electron energy lose spectroscopy (eels)
TRANSCRIPT
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)