MASS ANALYSIS OF NEUTRAL PARTICLES AND IONS RELEASED DURING

ELECTRICAL BREAKDOWNS ON SPACECRAFT SURFACES

NASA Grant NSG - 3301

Final Report

for the period

1 September 1979 to 21 December 1984

Submitted by: B. R. F. Kendall .

Professor of Physics

Department of Physics

104 Davey Laboratory

The Pennsylvania State University

University Park, PA 16802

Date of Submission: March 16, 1985

NASA Technical Officer: John V. Staskus

Spacecraft Environment Section

NASA Lewis Research Center

Cleveland, Ohio 44135
TABLE CONTENTS

Section

 Pa9e

1 Abstract 1

2 . Introduction to the Problem 4

3 Mass Spectrometer . . . 6

4 Other Apparatus 7

5 Samples 9

6 Results 9

7 Discussion and Conclusions 13

8 References 16

9 Publications, Papers Presented at Conferences, and Theses ... . 17
MASS ANALYSIS OF NEUTRAL PARTICLES AND IONS RELEASED DURING

ELECTRICAL BREAKDOWNS ON SPACECRAFT SURFACES

1. ABSTRACT

Charging of insulating surfaces and the resulting electrical breakdowns

are known to have been responsible for numerous malfunctions of orbiting spacecraft. Both theoretical and experimental studies of charged-particle fluxes

from breakdown events have been made in several laboratories.

The present research broadens the attack on this problem to include

neutral particles (molecules and molecular clusters) and specifically to develop

methods of measuring the mass spectra and total emitted flux of such particles.

The design and construction of the specialized mass spectrometer required

for this work was completed at the end of January 1981. Tests at Penn State

were entirely satisfactory but after transfer to the Tenney vacuum chamber at

NASA Lewis Research Center an immediate and progressive, deterioration of its

performance occurred, probably caused by oil vapor contamination in the Tenney

chamber. The mass spectrometer was subsequently restored to normal operation

by extensive cleaning and rebuilding. The reassembled instrument was then

operated satisfactorily for the remainder of the project in its original test

chamber at Penn State which was adapted to include the necessary apparatus for

electrical breakdown studies on polymer films.

Electrical breakdowns were initiated by a movable blunt contact touching

the insulating surface. A high-voltage ramp was applied to the contact through

"an energy-storing line until breakdown occurred. The resulting surface damage

sites could be made similar in size and shape to those produced by a high voltage

electron beam system operating at similar discharge energies. The contact
discharge apparatus was used for final development of two different high-speed

recording systems and for measurements of the composition of the materials

given off by the discharge. An additional advantage of this technique was that,

by progressively moving the sample relative to the contact, the observed gas

bursts could be correlated with actual discharge sites left behind on the sample.

The sample could .then be removed and observed under an optical or electron microscope.

With this apparatus it was shown that intense instantaneous fluxes of

neutral particles were released from the sites of electrical breakdown events.

For Teflon FEP and PFA films of 50 and 75 microns thickness the material released

consisted almost entirely of fluorocarbon fragments, some of them having masses

greater than 350 amu (atomic mass units). The material released from a 50 micron

Kapton or Mylar film consisted mainly of light hydrocarbons with masses at or

below 44 amu, with additional carbon monoxide and carbon dioxide. Tefzel films

released hydrogen, HF, hydrocarbons, carbon monoxide and carbon dioxide.

Additional studies were made with a Laser Micropulse Mass Analyzer, which

showed that visible discolorations at breakdown sites were correlated with

the presence of iron on the polymer side of the film, presumably caused by

punch-through to the Inconel backing. There was also a considerable amount

of sodium and potassium compounds, accompanied by hydrocarbons, on all samples,

including Teflon samples which had been handled only with tweezers since removal

from a bulk supply.

Further tests were done on Kapton samples which had been irradiated by an

oxygen ion beam at NASA Lewis Research Center. The irradiated samples were

free of surface hydrocarbon contamination but otherwise behaved in the same way

as the Kapton samples tested earlier.
Total emitted flux measurements were made with a special fast ion gauge and

-4

recording system. Most of the samples released 1 - 2 x 10 Torr liters of

gaseous products per discharge.

