* 

CONTAMINATION EFFECTS STUDY 

FINAL REPORT 

December 1988 

Contract No. NAS8-36955/D.O. 01 

Prepared for : 

National Aeronautics and Space Administration 

Marshall Space Flight Center, AL 

Prepared by: 

Center for Applied Optics 

University of Alabama in Huntsville 

Huntsville, AL 35899 

(WAS a-CE-18 36 1 3) 

STUDY Final Report (Alabama Univ.) 28 p 

CONT ABIN ATION EPP ECT S N 89- 247 46 

CSCL 13B 

Unclas 

G3/45 0187442 
In-Situ Optical Surface Measurement 

Apparatus 

1.0 Introduction ...................... 2 

2.0 System Components ................... 4 

2.1 Vacuum system ................... 5 

2.1.1 Chamber .................. 5 

2.1.2 Roughing pump ............... 6 

2.1.3 Cryopump .................. 6 

2.2 Electronics .................... 8 

2.1.4 Valving and Associated Hardware ...... 7 

2.2.1 Equipment Rack ............... 9 

2.2.2 Vacuum Feedthroughs ............ 10 

2.2.3 Internal Connectors ............ 12 

2.2.4 Chopper System ............... 14 

2.2.5 Photomultipliers and Their High Voltage 

Supplies ................... 15 

2.2.6 Temperature-Controlled Quartz Crystal 

Microbalance (TQCM) ............. 15 

2.3 Optical Train .................. 16 

2.3.1 RF Discharge Tub. es ............. 16 

2.3.2 Collimating Apertures ........... 17 

2.3.3 Sample Mirror Mounts ............ 18 

2.3.4 Detector Mounts .............. 18 

2.3.5 Detectors ................. 18' 

2.4 Contamination Subsystem .............. 18 

2.4.1 Contaminant Mount and Heat Source ..... 19 

2.4.2 Sample and TQCM Mount Cooling System .... 19 

2.4.3 Temperature Quartz Crystal Monitor (TQCM) . 19 

2.5 Data Acquisition ................. 20 

2.5.1 Telex AT Compatible Computer ........ 20 

2.5.2 Helios I1 Computer Front End ........ 20 

2.5.3 Software .................. 21 

3.0 GETTING STARTED .................... 22 

3.1 Starting With the Chamber at Atmospheric 

Pressure ...................... 22 

3.2 Starting from Vacuum Conditions .......... 23 

4.0 WHERE TO FIND HELP ................... 26 

4.1Cryopump. ..................... 26 

4.2 Photomultipliers ................. 26 

4.3 PMT High Voltage Supplies ............. 26 

4.4 Discharge Tubes .................. 27 

1 
In-Situ Optical Surface Measurement 

Apparatus 

1.0 Introduction 

The In-Situ Optical Surface Measurement System is a facility 

designed to study the deleterious effects of particulate 

materials on the surface reflectivities of optical materials 

in the vacuum ultraviolet (WV) . This arrangement is designed 

to simulate the on-orbit effects of contamination and 

degradation of optical surfaces. 

This simulation is accomplished through the use of noncoherent WV sources illuminating optical surfaces located in 

a high vacuum vacuum chamber. Employing several sources of 

contamination the reflectivity is measured both at the 

specular reflection as well as at two scattered positions, 

,--/’- forward and reverse. 

The facility has been out of operation for a number of years 

and most of the information concerning the experimental 

equipment and electrical wiring has been lost. With that in 

mind this task has been concerned mostly with gathering the 

information and gainingthe experience requiredto operate the 

system. In the following pages we will run through each piece 

of equipment used in the experiment, go through a series of 

steps to get the equipment up and running and also provide the 

operator some contacts to use if the going gets rough. Mixed 

in with the discussion will be some useful hints gleaned from 

the experience of this task period. 

2 
a 

The experimental arrangement is shown schematically in figure 

1. The chamber must be run at pressures below approximately 

Torr to eliminate the absorption effects of air on the 

WV wavelengths. 

