Description of Nano-Reactor Vacuum Procedures
Prepared for:
Francisco Zaera
By:
Christopher H. Clark
Egor Podgornov
Updated by Yurii Larichev (09/2009)
Contents
1. Introduction .................................................................................................................... 1
2. Basic Vacuum Procedures ............................................................................................. 1
2.1 Start-up ...................................................................................................................... 1
2.1.1 Evacuation.......................................................................................................... 1
2.1.2 Bakeout ............................................................................................................. 3
2.1.3 Filament Degassing ............................................................................................ 5
2.2 Normal UHV Operations .......................................................................................... 6
2.3 Shut-down ................................................................................................................. 6
3. Experimental Procedures ............................................................................................... 7
3.1 Ar+ Sputtering ........................................................................................................... 7
3.2 Oxygen Annealing .................................................................................................... 8
3.3 Temperature Programmed Desorption (TPD) .......................................................... 9
3.5 Gas Mixing.............................................................................................................. 10
3.6 Work with Nanoreactor
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1. Introduction
Basic operation and care of the Nanoreactor vacuum system consists of three
modes: start-up, normal operation, and shut-down. In addition to the basic modes of
operation, there are more advanced modes of experimental operations within the realm of
normal ultra-high vacuum operations. The current procedures for some basic
experimental operations available in the Nanoreactor system are: Ar+ sputtering, oxygen
annealing, temperature programmed desorption (TPD), different chemical reactions, and
gas mixing. Here the procedures for these operational and experimental modes will be
discussed. Figure 1 gives a connection diagram that will be referenced throughout this
procedural description.
2. Basic Vacuum Procedures
2.1 Start-up
The start-up procedure for obtaining clean vacuum conditions in the Nanoreactor
apparatus can be broken up into three stages: initial evacuation, bake-out, and degassing.
Evacuation is achieved when the maximum allowable vacuum is achieved in both
chambers without filling the diffusing pump cold trap, CT2, or baking the apparatus out.
2.1.1 Evacuation
The procedure for evacuating the apparatus is as follows as referenced to Figure 1:
1) With valves V6, V12 and V14 closed, turn on the turbo-pump roughing line
mechanical pump MP1 and the diffusion pump roughing line mechanical pump
MP2.
2) Wait for SV1 and SV2 to open and the foreline pressure to drop to 10-3 torr range.
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Figure 1: Vacuum Connections Diagram for the “Nanoreactor” Ultra High Vacuum (UHV) System
V14 valve located between SV2 and V12
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3) Evacuate the high vacuum pump forelines, as measured by thermocouple gauges
TC2 and TC4, into the mtorr (10-3 torr) range.
4) Slowly open valves V6, V12 and V14 assuring that the pressure measured by
TC2 and TC4 are in the same general range and do not exceed 5 torr (to prevent
diffusion pump oil back streaming assure that V6 is always opened prior to V12
and TC2 is at a lower pressure than TC4).
5) Once the valves are fully open and TC2 and TC4 are stable in the mtorr range
(10-3 torr) the diffusion pump, DP, can be turned on. This is done by first
throttling the cooling water supply valve to the diffusion pump, while observing
the liquid flow meter, to above 2 liter per minute (LPM). Next, the diffusion
pump protective lockout system (located in the instrument control rack) is turned
on. Then, the diffusion pump heater variac (located at the bottom of the
instrument control rack) is turned on to 70% of total power. The diffusion pump is
operating once the oil temperature exceeds 180°C.
6) Once the diffusion pump is operating (about than 280-290°C is the normal
operating temperature) the turbomolecular pump, TP, can be turned on. To turn
on the TP, first the cooling water supply valve to the turbo pump should be
throttled, while observing the liquid flow meter, to above 2 liter per minute
(GPM). Next, the Leybold-Heraeus Turbotronik NT 450 turbomolecular pump
controller should be powered up and the start button pressed. The pump will then
begin to spin-up. The controller “normal operation” indicator light will be
illuminated when the pump is operating properly.
