CA2186101A1

CA2186101A1 - Polymer surface treatment with pulsed particle beams

Info

Publication number: CA2186101A1
Application number: CA002186101A
Authority: CA
Inventors: Regan W. Stinnett; J. Pace Vandevender
Original assignee: Individual
Current assignee: National Technology and Engineering Solutions of Sandia LLC
Priority date: 1995-01-23
Filing date: 1996-01-23
Publication date: 1996-08-01
Also published as: IL116877A0; JPH09511016A; AU5352996A; IL116877A; EP0751972A1; RU2154654C2; EP0751972A4; WO1996023021A1

Abstract

A polymer surface and near surface treatment process produced by irradiation with high energy particle beams. The process is preferably implemented with pulsed ion beams. The process alters the chemical and mechanical properties of the polymer surface in a manner useful for a wide range of commercial applications.

Description

WO 96123021 21~6101 PCT/US96/00872 Polvmer Surface Treatment with Pulsed Particle Beams Back~round of the Invention This invention was made with Government support under ~ontract DE-AC04-94AL85000 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.
This invention relates to a process for treating the surface and near surface regions of a polymer with high intensity pulsed ion beams with sufficient beam fuence to achieve the various effects of cross-linking, pyrolizing, etching or ablating o the polymer in the treated areas. More particularly, the ion beam pulses are characterized by pulse widths of less than 10 microseconds per spatially contiguous pulse, beam intensities of 0.01 to 10 J/cm2, and ion energies of typically greater than 25 keV. This application is a continuation-in-part of co-pending patent application Serial No. 08/153,248 filed November 16, 1993, assigned to assignee of the present invention.
The use of beams of high energy particles or photons for modifying polymers has been known and practiced for years using sources of particles such as the radiation decay products of radioactive elements (e.g. 60Co) and electron beams produced from continuous and pulsed beam sources. Typical ion beam polymer 20 treatment uses sources of high energy ions from e~pensive, research-type accelerators such as linear accelerators (linacs) or Van de Graff accelerators that are e~pensive, produce very low dose rates and, although useful as diagnostic tools for research, are not suitable for commercial treatment. Electron beams (typically > 1 MeV electrons) are used to deliver dose rates to polymers up to several hundred 25 Mrad/hr. Photons (10-30 eV) have also been used to treat polymer surfaces by inducing chemical reactions. Continuous, high energy photon (y) sources (e.g. 60Co with 1-3.~ MeV photons) are most commonly used for commercial irradiation of polymers. These techniques have demonstrated the ability of high energy particles at dose levels ororder 10-100 Mrad to produce beneficial changes to polymers WO 96/23021 ~ 1 8 61~ i PCT/U$96/00872 including improved toughness, resistance to solvents, and increased adhesion, aswell as changes in optical density and electrical conductivity.
Although present techniques have been shown to be valuable in many polymer treatment applications, these treat~nPmefhods have several 5 shortcomings. ~
The treatment typically e~tends deep into the material (e.g., the range of 1 MeV electrons is approsimately 0.5 cm, the range of MeV photons is ~> 1 cm). This relatively deep treatment requires large total treatment doses to produce a significant effect. This occurs because of the difficulty in obtaining high fluences of lo low energy particles using e~isting treatment methods and the problem of surface heating that results from high continuous irradiation levels.
Any of the techniques described above for irradiation of polymers will produce reaction products, such as free radicals, ionized molecules, and broken bonds, along the regions caused by energy deposition from particles moving through 15 the polymer. Interaction between such reaction products would both increase the rate of the e~pected chemical reactions within the polymer (such as cross-linking) and enable unusual reactions normally precluded by the relative stability of thecarbon-carbon bond. ~owever, the low dose rates available using present technology precludes such interactions, as the density of reaction products is far too 20 low. Even if the total dose is large enough to produce closely spaced tracks (taking minutes to hours), the time between the creation of adjacent tracks is longer than the typical recombination lifetimes of many of the reaction products (< 1 microsecond for ions and e~cited states, ~ 1 ~lS and longer for free radicals). This means that the advantages of increased interactions between reaction products 25 resulting from high densities of reaction products cannot be realized using present techniques.
Present techniques also cannot produce dose rates sufficient to produce effective pyrolyzation (remo~al of hydrogen and o~ygen) or etching (removal of material by rapidly heating the surface material beyond the point at which it begins 30 to vaporize) of polymer surfaces without significantly affecting the underlying wo 96/23021 2 ~ B ô 1 fl ~ PCT/USg6/00872 material. In addition, high pulsed doses of particles delivered to polymer surface regions can also modify the topology of the near surface region (e.g. by producing a rougher surface te~ture) in a way that present technology cannot support.

5 Summarv of the Invention The limitations of the prior art techniques are surmounted by the present invention. The advantages of applying high intensity pulses of particles to the surface and near surface regions of a polymer simultaneously produce a high density of ion track e~cited regions within the trea~ed region of the polymer while limiting o the total energy deposition required for such e~citation. In addition, the invention makes possible effective dispersal of heat produced by the irradiation and a relatively energy-efficient means of irradiation.
The above abilities and their concomitant advantages are realized by a process which utilizes a pulsed high intensity particle beam to treat the surface and 5 near surface regions of the polymer. Pulsed ion beams are particularly useful for reasons that will be made clear below. Each spatially contiguous pulse of the ion beam delivers a fluence of typically 0.01 to 10 J/cm2 of a selectable ion species into the polymer surface in less than 10 microseconds. This level of ion fluence produces an ion track density within the polymer sumcient that a substantial percentage of 20 the polymer molecules e~cited (i.e., broken bonds, free radicals, e~cited bonding states, etc.) by interaction with the energetic ions can interact directly with other e~cited polymer molecules, thereby creating an environment for cross-linking andother chemical reactions unlike any conventional environment.
The relatively thin surface region of the polymer treated by this process is 25 instantaneously raised to a much higher temperature, then flash-cooled by rapid conduction of heat into the underlying regions of the polymer without the adverse effects normally produced by the longer duration heating periods necessarily produced by prior art techniques. Accordingly, the pulsed ion beam process is also useful ~or etching or ablating away unprotected portions of the polymer surface,30 pyrolizing of the polymer surface, changing the geometry and topology of the WO 96/23021 218 6 i ~ ~ PCT/US96/00872 :

polymer surface, and inducing thermally-activated chemical changes within the polymer.

