# Nanotechnology/Nanomanipulation#AFM manipulation

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# Nanomanipulation

-   Wikipedia Nanorobotics
-   Nanorobotics
    introduction
-   Video clips of Nanomanipulation
    on YouTube
-   1
    Pick and Place of NW in SEM on YouTube
-   Video of the manipulation of a nanowire for TEM observation on
    YouTube

!A slip stick actuator that provides coarse and fine positionoing
modes. Coarse positioning provides long range but low precision, while
fine positioning provides high precision and short range. The slip stick
principle: Slow actuation of the piezo element leads to fine
positioning. A combination of rapid contraction and slow extension can
make the actuator move in coarse steps Δx because the force on the base
becomes larger than the static friction force between the base and base
plate. Reversing the direction is done by using slow contractions
instead.{width="300"}

# AFM manipulation

With AFM nanostructures such as nanotubes and nanowires lying on
surfaces can be manipulated to make electrical circuits and measure
their mechanical properties and the forces involved in manipulating
them.

# STM manipulation

Using an STM individual atoms can be manipulated on surface this was
first demonstrated by Eigler et al. Here Xe atoms were manipulated on Ni
to spell out IBM. This was then extended by Crommie et al., where Fe
atoms were moved to create quantum corals. Here the electron standing
waves created inside the corral are imaged by the STM tip. The probably
demonstrates the highest resolution nanomanipulation.

# In-situ SEM manipulation

To monitor a three-dimensional nanomanipulation process, in-situ SEM or
TEM manipulation seems preferable. AFM (or STM) does have the resolution
to image nanoscale objects, even down to the sub-atomic scale, but the
imaging frame rate is usually slow compared to SEM or TEM and the
structures will normally have to be planar. SEM offers the possibility
of high frame rates; almost nanometer resolution imaging of
three-dimensional objects; imaging over a large range of working
distances; and ample surrounding volume in the sample chamber for the
manipulation setup. TEM has a much more limited space available for the
sample and manipulation systems but can on the other hand provide atomic
resolution. For detailed studies of the nanowires\' structure, TEM is a
useful tool, but for the assembly of nanoscale components of a well
defined structure, such as batch fabricated nanowires and nanotubes, the
SEM resolution should be sufficient to complete the assembly task.

As the STM and AFM techniques opened up completely new fields of science
by allowing the investigator to interact with the sample rather than
just observe, development of nanomanipulation tools for SEM and TEM
could probably have a similar effect for three-dimensional manipulation.
Recently, commercial systems for such tasks have become available such
as the F100 Nanomanipulator System from Zyvex in October 2003. Several
research groups have also pursued developing such systems.

To date the tools used for in-situ SEM nanomanipulation have almost
exclusively been individual tips (AFM cantilever tips or etched tungsten
tips), sometimes tips used together with electron beam deposition have
been used to create nanowire devices. Despite the availability of
commercial microfabricated grippers in the last couple of years, little
has been reported on the use of such devices for handling
nanostructures. Some electrical measurements and manipulation tasks have
been performed in ambient conditions with carbon nanotube nanotweezers.

! A microfabricated electrostatic gripper inside a scanning electron
microscope where it has picked up some silicon
nanowires.{width="300"}

### Companies selling hardware

-   Omniprobe
-   Zyvex
-   Imina Technologies

## The Optimal SEM Image for Nanomanipulation

As the typical SEM image is created from the secondary electrons
collected from the sample, compromises must always be made to obtain the
optimal imaging conditions regarding resolution and contrast. The
contrast in a SEM SE image depends on the variations in SE yield from
the different surface regions in the image and the signal to noise
level. The resolution depends on the beam diameter and is at least some
nm larger due to the SE range.

The optimal solution is always to use as good an emitter as possible
(high ß\_{e} in Eq.[^1]). This means using FEG sources. Working at short
r\_{wd} gives a narrow beam (Eq.[^2]), but will usually shield the
standard ET detectors from attracting sufficient secondary electrons.
Nanomanipulation often requires working with high resolution between two
large manipulator units which further limits the efficiency of signal
detection.

The manipulation equipment must be designed to make the end-effector and
samples meet at short r\_{wd}, and without obstructing the electron path
towards the detector. A short r\_{wd} also gives a short depth of focus,
which can be a help during nanomanipulation because it makes it possible
to judge the working distance to various objects by focussing on them.
The operator can use this to get an impression of the height of the
objects in the setup. Generally, for nanomanipulation, the above
considerations indicate an inlens detector often can be advantageous.

Reducing the beam current to narrow the electron beam necessarily limits
the number of detected electrons and make the signal-to-noise ratio low,
unless one makes very slow scans to increase the number of counts

`<footnote>`{=html}The signal to noise ratio S/N for Poisson distributed
count measurements n is S/N=vn and high counts are necessary to reduce
noise in the images. `</footnote>`{=html}.

When used for in-situ nanomanipulation one needs a fast scan rate to
follow the moving tools (preferably at rates approaching live video) and
this requires high beam currents. The acceleration voltage is also
important, and too high PE energy can make the sample transparent (such
as the carbon coating in Fig.[^3] b) while low energy usually make the
image susceptible to drift due to charging and similar effects.

# In-situ TEM manipulation

TEM offers atomic 3D resolution but the extreme requirements on
stability combined with very limited sample space makes the construction
of in-situ TEM manipulation equipment quite a task. With such systems,
people have observed freely suspended wires of individual atoms between
a gold tip and a gold surface; carbon nanotubes working as nanoscale
pipettes for metals and a wealth of other exotic phenomena.

Companies selling hardware

-   Nanofactory

# References

See also notes on editing this book about how to add references
Nanotechnology/About#How to
contribute.

```{=html}
<references />
```

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[^1]: eq SEM beam diameter

[^2]: eq SEM beam diameter

[^3]: fig INTRO 3 e depth