Many of the observed phenomena could have significant effects on spacecraft

surfaces. Jets of heavy polymer fragments from Teflon discharge sites could

form insulating layers on adjacent electrodes, could act as triggers for gas

discharges, and could change the secondary electron emission properties of distant

surfaces. The much lighter fragments from Kapton may also be capable of triggering remote discharges. The ejection of material from the conducting backing

of polymer films may result in metallic contamination of nearby insulation.

Photon-induced and electron-induced desorption of gas from surfaces adjacent to

a discharge site also occurs and adds to the intensity of the observed neutralparticle pulses.

Tefzel should probably be used with caution on spacecraft if there is a

possibility of electrical discharge through it because of the possible production

of HF.

The discovery of traces of both organic and inorganic molecules on the

surfaces of untouched samples of polymer film suggests sources of contamination

(possibly unavoidable) during production or packaging. Only the two samples

exposed to oxygen ion bombardment were relatively clean. This indicates an

additional variable that should be considered when testing spacecraft materials

in the laboratory.

2. INTRODUCTION TO THE PROBLEM

Spacecraft charging in geomagnetic substorms often leads to large changes

in potential of spacecraft surfaces relative to space plasma potential. Anadditional source of localized charging of spacecraft surfaces occurs in the
interaction of high-voltage solar arrays with the charge exchange plasma

generated by ion thrusters. In either case the resultant potential differences

may reach several kilovolts. The charging may lead to large potential gradients

across dielectrics used on the spacecraft surfaces or used to insulate one

part of the spacecraft from another. Brief but intense discharges may result.

Discharges across spacecraft dielectrics may produce spurious electromagnetic

signals. Discharges may also degrade thermal protective films, contaminate

optical surfaces, and cause direct structural damage to the dielectrics. Laboratory

tests indicate the possibility of degrading other insulators if metallic vapors

are emitted from the discharge, or of forming extremely thin insulating layers

on conductors which can then charge enough to modify critical electrostatic

field distributions near charged-particle detection equipment. In general there

will be a large and almost instantaneous release of both neutral and charged

particles from the site of a breakdown event.

Hundreds of charging-induced anomalies were identified in more than twenty

spacecraft between 1971 and 1976.

Because of the absence of existing data on the composition of the neutral

and ion fluxes from dielectric breakdown events, mass spectrometric analyses of

these fluxes are particularly important.

Mass analysis of particles from an electrical breakdown event involves a

particularly difficult set of constraints. The event occurs essentially at a

point in space and at an instant in time. The exact position and timing of the

event are not known in advance, although they can be influenced to some extent.

The event produces a swarm of neutral molecules, molecular clusters and ions of

different masses which presumably radiate from the breakdown site over a wide

range of speeds and directions. At a distance greater than a few cm from the

breakdown site the particle number density is likely to be quite low and falling

rapidly because of both speed variations and angular dispersion. The expanding
gas and ion burst will pass any given point in a time much shorter than the time

taken for any conventional mass spectrometer to scan once through its mass range.

For reasons discussed in the original proposal, it was decided that a timeof-flight mass spectrometer offered the most cost-effective approach to the study

of this problem.

3. MASS SPECTROMETER

The time-of-flight mass spectrometer and the vacuum chamber used for its

development are shown in Figure 1. The pulsed two-field ion source is

on the left. Incoming molecules are ionized by an electron beam inside the ion

source and the resulting ions are accelerated in approximately monoenergetic

bunches into the flight tube. The ions therefore reach the ion detector in

ascending order of mass, according to the formula

t = s(m/2eV)1/2

where t is the flight time through the flight tube, s is the length of the

flight tube, m is the ion mass, e is the ion charge, and V is the potential

difference through which the ions fall inside the source. With a 115cm flight

tube and 300V accelerating potential, the flight time of an ion of mass 100 amu

is approximately 47ysec.

A segmented cylindrical lens focuses the ion beam and centers it on the

input of the ion detector. The flight tube is operated at ground potential,

rather than at high potentials as in most time-of-flight mass spectrometers, in

order to minimize electrostatic interactions with the sample charging apparatus.

An electron multiplier ion detector is used for high sensitivity and fast response.
It follows from the equation for the flight time of an ion that the electrical signals leaving the ion detector represent a series of complete mass

spectra, each one having the corresponding source pulse at its t = 0 point.

