There are four major parts to the experimental setup - Mind Melt

unkindnesskindUrban and Civil

Nov 15, 2013 (3 years and 8 months ago)

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There are three major parts to the experimental setup. They are the optics, the
encasement, and the flow/pump system. Each of these systems has very specific
requirements and also has problems inherent in them that are not yet solved.


The first system i
s the optics system. In order to have the Fe bonded carbon
nanotubes align properly, they must first be orientated vertically, and then the sample
system must be struck by the laser’s standing wave in the precise spots as well. Also, Fe
requires a laser
source in the ultraviolet range to be effected enough to deposit properly.
All of these issues necessitate a complicated laser system. Luckily, due to other research
in the field, most of the laser system has already been designed. The AQT group at TUE
has designed, built and tested the laser system below:



This system provides the proper wavelength of laser light in order to perform this
experiment. The system works like so: An Ar ion laser at 20W/500 nm pumps a Ti:S
laser. This laser outputs 2W/744

nm, exactly double the required wavelength. With a
frequency doubling optical device, a non
-
linear crystal, the proper wavelength is
produced. It is frequency locked with an atomic transition frequency determined from
the hollow cathode discharge. Afte
r this laser light is produced, it needs to be first split,
then established as two separate standing waves in our encasement. This requires a beam
splitter, an acousto
-
optic modulator (AOM), two linear polarizers, two quarter
-
silvered
mirrors, two full m
irrors, and a cylindrical telescope. It also requires a moveable
attachment for one of the full mirrors in the nanometer scale. The setup for the beam
splitting and phase matching has been well established via various other experiments.
First, the beam
is split. Then, the upper beam is run through an AOM, a device that
manipulates both the phase and amplitude of the beam via ultrasonic waves. This lets the
experimenter vary the amount of optical collimation on the fly. After running through
the AOM, i
t is then input into the cylindrical telescope, which expands the beam while
maintaining its polarity. However, in order to completely catch any transient waves, the
beam is run through a linear polarizer before it passes through one side of the quarter
-
s
ilvered mirror and finally enters the encasement. The beam is then reflected off of the
full mirror on the far side of the encasement. This establishes the optical collimation
portion of the optical system. The second beam from the beam splitter is sent

through
another linear polarizer. It too then passes through a quarter
-
silvered mirror before
entering the encasement. The final full mirror is used to reflect this beam back. In order
to properly establish the standing wave, this mirror is on a moveab
le platform, much like
those used in STMs. This is the standing wave portion of the optical system. The system
can be recreated multiple times in order to establish a varying pattern of standing waves.
This will allow for different layouts of carbon nan
otubes across the entire substrate.




















The next system to be designed is the encasement. The encasement holds the
substrate, the liquid medium, and the magnet system. The substrate is mounted on a
moveable platform with accuracy in the
nanoscale. A system much like a reverse STM
would be appropriate here. The liquid medium must be inert with both the carbon
nanotubes and the substrate, of low viscosity and with a specific refractive index as to not
influence the lasers (we can also use

this to our advantage). The magnet system is
mounted below the substrate, and provides extra downward force to pull the nanotubes
towards the substrate. The encasement itself must be designed to withstand the pressures
of the liquid within, while being
optically inert, so the lasers can pass unhindered. Its
refractive index should match that of the liquid so that there is no scattering.


The final system to be designed is the flow/pump system. The carbon nanotubes
have to be well mixed in the solution,

and they must move quickly down the pipe to the
destination chamber. This is facilitated in two ways. First, the carbon nanotubes, while
in solution, are subjected to intense ultrasonic in order to break them apart from each
other. Second, the piping i
s constructed as to give the tubes nowhere to stick in their
entire path. The tubes enter the chamber from above the sample. The flow and the
magnet pull down those tubes not impacting on the surface of the sample. They naturally
migrate to the bottom o
f the encasement. This is where the outflow tube is located.
Again, it is designed similarly to the inflow, and it deposits its leftovers into the general
pool of nanotubes to be reused.

Moveable Mirror

Mirror

AOM

Laser Source

Beam Splitter

Mirror

Linear Polarizer

Linear Polarizer

Quarter
-
Silvered Mirror

Quarter
-
Silvere
d Mirror

Cylindrical Telescope

Encasement
















































Nanotube

Input Flow

Nanotube Output Flow

Substrate

Magnet

Liquid Filled Chamber

Substrate Holder and Frame

Nanotube Flow

References:


Atom lithography boosts nano
-
magnetics,
R.C.M. Bosch, K.A.H. v. Leeuwen, H.C.W.
Beijerinck, Vacuum Solutions, issue March/April 2000



Magnetic nanodots from atomic Fe: Can it be done?
, E. te Sligte, R. C. M. Bosch, B.
Smeets, P. van der Straten, H. C. W. Beijerinck, K.A.H. van Leeuwen, Proceedings of the
National Academy of Sciences
99
, pp.6509
-
6513, 2002



Supersonic Fe beam source for chromatic aberration
-
free laser focusing of atoms
, R.C.M.
Bosch, P. van der Straten, H.C.W. Beijerinck, K.A.H. v. Leeuwen, European Physical
Journal


App
lied Physics,
18
, pp.221
-
227, 2002



Progress towards atom lithography on iron
, E. te Sligte, B. Smeets, R. C. M. Bosch, K.
M. R. van der Stam, L. P. Maguire, R. E. Scholten, H. C. W.
Beijerinck, K.A.H. van
Leeuwen, Microelectronic Engineering,
67
-
68
, pp. 664
-
669, 2003



Laser frequency stabilization using an Fe
-
Ar hollow cathode discharge cell,
B. Smeets, R.
C. M.

Bosch, P. van der Straten, E. te Sligte, R. E. Scholten, H. C. W. Beijerinck, K.A.
H. van Leeuwen, accepted for publication in Applied Physics B.


http://www.phys.tue.nl/aow/Pages/Research
/Nano.htm


Nanostructure fabrication via laser
-
focused atomic deposition. R.J. Celotta, R. Gupta,
R.E. Scholten,, and J.J. McClelland, J. Appl. Phys.
79

(8), 6079


Fabricating nanometer
-
scale Co dot and line arrays on Cu(100) surfaces. S.L. Silva, C.R.
Jenkins, S.M. York, and F.M. Leibsle, Appl. Phys.
76

(9), 1128


Linear arrays of CaF
2

nanostructures on Si. J. Viernow, D.Y. Petrovykh, F.K. Men,
A.Kirakosian, J.
-
L. Lin, and F.J. Himpsel, Appl. Phys.
74
(15), 2125