Wide Band-Gap Photovoltaics

M.A. Prelasa, G. Popov1cia,b, Salim Khasawinaha, and Jeff Sunga

a) College of Engineering, University of Missouri, Columbia, MO 65211

b) Rockford Diamond Technology, Professional Arts Bldg., S. 6th Street, suite 101,

Champaign, IL 61801

Abstract

Wide bandgap materials will have many applications as coatings and as electronic devic­es. This paper describes an electronic application for wide bandgap materials in energy production. A specific portable power technology which converts the energy emitted from nuclear reactions to electrical energy using wide bandgap photovoltaic cells without in­termediate thermalization is described in this paper. The potential efficiency for the pho­

tovoltaic process is 35%, nuclear energy to electrical energy. And, if combined with high­temperature thermionic conversion the nuclear to electrical energy conversion efficiency is 41% while the overall size of the system remains small. The key to the process is to first convert the high-grade ion energy to photon energy, which can then be directly converted to electrical energy. This process is also usable as an advanced topping cycle for large scale energy production in conjunction with fusion power, as well as fission power. In ad­dition to improved efficiency, the process also promises advantages in smaller volumes,

smaller mass, and lower cost of the energy conversion hardware.

Introduction

The use of wide bandgap photovoltaics (e.g., diamond and aluminum nitride) in fusion

energy conversion was discussed in 1981 [1] and in fission energy conversion was dis­cussed in 1984 [2]. The focus of this discussion will be in the use and implementation of

radioisotopes. In this paper the process of nuclear energy conversion with wide bandgap

photovoltaics will be called the £hotovoltaic £nergy conversion of Nuclear energy fu's­tem (PENS). PENS can use both gaseous or solid nuclear fuels for power production. A

summary of how solid fuels can be introduced into PENS is given in References 3 and 4. The important underlying principle is to introduce the solid into the PENS so that it opti-

463

M.A. Prelas et al. (eds.), Wide Band Gap Electronic Materials, 463-474 © 1995 Kluwer Academic Publishers. Printed in the Netherlands.

464

cally thin. This can be achieved by introducing the solid as an aerosol, thin fibers, thin films, or encapsulating the individual atoms ofthe solid in Fullerenes [3,4].

In the first step of the PENS, the nuclear energy is transported to a fluorescer which converts it into photons. (The fluorescer could be a solid, liquid, or gas. This paper will focus on the use of a gas.) Then, in the second step of the process, the photons are transported out of the active region to high bandgap photovoltaic cells which efficiently convert the photon energy

to electricity.

Figure 1. Schematic Diagram of the PENS.

The efficiency of the two-step PENS process, while inherently less efficient than one-step

direct energy conversion has two major advantages over thermal energy conversion, which

is a many step process. These advantages are: 1) that it is a direct process producing a useful energy form from high grade energy and thus avoiding the Carnot cycle efficiency limits imposed by thermalization and 2) that it is much simpler, potentially leading to more com­

pact, more reliable, and less expensive energy conversion systems. '

The advantage of the PENS process over a one-step direct energy conversion process is that

of feasibility. The scale length for the transport of the primary high-grade energy must match the geometrical scale of the energy converter. Energetic ions have a transport length

of micrometers while useful energy converters, on the other hand, have a scale length of fractions of meters. For this reason direct conversion of nuclear energy has not previously been possible. What was required was the concept of an intermediate high-level energy con­verter that can be intermingled with nuclear material on a micrometer scale-length but pro­

duces an energy form that can be transported to meter scale-length direct converters

prod1 With

ores' COU{

quir1

med

effe ty ft

I

ep

ch

ful

ts )m-

that

lgth of

usly

con-

tpro-

465

producing useful output- a sort of "impedance matching" for scale length of energy forms.

With PENS that scale length matching medium is a fluorescing gas, the nuclear-driven flu­

orescer. The photons it produces can be transported great distances, making it possible to

couple them to various energy conversion processes. Also, some conversion processes re­

quire greater power densities than the primary energy sources can provide. A PENS inter­

mediate photon flux can be absorbed in a smaller volume than that in which it is produced,

effectively concentrating the flux, enabling achievement of the high threshold power densi­

ty for such conversion processes.

