electron energy lose spectroscopy (eels)

ELECTRON ENERGY LOSS SPECTROSCOPYPresented to:

Dr. Athar IbrahimPresented by:

Khushbakhat Nida (MME-13-25)Maria Iqbal (MME-13-

26)Nishat Riaz (MME-13-

27)

IAM, BZU, MULTAN

HISTORYJames HillierRF Baker in the mid 1940sResearch 1990s due to

advance in microscope instrumentations andvacuum technology

INTRODUCTION Electron energy loss spectroscopy (EELS) –The most versatile technique which involves analysis of the energy distribution of the in-elastically scattered electrons in the transmitted beamIt is:high-sensitive non-destructive technique for the study of

surface and adsorbate vibrations low-energy electronic excitations

MAGNETIC SPECTROMETERCOMPONENTS:

Source of electronsCondenser lensesSpecimenADF detectorDisplay screenEELS Spectrometer

Discriminates the energy loss electrons on

the basis of their absolute energy.The signal from the electron energy loss

spectrometer can be used to generate an EELS spectrum

The spectrometer can be used to produce a compositional map

EELS spectrumIt has Three regions :-Each region arises due to a different group of electron/sample interactions.Region 1 (0 to 10 eV) is the zero-loss region.  Region 2 (10 to 60 eV) is the low-loss region.Region 3 (>60 eV), the core-loss region

Zero-Loss PeakIt is the main feature in EELS spectra of thin specimens.Originates from electrons that have lost NO energyWidth of the zero-loss peak is energy spread of the electron sourceLess analytical information about the sampleUsed 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

Low-Loss areaIt reflects excitation of plasmons and interband

transitions.

Plasmons are longitudinal oscillations of free electrons, which decay either in photons or phonons.

It is caused by weakly bonded. It depends on local density of the weakly bonded

electrons.The typical lifetime of plasmons is about 10-15 s.

Interband transition: the transition between the conduction and valence bands (electrons and holes)

Intraband transitions: the transitions between the quantized levels within the conduction or valence band. It known also as the itersubband transition.

High-loss RegionThe most important region

of the EELS spectrum for microanalysis

The signal in the core-loss region is very weak relative to that in the zero-loss and low-loss regions. Therefore, the core-loss region of the spectrum is often amplified 50 to 100 times

The peaks or edges, arise because of

interactions between the incident electrons and the inner-shell electrons of atoms in the specimen

When an incident electron ionizes an atom, it produced a specific amount of energy. The amount of energy lost in ionizing the target atoms is the electron energy loss

ADVANTAGES

DISADVANTAGES

Higher core-loss signalHigher ultimate spatial resolutionAbsolute, standard less quantification Structural information available

Higher spectral background Very thin specimen neededPossible inaccuracy in crystalsMore operator intensive

APPLICATIONS:Thickness measurementsPressure measurementsAnalytical electron microscopy (AEM)