""E / 

H VACUUY CHAMBER 

ACCESS PORT n 58" LOMC X 24" DU 

II 12 I II 

IL 

Figure 1. In-situ Optical Surface Measurement Apparatus 

3 
2.0 system Components 

The system consists of the following components; 

2.1. Vacuum system 

2.1.1. Chamber 

2.1.2. Roughing Pump 

2.1.3. Cryopump 

2.1.4. Valving and associated hardware 

2.2. Electronics 

2.2.1. Equipment rack 

2.2.2. Vacuum feedthroughs 

2.2.3. Internal connectors 

2.2.4. Chopper system 

2.2.5. Photomultipliers and their high voltage 

2.2.6. Temperature-Controlled Quartz Crystal 

supplies 

Microbalance (TQCM) 

2.3. Optical Train 

2.3.1. Krypton RF discharge tubes 

2.3.2. Collimating apertures 

2.3.3. Sample mounts 

2.3.4. Detector mounts 

2.3.5. Detectors 

2.4. Contamination Subsystem 

2.4.1. Contaminant mount and heat source 

2.4.2. Sample mount cooling system 

2.4.3. Temperature-Controlled Quartz Crystal 

Microbalance (TQCM) 

2.5. Data Acquisition 

2.5.1. Telex AT compatible computer 

2.5.2. Helios I1 computer front end 

2.5.3. Software 

4 
2.1 Vacuum svsteq 

The experiment is housed almost entirely inside the system 

vacuum chamber. This section will discuss the procedures 

required to evacuate the chamber and prepare the system for 

operation. Figure 2 shows the block diagram of the hardware 

used in this system. 

Figure 2. Block Diagram of Vacuum System 

2.1 Chamber 

The chamber is a cylinder approximately 24 inches in diameter 

and 48 inches long. This works out to be approximately 12.5 

cubic feet in volume. 

To pump out this volume we use two pumps. First we use a 

roughing pump to take the volume down to approximately 10 

microns pressure and secondly we use a cryopump to further 

5 
reduce the pressure to the or better range. 

There are also various ports for physical as well as 

electrical and coolant access to the evacuated volume. See 

figure 2 for a block diagram of this layout. 

2.2 Rouahina Dump 

The roughing pump is a Welch Duo-Seal mechanical pump located 

on the floor directly underneath the rear of the chamber. 

This pump is isolated from the chamber, cryopump and other 

volumes by the use of two liquid nitrogen (LN2) cold traps. 

This is done to prevent backstreaming of pump oil during 

normal pumpdown of the system and associated parts. This pump 

should never be operated without the traps full of LN2. 

2.3 CrvoDumD 

For bringing the chamber down to operational pressures we use 

a Varian Cryostack 8 cryopump. This pump is bolted onto the 

rear of the chamber and is isolated by an eight (8) inch 

pressure actuated gate valve. This pump is an unvented, 

closed volume type pump where the gas removed stays in the 

pump. This means that the chamber pressure must be as low as 

the roughing pump can take it before the cryopump can be 

introduced to the system. 

If the cryopump has been subjected to a large gas load or has 

been operating a long time the pumping action will be greatly 

reduced. Under these conditions the cryopump will need to be 

regenerated. The following subsection details how to 

regenerate the cryopump. 

2.3.1 Reaeneratina the crYoDumD 

Under normal operating circumstances the cryopump will "fillup" and will require regeneration. This is a simple procedure 

and can be found in the operating manual for the particular 

Pump What follows is a short outline for doing this 

procedure. 

1. From a warm start (warm cryopump) . 

If the cryopump has been off long enough to warm up 

to room temperature (say overnight) you can skip to 

step 3. 

2. From a cold start (cold cryopump). 

Turn off the cryopump. This starts warming up the 

pumping surfaces. Since the pump uses cold surfaces 

to produce pumping action, no regeneration can take 

6 
Place before those surfaces are warmed to room 

temperature. Therefore you must warm up the pump. 

This is done by either turning off the pump and 

waiting until tomorrow or by opening the system to 

some buffer gas to warm the pumping surfaces. 

Purge the cryopump with warm, dry nitrogen through 

the purge port on the pump head. Remember to open 

the relief valve to allow the nitrogen to escape. 

Continue the purge for approximately 1 hour or until 

it appears the surfaces are warm. Do Not apply a 

heat source to the outside of the pump. 

3. Turn on the roughing pump and be sure the LN2 traps 

are filled. This pump will remove gas that has been 

condensed out on the cryopumps pumping surfaces. 

4. Make sure the purge and relief valves are securely 

closed and open the roughing port on the side of the 

pump head to pump down the head. This pump down 

should last approximately 2 hours. 

5. When the cryopump head has pulled down to low 

pressure close the roughing valve. 

6. Turn on the cryopump and wait for the temperature 

to fall to the operating range. This should take 

approximately 30 minutes. 

The cryopump is now ready for normal operating loads. 

