Major Benefits of Scanning
Thermal Microscopy (SThM)
Technology and Operating
Principles of Scanning Thermal Microscopy (SThM)
Major Applications of Scanning Thermal Microscopy
NT-MDT Scanning Thermal Microscopy (SThM)
Thermal Microscopy (SThM) Probes
Scanning Thermal Microscopy (SThM) is an advanced Scanning Probe Microscopy
technique that is useful for obtaining nanoscale thermal properties and
Scanning Thermal Microscopy equipment available from NT-MDT is
able to record and display the temperature and thermal conductivity distribution
at the surface of a sample.
Major Benefits of Scanning Thermal Microscopy (SThM)
The major benefit of Scanning Thermal Microscopy is that it displays a higher
spatial resolution than Infrared Microscopy, Laser Reflectance Thermometry and
Technology and Operating Principles of Scanning Thermal
The operation of a Scanning Thermal Microscope is based on Atomic Force
Microscopy (AFM) Techniques.
When the atomically sharp AFM tip is placed in proximity to a sample to be
studied there is a heat exchange which modifies the temperature of the tip.
It is then relatively straightforward to use signals from the tip to create
what is effectively a thermal map of the surface.
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The heat exchange or heat flow is affected by several factors; including the
temperature of the tip, the contact pressure and the inherent material
properties of the sample such as Thermal Conductivity and Specific Heat
Although the preferred method of operation is via solid to solid direct
conduction, it is possible that in the presence of aqueous species that
conduction occurs within the liquid meniscus at the tip surface which can also
be affected by gas conduction. For this reason the preferred method of operation
is to scan surfaces under vacuum conditions.
Two types of probes have been used in Scanning Thermal Microscopy -
- Thermocouple type - with this arrangement the temperature is measured by a
thermocouple junction at the probe tip. Typically Chromel Alumel, Au/Pd Au/Ni
- Bolometer type - in this arrangement the probe temperature is monitored by
the resistance of a thin film at the probe tip. The resistor can be used to heat
the probe and measure the temperature at the same time.
The signal from the Bolometer probe passes through a wheatstone bridge
readout circuit which provides a fixed power source and measures the resistance
of the bolometer probe.
Using this arrangement it is possible to use constant power or constant
temperature. The advantage of constant temperature is the improved speed and
reduced sample damage.
The fundamental limit of resolution is proportional to kT, where k is the
boltzman constant and T is the temperature. At room temperature kT is ~ 10-21
The key design issues relating to probes are the small size of the
microfabricated probes to attain a high degree of spatial resolution coupled
with good thermal isolation of a small thermal mass of probe.
Sample temperatures are typically measured on active device structures such
as magnetic recording heads, laser diodes or other forms of electrical
Conversely, thermal conductivity is more typically measured on composite
samples. In such a measurement, more voltage will be applied to the probe
increasing it further above room temperature. The thermal conductivity of the
sample will affect the temperature of the probe by draining more or less heat
away from the tip and thermal conductivity can thereby be calculated.
Major Applications of Scanning Thermal Microscopy (SThM)
Some of the major applications for SthM are for defect and hot spot detection
in semiconductors, photoresist metrology and the detection of sub surface
features which cannot be observed by AFM.
Typical material parameters that can be observed include the thermodynamic
characterisation of material properties such as conductance, specific heat
capacity, and glass transition temperatures.
The technology is also of particular relevance to pharmaceutical compounds
and for the analysis of biomolecules.
NT-MDT Scanning Thermal Microscopy (SThM) Equipment
Controller and Software
The SThM system hardware includes an electronic controller, software, and
The Scanning Thermal Microscopy controller (Figure 1) is connected to the
main Atomic Force Microscope electronics via a standard extension socket. The
system is easily adjusted through a user-friendly software interface.
Figure 1. Electronic controller
For ease of use, the SThM control program is integrated into the main NT-MDT
AFM software as one of the contact mode methods.
Due to high sensitivity of the system and the low noise of the output
voltage, the electronic controller provides high signal resolution.
An additional advantage is that the compact size of electronics hardware
simplifies the setup and optimizes the time involved in scanning high resolution
NT-MDT Scanning Thermal Microscopy (SThM) Probes
Scanning Thermal Microscopy mode of operation with an AFM utilizes a
specialized probe with a resistor built into the cantilever (Figure 2)
Figure 2. Cantilever holder
Figure 3. AFM Head
NT-MDT's SThM module allows users to monitor the changes in
resistance correlated with the temperature at the end of the probe. As a result,
the system is able to monitor relative changes of sample temperature and thermal
Figure 4. SThM Probe Setup
NT-MDT's thermal probes provide better than 100 nm lateral
resolution for both topography and thermal images (Figure 5).
Figure 5. Scanning Thermal Microscopy allows one to
obtain images of <100 nm lateral resolution.
Sample: Optical Fiber in
Epoxy. (Left) topography image; (Right) thermal conductivity image. Scan size: 6
x 6 µm.
The specialized SThM cantilever, made of SiO2 with a thin metal
layer, is deposited on the probe in such a way that the highest resistance
portion of the layer is concentrated near the tip apex.
Figure 6. SEM image of the SThM Probe