Charged Particles

Thin Rectangular Film Thin Cylindrical Fiber

Small Aerosol Particles

Figure 2. An illustration of the use of thin solid geometries which allow reaction products to escape the solid matrix into a surrounding gas.

The RECS concept of high efficiency production of light from radioisotopes makes this

concept useful for remote power applications.

The choice of the fluorescer is important to the process. What is desired is that the fluorescer

emits the energy deposited in it efficiently at a single wavelength without self absorption.

The closest thing to a perfect fluorescer in nature is an excimer or an exciplex. If an atom

(or molecule) is exited (So-> S1*) the atom or molecule can migrate and bond with an un­

excited molecule (SoS1 *). If the atoms or molecules are identical then the resulting mole­

cule is called and excimer, if the atoms or molecules are different then the resulting

molecule is called an exciplex. The excimer/exciplex rapidly falls apart after the emission

of narrow band fluorescence since the ground state is unbound. Excimers/exciplexes have

been experimentally shown to be efficient (up to 50%), narrow band (+/-10om), non self­

absorbing fluorescers [see review in reference 3].

466

Some of the most efficient excimers fluoresce in the vacuum ultraviolet (He2*- 80 nm- 50%

efficient, Ar2*-129 nm- 50% efficient, Kr2*- 147nm- 47% efficient, Xe2*- 172nm- 48% efficient).

Thus, to convert these excimer's narrow band fluorescence to electrical energy requires

wide bandgap photovoltaics. At this time the technology for wide bandgap photovoltaics is not mature. Several promising materials- such as SiC, C (diamond), and AlN- do exist.

Progress has been made in fabricating simple devices such as Schottky barrier diodes on diamond and platinum silicide [5,6], a primitive p-njunction in diamond [7], n-type dia­

mond material has been developed [8], and p-type and n-type aluminum nitride have been claimed [9,10]. Progress is being made on the fabrication of wide bandgap photovoltaics.

The use of portable power sources using radioisotopes have been reported [11] and could have immediate applications in space exploration. The current generation oflong lived por­table power supplies are based upon the isotope Pu238 which is used to power the Radio­isotope Thermion Generator (RTG) for missions such as the Voyager. In the Voyager, three

RTG units produced 7,200 watts of thermal power and 540 watts of electricity regulated to 30 volts from 12,900 grams of the isotope.

Fluorescers

The Ion Source

An example of the PENS is shown in Figure 3 where the ion source is from the decay of

radioisotopes dispersed within a fluorescer gas. Effective dispersal is essential so that the ions produced by the isotope decay deposit most of their kinetic energy in the excimer gas rather than in the radioisotope material. There are at least four methods of achieving the de­sired dispersal: gaseous radioisotopes, radioisotopes embedded in thin films, radioisotopes

embedded in thin fibers, or microscopic aerosol of radioisotopes. The efficiency of trans­port of the ion energy from the radioisotope to the fluorescer medium varies with the scale length of the thin film, fibers or aerosol, the chemical form of the radioisotope, and the uni­forrnity of the radioisotope density. The variation of ion energy transport efficiency from a

microsphere, to the fluorescer medium, with thin films and microspheres are discussed in

Reference 12. Energy transport efficiencies are about 50% for reasonably designed thin

films, 62% for reasonably designed fibers, and 70% for reasonably designed microspheres. The average atomic density in the medium must be on the order of 1x1019 particles cm-3,

enough to achieve reasonable power densities but not so great as to significantly degrade

the transport of the fluorescence through the aerosol. Combining the constraints of efficien­cy, and optical transparency determines scale length of the thin film, fibers, or microspheres

and number density. For example, a microsphere diameter of 5 j.!m and number density of

1xl06 cm-3, which should not create significant absorption of the fluorescence [12], results in a fuel density of 0.63 mg cm-3, quite reasonable dimensions, and good number densities

(3.9x1019 atoms cm-3). However, we believe that fibers would be an improvement. As dis-

-80 nm- 50%

'c. efficient).

nr requires .otovoltaics is

~-do exist. er diodes on , n-type dia­

ide have been >hotovoltaics.