2.4 Valvins and Associated hardware 

All valves except the relief valve located on the top left of 

the chamber are pressure actuated. The relief valve is a hand 

turned valve next to the thermocouple pressure gauge. Air 

pressure for these valves is supplied by building wide air 

supply lines. Our particular line enters the room on the west 

side of room E114. At this point there is a valve and 

regulator for controlling air pressure. For normal operation 

we typically need somewhere between 80 and 100 psi. Also 

located where the line enters the room is a bulb for removing 

condensed water from the air supply. The air system regularly 

comes with lots of water that will interfere with the cooling 

of the discharge tube so at these times it is recommended that 

you drain the bulb two or three times per day. 

There is also a vacuum line running from the roughing pump to 

the front volume of the source mounting flange. This line is 

used to rough the discharge tube mounting volume when you 

change tubes or insert a filter or attenuator in front of the 

7 
J 

discharge tube. This prevents a large pressure spike from 

entering the cryopump and vacuum chamber. 

.2.2 Electronicq 

The electronics consists mainly of home grown, personally 

built electrical work. Since all the important pieces of 

equipment are contained in the vacuum, we must provide vacuum 

feedthroughs for all the required electrical signals. Figure 

3 shows the primary connections and wiring diagrams for this 

experiment. 

SYNC SIGNAL OUTPUT 

FIGURE 3 CONTROL BOX CIRCUIT LAYOUT 

Figure 3. Control Panel Wiring Diagram 

8 
2.2.1 EauiDment Rack 

The major controlling components of this experiment are 

contained in the rack of equipment immediately adjacent to the 

vacuum chamber. This rack contains all the external 

electronics and provides for control of the PMT's and output 

to the data acquisition system. 

Turn on/ turn off of the vacuum contained electronics is 

provided at the switch panel near the top of the equipment 

rack. This panel, depicted in figure 4 has three two pole 

switches on the right and three potentiometers on the left. 

Main power to the panel and power to the chopper is supplied 

by the rightmost switch. The middle switch is not used and 

the leftmost switch provides +28 vdc to the PMT high voltage 

supplies. The three pots control the gain of the three PMT's, 

backscatter, specular and forwardscatter, respectively. 

BACK VIEW 

Figure 4. System Control Panel 

9 
This rack also contains the three lock-in amplifiers. They 

are from top to bottom connected to the backscatter, specular 

and forwardscatter PMT's. Output from these lock-ins is 

hardwired to the Helios computer front end (located 

immediately below the lower lock-in) and BNC cables are 

available to monitor the signals at the oscilloscope or strip 

chart recorder. 

Also at the bottom of the rack is the TQCM controller and 

below that is a frequency counter to monitor the output 

frequency of the TQCM. This output is also hardwired to the 

Helios. 

2.2.2 Vacuum Feedthrouahs 

Warnina! The chower uses 110 V, 60 cvcle wall current. Turn 

off the Dower before servicina the interior of the chamber. 

The required vacuum feedthroughs are pictured in figure 5. 

I have labeled these feedthroughs arbitrarily as #1 in the 

9:00 O'clock position, #2 in the 3:OO O'clock position and #3 

in the upper left position. These three feedthroughs provide 

all the signals to and from the vacuum required to operate 

this setup. Figure 6 shows the pin breakout for feedthrough 

#2 and #3. The #1 feedthrough only passes the evaporation and 

TQCM signals. 

Feed Thru #2 

Figure 5. Vacuum Chamber/ End View 

10 
FEEDTHROUCH #3 PIN # PIN # ON CONNECTCR #1 

#S MOTOR 

SPARE 

#2 LED 

4 SPARE 

6 

#3 GROUND 

#I PHOTOOIOOE 

7 #4 MOTOR 

8 #6 MOTOR 

FEEOTHROUGH #2 PIN # PIN # ON PIN ON 

#1 CONNECTOR EOUIPMENT RACK 

1 17, 18. 19 (Iy7 ORANGE WIRE) EVAP SOURCE 

2 - - COMMON/SPARE 

3 14 5 PUT 2 HV CONTROL 

4 13 7 PYT 1 HV CONTROL 

5 12 6 t28 Mc 

6 11 8 GROUND 

FIGURE 6 PINOUTS FOR FEEDTHROUGHS #2 AND #3 

11 
c 

2.2.3 Internal Connectors 

Figure 7 shows the block diagram of the equipment located on 

the plate inside the chamber. To provide electrical connection to the outside world there are two 22 pin edge 

connectors at the forward left side of the plate. Figure 8 

shows the breakout of the two connectors. Connector #1 

provides off plate communication while #2 is only for wiring 

on plate. Located in the storage cabinet is a couple of made 

up connectors that will allow you to patch from these 

connectors to the equipment rack to allow bench top operation 

of the equipment outside the vacuum chamber. 