7) Once the TP and DP are operating properly, the main chamber ion gauge, IG2,
and the probe chamber ion gauge, IG1, controllers and filaments can be turned on
and set in their normal operational modes.
A leak-free unbaked system should reach an ultimate pressure in the main chamber, as
measured by IG2, of ~5-6*10-9 torr. The absence of leaks should be further verified by
the absence, or insignificance, of a mass spectrum peak at 32 AMU. If a leak is detected,
the leak should be located using the helium leak detection method and fixed.
2.1.2 Bakeout
Once the Nanoreactor system reaches its ultimate unbaked pressure the system
should be baked to remove water. The procedure for bake-out is as follows:
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1) Four variacs are needed for bakeout to proceed. Three variacs should be
distributed with no more than 1.5 kVA of total heater load plugged into a single
variac. The fifth variac should be used to power the halogen light. Care should be
taken that each variac has its own power circuit (laboratory outlets are numbered
and overlap can be easily identified).
2) Assure vacuum chamber is properly grounded by testing the chamber resistance
with respect to each heater set. This is an important safety precaution as a heater
short could cause equipment damage and/or a personnel safety hazard.
3) Assure that the entire chamber is wrapped in aluminum foil to prevent convective
and radiation heat losses.
4) Turn all four variacs with heaters plugged into them on and set them at 70%
power. Turn the variac with the halogen light plugged into it on and set it to 80%.
5) Assure that the gas manifold cold trap, CT3, is filled with liquid nitrogen (it must
be full throughout bakeout to assure water is removed and oil vapors are removed
and not added). Additionally, the manifold mechanical pump, MP3, must be
operating with a manifold pressure, as measured by TC1, in the mtorr range.
6) Open the probe chamber and main chamber bypass valve, V11.
7) Open leak valve LV1 until the main chamber pressure, as measured by IG2, is
stable at 1x10-7 torr. Then open LV2 until the main chamber pressure, as
measured by IG1, is stable at 2x10-7 torr.
8) Turn off ion gauges, both IG1 and IG2.
9) The crystal should take ~2h to reach 200°C. The crystal temperature or any part
of the chamber should not exceed 200°C. All parts sealed with rubber gaskets or
viton o-rings should no exceed 150°C (rotary platform and valve V11). The turbo
pump should not exceed 120°C. If any of these limit temperatures are exceeded
the power on the heater attached to the corresponding part should be turned down.
10) After the crystal temperature has reached 200°C bake-out should continue for ~10
h.
11) At the end of bake-out the variacs should be turned off and the leak-valves cooled
to room temperature and then shut.
12) Fill cold trap CT2 with liquid nitrogen.
13) The gas manifold, vol 1, should be filled with ~200 torr, as measured by the
manifold diaphragm gauge (DG), of pure oxygen.
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14) The oxygen leak to the vacuum chambers should be adjusted, using LV1 and
LV2, so the pressure will not exceed 10-7 torr.
15) Throttle valve V11, allowing oxygen is leaking into the probe chamber.
16) Wait until chambers cool to room temperature.
17) Once chamber has cooled to room temperature, close leak valves.
A leak free system that has been baked out should reach an ultimate pressure ~2*10-9 torr
in main chamber and ~5*10-9 torr in probe chamber.
2.1.3 Filament Degassing
The last stage of the start-up procedure is the degassing of instruments with
filaments. The instruments that need degassed are the two mass spectrometers, the LEED
electron gun, the “extra” electron gun, the Ar+ ion gun, the two ion gauges, and the
halogen light. This should be done shortly after bake out is complete (preferably while
the chamber is still warm). The procedure for filament degassing is as follows:
1) Turn on main chamber ion gauge to degassing mode, IG2.