Any number of successive spectra can be displayed, from a single spectrum up to

as many as 100 spectra per millisecond. A typical mass spectrum of residual

gases in the vacuum chamber is shown in Figure 2. Special techniques are needed

2

for operation at repetition intervals faster than the ion flight times and for

3 4 displaying the rapidly-changing spectra.

The layout of the vacuum system, which is based on a Leybold TMP-350 turbomolecular pump, is shown in Figure 3.

4. OTHER APPARATUS

A. Direct-Contact Charging Apparatus

This apparatus is shown in Fig. 4. Electrons are fed onto the insulating

surfaces from a smooth platinum contact. A slowly increasing negative potential

from a high-impedance, low-capacitance source is applied to the contact until

breakdown occurs. The sample is held in place on a perforated, rotatable 9 cm

disc by a circumferential retaining ring.

The discharge current waveforms, peak currents, and surface damage characteristics obtained with this apparatus were made similar to those produced by a

high-voltage electron beam charging system by choosing a suitable length (about

45 cm) of RG-62 coaxial cable as an energy storage line. A useful feature was

that, by progressively rotating the sample beneath the contact, the observed gas

burst could be correlated with actual discharge sites left behind on the sample,

which could then be removed and observed under an optical or electron microscope.

Most discharges occurred within about 2mm of the contact, with occasional discharges up to 4 mm away. Few occurred directly beneath the contact. Breakdown

voltages were similar to those obtained elsewhere with monoenergetic electron

beam charging systems.
B. Miniaturized Electron Beam Charging System

A miniaturized electron beam charging system similar in principle to that

used at NASA Lewis Research Center was built. It used a small commercial electron

gun modified in our laboratory to allow operation at up to 20 Kv instead of the

original 7 Kv.

Although the electron energies and current densities, sample materials and

pulse detection circuit were essentially identical with those used by other

experimenters, no large pulses were detected. The limited diagnostic techniques

possible in such a small system showed a reasonably uniform beam distribution

and surface potentials high enough for breakdown to occur. Test pulses of

current were correctly recorded when passed through the sample support. Numerous

very small current pulses were observed, with larger pulses occurring only

during sudden reductions of beam energy or movements of the beam.

C. High-Speed Recording and Display Apparatus

High-resolution mass spectra were generated at such a rate in this experiment

4

(up to 5 x 10 /sec) that even modern digital recorders were barely adequate for

following complex events. Photographic techniques have been used almost

exclusively to date. For semiquantitative measurements a simple intensitymodulated display was used, as described in the next section. When accurate

quantitative measurements of peak heights were desired an offset raster display

was used. Here successive conventional mass spectra were superimposed upon one

another, after which the oscilloscope trace was moved upwards and to the right

for display of-the next group.

An improved signal-to-noise ratio would be possible if the superimposed

spectra could be averaged in the mathematical sense. Digital circuits for

achieving this have been designed.
D. Apparatus for Measuring Total Volumes of Evolved Gas

A fast-response nude hot-cathode ion gauge was used to detect the pressure

transients following electrical breakdown of a sample. From knowledge of the

system volume, the total amount of gas was determined. From the time constant

of the near-exponential pressure drop following the peak, the approximate mean

molecular weight of the evolved gases could be determined independently of the

mass spectrum.

5. SAMPLES

The samples tested in the main series of direct-contact experiments were

Teflon FEP and Kapton H films of 50 and 75 micron thicknesses. They were metallized on one side with silver overlaid by an Inconel protective coating. No

adhesive backing was used. These materials are widely used in spacecraft

applications.

A subsequent series of tests was carried out -on 50 micron Mylar film with

an aluminum backing, 125 micron Teflon film with silver/Inconel backing, 50 micron

Tefzel and 50 micron Teflon PFA. The latter two samples were without backing.

A final run was made with three special 75 micron Kapton samples supplied

by Dale Ferguson of NASA Lewis Research Center. Two of these samples had been

exposed to an oxygen ion beam to simulate conditions in Shuttle orbit, and one

was an unexposed reference sample from the same bulk supply.

6. RESULTS

A. Mass Spectra of Neutral Particles

Tests with Teflon FEP samples showed that an intense burst of neutral fragments was being released from each discharge. A large number of peaks representing
10

Teflon fragments of the form C F could be seen in each mass spectrum.

The variation with time of the number density of these Teflon fragments was

obtained by using the mass peak amplitude signals to intensify a cathode-ray

oscilloscope trace, producing an array of dots. By deflecting this display

downwards, a semiquantitative indication of the various changes in number densities

was obtained. Such a display is shown in Figure 5 with the major peaks identified.