CHAMBER 

WAUS 

I 

1 ILLUYINATK)N I SOURCE 

Figure 7. Arrangement of Equipment Inside Vacuum Chamber 

12 
1 

c-, RIOTOO~ 

EO 

SPARE 

SPARE 

MOlOR EM OM 

MOTOR UM WO 

10 ENC I2 WlPUr/ EAu( XAlTER WANYL 

10 8HC I4 WlPUr/ fO(IWAR0 XAITER CHW 

Pur3 (FWWMO) KV. Catm 

POWER SUPRY CRWNO 

tza VM: 

Pur 1 (EACK) H.V. CWM 

PUT 2 (SPECUUII) H.V. MRX 

mcc GROVWD 

MOTOR LDD MREE 

10 ENC I3 cUlP~/ SPECULAR CHINNEL 

1 

I7 I 

I 

Pur I1 wor Pur I1 CWYOH 

Pur I2 wor Pur 12 CWYW 

FUl I3 HOl 

Pur I3 CWYW 

UL Pur WEUK 

SPARE 

SPARE 

Figure 8. Connector Pin Assignments 

13 
2.2.4 Chomer Svstem 

The chopper is internal to the vacuum chamber and is operated 

by the on/off switch on the equipment rack. The purpose of 

the chopper is to chop the W source illumination in order to 

allow synchronous detection using the lock-in amplifiers. 

Do Not operate the chopwr without cooling water. The water 

supply is turned on with the valve located on the left side 

middle next to the W source. 

The chopper reference signal is generated using the circuit 

shown in figure 9. The LED and photodiode are physically 

located around the chopper wheel using the same holes that the 

W illumination passes through. Note that the LED operates 

in the infrared and the photodiode cuts off longward of the 

visible SO that there is no stray light problems from the UV 

sources. This arrangement produces a reference square wave 

of 1 khz 2.8 volt peak-to-peak biased down by -15 volts (runs 

from -12.2 v to -15 v) . 

Figure 9. Chopper Reference Circuit 

14 
2.2.5 Photomultipliers and Their Hiah Voltaae Supplies 

The photomultipliers are solar blind UV tubes supplied by EMR 

Photoelectric (see section 4.2). These tubes are 18 stage, 

end-on, magnesium fluoride window tubes with a 9.5 mm 

diameter, semi-transparent cesium telluride photocathode. 

The spectral sensitivity extends from 115 nm (mag-fluoride 

cutoff) to approximately 350 nm (photocathode threshold). 

The typical quantum efficiency is 6% at the Lyman alaha line 

and a typical room temperature dark current of 2x10' ampere 

at a gain of lo6. The original calibration curves are in the 

storage cabinet if you need them. 

The high voltage supplies for these PMTs are vacuum compatible 

and are located on the plate in the chamber (see figure 7). 

As of the end of 1988 there was only one supply working so 

that you can only run one PMT at a time. You can switch 

between PMTs by turning off the high voltage and switching to 

another PMT with the two high voltage switches located on the 

table immediately to the lower left of the chamber. CAUTION!, 

the output of the high voltage supplies can reach 4 kilovolts 

so be careful. 

The HV power supply is a +28 vdc input and up to 4 KV output 

depending on the 0-5 vdc input control voltage. This control 

voltage is supplied through the potentiometers located on the 

equipment rack. The numbering system is discussed in section 

2.2.1. 

2.2.6 Temperature-Controlled Ouartz Crystal Microbalance (TOCM) 

The controller for the TQCM is located in the equipment rack 

and is wired through feedthrough #1 straight to the TQCM head 

(note that the wires do not connect through connector #1 on 

the plate). In our application the TQCM is mounted above the 

sample in direct view of the evaporation source (approx. four 

inches away). A large brass heat sink is provided to 

stabilize temperatures. Also provided is tubing soldered to 

the heat sink containing coolant to maintain constant temps. 

Also provided in the rack is a frequency counter to monitor 

the frequency output of the TQCM. The controller output is 

hardwired to the Helios for data recording. 

For more discussion on TQCMs and our application see section 

2.4.3. 

15 
2.3 Optical Train 

Since the light sources for this experiment operate in the 

WV, we must provide an evacuated path for the light. But to 

allow for a change in either source or optical filter there 

is a source mounting flange attached to the back left portion 

of the chamber where the source is attached. Figure 7 shows 

the essential features of the optical system. 

2.3.1 RF Discharae Tubes 

The source is an RF discharge tube supplied by Opthos 

Instruments. This is a sealed tube with a low pressure inert 

gas (We are currently using Krypton). The following table 

gives a listing of the wavelengths and tubes available from 

Opthos. 

