: A single DNA strand is composed of purine and pyrimidine bases linked
to a back bone of phosphorylated sugars. The DNA double helix combines two
antiparallel stands which are held together by complementary hydrogen bonds
between pairs of bases.
10
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