A background spectrum is included for comparison. The most intense peak corresponds

to CF- but ions up to and beyond CgF are present. Switching off the ionizing

electron beam in the mass spectrometer ion source causes these peaks to disappear,

showing that they are ionization products of even larger neutral fragments and

not ions released directly from the discharge. Far more of these heavy ions were

observed than are present in the mass spectrum of the heaviest fluorocarbons for

which published data are available (cg

F

14)/ suggesting that very large neutral

fragments, of mass much greater than 350 amu, were leaving the Teflon surface

during the discharge. Later experiments with Teflon PFA samples showed similar

results.

A 50 micron Kapton H film with metal backing was then installed in the

apparatus and a new series of breakdown measurements was begun. The Kapton

produced only light fragments, giving rise to mass spectra containing mainly

masses 44, 28, and 15, as shown in the intensity-modulated spectrum of Figure 6.

It appears that the mass 44 peak represents C02 and C H ; mass 28 is CO and

C H + , and mass 15 is CH . It should be noted that Kapton contains a sub-

^4 -j

stantial amount of oxygen.

To confirm these findings and to show the relative amounts of the various

ion fragments, the same data were displayed in an offset raster display (Fig. 7).

For comparison, a background gas spectrum is shown in Fig. 8.
11

Samples of 50u metal-backed Mylar [Polyethylene Terephthalate] film were

then tested in a similar way. Results, shown in Fig. 9, were very similar to those

obtained with Kapton samples. Most of the evolved gas molecules had masses at

or below 44 amu. Carbon monoxide, carbon dioxide, and light hydrocarbons

were seen. The basic polymer unit of Mylar has some of its carbon atoms

immediately adjacent to oxygen atoms. It is known that electron beams destroy

or modify these oxygenated functional groups.

A sample of clear 50y Tefzel (ethylene/tetrafluoroethylene polymer) was

then tested in the same way. The main gases evolved during breakdown were HF,

H , CO , and CO plus C and C hydrocarbons (Fig. 10). The material appeared

to release H_O and C hydrocarbons in small quantities during sample pumpdown,

as determined by operating a cold finger near the sample and cyclically heating it.

The Kapton samples which had been exposed to an oxygen ion beam -gave results

generally similar to those already described for unmodified Kapton, except for

greatly reduced hydrocarbon production, especially during the immediate pre-discharge period which probably represents removal of surface contaminants by surface

currents.

B. Breakdown Voltages

In general breakdown voltages were slightly higher for a given thickness

of Kapton than with Teflon, but there was otherwise little variation between

samples. A typical 50u sample of Kapton broke down at about 16-18KV, while

the same thickness of Teflon usually broke down at 8-lSKv. Thicker films broke

down at somewhat higher voltages, but even 125y Teflon often broke down before

20Kv was reached. This suggests that defects in the films may play a major part

in determining breakdown voltages.
12

C. Total Gas Evolution

—4

The Kapton» Teflon and Mylar samples typically evolved about 1 - 2 x 10

Torr liters of gas per discharge with the Teflon usually towards the low end of

this range. The mean molecular weight of the evolved gas was much higher for

the Teflon (by a factor of about two) so that the actual mass of the evolved

material was probably similar for each type of sample. Tefzel was not tested

in detail but appeared to behave similarly to Mylar.

Photon-induced desorption and electron-induced desorption of adsorbed gases

from surfaces near discharge sites are also to be expected and have been observed.

The effect is not directly linked with the presence of a polymer film, since any

spark could supply the necessary photons and electrons. The effect appears to

be about one order of magnitude smaller than the direct gas evolution from

polymer film breakdowns.

D. Surface Changes After Testing

Removal of metal from the backing film was detected with Kapton samples.

In some cases the Kapton film remained intact above the damage site. The effect

is originally observable only under magnification but after several months in

air the holes are easily visible with the naked eye because of local discoloration

of the Kapton.

Some of the Teflon samples with metal backing also showed progressive

discoloration over a period of months after removal from the test chamber. Reference samples stored under identical conditions showed no such effect. The

yellow discoloration has the appearance of corrosion of the silver coating

beneath the Teflon. There is a complex pattern of discoloration with little

correlation with the sites of discharges.
13

Mylar and Tefzel samples showed no long-term deterioration after testing.