Table I. Resonance Tubes Available From Opthos 

Lamp Type Lines Window 

Hydrogen 1216 A MgF2 

Argon 

Krypton 

Xenon 

1048 LiF 

1066 

1165 

1236 

1296 MgF2 

1470 

Mercury 1849 Suprasil 

2537 

Iodine several Suprasil 

The major output of the Krypton tube is at 1236 angstroms with 

some at 1165 angstroms and has a beam divergence of around 45 

degrees full ang175. According to the literature the tube 

should provide 10 quanta/second or around 1.5 milliwatts 

total power. In all measurements so far we have not been 

starved for signal in the specular channel. 

When using this tube the following procedure should get the 

arc going. 

16 
1. 

2. 

3. 

4. 

5. 

6. 

7. 

You 

Turn on the cooling air supply line located above and 

behind the tube. Failure to supply cooling will break 

the tube. 

While watching the gauges on the KIVA power supply slowly 

increase the power until the forward power (upper gauge) 

read slightly more than 10 watts. The backward power can 

read upwards to 20 watts. 

Since this is an RF excited system we want to optimize 

the coupled energy to the RF cavity surrounding the neck 

of the discharge tube. To do this you slowly adjust the 

brass tuning screw on the cavity, located on the 

discharge tube, to minimize the backward power on the 

lower meter. 

You now need to provide the cavity (this includes the 

gas in the tube) with a spark to start the discharge. 

This is done by llticklingll the tube with the tesla coil 

normally located on the shelf on the wall behind the 

vacuum chamber. You will only need to spark it a little 

to get it going, so if it doesn't strike right off don't 

rush it. If the discharge starts proceed to step 7. 

If the discharge didn't strike in part 4 you may need to 

increase the forward power. You should never increase 

it above 20 watts. 

If it still doesn't strike you can try tickling the tube 

while adjusting the cavity tuning. There is no chance 

for shock so don't be afraid of touching the brass RF 

cavity and its tuning screw. 

After the arc is going I usually back the power down to 

10 watts forward power and adjust the tuning screw for 

zero on the backward power. 

are now ready to illuminate your sample. 

2.3.2 Collimatina ADertures 

There are two hard apertures in the system providing for 

simple collimation of the WV light (see figure xx for 

location of these holes). These are co-aligned with the holes 

in the chopper wheel and provide a 5/16 inch diameter spot of 

light on the mirror. The holes are made from 1/8 inch 

aluminum plate drilled with ordinary drill bits. No effort 

was made to bevel the edges to provide scattering control at 

the holes. 

17 
2.3.3 Sample Mirror Mounts 

The sample mirrors are mounted externally in a sample holder 

which is then screwed into the mirror stage in the vacuum 

chamber. This stage is fixed in angle and height and is 

thermally isolated from the base by ceramic standoffs. Proper 

indexing of the sample in orientation is accomplished by 

screwing the holder tightly up onto the copper sample mount. 

There is provision for a small adjustment in translation and 

angle by loosening the three bolts at the base of the sample 

mount and adjusting it by hand. There is no fine tuning 

adjustments since all fine tuning can be accomplished by the 

PMT detector mounts. 

In addition temperature stability for the sample is provided 

by a coil of tubing that is soldered in hard contact with the 

sample mount. This tube is open to the outside to allow 

coolant flow from a refrigerated circulator or chilled water. 

This coolant is also routed to the TQCM heat sink to help 

regulate its temperature. 

2.3.4 Detector Mounts 

The three photomultiplier detectors are located as shown in 

figure 7. The three are labeled 1, 2 and 3 for back scatter, 

specular and forward scatter channels, respectively. 

Each PMT mount is a 5 degree of freedom mount consisting of 

a set of three Newport Research Corp translation stages to 

provide x, y and z control and two rotation stages for azimuth 

and elevation control. There is also a grounded four inch 

long aluminum baffle cylinder with a 1/2 inch acceptance hole 

attached to the front part of each photomultiplier. This 

baffle cuts down on directly scattered light. 

2.3.5 Detectors 

There are three detectors for measuring reflectivity off 

sample surfaces. These detectors are arranged coplaner with 

the incoming W light but are arrayed to measure the back 

scattered light, specular reflected light and the forward 

scattered light (see figure 7). 

See Section 2.2.5 for a discussion of the photomultipliers 

used as detectors in this experiment. 

2.4 Contamination Subsvstem 

The contamination subsystem provides the experimenter with a 

controllable way to deposit material onto a sample mirror. 