Brief Description of the Drawin~s ~?
Figure 1 is a cut away cross sectional view of a surfa~of a polymer undergoing irradiation by the pulsed ion beam; ~
Figure 2 is a graph plotting norm~li7e-1 density of states as a function of binding energy for Kapton, obtained by using ~-ray photoemission spectroscopy, both with and without an o~ygen-containing chemical coating, demonstrating the change in o~ygen concentration in the Kapton;
Figure 3 is graph plotting absorbance (measured using Fourier Transform Infrared Spectroscopy) as a function of wavenumber for treated and untreated polycarbonate, again demonstrating the change in chemical composition of the polymer before and after treatment;
Figure 4 is a microphotograph showing the change in the surface structure of a polypropylene surface after irradiation;
Figure 5 is a bar chart showing the improved adhesion characteristics of a polycarbonate surface with varying degrees of ion beam irradiation; low ~ 0.1 J/cm2, med. ~ 0.5 J/cm2, high ~1-2 J/cm2;
Figure 6A is a scanning electron microscope photograph showing an untreated polyethylene surface;
Figure 6B is a scanning electron microscope photograph showing a similar polyethvlene surface (from the same batch as Fig. 6A) after treatment with a 0.5-1.0 J/cm2 ion beam;
Figure 7 is a schematic of the RHEPP pulsed power system;
Figure 7A is a circuit diagram of a pulse compression system utilized in the pulsed po~ er system of Figure 7;
Figure 7B is a cross sectional view of a pulse forming line element;
Figure 7C is a cross sectional view of the Linear Inductive Voltage Adder (LIVA);

WO 96123021 ~; 8 fi~ oll PCT/US96/00872 Figure 8 is a partial cross sectional view of the magnetically-confined anode plasma (MAP) source 25;
Figure 8A is a modified version of Figure 8 showing the magnetic field lines produced by the fast and slow coils in the MAP source;
Figure 8B is an e~panded view of a portion of Fig. 8 showing the gas inlet valve and the gas inlet channel;
- Figure 8C is a schematic diagram of the electric circuit for the fast coil; and Figure 9 is a schematic full cross-sectional view of the MAP ion diode.