11] and could long lived por­•er the Radio­Voyager, three

ty regulated to

n the decay of

1tial so that the the excimer gas lChieving the de­IS, radioisotopes

ciency of trans­

~s with the scale ope, and the uni­

:fficiency from a

are discussed in ' designed thin

ed microspheres. ·9 particles cm-3,

ficantly degrade

traints of efficien­;, or microspheres

mmber density of

:ence [12], results

number densities

>rovement. As dis-

467

cussed in Reference 12, a diameter of 5 flm results in an ion transport efficiency of about 60%.

Pressure Vessel

Wide Band Gap Photovoltaics

Figure 3. Schematic Diagram of the PENS which uses a radioisotope fuel in aerosol form.

The structure of a fission fueled PENS is discussed in Reference 12, and a fusion fueled PENS in Reference 13.

Excimer Fluorescers

Excimer fluorescers are the most efficient radiators known and, because of their unbound lower levels, do not self absorb. They radiate in the single, relatively narrow, band of wave­

lengths required for efficient photovoltaic energy conversion [12]. The intrinsic fluores­

cence efficiencies of rare-gas and rare-gas halide excimers, based on standard W -value

theory [12], are listed in Table 1. Achievable efficiencies should be near the intrinsic values

at the power and electron densities characteristic of nuclear reactions.

In fact one group has reported measuring a nuclear-driven rare-gas excimer fluorescence

efficiency higher than that predicted by W-value theory [12]. Measurements of actual flu­

orescence efficiencies at various laboratories, including Lawrence Livermore National

Laboratory, have demonstrated high fluorescence efficiencies for excimers. Experiments with a variety of excitation sources (e.g. electrons, fission fragments, protons) and particle densities have given fluorescence efficiency values ranging from a few percent to as high

as 68% (see review paper by Prelas et al. [12]). The most efficient excimer fluorescers are the rare-gas excimers. Ion-Driven Fluorescers are discussed in much greater detail in the

paper "Nuclear-Driven Flashlamps" [12].

468

Table 1: Theoretical Maximum Intrinsic Photovoltaic, T\pv• and Ion-to-Electric, T\ie• Efficiencies for Selected Rare-Gas and Rare-Gas Halide Excimer Fluorescers with

Matched High-Bandgap Photovoltaic Materials.

Energy Photovoltaic Bandgap

Tti= TtpvX Ttf Ttf Energy Tlpv= EgfEI

Excimer (eV) Material (eV)

Efficiency

Ar2* 0.50 9.6 A1N 6.2 0.65 0.33

Kr2* 0.47 8.4 AlN 6.2 0.74 0.35

Diamond 5.5 0.65 0.31

F2* 0.44 7.8 AlN 6.2 0.79 0.35

Diamond 5.5 0.71 0.31

Xe2* 0.48 7.2 AlN 6.2 0.85 0.41

Diamond 5.5 0.76 0.37

ArF* 0.35 6.4 AlN 6.0 0.94 0.33

Diamond 5.5 0.86 0.30

KrBr* 0.33 6.0 Diamond 5.5 0.92 0.30

KrCl* 0.31 5.6 Diamond 5.5 0.98 0.30

Na2* 0.46 2.84 ZnSe 2.7 0.95 0.44

SiC 2.4 0.845 0.39

Li2* 0.42 2.7 CuA1Se2 2.6 0.96 0.40

SiC 2.4 0.89 0.37

Hg2* 0.21 2.58 GaS 2.5 0.97 0.20

SiC 2.4 0.93 0.19

ArO* 0.11 2.27 GaP 2.2 0.97 0.105

GaAlAs 2.2 0.97 ' 0.105

KrO* 0.13 2.27 GaP 2.2 0.97 0.125

GaA1As 2.2 0.97 0.125

X eO* 0.15 2.27 GaP 2.2 0.97 0.145

GaA1As 2.2 0.97 0.145

Th

Theke: commc

standin cells.".

reachin

to thee

peciall~

trum is

(FWID

foreffi

these c'

