A small introduction into
The near-field scanning probe based thermal microscope (SThM) gives information
about the temperature distributions and allows to determine the local thermal
conductivity quantitatively. We use a resistive probe based method, which
provides both the topography with a spatial resolution in the nanometer
scale and the temperature/thermal conductivity profile, with a resolution
of a few millikelvin and an accuracy of 2% simultaneously.
Scanning Thermal Microscopy
The probe is made of a wire with a thin platinum core surrounded by
a thick silver cladding and is integrated in a Wheatstone bridge which
is connected to a signal generator. A small current is applied for the
determination of the probe resistance in order to perform measurements
of temperature distribution of a device. The application of a significantly
higher current at the frequency w is used for
heating the probe periodically and the thermal conductivity of the sample
can be determined by measuring the 3 w component
of the output voltage of the Wheatstone bridge at two different frequencies.
Fig. 1: Set-up of scanning thermal microscope to perform quantitative
temperature and conductivity measurements.
||Fig. 2: a) Temperature distribution on a short channel n-MOSFET b)Quantitative
thermal conductivity analysis on a MW-CVD diamond film
Scanning Acoustic Microcscopy
Mankind is used to see with their eyes by the use of light. In nature,
however, there exist also other techniques for exploring the environment.
There are some animals which can see by the use of sound, such as bats
or whales. Learning from nature, man has adapted this technique for the
benefits of human beings and uses it now in many different fields like
for example sonar systems and non-destructive testing in industry.
With the development of modern industry, especially with the rapid
development of ultra-large-scale integrated circuit technology, there are
more and more requirements to research the material properties at the resolution
of micro- or nanometer range.
The so-called scanning acoustic microscope (SAM) is developed to analyse
the acoustic (mechanical) properties of materials. This kind of microscope
has to use focused beams to detect acoustic properties, it has naturally
a limit of resolution because of Rayleich diffraction limits of focused
To overcome this resolution limit, the so-called near-field acoustic
microscope has been developed. The principle of this kind of microscopes
is almost the same: an acoustic wave is produced in a tiny area just in
the vicinity of surface (near-field area) through different interaction
mechanisms and by detecting this acoustic wave, we can gain the acoustic
properties of materials at a high resolution which is not dependent on
Scanning Electron Acoustic Microscope (SEAM) and Scanning Probe Acoustic
Microscope (SPAM), which are developed from the commercial Scanning Electron
Microscope (SEM) and Scanning Probe Microscope (SPM), are two typical microscopes
of this kind with highest resolution.
The following figure describes the main structure of SEAM and SPAM:
Fig. 1: Principle of operation of a Scanning electron acoustic
and Scanning probe acoustic microscope
The typical results of SEAM and SPAM with ferroelectric BaTiO3
ceramic sample are as follows:
|Topography of SEM
||Acoustic image of SEAM
||Topography of SPM
||Acoustic image of SPAM
Fig. 2: Typical Results of acoustic near-field microscopes
So with these techniques it is possible to obtain the acoustic properties,
which are different from topography, at the resolution in the micro- and