lo Detailed Description of the Invention The invention herein is most readily implemented in either of two techniques, called Ion Beam Surface Treatment (IBEST) and Electron Beam Surface Treatment (EBEST), as illustrated in Figure 1. IBEST and EBEST avoid the problems listed above by providing a method for producing commercially viable fluences (0.01- 10J/cm2) of selectable particle species with energies of typically > 25 keV in pulse lengths that can range from a few nanoseconds to several microseconds. The valueof this new capability is based on several factors.
IBEST uses pulsed power and intense ion beam technology to treat polymer surfaces with very intense, but relatively short, pulses of ions. The ability toproduce such pulses of ions in single or few pulse bursts at relatively low (~ 1 ~z) repetition rates has e~isted for several years but the potential benefits of such pulses have not previously been recognized. This lack of recognition is probably because these techniques could not be developed into commercially viable processes, partially because of a very limited lifetime (< 1000 pulses) for key components and partially because of severely limited average power.
A new capability that enables and adds to the value of this process is the combination of repetitively pulsed power technology as demonstrated by R~EPP I
and R~EPP II, developed at Sandia National Laboratories, with repetitive intenseion beam technology as demonstrated by the ~lagnetically-confined Anode Plasma ion beam system. We can use a variety of methods to produce and deliver intense 2 1 8u ~ f ~ t f~ ~ PCT/US96/00872 pulses of ions to a polymer surface. REEPP/I~P technology is a representative e~ample of this new capability. These technologies combine to provide a new, commercially viable method to deliver up to several hundred kW or more of average ion power at tens of keV to MeV ion kinetic energies in intense shor~ duration (~30nsec - ~ 10 ~lsec) pulses. Such ion beam pulses are capable of producing theeffects described above. These parameters allow low cost (on the order of 1 cent/sq.
ft) treatment of high volumes of polymer with long lifetime (>> 1000 pulses) systems.
This capability is the first of its kind.
The depth of treatment can be chosen by selecting different ion species and 0 kinetic energies. In many cases it is desirable to treat only the near surface region of a polymer with the object of providing a tougher, scratch and solvent resistant surface with improved adhesive properties. For such surface treatment applications it may only be necessary to treat a near-surface region having a depth of perhaps a few microns. By contrast, a high energy pulsed electron beam system will affect on the order of a few mm before the electrons stop in the polymer. Accordingly, theability to use high energy pulses of ions and to adjust the ion energy and species to treat only this depth allows us to greatly reduce (typically by factors of up to 1000) the energy needed per unit area while still achieving the desired modification of near surface properties.
There are other advantages to the use of high energy ion beam pulses. The ability to deliver a short, high-intensity pulse (0.01 - 10 J/cm2 ) of ions in a few ns to several microseconds produces a relatively uniform high-density treatment of thenear-surface region in which the reaction products (e.g. polymer ions, e~cited states, free radicals) resulting from interaction with the energetic ions can dir~ctly 25 interact with other such reaction products as w ell as with une~cited polymermolecules. This mode of chemical reaction contrasts to the low ion density case where ion-induced reaction products interact only with neighboring une~cited polymer molecules. No e~isting technology is capable of achieving conditions w ithin several orders of magnitude of that required to produce the desired high-density30 treatment. This new capability has been sho- n to produce changes in the chemistry WO 96/2302l 218 61 01 t ~ ~ ~PCT/US96/00872 and bond structure of polymers (Figures 2 and 3) and has been shown to improve adhesion of coatings to different polymer surfaces (Figures 4 and 5). This new technology will also enable new surface topologies, compositions, chemistries and bond structures to be produced due in part to the novel high-densit~ treatment 5 capability.
From TRI~I-90, a well-known computer simulation package, the local dose from a 400 keV ~ ion moving through polycarbonate (density of 1.2 g/cm2) is approsimately 1.3 s 10 l J/g ~1.3 ~10-5 rad) per incident ~+ ion. A pulse of 0.2~ J of ~ at 400 keV contains 4 s 10l2 ~ ions. This results in a local dose of appro~imate}y 50 I~rad delivered in 100 ns for a dose rate of 5 ~ 108 Mrad/second. During thistime the temperature of the polymer rises appro~imately 500 K. The radius, rp ofeffects induced around the ion track (due to ionization, escitation, and the effects resulting from secondary electron formation and their resulting ionization and escitation, and the effects resulting from surrounding region) is approsimately 15nm 15 (from Radiation Effects on Polymers, ed. R Clough and S. Shalably, Ch. 2, p48) for 400 keV ~. The density needed for overlapping of these track effects occurs whenthe incident ion density esceeds N = (1/2rp)2 = 1 s 10ll/cm2. Our incident ion density of 4 s 10l2 greatly esceeds this threshold and will allow produce significantly enhanced reaction product densities because they are delivered on a timescale short 20 or comparable to the recombination times of the reaction products formed along the trac~ Our treatment will also produce microscopically homogenous treatment of the surface due to the overlapping tracks.
There are other aspects of the use of high-density pulsed ion beam treatment of polymers which require some analysis. The temperature increase from a 0.25 2i J/cm2 pulse of protons on polycarbonate is about 500 K, as mentioned above. If one pulse is adequate for the desired treatment, this level of temperature rise is safe for the great majorit~ of polymers. IIowever, if a multi-pulse treatment is necessary, the polymer surface must have time to cool bet~ een pulses, or the temperature increase ~ill be much greater, perhaps causing significant problems. Also, if the Wo 96123021 2 ~ 8 G 1 0 1 PCT/US96/00872 temperature rise is maintained for t~oo long, the polymer may be damaged. The essential problem here is the e~tremely low thermal conductivity of some polymers.
The characteristic timescale for heat to diffuse a length ~ in a material is ~t~cp~ /K, where c is the specific heat per gram of the polymer, p is the density of the polymer, and K is the thermal conductivity of the polymer. Using this relation, one can easily show that the increase in temperature over that of the polymer bulk falls to about 250K after~3 llsec, and to a mere 30K after ~250 ~sec. Clearly multiple pulsespose no problem as long as t,le repetition rate is less than about 105 per second, and we contemplate a maximum of~1000 pps. Damage to the polymer resulting from one pulse is not as clear an issue, but a material would have to be very sensitive to sustain significant damage from such a modest temperature rise that is effectively quenched in about 10 llseconds.
The other issue coming out of the thermal timescale analysis concerns the thickness of the polymer near-surface region which may be e~cited. If there is areason, a region as thick as ~100 llm may be irradiated. For such a thick layer, the thermal time constant is ~ 2 milliseconds. Clearly this does not offer either rapid quenching or e~tremely short e~posure to heat, but also does not represent a major limitation to use of pulsed ion beam treatment on polymer surfaces.
The ability to deliver high nuences of ions to a surface in a short pulse enables this process to be used for pyrolyzing (removing hydrogen and/or o~ygen from) polymer surfaces as well as etching and modifying the geometry of the surface.
An e~ample of the ability of this technology to modify the surface geometry is sho- n in Figure 6 in which a polyethylene surface was treated with an ion beam at a level of appro~imately 0.5 Jlcm2 resulting in the production of a relatively uniform array of holes or pits ~ ith micron size dimensions. Altering a polymer in this manner can be beneficial by providing adjustable electrical conductivity, increased surface area, WO 96/23021 2 l 8 ~ 101 PCT/US96/00872 improved adhesion of coatings, and with masking, the ability to spatially vary these properties along the surface.
The combination of the reduced energy/unit area needed for treatment and the high intensities available on a repetitively pulsed basis with this new technology 5 enables, for the first time, vary rapid treatment of polymer surfaces at low cost with a totally chemical-free process. It is estimated that treatment rates of > 100 sq.
ft./second at a cost of 1 cent/sq. ft. are possible using this technology.
The present invention provides the first capability to achieve high densities offree radicals, even up to conditions in which the effects of reaction products from 0 adjacent ion tracks overlap. This allows an entirely new regime of radiation treatment to be e~plored in which tne re~ction products react more strongly witheach other, rather than simply with the polymer.
Esisting continuous techniques deliver doses of perhaps 500 Mrad per hour (0.14 Mrad/sec.). Prior art pulsed techniques are based on long pulsed electron lS beams or very low average power research accelerators capable of dose rates of order 105 Mrad/sec. This is still too low to produce overlapping tracks. Typicaldose rates with the present process will be 100 Mrad in 1~10-~ seconds (> 108 Mrad/sec.), appro~imately three orders of magnitude faster. One effect of this will be that the resulting higher free radical density will allow free radicals to combine 20 quickly with each other, resulting in greatly increased emciency of crosslinking and other reactions. With e~isting techniques, free radicals may remain uncombined for hours to days, finally combining in many cases with o~ygen, permanently terminating the chain and resulting in scission rather than crosslinking.
The ability to localize treatment to the surface will result in many 25 applications that can be done at greatly reduced cost. E~isting techniques use particles that penetrate much more deeply into the material (>lmm) rather than only the few microns or less that can be achieved by ion beams. The reduced penetration can result in orders of magnitude less energy needed to reach the same local treatment dose, correspondingly reducing the cost of treatment in applications 30 that only require near-surface treatment.