Photov

willre< es the 1

driven

dicate 1

p

ForXe trum.F

spectru

Forag

of the i

tovo1ta the sol1

that the

sufficit power,

where'

converl

howev<

photon

de, 11ie• rs with

11pvX 11t kiency

0.33

0.35

0.31

0.35

0.31

0.41

0.37

0.33

0.30

0.30

0.30

0.44

0.39

0.40

0.37

0.20

0.19

0.105

0.105

0.125

0.125

0.145

0.145

469

The Photon Energy Converter

The key to the feasibility of the PENS is the photovoltaic Photon Energy Converter. The

common impression of photovoltaics is that they cannot be very efficient. This misunder­

standing comes from the fact that photovoltaics are most commonly employed as "solar

cells." And solar cells are not very efficient, ranging from 10-20% for commercial units and

reaching as high as about 25% for laboratory cells. However the low efficiency is more due

to the characteristics of the solar spectrum than to the photovoltaics devices themselves, es­pecially for the laboratory units with efficiencies of -25%. The problem with the solar spec­trum is that it is very broadband - its ratio of the average photon energy to the width

(FWHM) of the spectrum (Emeanl ~E) is about 1. This is good for color vision but quite bad

for efficient energy conversion.For excimers, however, this ratio is greater than 10. Under

these conditions photovoltaics have intrinsic efficiencies of75-95%.

Photovoltaic cells for use in photon-intermediate direct energy conversion of electricity

will require the development of a doped semiconductor material with a bandgap that match­es the UV radiation. With such photovoltaic cells, a system efficiency of 56% for fusion ion

driven fluorescence has been projected [13]. Studies of fission ion driven fluorescence in­

dicate that system efficiencies of about 40% are possible [12].

Photovoltaic Conversion of Narrowband Fluorescence

For Xe2 *, E,eanl ~ = 14,compared to a corresponding value of 1.3 for the AM2 solar spec­

trum. For a narrow distribution one can have E/Emean -1 and still have 11E0 -1. A narrowband

spectrum will consequently have the highest intrinsic efficiency.

For a given spectrum, the efficiency of conversion is basically determined by the variation

of the irradiance with photon energy and by the substrate bandgap energy, Eg, of the pho­

tovoltaic converter. Complete conversion (100%) is not possible because of the width of

the solar spectrum. This leads to two competing effects on the efficiency. The first effect is

that the energy of all photons with quantum energy hv<E8 is lost because they do not have

sufficient energy to excite electrons from the valence band to the conduction band. The

power density lost in this case is given by

Es

plost = JW(E)dE 0

(eq. 1)

where W(E) is the irradiance in W/cm2/eV. Thus, the lower the bandgap of the photovoltaic

converter, the larger the fraction of the total spectrum converted. Competing with this effect

however is the fact that, for the photons with quantum energy hv>E8 that do contribute, the

photon energy in excess of the bandgap energy is lost. Thus the maximum intrinsic efficien-

470

cy for photovoltaic conversion is assuming an ideal collection device is given in equation 2.

- E J (W(E) ;dE) E

(eq. 2} 'TI;n = -L------

JW(E)dE E,

Typically the effect of the details of the solar radiation spectrum on calculating overall con­

version efficiency is translated into a photon flux density, which then relates to an ideal

short circuit current density. This is convenient because it is a good assumption that each

photon absorbed and collected effectively causes one electron to move around the circuit.

Also after each electron thermalizes, that is, gives off energy in excess of Eg to the lattice, it contributes maximally a constant Eg in energy to the overall process [13].

Figure 4. The theoretical maximum conversion efficiency of photovoltaic cells with vari­ous bandgap energies using either a solar spectrum or a Xe2* spectrum. Band­gap energies associated with Si, GaAs, diamond, and AlN are shown [13].

This contribution is conveniently modeled in the photovoltaic device using the ideal Shock-

ley model

be written

1l

whereNp1

valE>Eg,

Figure4i

ergy ofth trumand,

these coo

materials ing Sian(

thought!< spectrum

tained wi

In contrru

from fig~

junction I not high(

couraginJ

Wic

Table lli

anddesir

intrinsic)

from 759, of ion en

rescence

fluoresce

to 56%.: photone1

fluoresce

gy falls iJ

Radiatio1

1uation 2.

rerallcon­

an ideal ~hat each

te circuit.

