Transcript Metode şi tehnici de studiu a suprafeţelor

Methods and Tehniques in
Surface Science
Prof. Dumitru LUCA
“Alexandru Ion Cuza” University, Iasi, Romania
Surface imagistics and topography
The most widespread techniques for surface imaging and morphological
characterization
SPM - Scanning probe microscopy
A comparison between the main applications of SPM
Atomic force microscopy - AFM
Laser
Mirror
Photodiode matrix
Cantilever
Specimen
Tip
XYZ piezoelectric scanner
Specimen surface is scanned by the cantilever tip attached to the cantilever.
The system is able to detect and measure forces in the nN range using the optical lever.
Atomic force microscopy - AFM

Contact mode
Interaction between individual atoms of the tip and the surface.
The theory is very complex (Coulomb forces and/or forces induced by polarization).
Strong interactions which may affect the physical condition of the surface.
Used for morphological caracterization of the surface.

Non-contact mode
The tip-to-sample distance is maintained constant in the 2-30 nm range.
The theory is quite simple, since only there are only the interaction between an atom in the
apex and entire specimen as a whole.
Coulomb, magnetostatic, van der Waals forces (2 - 4 orders of magnitude smaller than in the
case of contact mode).

Tapping (resonant) mode
A combination of the previous two modes. It is based on the damping of the cantilever
oscillations upon approaching the tip to the surface. Scratching the sample is thus avoided.
Atomic force microscopy (AFM)
 In principle, the AFM reminds of a record player
transducer or the stylus profilometer.
 AFM incorporates, however, many more technical
refinements allowing atomic scale resolution:
1. Phase sensitive detection (lock-in)
2. Sensitive cantilevers
3. Sharper tips
4. Posibility of positionning the tip under high spatial
resolution conditions.
5. Feedback loop for force control.
AFM in contact mode. Constant height
 Less frequently used technique.
 Allows for the determination of surface topography via surface scanning by the tip. There are
mainly, 3 operation modes:
A contact mode image of a laser ablation
deposited TiO2 surface.
AFM in contact mode. Constant force
An image of the surface of a rf
magnetron sputtered TiO2 film.
AFM in contact mode. Error contact mode
A contact mode image of a laser ablation
deposited TiO2 surface.
AFM in contact mode. Force imaging
It is used to scan flat surfaces. This is done in a
more precise and rapid way by eliminating
the feedback loop. z = const.
Applications in polymer physics, semiconductors, composite materials and so on.
AFM in contact mode. Force imaging
 Distinguish regions with different
values of static friction coefficients.
 Allows for taking sharp contour
images of any surfaces.
 Can be used in association with
other AFM techniques for more
complete characterization.
 Applications in semi-conductor and
polymer physics, mass storage
devices, surface contamination, nanotribology.
AFM in contact mode. Force imaging
Force-distance characteristics are
plotted.
The vertical component of the tip-to
surface force is derived in the
contact mode.
 Application: characterization of
catalist,
semiconductors,
polymers,
thin films,
mass storage devices.
AFM in contact mode. Adhesion force imaging
 Information is derived concerning the adhesion features of the sample.
 Sample surface is scanned. The F(d) plots are used to get a 2-D map of the forces for
which the SNAP BACK occurs.
AFM in contact mode. Spreading resistance mode
 Here, a sharp tip is used to find, for example,
the dopant concentration in the sample.
 A relatively strong force is ensured so as to
punch the native oxide film which usually
covers the surface (ex. Si).
 By using a conductive cantilever, the local
conductivity of the surface is mapped.
 It is currently used in association with an
other conventional AFM imaging technique.
AFM in Tapping Mode
The TM image of a working surface of
a stamping device for CD
manufacturing.
AFM in tapping mode. Phase mode
 Measurements are performed in
association with other conventional
imaging techniques.
 Maps of various surface physical
quantities (such as composition,
adhesion, friction, viscoelasticity) are
drawn.
 Useful information for a wide range
of application (chemistry, biologie,
physics, engineering etc.)
Kelvin SPM
 In this case a voltage is applied
between the tip and the sample to get
information between the tip and the
sample and subsequently the superficial
distribution of the electric potential.
 The method allows for the localization
and identification of failure causes of
multi-material, multi-level devices.
Magnetic Force Microscopy (MFM)
This technique is used for basic and applied research to obtain the image of ferro-magnetic thin films,
magnetic disk and tapes, permanent magnets and soft magnetic materials.
.