Post on 29-Apr-2017
RUTHERFORD BACKSCATTERING SPECTROMETRY(RBS)Course Instructor:- Dr. Ravi Mohan Prasad
INDIAN INSTITUTE OF TECHNOLOGY ROORKEE
MEL471 - MATERIAL CHARACTERIZATION TECHNIQUES
PRESENTATION BY:
INTRODUCTION
• RBS is an analytical technique
• determine the structure and composition of materials by measuring the backscattering of a beam of high energy ions
• It involves measuring the number and energy of ions in a beam which backscatter after colliding with atoms in the near-surface region of a sample at which the beam has been targeted
Source - http://www.mrsec.harvard.edu/cams/RBS.html
• Rutherford backscattering spectrometry is named after Lord Ernest Rutherford, a physicist sometimes referred to as the father of nuclear physics.
• Presented the concept of atoms having nuclei
• According to the then-dominant plum-pudding model of the atom backscattering of the high-energy positive alpha particles should have been non-existent
• Supervised a series of experiments carried out by Hans Geiger and Marsden studying the scattering of alpha particles through metal foils.
HISTORY
Source - http://en.wikipedia.org/wiki/Rutherford
Cont..• When Marsden positioned the detector
on the same side of the foil as the alpha particle source, he immediately detected a noticeable backscattered signal.
• Rutherford interpreted the result as an indication of a Coulomb collision with a single massive positive particle.
• Concluded that the atom's positive charge could not be diffuse but instead must be concentrated in a single massive core: the atomic nucleus
• Led to the development of the Rutherford model of the atom Top: Expected results: alpha particles
passing through the plum pudding model of the atom undisturbed.Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.
Source - http://en.wikipedia.org/wiki/Rutherford Backscattering
INSTRUMENTATION
An RBS instrument generally includes three essential components :-
1) Ion Source
2) Linear particle accelerator
3) Detector
Source - http://www.eag.com/mc/rbs-instrumentation.html
ACCELERATOR
Cont..
Source - http://www.eag.com/mc/rbs-instrumentation.html
Cont…
Source - http://www.eag.com/mc/rbs-instrumentation.html
• The basic principle is contained in the kinematics for binary collisions.
• Rutherford backscattering as an elastic collision between a high kinetic energy particle from the incident beam and a stationary particle located in the sample.
• The incident ions scatter from the nucleus of the atoms in the sample (called the target nucleus) and are backscattered owing to the coulomb repulsion with the positively charged target nucleus.
• . By monitoring the number of backscattered ions as a function of energy, the elemental composition and depth distribution of elements can be determined
BASIC PRINCIPLE
Source - http://en.wikipedia.org/wiki/Rutherford Backscattering
ENERGY LOSSStopping Power• Energy loss depends on material's stopping power.
• Particles lose energy both before and after a collision.
• Projectile energy dissipates due to interactions with electrons (electronic stopping)
• A particle will also lose energy as the result of the collision itself.
• The collisional lost depends on the masses of the projectile the target atoms .
Scattering Cross-section
• Relative number of particles backscattered is related to the differential scattering cross section
• Scattering cross section is basically proportional to the square of the atomic number of the target atom.
• Graph indicates that RBS is over 100 times more sensitive for heavy elements than for light elements Source - http://www.eag.com/mc/rbs-
scattering-cross-sections.html
ADVANTAGES LIMITATIONS Provides Depth
Information
Well Suited For Thin Film Analysis
Rapid Analysis
High Sensitivity
Simple Calculations
Sample must be smooth, thin films
No qualitative analysis possible
Useful information limited to top 1-2 um of sample
APPLICATIONS :-
• Semiconductor: quantitative depth analysis of metal silicide films, barrier metals, insulating layers, multilayer stacks and crystal damage vs. depth.
• Superconductors: quantitative depth profiling
• Polymers: depth profiling of halogens and impurities
REFERENCES• http://en.wikipedia.org/wiki/Rutherford• Http://www.eag.com/mc/rbs-scattering-cross-sections.html• http://www.mrsec.harvard.edu/cams/RBS.html• EAG Instrumentation Tutorial:
http://www.eaglabs.com/training/tutorials/rbs_instrumentation_tutorial/rspect.php
THANK
YOU