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