218~01 WO 96/23021 i- ~ PCT~S96/00872 ,, This process allows rapid treatment of material because of its intense, pulsed nature. The short pulse allows one to easily control and limit the local dose and heating of the surface, allowing it to cool between pulses while still preserving the advantages of the high intensity.
In addition to the reaction products, this technique, because of its high intensity, can also modify the surface of polymers by changing the topology of the surfaces. Figures 6A and 6B show an e~ample of this modification. The holes formed in the surface can be advantageous in various ways, including the ability of deposited films to more easily mechanically adhere to the rough surface. Pyrolyzing and etching by ablation of the surface are also techniques made possible by the high intensities. The short pulse nature of this process allows these effects to be e~ploited near the surface without affecting the underlying material.
Another important advantage of this short pulsed technique is that the polymer surfaces can be raised to temperatures higher than those that can be used in long timescale processing without degradation due to heating. This is heating to high temperatures for only very short times do not have the same degrading effect on polymers that a similar temperature would have for long times. For example, pulsed laser heating has shown that Kapton can be raised to 1000 C for microsecond periods without deleterious effects. This advantage can also have beneficial effects in cases for which processing at elevated temperatures is desirable.
Turning now to the drawings, Fig. 1 shows a cross section of a polymer undergoing irradiation by the process of this invention. The process is described in terms of ion beams, but electron beams and gamma ray beams are also useful in this process. The ions 100 from the pulsed ion beam enter into the surface 115 of thepolymer 116 down to a depth 117 determined by the species and the kinetic energ~of the particular ion used. It is in this upper region between 11~ and 117 that the effects of the irradiation are most pronounced. The heat created in this region by the ion pulse is very rapidly dissipated into the region of the polymer underlying the - interface 117, thereby preventing the adverse effects of longer term heat buildup in the upper region. This figure also shows another layer of material 112 emplaced wo 96/23021 2 1 8 ~ 1~ 1 PCT/US96/00872 above the upper surface 115 of the polymer 116. The layer can be one of two different types of materials. If it is used as a mask layer, it will protect theunderlying areas of the polymer from the effects of the radiation. If it is to be a surface coating layer for the polymer or another material which is ihtended to be 5 incorporated in some more or less permanent fashion onto or into the upper surface of the polymer, it will be a type of material through which the ion beams pass to the e~tent necessary to bond the material at the interface 115 with the polymer or to otherwise melt or diffuse the material thereinto. For e~ample, an ~+ beam at 0.4- MeV, will have a 5 micron range in polypropylene and cause a temperature increase of ilO K for a 10 Mrad pulse (0.1 Jlcm1). The resulting ionization and disruption of polymer bonds caused by the ion pulse will form free radicals wh-ch then recombine to cross-link the polymer chains within the polymer surface. Additionally, if the-material 112 is of the appropriate type, such as epo~y or another polymer material, it also will be treated by the ion pulse and bind to the underlying polymer.
A 30 keV electron beam has a 10 micron range in polypropylene, produces a temperature increase of 112 C for a 10 Mrad pulse (0.2 J/cm2) and produces similar polymer alteration effects to those described above for ion beam irradiation.
Figure 2 is a graph obtained using the ~-ray photoemission spectroscopy diagnostic showing the changes in the polymer chemistry of Kapton (polyimide) 20 under control conditions without irradiation, after being irradiated with a low dose ion beam pulse (a mi~ed carbon, electron beam at 0.2 - 0.6 MV), and after being irradiated with a low dose beam through a 50 - 100 nm thick o~ygen-containing coating . The graph reveals that the carbo~ylic acid level of the Kapton has increased with the pulsed ion beam treatment, verifying chemical changes induced25 by treatment.
Figure 3 is a graph obtained using Fourier Transform Infrared Spectroscopy showing the chemical signature shift in a polycarbonate before and after treatment with the pulsed ion beam. The parameters of the treatment were appro~imately 0.
J/cm2 of mi~ed ~ and C~ delivered in an appro~;imately 200 ns pulse.