2) Turn on probe chamber ion gauge to degassing mode, IG1. This is done by first
putting the grey emission control knob (secondary knob) to zero. Then turn the
black knob to degas. Next turn on the filament and finally turn the grey emission
on slightly, ~1 (if use of the probe chamber mass spectrometer is not planned
within one day this step should be avoided as not to burn out the filament).
3) Turn on the two probe chamber and main chamber mass spectrometers to 75% of
the normal filament current in Faraday Cup mode.
4) Turn the ion gun knob to degassing mode.
5) Turn on the “extra” electron gun and set it to limit current of 1.5-2A. This is done
by plugging in only the filament wires (4 and 5) with no high voltage source.
6) Turn on LEED electron gun and set it to a filament current of 1.5-2A.
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7) Leave all filaments on for 2-3 minutes, then turn off the mass spectrometer and
electron gun filaments.
Once filament degassing is complete and ultimate pressure is reached, the chamber is
considered to be in operational mode.
(In current system mode LEED unit disassembled from main chamber and changed
steel blank). Now LEED unit kept in room 137 and need to repair.
2.2 Normal UHV Operations
Normal operational mode requires very few procedures outside of the realm of
details involved in specific experiments. To assure the Nanoreactor has a good clean
vacuum in operational mode the liquid nitrogen tank hooked to the auto-fill system for
CT2 should always keep the cold trap full. This requires changing the liquid nitrogen
tank every 2 days depending on the tank used. A daily check of the chamber should
include assuring the pressure is in range (10-9 torr in the main chamber), CT2 is full of
liquid nitrogen, the diffusion pump is at the proper temperature (290°C), and the
roughing lines for the diffusion pump and turbomolecular pumps are at a pressure of
5x10-3 torr or below (this assures the zeolite traps ZT1 and ZT2 are clean and the
mechanical pumps MP1 and MP2 are operating properly). Also needs to add a little
quantity of water to chiller 1-2 times per week. In case any chiller brokerages ask Wayne
Goodman. Once per 4 month is recommended baking zeolite traps and changing oil in
mechanical pumps (especially in MP3).
2.3 Shut-down
When there is maintenance or upgrades needed to the chamber, power outages, or
problems with equipment it becomes necessary to shut down the chamber and break
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vacuum. The procedure for doing so is specific as not to damage the pumps or
contaminate the system. The procedure for shutting down the system is as follows:
1) Turn off the liquid nitrogen auto-fill mechanism used for the diffusion pump cold
trap, CT2, and flush all the liquid nitrogen from this trap.
2) Once the liquid nitrogen is removed from CT2 and the cold trap has reached room
temperature, turn the diffusion pump heater variac off (this allows the interlock to
stay on and the temperature of the diffusion pump to be monitored as it cools).
3) Turn off the ion gauges, IG1 and IG2.
4) Once the diffusion pump has cooled below 100°C valves V6, V12 and V14 can be
closed and the turbomolecular pump turned off. (the turbo pump can be slowed
with a controllable leak of argon, but it otherwise takes ~15 minutes to reach a
complete stop).
5) Once the turbomolecular pump has stopped affix the kwik-flange connection
(blank) between V12 and V14 placed into a full Dewar of liquid nitrogen and
slowly open V12 to fill the chamber with nitrogen.
Once the chamber has been filled with nitrogen at atmospheric pressure the system is
considered shut-down.
3. Experimental Procedures
3.1 Ar+ Sputtering
Ar+ sputtering is a common method of crystal cleaning that removes surface
material through accelerated collision of large argon cations. In the nano-reactor chamber
the system Ar+ sputtering is to obtain a clean metal single-crystal surface. The general
procedure for Ar+ sputtering is as follows (ion energy, sample current, and sputtering
time must be varied depending on the material, literature should be reviewed to identify
the specific sputtering conditions):
1) The crystal should be oriented at a 45° to the incident ion beam at the same height
as the ion beam.
