NANOMETRE ACCURACY
FOR AUSTRALIA
METROLOGICAL
SCANNING PROBE
MICROSCOPE
"Nanotechnology presents amazing
opportunities for Australia"
Australian Academy of Science
NANOMETRE ACCURACY FOR AUSTRALIA
Nanoscience and nanotechnology
promise to improve the quality of life
of all Australians in sectors such as
health, energy and the environment:
think targeted drug delivery,
smart coatings for energy efficient
buildings, lighter and longer lasting
batteries. To realise the potential of
nanotechnology, we must be able to
understand and control matter at a
length scale of billionths of a metre.
Accurate length measurements are
critical to meet this challenge.
The metrological scanning probe
microscope (mSPM) developed
by the National Measurement
Institute (NMI) establishes a direct
link between Australia’s legal unit
of length, the metre, and practical
nanoscale length measurements.
It will give Australian industry,
researchers and the community
confidence when making decisions
where nanoscale accuracy is
paramount.
THE METROLOGICAL SCANNING PROBE MICROSCOPE:
A FUNDAMENTAL TOOL FOR NANOSCIENCE
AND NANOTECHNOLOGY
What is it?
Why is it so important?
Key applications
The mSPM operates in a similar
way to a conventional atomic force
microscope with one key difference
– the three-dimensional scanning
motion is monitored with laser
interferometry, and therefore all
displacements are measured in
units of the laser wavelength.
This means that measurements
made with the mSPM are highly
accurate and are directly traceable
to the SI metre. The mSPM thus
enables NMI to measure the
dimensions of artefacts extremely
accurately, thereby transforming
them into traceable ‘nano-rulers’
for the calibration of other scanning
probe or electron microscopes
used in industry and research
laboratories.
n
Calibration of pitch length and
step-height transfer standards
n
Accurate measurement of
nanoparticle size
AUSTRALIA’S PRIMARY STANDARD FOR
NANOMETRE SCALE LENGTH MEASUREMENT
Australia’s legal unit for
measurement of length, the metre,
is defined in accordance with the
International System of Units, the SI,
as the length of the path travelled
by light in vacuum during a time
interval of 1/299 792 458 of a second.
It is realised using an extremely
stable laser source.
Practical length measurements can
be made traceable to this primary
reference by using a technique called
laser interferometry. The wavelength
of the laser light used in this method
can be very accurately calibrated by
comparing it with that of the laser
source used in the realisation of
the metre. This calibration provides
metrological traceability.
NMI’s metrological scanning
probe microscope uses five laser
interferometers to measure the
motion of a sample surface relative
to a fixed sensor. The resulting
image of the sample can be used
to measure the distance between
features on the sample surface
with nanometre accuracy, and this
measurement result is directly
traceable to NMI’s realisation of the
SI metre.
SOME TECHNICAL DETAILS
Flexible microscopy platform with moving sample and fixed tip
Quartz tuning fork force sensor for non-contact atomic force microscopy (AFM)
Operation in frequency modulation mode
Typical resonance frequencies: 32.7 kHz; 191 kHz
Addressable volume: 100 µm × 100 µm × 25 µm
Real-time displacement measurement via laser interferometry
Highly stable heterodyne light source
(wavelength: 633 nm, stable to 1 part in 109; beat frequency adjustable up to 10 MHz)
Digital phase meters implemented on field programmable gate array
(displacement noise: 0.02 pm Hz-1/2 at 1 Hz; bandwidth: 10 kHz)
Differential measurement between moving sample and fixed tip using high-precision mirrors
(measurement noise: < 0.05 nm Hz-1/2 at 1 Hz)
Cyclical error: < 0.1 nm
Temperature stability over the course of a typical measurement (~4 h)
Instrument: < 0.01 K
Laboratory: < 0.1 K
Target uncertainty of length measurement: < 1 nm
Left: Optical configuration of mSPM laser interferometry system. Centre: AFM image (80 µm × 80 µm × 3 µm) of a three-dimensional silicon
calibration artefact. Right: AFM image (10 µm × 10 µm × 0.02 µm), taken with the mSPM, of gold nanoparticles on a silicon substrate.
Nanometrology
National Measurement Institute
Bradfield Road
West Lindfield NSW 2070
PO Box 264
Lindfield NSW 2070
Australia
Telephone: +61 2 8467 3784
[email protected]
JULY 2013
www.measurement.gov.au
ABN 74 599 608 29