Microstructure Determination: A Materials Characterisation Protocol

This report proposes a detailed materials characterisation protocol for determining if a chosen processing route has delivered the intended microstructure, focusing on iron oxides and their various structures. The protocol emphasizes efficiency and cost-effectiveness by selecting appropriate techniques and avoiding unnecessary steps. The synthesis of magnetic nanoparticles (MNPs) using the co-precipitation process with iron oxides is described, highlighting its cost-effectiveness and suitability for mass production. The characterisation methods include X-Ray Diffraction (XRD) for crystalline phase analysis, inductively coupled plasma atomic emission spectroscopy for total iron concentration, and Electron Energy Loss Spectroscopy (EELS) for studying electron energy loss processes and localized surface plasmons. The advantages and disadvantages of EELS are discussed, including its high spatial resolution and the need for thin specimens. The protocol aims to correlate experimental data with theoretical models to optimize material properties and applications.

TASK C. MATERIALS CHARACTERISATION PROTOCOL
On the basis of your knowledge from the second semester lectures on materials
characterization, and your researches of available literature and the internet:
 Propose a complete, rigorous characterization protocol to determine whether you chose
processing route has delivered the intended microstructure;
The answer to the Question
Iron oxides occurring various structures have diverse properties. There are seven crystalline
phases of ferrous and ferric iron oxides in which Fe3O4 and gamma- Fe2O3 maghemite have been
used in areas like biotechnology and bio-medicines related to its size and composition.
Maghemite is used in magnetic resonance imaging due to its ferri-magnetic properties. Different
magnetic nanoparticles can be synthesized from these iron oxides and implemented in Vivo and
Vitro studies. For the synthesizing of these nanoparticles, the co-precipitation process using these
iron oxides is cost-effective and proves the capacity of mass production and is properly
functionalized. This method is easy for preparation of aqueous dispersion of magnetic
nanoparticles as the synthesis process is conducted in water. It is the simplest method of
synthesizing magnetite and maghemite with the appropriate ratio in an aqueous solution
containing Fe2+ Fe3+after the base is added. The size, shape and composition depend on the salt
used chloride. The magnetic nanoparticles that form stable colloidal suspension should be non-
toxic. The nano-size distribution of spherical nanoparticles is obtained. The synthesized MNP are
coated with bio-compatible layers that are made from polymers such as proteins, lipids or shorter
organic chains. Firstly the analytic grade reagents iron(III) chloride hexahydrate (Fecl3,4H2O)
and iron(II) chloride tetrahydrate (FeCl2,4H2O) are required. Solutions of
Fecl3,6H2O(0.1M),FeCl2,4H2O(0.2M) and HCl(1.5M) are placed in a reactor with N2
atmosphere. The synthesis followed the precipitation of Fe3O4 when NH4OH is added to the
solution containing salts of Fe2+ and Fe3+ in water with a PH value of the solution as 12. The
chemical reaction is as follows :
Fe2+ + Fe3+ +8OH- = Fe3O4 +4H2O
The precipitate was washed with butyl alcohol.
For the coating lauric acid (LA) and MNP with a ratio 3:2 is dissolved in de-ionized water heated
to 333K and shaken it until flocculation occurs. Then it is washed with acetone to remove excess
fatty acid which forms a stable colloidal solution of MNP coated with LA.
Characterization of MNP.
The total iron concentration in the colloidal suspension of MNPs is studied through the
inductively coupled plasma atomic emission spectroscopy.

X-Ray Diffraction: The result for the crystalline phase of non-coated MNPs is obtained through
X-Ray Diffraction method. The peaks in the diffraction patterns are measured and Debye-
Scherrer formula can be used for obtaining the average diameter from the most intense peak.
Magnetization and AC Susceptibility Behaviour
Iron oxide nanostructure can be studied extensively with respect to electron energy loss
processes.
Electron energy loss spectroscopy in studying nanoparticles
What is Electron energy loss spectroscopy?
This is one of the best techniques by which the energy distribution of the elastically scattered
electrons in the transmitted beam is analyzed.
It is a. highly sensitive non-destructive technique. It is used to study surface and adsorbate
vibrations. It is also used for low-energy electronic stimuli
MAGNETIC SPECTROMETER COMPONENTS: EELS Spectrometer Fig 1
a. Source of electrons b.Condenser lenses c Specimen d.ADF detector e.Display
Fig 1 : Components of EELS Spectrometer
It distinguishes the electrons having energy loss based on the absolute energy of the electrons.
For generation of an EELS spectrum, the signal of electron energy loss spectrometerl is used..
For the composition map the spectrometer is \used to create an EELS spectrum..

It has three areas: - Each area appears because of a different set of electron / probe interactions.
Region 1 is the region without loss (0 to 10 eV). Region 2 is the region of low loss. (10 to 60
eV)
Region 3 (>60 eV), the core-loss region. This is shown in Fig 2
Fig 2 : Three regions of EELS Spectrum.
Zero-loss peak is the most important part in EELS spectra of thin specimens.. It is originated
from from electrons that have not lost any energy, Width of the zero-loss peak is energy spread
of the electron source ,It gives less analytical information about the sample, It is used to calibrate
the Energy scale. Phonons are lattice vibrations, which are equal to heating the specimen. This
effect may lead to a damage of the sample.

Fig 3 : Low Loss area
Low-loss region
The excitation of plasmon and interband transitions are reflected in this region. . Plasmons are
longitudinal waves showing the oscillations of free electrons and the decaying stages of
plasmons are either photons or phonons.
The typical lifetime of plasmons is about 10-15 s.
High loss region
For microanalysis high loss region is the most important part of the EELS spectrum (Figure 4).
In the core-loss area the signal is very weak in comparison to that in the low-loss and loss-free
regions.
Therefore, the spectrum’s core loss region is often amplified up to 100 times..

Fig 4 : High Loss region
The peaks or edges are created due to interactions between the incident electrons and the inner-
shell electrons of atoms in the specimen. When an atom is ionized by an incident electron a
specific amount of energy is produced. Due to ionization of the target atom some energy is lost
which is called electron energy loss.
ADVANTAGES
High ultimate spatial resolution, high core-loss signal, Structural information available,absolute
standard less quantification.
DISADVANTAGES
Very thin specimen needed, high spectral background, possible inaccuracy in crystals, more
operator intensive
Tthe electron energy loss spectrometer helps in studying localized surface plasmon in MNP. It is
found that the plasmon modes is affected with the changes in the nanostructure and damage the
electron beam which shows that the delineation of the two effects can occur through the
specimen optimization preparation techniques and the related parameters. The results obtained
from the experimental mapping of bright and dark plasmon energies match with the theoretical
modeling.