XPS--入门
[ 2009-9 | Author: nwf1982 ]
XPS - Xray Photoelectron Spectroscopy-
X-ray Photelectron Spectroscopy (XPS) is used in research， development and m
anufacturing. This technique is able to obtain the chemical composition of v
arious material surfaces up to 1 nm depth. It is possible to find out if thi
s material is superficially oxidised， if it contains iron， or carbon， etc. M
ost of the elements can be detected except hydrogen. Our main interest is to
find out the composition i.e. the atomic percentage of each of the componen
ts. Using these characterisation means implies defined rules. Let me explain
for you the principle and the various steps of such an analysis.
XPS analysis basics.
Let's refresh our knowledge together:
Matter is made of atoms.
Atoms are made of a nucleus and several electrons.
These electrons are orbiting around the nucleus with defined orbits.
Each electron is carrying an ID card with its address. The goal is to catch
them in order to find out from which atom they are coming. To be able to fre
e them from the nucleus attractive force we excite them by exposure to X-ray
bombardment. This kind of light is bringing them enough energy to free them
from the nucleus. Once they have been freed up some on them travel through
the matter and reach its surface. Electrons which carry enough energy at thi
s point， may leave the solid matter for the surrounding vacuum.
Once they are in the vacuum， they are collected by and electron analyser. Fu
rthermore they are classified according to their ID cards. The information w
e are interested in is the so-called binding energy which they had before le
aving the atom. All what we do is counting these electrons versus their bind
ing energy and we obtain a spectrum looking like the one shown below:
Electron count plot versus energy (energy spectrum)
If we observe the spectrum， we see two main peaks at 284.6 and 532.5 energy
counts. The unit used for counting energy is electronvolt - abbreviated as e
V. - We simply mention that there are peaks at 284.6 eV and 532.5 eV.
Each energy matches a specific atom type， e.g. 284.6 eV matches carbon and 5
32.5 matches oxygen. From this we can conclude that this specimen contains c
arbon and oxygen. Each peak area is proportional to the number of atoms bein
g present in the studied element. By calculating the respective contribution
of each area we obtain the specimen chemical composition， for example: 25%
Oxygen and 75% Carbon. In other words， among 100 atoms present at the surfac
e of the material， 75 are carbon atoms. By studying the energy of this carbo
n peak， it is possible to find out if the surface of this material correspon
ds to C-O or C=O chemical form. We can interpret the experiment by the mean
of result modelling. For more information， select a higher level of knowledg
e: Beginner.
A step-by-step XPS analysis.
In a first step it is necessary to prepare of the specimen. The size may var
y from a few millimetres to a few centimetres， depending partly on the instr
ument but mainly on the technology being used.
The specimen is then introduced in the first chamber (sample preparation cha
mber). This chamber is then pumped by high vacuum pumps (also called seconda
ry vacuum pumps) down to a vacuum below 10-7 mbar. When the proper vacuum ha
s been achieved， the specimen is transferred into the analysis chamber and t
he XPS experiment may begin. The analysis chamber vacuum ranges from10-8 mba
r to 10-11 mbar. The next illustration shows a schematic drawing of the XPS
spectrum acquisition principle. For clarity， the drawing scale has been chan
ged.
X ray， without monochromator.
Electron.
Scan area by the lens.
Conclusion.
Photoelectron spectroscopy (XPS) is a dedicated surface characterisation spe
ctroscopy. It reveals which chemical elements are present at the surface， fo
r example carbon and oxygen; it informs us about the chemical bound nature w
hich exists between these elements. An appropriate data processing leads to
the specimen elemental composition.
此文发布于:工程材料与热处理技术 (http://www.ent100.org.cn),转载请注明.
X-ray Photelectron Spectroscopy (XPS) is used in research， development and m
anufacturing. This technique is able to obtain the chemical composition of v
arious material surfaces up to 1 nm depth. It is possible to find out if thi
s material is superficially oxidised， if it contains iron， or carbon， etc. M
ost of the elements can be detected except hydrogen. Our main interest is to
find out the composition i.e. the atomic percentage of each of the componen
ts. Using these characterisation means implies defined rules. Let me explain
for you the principle and the various steps of such an analysis.
XPS analysis basics.
Let's refresh our knowledge together:
Matter is made of atoms.
Atoms are made of a nucleus and several electrons.
These electrons are orbiting around the nucleus with defined orbits.
Each electron is carrying an ID card with its address. The goal is to catch
them in order to find out from which atom they are coming. To be able to fre
e them from the nucleus attractive force we excite them by exposure to X-ray
bombardment. This kind of light is bringing them enough energy to free them
from the nucleus. Once they have been freed up some on them travel through
the matter and reach its surface. Electrons which carry enough energy at thi
s point， may leave the solid matter for the surrounding vacuum.
Once they are in the vacuum， they are collected by and electron analyser. Fu
rthermore they are classified according to their ID cards. The information w
e are interested in is the so-called binding energy which they had before le
aving the atom. All what we do is counting these electrons versus their bind
ing energy and we obtain a spectrum looking like the one shown below:
Electron count plot versus energy (energy spectrum)
If we observe the spectrum， we see two main peaks at 284.6 and 532.5 energy
counts. The unit used for counting energy is electronvolt - abbreviated as e
V. - We simply mention that there are peaks at 284.6 eV and 532.5 eV.
Each energy matches a specific atom type， e.g. 284.6 eV matches carbon and 5
32.5 matches oxygen. From this we can conclude that this specimen contains c
arbon and oxygen. Each peak area is proportional to the number of atoms bein
g present in the studied element. By calculating the respective contribution
of each area we obtain the specimen chemical composition， for example: 25%
Oxygen and 75% Carbon. In other words， among 100 atoms present at the surfac
e of the material， 75 are carbon atoms. By studying the energy of this carbo
n peak， it is possible to find out if the surface of this material correspon
ds to C-O or C=O chemical form. We can interpret the experiment by the mean
of result modelling. For more information， select a higher level of knowledg
e: Beginner.
A step-by-step XPS analysis.
In a first step it is necessary to prepare of the specimen. The size may var
y from a few millimetres to a few centimetres， depending partly on the instr
ument but mainly on the technology being used.
The specimen is then introduced in the first chamber (sample preparation cha
mber). This chamber is then pumped by high vacuum pumps (also called seconda
ry vacuum pumps) down to a vacuum below 10-7 mbar. When the proper vacuum ha
s been achieved， the specimen is transferred into the analysis chamber and t
he XPS experiment may begin. The analysis chamber vacuum ranges from10-8 mba
r to 10-11 mbar. The next illustration shows a schematic drawing of the XPS
spectrum acquisition principle. For clarity， the drawing scale has been chan
ged.
X ray， without monochromator.
Electron.
Scan area by the lens.
Conclusion.
Photoelectron spectroscopy (XPS) is a dedicated surface characterisation spe
ctroscopy. It reveals which chemical elements are present at the surface， fo
r example carbon and oxygen; it informs us about the chemical bound nature w
hich exists between these elements. An appropriate data processing leads to
the specimen elemental composition.
此文发布于:工程材料与热处理技术 (http://www.ent100.org.cn),转载请注明.