18 
, 

The subsystem consists of a heat source in contact with the 

material to be evaporated and a device (TQCM) to measure the 

material deposited onto the sample. The subsystem is 

instrumented with thermocouples to monitor the temperatures 

at various places in the experiment. 

2.4.1 Contaminant Mount and Heat Source 

The contaminant is loaded into the chamber by clamping the 

material onto a vertically mounted aluminum plate soldered to 

a resistance heater (a simple enclosed heater wire). The 

heater is controlled by a variac source externally located on 

top of the KIVA power supply (left side of table under the 

chamber). The mount has one thermocouple attached to provide 

evaporation source temperature readings. This thermocouple 

is wired into the Helios for data recording. 

2.4.2 SamDle and TOCM Mount Coolina System 

The sample and TQCM are maintained at a constant by the use 

of an external coolant source. The coolant is delivered 

through a liquid feedthrough located on the right side middle 

of the vacuum chamber. The copper delivery tube is soldered 

to the sample mount and to the TQCM heat sink and is thermally 

isolated from the remainder of the chamber by ceramic 

standoffs and by the vacuum in the chamber. Coolant can be 

either gas or liquid. Currently a refrigerated recirculator 

is attached to provide both coolant flow and temperature 

control. 

A thermocouple is attached to the sample mount and is wired 

to the Helios for data recording. 

2.4.3 TemDerature Ouartz Crystal Monitor (TQCM) 

The use of quartz crystal microbalance (QCM) is a well 

established method for weighing thin films of materials that 

deposit on a surface in the solid state. Solid films couple 

strongly into the oscillating QCM and its frequency change is 

proportional to the mass loading. Controlling the temperature 

allows the device to operate below the ambient environment and 

increase the loading efficiency from the vapor phase. 

The mass sensor is a precision matched set of 10 or 15 Mhz 

quartz crystals, one being the sensor and the other the 

reference. The output frequency of the TQCM is the beat 

frequency between the two crystals. By using the beat 

frequency, changes in frequency caused by ambient temperature 

variations is eliminated. Because only the sensor crystal 

sees the contamination flux, the TQCM output frequency will 

increase with mass loading, m, and for a 15 Mhz crystal 

19 
, 

m = 1.56 x g/cm2 hz 

For a detailed discussion of TQCMs see the engineering report 

provided by Faraday Laboratories in the storage cabinet. 

In our application the TQCM is located directly above the 

sample mount (see figure 7) staring at the evaporation plate 

(approx. 4 inches away). With proper cooling the evaporated 

material condenses out on the TQCM and since the device is 

close to the sample mirror (approx. 2.5 inches) we get a good 

reading of the mass deposited onto the sample. 

2.5 Data Acauisition 

The data acquisition system, shown in figure 11, consists of 

an IBM AT compatible computer for control and storage, 

connected to a Helios I1 computer front'end for the actual 

acquiring and communication functions. Also included is a 

commercial software package (Labatech Notebook) to provide 

communication control between the computer, the front end and 

the individual pieces of hardware. 

2.5.1 Telex AT Compatible Computer 

The Telex computer is an IBM AT clone with a forty megabyte 

hard disk, 640 kilobyte ram, single 5 1/4 inch floppy disk 

drive, 384 kilobyte extended ram and a color monitor with EGA 

driver card. 

The system uses the first serial port and an RS232 null modem 

cable to communicate with the Helios front end. Using the 

software package in conjunction with the computer front end, 

tens of data channels can be acquired at close to one hertz 

dat rate. 

2.5.2 Helios I1 Computer Front End 

The Helios I1 computer front end is manufactured by Fluke 

Instruments as a go between the computer and data generating 

devices such as thermocouples, dc voltage sources, etc. The 

Helios contains A/D and D/A boards, frequency counters and a 

thermocouple controller board, among other input boards, to 

convert the raw analog data to a form to be transferred to the 

computer's display and storage. 

Currently we have the following data channels wired into the 

Helios; 

- Three PMT outputs 

- TQCM frequency 

20 
TELEX COMPUTER 

___* 

I1 RS232 LINE 

If 

tI 

TOCM CONTROLLER 

/ 

- 

*--- 

TEMPS AND 

PRESSURE 

LOCK-IN AUPUFIERS 

Figure 10 Data Acquisition System 

- Evap source thermocouple 

- Sample thermocouple 

- Chamber pressure 

2.5.3 Software 

The data acquisition system uses two major pieces of software 

in its task. One is the Labtech Notebook and the second is 

Lotus 123. The first is for acquisition and storage and the 

second is for replay. Labtech Notebook produces files that 

are in a format that is importable to Lotus. 