2i~6~01 W O 96/23021 ~ PCTAUS96/00872 - Figure 4 is a microphotograph showlng the change in surface geometry of a polypropylene surface coated with one ~n~f copper at the transition between a treated and an untreated region. The treatment parameters here were as above.
Other tests of this material indicated improved copper adhesion to t'he 5 polycarbonate in similarly treated areas.
Figure S is a bar chart showing different adhesion strengths as a function of treatment intensity for polycarbonate coated with one micron of copper. A stud was attached to the copper coating and pulled until the copper layer separated from the polycarbonate. The treatment levels were 0.1 J/cm2 (low), 0.5 J/cm2 (med.), and 1-2 lo J/cm2 (high).
Figure 6A is a microphotograph of an untreated polyethylene surface.
Figure 6B is a microphotograph of the surface after treatment at 0.~ - 1.0 J/cm2 to form the uniformly pitted surface shown. This treated surface exhibits increasedadhesion characteristics.
The invention requires a system capable of delivering ion beams of the requisite power and timing over commercially realistic work periods. One such system is described in co-pending patent applications serial numbers 08/1~3,248 filed November 16, 1993, 08/317,948 filed October 4, 1994 and 08/340,~19 filed November 16, 1994, which are incorporated herein by reference in their entirety.20 The discussion that follows is e~cerpted from these applications to describe the best mode presently known for the practice of this invention.
The following dicc~ssion is a description of one system which can be utilized to produce the ion beams for surface treatment of various materials. This systemhas two major subsystems, a pulsed power source and a Magnetically-confined 25 Anode Plasma (MAP) ion diode.
The MAP ion diode, when combined with the repetitive high energy pulsed power (R~EPP) source, provides for an ion beam generator system capable of high average power and repetitive operation over an extended number of operating cycles for treating large surface areas of materials at commercially attractive costs.
30 In particular, the ion beam generator of the present invention can produce high wo 96123021 21~ ô 10 ~ PCT/USg6/00872 average power (lkW-4MW) pulsed ion beams at 0.025 - 2.5 MeV energies and pulse durations or lengths of from about 10 nanoseconds (ns) - 2 microseconds (~s) or longer as necessary for the particular application. The ion beam generator can directly deposit energy in the upper regions of the surface of a material. The depth 5 of treatment can be controlled by varying the ion energy and species as well as the pulse length. The MAP ion diode can be combined with other power sources where less demanding power demands are present.
The first of the components in the pulsed ion beam generating system is a compact, electrically emcient, repetitively pulsed, magnetically switched, pulsed 10 power system capable of 109 pulse operating cycles of the type described by H. C.
~Iarjes, et al, Pro 8th IEEE Int. Pulsed Power Conference (1991), and D. L. Johnson et al., "Results of Initial Testing of the Four Stage R~IEPP Accelerator" pp. 437-440 and C. ~arjes et al., "Characterization of the R~IEPP 1 lls Magnetic Pulse Compression Module", pp. 787-790, both reprinted in the Digest of Technical 5 Papers of the Ninth IEE~: International Pulsed Power Conference, June, 1993, all of which is incorporated by reference herein. These references in conjunction with the discussion herein below place fabrication of such a pulsed power source within the skill of the art.
A block diagram of a power system produced according to the teachings of 20 the present application is shown in Figure 7. From the prime power input, several stages of magnetic pulse compression and voltage addition are used to deliver a pulsed power signal of up to 2.5 MV, 60 ns FWHM, 2.9 kJ pulses at a rate of 120 ~Iz to an ion beam source for this particular system. The power system converts AC
power from the local power grid into a form that can be used by an ion beam source 25 25.
Referring to Figure 7, in one embodiment of the invention, the power system comprises a motor 5 which drives an alternator 10. The alternator 10 delivers a signal to a pulse compression system 15 which has two subsystems, a 111s pulse compressor 12 and a pulse forming line 14. The pulse compression system 15 wo 96/23021 218 ~ ~ ~ I PCTtUS96/00872 provides pulses to a linear inductive voltag~ der (LIVA) 20 which delivers the pulses to the ion beam source 25.
The alternator 10 according to one embodiment is a 600 kW, 120 ~z alternator. In the unipolar mode, it provides 210 A rms at a voltage` of 3200 V rms with a power factor of 0.88 to the magnetic switch pulse compressor system 15. The alternator is driven by a motor connected to the local 480V power grid. The particular alternator used herein was designed by Westinghouse Corporation and fabricated at the Sandia National Laboratories in Albuquerque, New Me~ico. It isdescribed in detail in a paper by R M. Calfo et al., "Design and Test of a o Continuous Duty Pulsed AC Generator" in the Proceedings of the 8th IEEE Pulsed Power Conference, pp. 715-718, June, 1991, San Diego, California. This reference is incorporated herein in its entirety. This particular power system was selected and built because of its relative ease in adaptability to a variety of loads. Other power sources may be used and may indeed be better optimized to this particular use. For e~ample, a power supply of the type available for Magna-Amp, Inc. comprising a series of step-up transformers connected to the local power grid feeding through a suitably-sized rectifier could be used. The present system however has been built and performs reasonably well.
In one embodiment, the pulse compression system 15 is separated into two subsystems, one of which is a common magnetic pulse compressor 12 composed of a plurality of stages of magnetic switches (i.e., saturable reactors) the operation of which is well known to those skilled in the art. This subsystem is shown in moredetail in Fig. 7A. The basic operation of each of the stages is to compress the time ~ idth (transfer time) of and to increase the amplitude of the voltage pulse received from the preceding stage. Since these are very low loss switches, relatively little of the po~ er is wasted as heat, and the energy in each pulse decreases relatively little as it moves from stage to stage. The specific subsystem used herein is described indetail by ~I. C. ~arjes, et al., "Characterization of the R~IEPP 1~s Magnetic Pulse Compression Module", 9th IEEE International Pulsed Power Conference, pp. 787-790, Albuquerque, Nl~I, June, 1993. This paper is incorporated by reference herein WO 96/23021 2 1~ 61 a 1 PCTtUS96/00872 in its entirety. These stages as deve!oped for this system are quite large. In the interest of conserving space, it would be possible to replace the first few stages with appropriately designed silicon control rectifiers (SCR's) to accomplish the samepulse compression result.
s These stages 12 convert the output of the alternator 10 into a 1~Ls wide LC
charge waveform which is then delivered to a second subsystem 14 comprising a pulse forming line (PFL) element set up in a voltage doubling Blumlein configuration. The PFL is a tria~ial water insulated line that converts the input LC
charge waveform to a flat-top trapezoidal pulse with a design 15 ns rise/fall time and 0 a 60 ns FWHM. The construction and operation of this element is described indetail by D. L. Johnson et al. "Results of Initial Testing of the Four Stage RHEPP
Accelerator", 9th IEEE International Pulsed Power Conference, pp.437-440, Albuquerque, NM, June, 1993. This paper is also incorporated by reference in itsentirety. A cross sectional view of the PFL is shown in Figure 7B.
The pulse compression system 15 can provide unipolar, 250 kV, 15 ns rise time, 60 ns full width half ma~imum (FWEIM), 4 kJ pulses, at a rate of 120 Hz, to the linear inductive voltage adder (L~VA) (20). In a preferred embodiment, the pulse compression system 15 should desirably have an emciency >80% and be composed of high reliability components with very long lifetimes (~109-10l pulses).
Magnetic switches are preferably used in all of the pulse compression stages, MS1-MS5, because they can handle very high peak powers (i.e., high voltages and currents), and because they are basically solid state devices with a long service life.
The five compression stages used in this embodiment as well as the PFL 14 are shown in Fig. 7A. The power is supplied to the pulse compression system 15 from the alternator 10 and is passed through the magnetic switches, MS1-MS5, to the PFL 14. The PFL is connected to the linear induction voltage adder (LIVA) 20 described below. The second and third magnetic switches, MS2 and MS3, are separated by a step-up transformer T1 as shown. Switch MS6 is an inversion switch for the PFL.