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2) The gas manifold should be filled with ~50 torr of Ar, as measured by the manifold
DG (the manifold cold trap, CT3, should be filled prior to pumping the manifold or
filling it with any gas). (WARNING: If opening of the main valve to the argon
cylinder is needed, disconnect it from the manifold, to prevent accidental
pressurization if the pressure regulator fails)
3) LV1 should be opened until the system pressure, as measured by IG2, is ~10-6 torr.
4) Once Ar is flowing through LV1 to the ion gun, the ion gun power supply should
be turned on, the function knob placed in “operate” mode, and the ion energy set to
the desired value (~2 keV).
4) LV1 should then be adjusted to obtain the desired sample current (the sample
current is measured by measuring the current in μA between the sample and the
ground).
5) The sample current can be optimized by adjusting the x, y, and z position of the
sample.
6) Once the desired sputtering conditions are reached the sputtering should continue
for the desired amount of time (5-15 minutes).
6) Once the desired sputtering time has elapsed the function knob should be turned
to “0” and the ion energy to 0.
Once Ar+ sputtering is complete the sample is usually annealed in oxygen.
3.2 Oxygen Annealing
Oxygen annealing is done to “burn off” carbon on the surface and mobile
subsurface carbon. Before beginning oxygen annealing the literature should be consulted
to prevent oxygen diffusion into the bulk of the sample or sample oxide formation.
1) The gas manifold should be filled with ~100 torr of oxygen, as measured by the
manifold DG (the manifold cold trap, CT3, should be filled prior to pumping the
manifold or filling it with any gas).
2) LV2 should then be adjusted until the desired oxygen pressure is reached, usually
2x10-7 torr as measured by IG2.
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3) The sample should then be heated quickly to the desired annealing temperature,
usually 1000-1100 K, and held there for the desired length of time (10s-10min.
depending on the type of crystal and its initial cleanliness).
4) The crystal should then be cooled in oxygen to room temperature.
5) Once the crystal has cooled to room temperature, the oxygen leak should be
terminated by closing LV2.
6) A temperature programmed desorption (TPD) should be conducted to desorb
oxygen adsorbed during crystal cooling in oxygen and assess amount of carbon
still present at the crystal surface.
Oxygen annealing is almost always followed by TPD, to ascertain the approximate
amount of carbon removed. Oxygen annealing is generally done when one suspects that
carbon from experiments or the vacuum environment has diffused into the subsurface.
3.3 Temperature Programmed Desorption (TPD)
TPD is a powerful technique for not only determining crystal cleanliness, but
ascertaining interesting surface chemistry of adsorbates. Although the procedure outlined
here will be for TPD following oxygen adsorption, the procedure could be applied to
many other adsorbates by changing the ramping rate, final temperature, and masses
observed in the mass spectrum. The procedures for collecting mass spectrometer data are
explained in the manual for the software on CD. The procedure for TPD is as follows:
1) Once the sample has cooled to room temperature, the mass spectrometer should be
prepared to monitor masses of expected desorption (or reaction) products. For
oxygen TPD this should be masses 32 (O2), 28 (CO), and 44 (CO2).
2) The temperature program should then be set (at the temperature controller) to ramp
at the desired rate (usually 8 K/s) to the desired temperature (usually 1100 K=827
°C).
3) The UTI mass spectrometer (MS) controller for the main chamber mass
spectrometer should be turned on, then turned to “FAR CUP” mode, the filament
emission current set, and finally the controller set in “MULT” mode. It should be
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noted that if the MS controller is not set to “EXT” mode and is instead set to
“NORM” the computer will not record the mass spectrum.
4) Next the mass signal of the masses of interest should be recorded by the computer.
5) Once it is assured that the mass spectrum is being recorded correctly (although the
signal for mass 32 (O2) should be nearly 0, there will always be some signal at
mass 28 (CO) and mass 44 (CO2) in the system due to unavoidable diffusion
pump back streaming), the temperature program should be started and the
temperature desorption spectra (TDS) recorded.