21 
t 

3.0 GETTING STARTED 

This section will take you through the procedures required to 

bring up all the various subsystems. After running through 

all the following steps, you should be able to take data on 

a surface of choice using a contamination source and be able 

to store and retrieve the resulting data. 

3.1 Startina with the chamber at atmospheric pressure. 

This section assumes you are starting with either the chamber 

open to atmosphere or that the chamber has been under vacuum 

and you have replaced the sample or contamination source. 

To start up follow the following steps; 

I. Rough Pump the Chamber 

1. Fill the liquid nitrogen (LN2) traps. 

2. With the gate valve between the chamber and the roughing 

pump closed rough out the LN2 trap by opening the hand 

operated roughing valve located under the chamber at the 

red rubber hose. 

3. Once the traps are pumped out close the roughing valve. 

4. Open the large gate valve under the chamber. This opens 

the chamber to the LN2 trap. 

5. Slowly open the roughing valve. This will open the 

system to the roughing pump and you will hear the pump 

start to gurgle and produce oil smoke. This should last 

only a few minutes as the large chamber is pumped out. 

6. Pump out the chamber until you reach about 10 millitorr 

pressure or better on the gauge located atop the 

electronics rack. This can sometimes take several hours 

and shouldn't be rushed. 

7. Once the pressure has reached the correct level you can 

close the gate valve shutting off the roughing pump. 

This valve sometimes doesn't close so make sure it does 

before moving to the next step. 

11. Cryopump the Chamber 

1. Open the gate valve to the cryopump. Be sure that the 

roughing valve is closed. 

2. The wait for the system to pump down to the operating 

pressure of torr can sometimes take several days 

depending on how long the chamber has been open and what 

has been in it. 

You are now ready to fire up the rest of the system. To turn 

on the system at this point follow the directions for 

"Starting from Vacuum Conditionst1 given below. 

22 
3.2 Startina from Vacuum Conditions 

On a day to day situation you won't have the chamber open to 

the air, so you only need to concern yourself with the 

following steps. 

I. Turn on the computer. It takes a while to initialize. 

11. Turn on the water to the chopper. Without cooling the 

chopper will have heating problems in vacuum. 

111. Turn on the KIVA RF power supply. It typically takes 5 

minutes for this supply to warm up and there is an 

interlock to keep the high voltage off until these five 

minutes have passed. 

IV. Turn on the equipment in the equipment rack. 

1. Turn on the three lock-ins. - 

2. Switch on the Helios computer front end. 

3. Turn on the TQCM and the frequency counter. 

4. If you're using them turn on the oscilloscope and the 

HP pen plotter. 

V. Turn on water chiller and set to desired temperature. 

VI. Use the following procedure to turn on the illumination 

source. 

1. Turn on the cooling air supply line located above and 

behind the tube. Failure to supply cooling will break 

the tube. 

2. While watching the gauges on the KIVA power supply 

slowly increase the power until the forward power 

(upper gauge) read slightly more than 10 watts. The 

backward power can read upwards to 20 watts. 

3. Since this is an RF excited system we want to optimize 

the coupled energy to the RF cavity surrounding the 

neck of the discharge tube. To do this you slowly 

adjust the brass tuning screw on the cavity, located 

on the discharge tube, to minimize the backward power 

on the lower meter. 

4. You now need to provide the cavity (this includes the 

gas in the tube) with a spark to start the discharge. 

This is done by ltticklingtthe tube with the tesla coil 

normally located on the shelf on the wall behind the 

vacuum chamber. You will only need to spark it a 

little to get it going, so if it doesn't strike right 

23 
off don't rush it. 

step 7. 

If the discharge starts proceed to 

5. If the discharge didn't strike in part 4 you may need 

to increase the forward power. You should never 

increase it above 20 watts. 

6. If it still doesn't strike you can try tickling the 

tube while adjusting the cavity tuning. There is no 

chance for shock so don't be afraid of touching the 

brass RF cavity and its tuning screw. 

7. After the arc is going I usually back the power down 

to 10 watts forward power and adjust the tuning screw 

for zero on the backward power. 

VII. Turn on the main switch (located on the right of the 

control panel at the top of the equipment rack). You 

should ensure that the chopper is running by listening or 

by observing the sync signal on the scope or by waiting 

for the lock-ins to sync. This step could be done any 

time after water is turned on to the chopper motor. 

VIII. Load the computer software. 

1. Go to the directory on the computer where Labtech 

2. Insert the Labtech Notebook Key disk into drive A. 

3. If you are in DOS type IINBII enter. 

Notebook is located. Probably C:\NB 

This will load the 

interactive environment of Labtech Notebook. 