WO 96/23021 ~ 18 ~ t o 1 PCT/US96/00872 The pulse forming line (PFL) element 14 is shown in schematically in ~ig. 7A
and in cross section in Fig. 7B. M~6~n~ig~. 7A corresponds to the inversion switch 302 shown in Fig. 7B located on the input side of the tri-a~ial section 314 of the PFL.
Output switches 304 and charging cores 306 are also shown. The re~ions 310 are 5 filled with deionized water as the dielectric. The interior region 308 is filled with air and oil coiling lines, not shown, for the output switches 304. The output of the PFL
is fed in parallel to each of the individual LIVA stages 20, with the positive component flowing through conductors 316 and the shell 318 of the PFL serving asground. The positive conductors 316 are connected to each of the LIVA stages.
i The LIVA (20) is preferably liquid dielectric insulated. It is connected to the output of the PFL and can be configured in different numbers of stages to achieve the desired voltage for delivery to the ion beam source. The LIVA 20 can delivernominal 2.5 MV, 2.9 kJ, pulses at a rate of 120 ~Iz to the ion beam source 25 when configured with 10 stages of 250 kV each. For most of the ion beam treatments, the 15 LIVA was configured with four stages of 250 kV each, such that the LIVA delivered a total of 1.0 MV to the ion beam source. ~owever, this voltage can be increased or decreased by changing the number of stages in the LIVA to match the particular material processing need. The nominal output pulse of the LIVA 20 is the same asthat provided to it by the PFL, namely, trapezoidal with 15 ns rise and fall times 20 and 60 ns FW~IM (full width half ma~imum). Figure 7C shows a cross section ofthe four stage LIVA. The four stages, 320, 322, 324, and 326, are stacked as shown and fed the positive pulses from the PFL via the cables 321, 323, 325, and 327. The stages are separated by gaps 330 and surrounded by transformer oil for cooling.
The output from each of the LIVA stages adds to deliver a single total pulse to the 25 ion beam source shown here schematically as 2~ which is located within a vacuum chamber 332, shown in partial view. As with the PFL, the outside shell of the LIVA
is connected to ground.
The power system P (Figure 7) as described, can operate continuously at a pulse repetition rate of 120 ~Iz delivering up to 2.5 kJ of energy per pulse in 60 ns 30 pulses. The specific power system described here can deliver pulsed power signals of -l~)-W O 96/23021 2 18 C 1 0 1 PCT~US96/00872 about 20-1000 ns duration with ion beam energies of 0.25-2.5 MeV. The power - system can operate at 50% electrical efficiency from the wall plug to energy delivered to a matched load. The power system P uses low loss pulse compression stages incorporating, for e~ample, low loss magnetic material and solid state components, to convert AC power to short, high voltage pulses.
The ability to produce voltages from 250 kV or less to several MV by stacking voltage using a plurality of inductive adders incorporating low loss magnetic material is a principle feature when high voltages are needed, although it is also possible to use a single stage pulse supply, ~limin~ting the need for the adder.
lo The power system can operate at relatively low impedances (' 100Q) which also sets it apart from many other repetitive, power supply technologies, such as transformer-based systems. This feature allows high treatment rates and the treatment of large areas (5 to more than 1000 cm2) with a single pulse so as to reduce edge effects occurring at the transition between treated and untreated areas.
The second component of the pulsed ion beam system is the MAP ion beam source 25 (shown in Figure 8). The MAP ion beam source is capable of operating repetitively and efficiently to utilize the pulsed power signal from the power system efficiently to turn gas phase molecules into a high energy pulsed ion beam. It can also be operated in the single shot mode~ as necessary for a particular application. A
precursor of the ion beam source is an ion diode described generally by J. B.
Greenly et al, "Plasma Anode Ion Diode Research at Cornell: Repetitive Pulse and0.1 TW Single Pulse E~periments", Proceedings of 8th Intl. Conf. on ~igh Power Particle Beams (1990) all of which is incorporated by reference herein. Althoughthis reference ion diode differs significantly from the ion diode utilized in the present system as discussed above, the background discussion in this reference is of interest.
The ion beam source 25, according to the principles of the present invention, is shown in Figure 8. The ion beam source 25 is a magnetically-confined anode plasma (I-IAP) source. Figure 8 is a partial cross-sectional view of one symmetric side of the ion beam or MAP source 25. The ion beam or MAP source 25 produces an annular ion beam K which can be brought to a broad focus symmetric about the W O 96n3021 218 ~1~ 1 PCT~US96/00872 a~is X-X 400 shown. In the cathode electrode assembly 30 slow (lms rise time) magnetic field coils 414 produce magnetic flu~ S (as shown in Fig. 8A) which provides the magnetic insulation of the accelerating gap between the cathodes 412 and the anodes 410. The anode electrode~4~0 also act as magnetic hu~ shapers.
The slow coils414 are cooled by adjacent water lines, not shown, incorporated into the structure 30 supporting the cathodes 412 and the slow coils414. The main portion of the MAP structure shown in this Figure is about 18 cm high and wide.
The complete MAP ion diode can be visualized as the revolution of the cross-sectional detail of Fig. 8 about the central a~is 400 of the device to form a cylindrical 0 apparatus. A full cross sectional view appears in Fig. 9.
The ion beam or MAP source 25 operates in the following fashion: a fast gas valve assembly 404 located in the anode assembly 35 produces a rapid (200~1S) gas puff which is delivered through a supersonic nozzle 406 to produce a highly localized volume of gas directly in front of the surface of a fast driving coil 408 located in an insulating structure 420. The nozzle is designed to prevent any transverse flow of non-ionized gas into the gap between the anodes 410 and cathodes 412. After pre-ionizing the gas with a 1 ms induced electric field, the fast driving coil 408 is fully energized from the fast capacitor 150, inducing a loop voltage of 20 kV on the gas volume, driving a breakdown to full ionization, and moving the resulting plasma toward the anode electrodes 410 in about 1.5 ~s or less, to form a thin magnetically-confined plasma layer. The plasma momentarily stagnates at this B=0 region, the separatri~, ne~t to the insulating field S produced by the slow coils 414, awaiting the delivery of the main accelerating positive electrical pulse to be delivered at the anodes 410 from the LIVA discussed above.
The gas can be effectively pre-ionized b~ placing a small ringing capacitor 160 in parallel with the fast coil. The field oscillations produced by this ringing circuit pre-ionize the gas in front of the anode fast coil. A schematic electrical diagram of this circuit is shown in Fig. 8C.
It was also discovered that, prior to pro- ision of the main pulse to the fast coil, it is beneficial to have the ability to adjust the configuration of the magnetic WO96t23021 2 ~ ~ 6 ~ 01 PCT/US96/00872 field in the gap between the fast coil and the anode to adjust the initial position of plasma formation in the puffed gas pulse prior to the pre-ionization step. This is accomplished by the provision of a slow bias capacitor 180 and a protection circuit both being installed in parallel with the fast coil and isolated therefi'om by a5 controllable switch S2. A slow bias field is thus created prior to pre-ionization of the gas by the fast coil. This circuit is also shown in Fig. 8C.
In further e~planation of the electrical circuit for the fast coil as shown in Fig. 2C, the bias field capacitor 180 drives a greater than 1 microsecond risetime current in the fast coil before the main capacitor pulse begins. This allows 0 adjustment of the field configuration produced by the fast capacitor current. The fast capacitor 150 drives a 1 microsecond risetime pulse in the fast coil. The preionizer capacitor 160 causes the voltage across the fast coil to ring with a much less than 1 microsecond period, inducing a large oscillating electric field in the gas to be ionized, leading to partial ionization of the gas. The rising magnetic field 5 produced by the fast coil 408 pushes the ionized gas away from the fast coil, stagnating it against the pree~isting magnetic field from the slow coil 414.
After pre-ionization the fast coil is then fully energized as described above tocompletely breakdown the gas into the plasma. After this pulse the field collapses back into the fast coil which is connected to a resistive load which is in turn 20 connected to a heat sink, not shown. In the present embodiment, cooling channels in the supporting structure are used, but other solutions are possible and relatively straightforward. In this manner heat build up in the fast coil is avoided.
The fast coils 408 have been redesigned from the reference fast coils in several ways as well as the heat sinking mentioned above. The gap between the fast 25 coil and the anode electrodes 410 has been reduced with the result that the amount of necessary magnetic energy has been decreased by over 50%. The lower energy requirement permits repetitive use at higher frequencies and reduces the complesi~
of the feed system v oltages for the fast coils. The design of the new flu~-shaping anode electrode assembly has also contributed to these beneficial results.