6) Not recommended cooling crystal holder to liquid nitrogen because holder can get
a little leak (to the 10-8 torr) during liquid nitrogen cooling.
7) For MS high sensitivity gain of photomultiplier must be 100000 and higher.
Actually you can slightly increasing voltage on multiplier for increasing gain, but
in this case photomultiplier can be damaged more quickly comparing to default
voltage. (In any question about MS see UTi 100C manual).
3.5 Gas Mixing
The Nanoreactor system has been designed with a gas manifold allowing for
accurate mixing of two gases. This procedure is crucial for gas phase catalytic kinetic
study. The procedure for mixing to gases in the gas manifold is:
1) Pump (with MP3) the entire manifold (by opening V10), up to the leak valves
LV1 and LV2, and the gas supply lines up to the regulators (the regulators should
be pressurized with pure gas). This entails assuring that V1, V2, V3, V4, V5, V7,
V8, V9, and V10 are open. As mentioned previously, the manifold cold trap,
CT3, should be filled prior to pumping the manifold or filling the manifold with
any gas.
2) With V10 still open, close V1, V4, V7, V8, and V9.
3) Assure that the DG controller reads zero (there is a zero setting on the controller,
operated by a set screw).
4) Next calculate the desired mixture as follows:
 Vol1  1
P2  P1 

 Vol 2  x A
(1)
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Equation 1 is used to calculate Vol 1/Vol 2 (3.3 for 26 mL bulb and 1.1 for 90 mL
bulb), the ratio of the manifold volume (Vol 1) to the bulb volume (Vol 2) (this is
constant for a given bulb Vol 1). P2 is the value calculated, where this is the
pressure set in the manifold with V3 closed, P1 is the initial bulb pressure (set as
desired), and xA is the volume fraction of the desired component.
Example:
For a 1:10 mixture of CO:O2, where xA=0.1, first pressurize Vol 1 to P1=50 torr
(this value is chosen). Next, evacuate Vol 2. Then, pressurize Vol 2 to P2=500
torr. Finally, open V3 to mix.
5) Close V10.
6) Throttle the valve of the concentrated component (V1, V2, V7, or V8), and
pressurize Vol 1 to P1 (usually about 500 torr) as measured by DG
7) Close V3 and evacuate the manifold (by opening V10 and then closing V10 once
the manifold pressure, as measured by TC1, has dropped below 50 mtorr).
8) Throttle the valve of the dilute component (V1, V2, V7, or V8), and pressurize the
manifold, Vol 2, to P2, as measured by DG.
9) Open V3 to create binary mixture.
10) Open either V4 to allow introduction of mixture through the doser at LV1.
This procedure can be extended to ternary mixtures.
3.6 Work with Nanoreactor
After crystal cleaning and preparation gas mixture you can work with Nanoreactor:
1. Shifted crystal to the gas nozzle. The optimal distance between surface and gas nozzle
is about 100-200 mkm. For measuring this distance you can use correlation between
distance and charge. For measuring this charge you need to use a special tester. The
second way is just using photo camera and measured the distance by photo pictures.
2. When crystal achieved optimal distance to nozzle turn on the gas flow using LV1.
Maximal gas pressure in capillary is about several torr. Pressure in chambers in this case
is about 10-5-10-6 torr range. Maximal local pressure on crystal surface is about 0.04 torr.
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For more precision calculating of local pressure needs to use old reports of E. Podgornov.
(These data calculated for H2/C2H4 mixtures only. In cases different gas mixtures you
need additionally made calculations of gas flows).
3. In bottle for gas mixture you need hold gas by high pressure (0.5-1.0 atm). It needs for
more stability gas flow. Usually, during the time gas flow became slowly down.
4. After ending experiment stopped gas flow by LV1. Shifted crystal from nozzle to the
opposite direction. Than open valve located near LV1 and wait some time for gas
evacuated.
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