Small areas of discoloration and cracking of the surface were visible close to

some discharge sites, especially with Tefzel, but these did not change with time.

E. Laser Micropulse Mass Analyzer (LAMMA) Experiments

Phenomena such as the remote breakdown observed in some samples (up to

4 mm from the platinum contact), and the development of visible discolorations

of samples during storage after breakdown tests, indicated the need for surfacesensitive studies.

Arrangements were made, with the kind cooperation of Leybold-Heraeus, Inc.,

for analysis of several of our samples on one of their LAMMA 1000 instruments.

No obvious surface defects could be found with the optical target finding system,

and so the remote breakdown mechanism could not be studied. The visible discolorations at former breakdown sites were found to correlate with the presence of

iron on the polymer side of the film, presumably caused by punch-through to the

Inconel backing. Considerable amounts of sodium, potassium and .hydrocarbons

were present on all samples, including Teflon samples which had been handled

only with tweezers since removal from a bulk supply. There is an implication

that the surfaces may be picking up contaminants during manufacture or packaging.

7. DISCUSSION AND CONCLUSIONS

Figure 11 shows the chemical structure of Teflon FEP and Kapton H.

The origins of many of the observed fragment ions (formed in the mass spectrometer ion source by electron bombardment of polymer fragments released by the

discharge) are obvious.'
14

It must be remembered that fragmentation, occurs also in the process of

ionization inside the mass spectrometer, so that the parent polymer fragments

are always at least as big as the resulting ions and in some cases are very much

bigger. Thus, in the case of the Teflon samples, which show a higher proportion

of heavy ions that the heaviest fluorocarbon for which data could be found in the

literature, it can be concluded that many of the released neutral fragments have

masses above 350 amu. They probably form surface films after a few collisions

with the system walls.

The Kapton samples showed mainly light ions in their mass spectra and the

approximate independent check on molecular weight provided by the total-pressure

waveform measurements confirmed that the parent neutrals were also light (at or

below 44 amu). Such gases would be quickly desorbed from any surface they

might hit except at low temperatures.

Figure 12 shows the chemical structures for Teflon PFA, Mylar and Tefzel.

Trie former gave results similar to those of Teflon FEP. The latter two showed

mainly light ions in their mass spectra during electrical breakdown, proving that

the parent neutrals were also quite light. An important neutral fragment evolved

from Tefzel appears to be HF, which is extremely reactive and could easily alter

the work function of adjacent surfaces.

Items (1) - (3) of Figure 13 summarize the results of many of these experiments. The figure also shows the following additional phenomena which have

been identified and studied:

Secondary discharges were seen on several occasions. Electrical breakdowns were triggered at distances up to 15cm from the site of a Teflon film

breakdown. In some cases the metallic electrodes between which the secondary

discharge occurred were operating at less than 65% of their normal breakdown

potential difference. Triggering.is presumably caused by the burst of neutral
15

and ionized material from the. polymer breakdown site. The effect probably occurs

also with other polymers, but this has not been confirmed This-phenomenon has

been seen with both electron beam and direct contact charging of the sample.

Direct transfer of Teflon fragments is obviously likely because of the

large fragments observed in the mass spectrum. It has been confirmed by the

formation of insulating layers near the breakdown site arid by instantaneous

decreases in the secondary electron emission coefficient of dynode surfaces in

electron multipliers up to 100 cm away. Partial recovery occurs- over.a^period

of several days. The effect does not appear to occur with the other polymers

tested

indirect transfer of Teflon has similar effects. It appears to be the

result of Teflon fragments striking an intervening surface and then being almost

instantaneously re-emitted into areas which are not on a direct line of sight

from the discharge.

Removal of metal backing and Induced desorption have been discussed

previously.

Many of the phenomena listed in Figure 13 could have significant effects on

spacecraft surfaces. Jets of heavy polymer fragments from Teflon discharge sites

could form insulating layers on adjacent electrodes, could act as triggers for

gas discharges, and could change the secondary electron emission properties of

distant surfaces. The much lighter fragments from Kapton may also be capable of

triggering remote discharges. The ejection of material from the conducting backing of polymer films may result in metallic contamination of nearby insulation.