WO 96/23021 2 ~ 8 6 ~ O ~ PCT/US96100872 The pulsed power signal from the power system is then applied to the anode assembly 35, accelerating ions from the plasma to form an ion beam K. The slow (S) and fast (F) magnetic nu~ structures, at the time of ion beam e~traction, are shown in Figure 2A. The definite separation betwee~ the nu~ from the fast coil from the 5 nu~ from the slow coil is shown therein.~is is accomplished by the 11u~-shaping effects of the anodes 410 and also by the absence of a slow coil located in the insulating structure 420 as was taught in the earlier MAP reference paper. The slow coils in the present MAP ion diode are located only in the cathode area of the MAP.
This anode flu~ shaping in conjunction with the location of slow coils in the cathode 10 assembly is different from that shown in the l~P reference paper and permits the high repetition rate, sustained operation of the MAP diode disclosed herein. This design allows the B=0 point (the separatri~) to be positioned near the anode surface, resulting in an estracted ion beam with minimal or no rotation. This minimal rotation is necessary for effective delivery of the beam to the material to be treated.
Figure 8B is a detailed view of the gas valve assembly 404 and the passage 425 which conducts the gas from the valve 404 to the area in front of the fast coil 408. The passage 425 has been carefully designed to deposit the gas in the localized area of the fast coil with a minimum of blow-by past this region. The details of the cross sections of the passage 42~ were designed for supersonic transport of the gas 20 puff. The design was done with readily available gas flow computer programs and is within the skill in the art. The gas valve flapper 426 is operated by a small magnetic coil 428 which opens and closes the f~apper 426 upon actuation from the MAP
control system. The flapper valve is pivoted on the bottom end 427 of the flapper.
The coil 428 is mounted in a high thermal conductivity ceramic support structure25 429 which is in turn heat sinked to other structure, not shown. Alternatively, e~ternally cooled wires surrounding the coil could also serve to e~tract the heat from the coils. This heat sinking is necessary for the sustained operating capability of the MAP. The gas is delivered to the valve from a plenum 431 behind the base of the flapper. The plenum 431 should be visualized as being connected to a larger plenum 30 located at the central core of the complete l\IAP ion diode as shown in Fig. 9.