If you are in a DOS shell (Pathminder, lDIR, etc.) use 

its particular method to run the file NB.EXE. 

4. The menus are currently set up to acquire data for two 

and on half hours and take five channels of data. 

-Specular signal 

-TQCM frequency 

-Chamber pressure 

-Evaporation source temperature 

-Sample temperature 

To change any data channels refer to the documentation 

on Labtech Notebook. 

5. Before you run the program be sure to go to the 'IFILES" 

menu and change the file you will be writing to. If 

you don't change this, you will write over the previous 

data run. 

6. Run the program. It will wait for you to hit a key 

before actually taking data. 

IX. Turn on the photomultipliers. Use the left switch on the 

control panel. You should see a signal on whichever 

lock-in corresponds to the PMT that is powered. 

To select a different PMT use the following procedure. 

24 
1. Turn off the photomultipliers. This turns off the high 

voltage power supply. 

2. Switch to another PMT on the high Voltage switches 

located on the table at the lower left of the chamber. 

Remember that there is normally high voltage through 

these switches so be sure the power is off. Only one 

PMT will work with the power supply so be sure that 

only one is selected at the high voltage switches. 

3. Turn on the photomultipliers at the control panel. 

This returns high voltage so be careful. 

4. Remember that the software thinks you are recording the 

specu' r channel so you will need to change that in 

Labtec Notebook 

X. If you have a signal you can now either start the data 

acquisition by queuing the computer'or by recording the 

output on the pen recorder. 

XI. Good luck! 

To turn off the system perform the steps in reverse order 

following these rules: 

- Turn off the PMTs to remove high voltage 

- Turn off the high voltage to the discharge tube 

early to allow the tube to cool down before you turn 

off the cooling air supply 

Don't forget the water supply to the chopper and the 

air supply to the discharge tube 

Be sure to park the hard drive using HDPARK before 

turning off the computer 

- 

- 

25 
, 

4.0 WHERE TO FIND HELP. 

This section will be devoted entirely to contacts to call when 

you've tried everything and have had no luck. Not all system 

components will have information in this section so feel free 

to contact me through UAH for any questions. 

4.1 CrvoPUmD 

The cryopump is manufactured by 

Varian Associates 

Industrial Components Division 

3100 Jay Street 

Santa Clara, California 95054 

Toll Free # 1-800-227-9722 

It is a Cryostack 8 Cryopump, Serial # K3F4060. For 

information concerning the regeneration or other maintenance 

on this pump, see the manual kept in the file cabinet next to 

the phone in room E114 or look in the cryopump section in part 

I1 of this manual. 

4.2 Photomultipliers 

The photomultipliers are solar blind tubes furnished by 

EMR Photoelectric 

Box 44 

Princeton, New Jersey 08542 

phone 609-799-1000 

I have had great luck with questions directed to EMR. Their 

marketing person is Mr. Dan Lister and their technical person 

is Mr. Steve Meddaugh. 

Our tubes are type 541F-09-xx-xx with the following serial 

numbers ; 

1. #23248 purchased Aug 1978 

2. #28229 purchased Apr 1980 

3. #28230 purchased Sept 1980 

The high voltage supplies were provided with the original 

tubes but they currently sell for around $4800 whereas the 

PMT's sell for around $4200 each. 

4.3 PMT Hiah Voltaqe Supplies 

The vacuum compatible high voltage supplies for the 

photomultipliers are manufactured by EMR Photoelectric but 

26 
there is a cheaper source for identical supplies. This 

information was supplied by Mr. Dan Lister of EMR. Vacuum 

compatible supplies costing approximately $1200 can be had 

from the following; 

Research Support Instruments, Inc. 

10610 Beaver Dam Road 

Cockeysville, Maryland 21030-2288 

phone 301-785-6250 

The contact for technical and marketing information is also 

the company president. His name is Bob Crabbs and is a good 

source of information. 

4.4 Discharae Tubes 

The WV source is an RF excited Krypton filled low pressure 

discharge tube supplied by the following; 

Opthos Instruments, Inc. 

17805 Caddy Drive 

Rockville, Maryland 20855 

phone 301-926-0589 

This is a company run by an individual, Dr. Joe Reader who 

works at another job full time and runs this company as a 

side-line. To get help you must call and leave a message with 

the secretary (who knows no technical information) who will 

then pass the message to Dr. Reader and will call back with 

the now second hand answers. All this appears to work because 

they have managed to answer my questions satisfactorily. This 

company also supplies the KIVA power supply that feeds the RF 

to the discharge tube. 

27