Photon-induced and electron-induced desorption of gas from surfaces adjacent to

a discharge site also occurs and adds to the.intensity of the observed neutralparticle pulses.
16

Tefzel should probably be used with caution on spacecraft if there is a

possibility of electrical discharge through it because of the possible production

Of HF.

The discovery of traces of both organic and inorganic molecules on the surfaces of untouched samples of polymer film suggests sources of contamination

(possibly unavoidable) during production or packaging. Only the two samples

exposed to oxygen ion bombardment were relatively clean. This indicates an

additional variable that should be considered when testing spacecraft materials

in the laboratory.

8. REFERENCES

1. Wiley, W. C. and McLaren,. I. H. : "Time-of-Flight Mass Spectrometer with

Improved Resolution," Rev. Sci. Instrum. 26, pp 1150-1157 (1955).

2. Kendall, B. R. F.: "Automatic Data Processing for a Sensitive Time-ofFlight Mass Spectrometer," Jour. Sci. Instrum. 39, pp 267-272 (1962).

3. Meyer, R. T.: "Fast Recording Techniques for Time-Resolved Mass Spectrometry;" in "Time-of-Flight Mass Spectrometry" (ed. D. Price and J. E.

Williams), Pergamon Press, London, 1969, pp 61-87.

4. Lincoln, K. A.: "Data Acquisition Techniques for Exploiting the Uniqueness

of the Time-of-Flight Mass Spectrometer: Application to Sampling Pulsed

Gas Systems;" in "Dynamic Mass Spectrometry" (ed. D. Price and J. F. J. Todd),

Heyden and Son, London, 1981, pp 111-119.
17

9. PUBLICATIONS*

1. B. R. F. Kendall and F. A. Schwab, "Production of Pulsed Electric Fields

Using Capacitively Coupled Electrodes," Review of Scientific Instruments ,

51_, 1560 (1980).

2. B. R. F. Kendall, "Vacuum Applications of Metal Foams", Journal of Vacuum

Science and Technology 17, 1385 (1980).

3. B. R. F. Kendall, "Cyclic Pressure Fluctuations Above Rotary Pumps and

Their Effects on Pumping Speed Measurements", Journal of Vacuum Science

and Technology 19, 109 (1981).

4. B. R. F. Kendall, "Anaerobic Polymers as High-Vacuum Leak Sealants",

Journal of Vacuum Science and Technology 20, (2), 248 (1982).

5. B. R. F. Kendall, "Obtaining Pressures in the 10 Pa Range with Oil-Sealed

Rotary Vacuum Pumps", Journal of Vacuum Science and Technology 21, 886-890

(1982).

6. S. M. Danziger, B. R. F. Kendall, and J. Dormer "Pressure Pulsations Above

Turbomolecular Pumps", Journal of Vacuum Science and Technology 21, 893-

895 (1982).

7. B. R. F. Kendall, "The Pressure Multiplier Revisited", Journal of Vacuum

Science and Technology Al, 1875-1877 (1983).

*Only publications directly connected with this Grant are listed.

PRESENTED PAPERS

1. B. R. F. Kendall, "Mass Spectra of Neutral Particles Released During Electrical Breakdown of Thin Polymer. Films", Proceedings of the Spacecraft

Environmental Interactions Technology Conference - 1983, Edited by C. P.

Pike and C. K. Purvis.

2. B. R. F. Kendall, "Mass Spectrometric Studies of the Electrical Breakdown of

Thin Polymer Films", presented at American Vacuum Society Conference,

Clearwater, Florida, February 1984.
18

THESES COMPLETED

1. S. M. Danziger, "Electron Gun Modeling with an Electrolytic Tank",

M. S. Thesis, March 1981.

2. P. Desai, "High-Frequency Integrated - Circuit Preamplifiers", M. S.

Thesis March 1983.

3. J. Dormer, "Recording Very Fast Changes in Gas Composition'1, M. S. Thesis

March 1983.

THESES IN PROGRESS

1. V. Bojan, "A Real-Time Spectrum Averager for Use with a Time-of-Flight Mass

Spe ctromete r."

2. V. Rohrer, "Mass Spectra of Neutral Particles Released During Electrical

Breakdown of Spacecraft Insulating Materials."
\0lscharga Flange

Point-Contact

Surface Breakdown

Apparatus

Ion

Sourca

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Electrical

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LN Cold Trap

• Flight Tuba Detector

Electronics Housing

(atmospheric prassurel

IPre - Amp!