WO 96123021 2 ~ 8 G 1 0 1 PCT/US96/00872 The vacuum in the nozzle 406 rapidly draws the gas into the MAP once the flapper 426 is opened. The function of the nozzle is to produce a directed flow of gas only in the direction of tlow and not transverse to it. Such transverse flow would direct gas into the gap between the anode and the cathode which would produce detrimental arcing and other effec~ts. The reduction of the fast coil-anode gap discussed above makes the design of the nozzle very important to the successful operation of the MAP. Fortunately, gas llow design tools are available and were used to develop a nozzle with improved gas flow (higher mach number) and minimalboundary effects. This improved nozzle has an enlarged opening into the gap o between the fast coil and the near edge of the anode which tapers from 9 to 15 mm instead of the straight walled 6 mm cor.~uit in the reference MAP. The operatingpressure of the gas in the puff valve has been increased from the range of 5-25 psig to the range of 25-40 psig. Esperiments have confirmed much improved MAP
operation as a result of this new design.
The ion diode of this invention is distinguished from prior art ion diodes in several ways. Due to its low gas load per pulse, the vacuum recovery within the MAP allows sustained operation up to and above 100 ~z. As discussed above, the magnetic geometry is fundamentally different from previous ion diodes. Prior diodes produced rotating beams that were intended for applications in which the ion beam propagates in a strong asial magnetic field after being generated in the diode.
The present system requires that the ion beam be estracted from the diode to propagate in field-free space a minimum distance of 20-30 cm to a material- surface.
The magnetic configurations of previous ion diodes are incapable of this type ofoperation because those ior. beams were forced by the geometries of those diodes to cross net magnetic flu~ and thus rotate. Such beams would rapidly disperse and be useless for the present purposes. By moving the slow coils (the diode insulatingmagnetic rleld coils) to the cathode side of the diode gap eliminated the magnetic field crossing for the beam but required a total redesign of the magnetic system for - the anode plasma source.
.

wo 96/23021 2 ~ 8 ~101 PCT/US96/00872 The modifications to the fast coil discussed above can result in an energy requirement that is 5-10 times less than previous configurations. The modifications include: the elimination of a slow coil on the anode side of the diode and its associated feeds, better control over the m~gi~etic field shaping and contact of the 5 anode plasma to the anode electrode structure through use of the partially field-penetrable electrodes, the elimination of the separate pre-ionizer coil from the prior ion diodes, the circuit associated with the fast coil to provide "bias" current to adjust the magnetic field to place the anode plasma surface on the correct flux surface to eliminate beam rotation and allow optimal propagation and focusing of0 the beam, and the redesign of the gas nozzle to better localize the gas puff which enables the fast coil to be located close to the diode gap which in turn reduces the energ~ requirements and complexity of the fast coil driver.
The plasma can be formed using a variety of gas phase molecules. The system can use any gas (including hydrogen, helium, o~ygen, nitrogen fluorine, 15 neon, chlorine and argon) or vaporizable liquid or metal (including lithium, beryllium, boron, carbon, sodium, magnesium, aluminum, silicon, phosphorous, sulfur, and potassium ) to produce a pure source of ions without consuming or damaging any component other than the gas supplied to the source. The ion beam K propagates 20-30 cm in vacuum (~10-3) to a broad focal area (up to 1000 cmZ) at 20 the target plane 195, shown in Fig. 3, where material samples are placed for treatment and can thermally alter areas from 5 cm2 to over 1000 cm2.
The ion beam or MAP source 25 is capable of operating at repetitive pulse rates of 100 l~z continuously with long component lifetimes >106. The ion beam or MAP source 25, according to the principles of the present invention, draws ions 25 from a plasma anode rather than a solid dielectric surface llashover anode used in present single pulse ion beam sources. Use of a flashover anode typically introduces a variety of contaminants to the surface of the material, often with detrimentalresults. One of the significant advantages of using the improved MAP source disclosed herein is that one has precise control over the components in the ion beam 30 by controlling the composition of the gas source.

Claims

We claim:

1. A process for treating polymers with pulsed ion beams comprising irradiating a surface of a polymer with at least one pulse of high energy ions, each spatially contiguous pulse having a duration of less than 10 microseconds and a fluence of between 0.01 and 10 J/cm with ion kinetic energies above about 25 ke V.

2. The process of claim 1 wherein the pulses are repeated across the surface of the polymer at repetition rates greater than 1 Hz.

3. The process of claim 1 wherein the ion fluence is sufficient to produce an ion track density within the polymer such that reaction products produced along different ion tracks have a high probability of interaction with one another within the recombination time of the reaction products.

4. The process of claim 1 further including the placement of a second layer of material over the polymer such that upon irradiation of the second layer and thesurface of the polymer, the second layer will be bonded to the surface of the polymer.

5. The process of claim 1 wherein the polymer exists as a layer covering a material to which to polymer is bonded after irradiation.

6. The process of claim 1 further including the placement of a mask layer above the surface of the polymer to shield the underlying regions of the polymer from the effects of the pulsed ion beams.

7. The process of claim 6 wherein the ion fluence is sufficient to etch away those regions of the polymer that are unshielded by the mask layer.

8. The process of claim 1 resulting in the pyrolyzation of the surface of the polymer.

9. The process of claim 1 resulting in the cross-linking of the irradiated polymer.

10. The process of claim 1 resulting in changes in electrical conductivity of the treated layer.

11. The process of claim 1 resulting in changes in the optical density of the treated layer.

12. The process of claim 1 resulting in increased toughness and scratch resistance.

13. The process of claim 1 resulting in increased resistance to solvents and environmental degradation.

14. The process of claim 1 wherein the irradiation is of sufficient density to cause disruption of the chemical bonds of the polymer to an extent such that recombination of the disrupted bonds results in the formation of new chemical compounds.

15. The process of claim 1 wherein the areas of irradiation are shifted across the polymer in an overlapping manner so as to form a continuous, treated polymer surface.

16. The process of claim 1 wherein the ion is an ion created from gas phase molecules.

17. The process of claim 16 wherein the gas phase molecules are selected from the group consisting of H, He, N, and Ar.

18. The process of claim 1 wherein the polymer is selected from the group consisting of polyethylene, polypropylene, polycarbonate, poly (methyl methacrylate), poly (vinyl chloride), poly (tetrafluoroethylene), polyimide, Mylar and combinations thereof.

19. The process of claim 1 wherein the irradiation causes a modification of the adhesion characteristics of the surface.

20. The process of claim 1 wherein the irradiation modifies the topography of the surface.

21. The process of claim 1 wherein the irradiation causes etching of the surface.

22. The process of claim 1 wherein the heat per pulse delivered into the polymerand the interval between pulses are such that heat-induced degradation of the polymer is minimized.

23. The process of Claim 2, conducted continuously for periods greater than two minutes.

24. The product of the process of claim 3.