Scanning Probe Microscopy
SPM 250 EVTState-of-the-Art AFM and STM Technology for Advanced SPM Research
� Extreme Stability � Highest Productivity � Variable Sample Temperature Range
<20 K to 450 K � Low LHe Consumption Flow Cryostat � Video Speed STM � KolibriSensor™ for nc-AFM � SPC 260 or Nanonis™ Control System
Customized Systems and Solutions
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Components for Surface Analysis
SPM 250 EVT
Introduction
With scanning probe microscopy (SPM) being a powerful
tool for nanotechnology on the atomic scale, SPECS li-
censed the STM (scanning tunneling microscopy) system
from University of Aarhus. Up until then, commercial
SPM systems were approaching the needs of scientists
with a wide variety of SPM techniques, yet neglecting
fundamental problems arising from the lack of mechani-
cal stability and from time-consuming operational re-
quirements from its users. The STM 150 Aarhus, entered
the market showing ultimate stability and ease of use at
the very same time. In doing so SPECS managed to of-
fer STM systems that operate productively and stable on
a daily basis, thereby allowing scientists to spend more
time thinking about possible experiments rather than
investing valuable time operating the instrument itself.
Mechanical Loop
One of the key features of the Aarhus SPM family mem-
bers is the smallest possible mechanical loop between
sensor and surface using the miniaturized approach
mechanism. With most other instruments not having
such a feature, the Aarhus SPM gains its fundamental
stability from this miniaturized mechanical loop.
Tip Replacement
Another key feature for all Aarhus SPM family members
is not having to replace probing sensors, e.g. a tunneling
tip. The lack of instrumental stability, i.e. from sensor
damaging contact with the surface (‘tip crashes’) along
with the lack of cleaning possibilities, i.e. removing con-
taminants and sensor sharpening, made ‘in-situ’ tip re-
placement necessary for most other instruments. Within
the Aarhus SPM family a different approach is used. By
using a protection shield all sensors are left within the
instrument and are bombarded with a parallel ion beam.
The sensors are not just cleaned but also sharpened in a
very reproducible and time-efficient manner.
Extended Variable Sample Temperatures < 20 K
The SPM 250 Aarhus EVT transfers the extreme produc-
tivity and stability of the Aarhus STM familiy into an Ex-
tended Variable Temperature (EVT) range using a special
designed high-end liquid helium (LHe) based cooling
device. Its extremely low accoustic noise enables guar-
anteed best „Aarhus-stability“. For this the flow cooler
is decoupled from the sample stage by a series of spring
suspended masses followed by a double stage suspen-
sion of the stage. Those decoupling masses of 2 kg each
perfectly suppress possible “bubble” noise originating
from the flow cryostat.
Highest temperature accuracy during LHe cooling to low-
est temperatures is mandatory to reach extremely low
drift. For this an ultra-precise measurement of true sam-
ple temperature is realized.
SPM 250 Aarhus EVT with shielding open (left) and closed (right)
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A tight mechanical and thermal contact of sample hold-
er and SPM stage is realized by a locking mechanism.
Together with the shielded stage a
fast cool down of samples to mini-
mum temperatures can be realized.
A typical time span of 20 min from
insertion of a sample at room tem-
perature to “ready for SPM” at
below 20 K and has been shown.
Furthermore the shielding by a
cooled copper encapsulation
avoids fast contamination of
the cold sample. For tem-
perature ramps counter
heating of the sample is
possible even to elevat-
ed temperatures up to
450 K.
A comparably low LHe con-
sumption can be realized in
operation as well as during
the fast cool down of the
cryostat from
room tem-
perature.
Only about 10 l of
LHe is consumed
while in between
3 h the SPM stage
is completely
cooled down to
minimum tem-
perature <20 K.
The typical LHe
consumption
during opera-
tion at 20 K is
about 2 litres
per hour.
Cross sectional view of SPM 250 Aarhus EVT
Close-up of sample stage
Results
The adsorption of physisorbed argon on the Au(111) sur-
face has been studied by STM at a sample temperature
of 14 K. Even locally the sample temperature does not
change strongly by the close-to-room temperature tip
in front of the sample indicating the temperature stabil-
ity of the sample stage. In other cases the argon layer
would have vanished during scanning. From Fig. 4 it is
obviously, that the Ar adlayer does not affect the Her-
ringbone structure of the underlying Au substrate.
Physisorbed Argon on Au(111): T = 14 K (I = 0.2 nA; U = 1.2 V)
The next result shows local defects in the Ar adlayer indi-
cating true atomic resolution. The excellent stability and
resolution of the instrument is demonstrated by imaging
the corrugation of only about 0.02nm.
Physisorbed Argon on Au(111): T = 14 K (I = 0.5 nA; U = 0.63 V)
SPM 250 EVT
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KolibriSensor and Nanonis Control System
Using Nanonis’ state-of-the-art control in atomic force
microscopy (AFM), the Aarhus SPM family allows imag-
ing of non-conductive samples in non-contact AFM (nc-
AFM) mode. In combination with SPECS’ development
of the KolibriSensor, a quartz oscillator-based sensor,
atomically resolved imaging is possible. Furthermore,
considering the significantly more demanding AFM tech-
nology, this Aarhus SPM family member makes atomi-
cally resolved imaging of conductive and non-conduc-
tive samples possible on a daily basis. By separating the
tungsten tip from the resonator, force and tunneling
signals can be recorded simultaneously and completely
independently of one another. The SPM 250 Aarhus EVT
represents a new generation of UHV systems to examine
every possible surface at the atomic scale even at sample
temperatures below 20 K.
Technical Data
SPM 250 EVT
Mounting Flange DN 250CF
Temperature Range 20 K - 450 K
Temperature Stability Better 0.2 K
LHe-consumption at 20 K Approx. 2 litres per hour
In Situ Access Specular and evaporation
Scan Range 1.500 nm x 1.500 nm
Sensitive Z Range ±175 nm
Approach Speed ≤1 mm/min
Drift-rate T <= 50 K < 0,1 nm/min (vert), < 0,5 nm/min (lat)
Stability < 10 pm
SPM 250 EVT
Compact SPM 250 Aarhus EVT System with vibration isolaton
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Technical alterations reserved. The information in this document is provided with greatest care but SPECS does not assume any liability arising from the application or use of the information or product described here. SPECS, Kolibri and Tyto as well as the corresponding logos are registered trademarks of SPECS Surface Nano Analysis GmbH in Germany and other
countries worldwide. Nanonis is a registered trademark of SPECS Zurich GmbH in Switzerland and other countries worldwide. Other product and company names mentioned herein are trademarks or trade names of their respective companies.Printed in March 2011
Innovation in Surface Spectroscopy and Microscopy Systems