Supporting

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System

Electrical

Laads

1 2

PHYSICAL LAYOUT OF THE TOFMS

Figure I.

H2O

28

18

7x 10'8Torr

Figure 2. Mass Spectrum of Background Gaaea In Vacuum Chamber
DISCHARGE [~

FLANGE — -*

(VENT)

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Rotatabl e Sample Holder

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Ring

High

Voltag e

Power

Supply

Coaxial Storage Line

HWWlr

Sensing Coil

Atmospheri c Pressure—|—Vacuu m

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Figure 4. Direct-Contact Surface Breakdown Apparatus
Mass

Time

(sec)

Time

(seel

0.5

Mass

o

Figure 5. Variations with time of intensity - modulated mass spectrum associated with point-contact

breakdown of 50u. Teflon FEP layer. Teflon PFA gives similar results.

O

Upper Left: Background spectrum, no breakdown. 9 X 10 Torr.

Upper Right: Breakdown at 13 KV. Approx. 0.01 joule.

Lower Left: Breakdown at 16KV. Multiple strike.

Lower Right: Continuous discharge through spark-damaged area of surface at 12-13KV.

o o
40

14 15

Mass (a.m.u.)

44

Figure 6. Intensity-Modulated Raster Display for Breakdown of 50 micron Kapton Film at 18 KV.

Main Peaks 44 CCO* C,H0

+

) , 28 (CO+, cV") , 15

/ J o / 4
6.4-8.0

o

0)

IA

.§ 4.8-6.4

O)

(O

2 3.2-4.8

<

a) 1.6-3.2

0-1.6

28 44 55 57

I I II

44 i>57

55

15 28

Mass (a.m.u.)

Figure 7. Contact Discharge Through 5q«. Kapton Film at 16 KV.

16 Spectra per Trace.

Offset Multitrace Raster Display,
6.4-8.0

2

I

18 28 32

I II

2 18 28 ^32

Mass (a.m.u.)

Figure 8. Background Gas Spectrum (No Discharge) -. Offset Multitrace Raster Display, 16 Spectra per Trace.
s

o>

a»

to

;= 100

2 15 28 44

Mass (a.m.u.)

Figure 9. Intensity-modulated raster display of neutral mass spectra for

breakdown of 50 micron Mylar film at 13 Kv. Main peaks 44

(CO+,C3H+), 28(CO-|',C2Ht) , 15 (CH*) and 2 (H*) . Small peaks at

masses 12, 14, 15, 16 appeared just before actual breakdown.
a.

TIM E

(sec)

28 18

MASS (a.m.u.)

44 28A

 2

J

6

MASS (a.m.u.)

Figure 10. Intensity-modulated raster display of a.) background gas at 2X10 Torr and

b.) breakdown of 50 micron Tefzel film at 18KV with main peaks at 44(CO , C,H ),

£. J O

+ + +

26(C H ), 20(HP ). Mass 2 (H ) present during breakdown but off scale.
TEFLON FEP: COPOLYMER

KAPTON H

F

F

F

F

F F C F

F

Figure 11. Polymer Structures. Hydrogen Bonds Omitted in Kapton Structure for Clarity.
TEFLON PFA

:

 \

C CF F /x

MYLAR

TEFZEL

H H

H H

Figure 12. Polymer Structures. The OR in Teflon PFA represents a

perfluoroalkoxy group.
PHENOMENON POLYMER SYMBOLIC REPRESENTATION COMMENTS

1. Intense neutral-particle pulse

2. Emission of heavy fragments

3. Emission of light fragments

4. Secondary discharge

5. Direct material transfer

6. Indirect material transfer

7. Removal of metal backing

8. Photon-induced desorption

Electron-induced desorption

Teflon Kapton

Mylar Tefzel

Teflon

Kapton Mylar

Tefzel

Teflon

Teflon

Teflon

Kapton

CaHb ,CO,C02 ,etc.

^

Easily detectable by fast

ion gauge.

>350amu

amu

Gases emitted from

electrode surfaces.

Change in secondary

emission characteristics.

As for(5).

C 0 2 ,CO,H2 , H2 0,CH4

Fig. 13 Neutral-particle phenomena observed during electrical breakdown of polymer films (contact charging).

Insulating side of metal-backed polymer films indicated by (P).