1e lattice,

with vari­lm. Band­t [13].

eal Shock-

471

ley model for the p-njunction. Using these concepts the intrinsic conversion efficiency can be written in the following terms [13],

EgJNph(E)dE Eg N(E>Eg) = E - N

n = 8 - E tot 'lin J N (E) EdE mean ph

Es

Eg ~11eg

mean (eq. 3)

where ~ph is the photon flux density, in #/s-cm2-eV, N(E>E8) is the photon flux in the inter­val E>E8 , N101 is the total photon flux, and 1'\eg is the fraction of photons with E>E8 •

Figure 4 is a plot of maximum efficiencies for a p-n junction converter versus bandgap en­ergy of the converter substrate material. Two plots are shown, one for an AM2 solar spec­

trum and one for a Xe2* spectrum. The previously derived equations were used to calculate these curves. Also shown are vertical lines representing the bandgap energies of the two materials theoretically predicted to maximally convert these two spectra. Lines represent­ing Si and diamond are shown for comparison. The approximately 30% maximum is thought to be an upper bound on the ability of a single material junction to convert the solar spectrum. The highest known conversion efficiency for silicon, to date, has been 26% ob­tained with a highly optimized MIS solar cell.

In contrast to the relatively low values for conversion of the solar spectrum, it can be seen from Figure 4 that efficiencies as high as 80% can theoretically be obtained using a p-n junction and converting the Xe2 • spectrum. Although it is still speculative about whether or not high quality p-njunctions can be made in materials with bandgaps above 4 eV, it is en­couraging to note that high conversion efficiencies are possible.

Wide Bandgap Photovoltaic Materials

Table 1 lists several potential wide bandgap materials. Table 1 matches the more efficient

and desirable fluorescers to materials with appropriate band gaps. The theoretical maximum

intrinsic photovoltaic efficiency (the ratio of the bandgap to the mean photon energy ranges

from 75% to 95%) while the corresponding theoretical maximum efficiency for conversion

of ion energy to electrical energy (the product of the photo voltaic efficiency and the fluo­

rescence efficiency) ranges from 30% to 45%. If the most optimistic reported values of the fluorescence efficiency were used, the maximum ion-to-electric efficiency would increase to 56%. The outlook for such cells is hopeful [11]. Rare-gas halide excimers have lower

photon energies (3.5 eV for XeF*, 5.0 eV for KrF*, and 6.4 eV for ArF*) and, while their fluorescence efficiency may be lower than that of the rare-gas excimers, their photon ener­

gy falls in the range of well known semiconductor materials.

Radiation damage to the photovoltaics from X-rays and neutrons is a concern. However, it

472

is well known that ionizing radiation appears to enhance fluorescence absorption efficiency

in continuous-wave insulating crystal lasers. Additionally, if a radiation damaged crystal is

thermally annealed, the damage disappears. Potential crystalline photovoltaic materials

which may experience the positive effects described above exist (Diamond and Aluminum

Nitride).

Integration of Ion Source to Photovoltaics

Ion Source

There are many potential ion sources which can be used for the conversion method. For ex­ample, it is possible to use fission reactions (e.g., u233(n,ff1)ffh, u235(n,ff1)ffh, or Pu239(n,­

ff1)ffh), fusion reactions (when such sources become feasible), or radioisotopes (e.g, A~9• ~5, s~o. Po210, Pu238, etc.). We have chosen in this discussion to focus on the use of ra­

dioisotopes for scaling estimates (see Figure 5).

In these studies the parameter which influenced the systems scale and power source life­

time was the radioisotope halflife (Kr85-10.76 yrs, s~0-29 yrs, Po210-0.38 yrs, and Pu238-

87.74 yrs).

Both the scale size and the gamma ray emitted from the reaction influenced the system's

mass. We were conservative in our estimate of a personnel radiation shield by requiring that

the contact radiation be less than 2.5 millirems per hour (e.g., Kr85 -0.514 MeV y 0.38% of

decays, S~0-no y, Po210-0.802 MeV y0.0011% of decays, and Pu238-0.567 MeV y 5x10-5% of decays).

Coupling of Ion Energy to the Fluorescence Source

Based upon the above criteria, we believe that compact power sources can be made from

radioisotopes. The radioisotope ion source can be gaseous (e.g., Kr85 with a half life of

10.76 years which emits a 0.67 MeV beta 100% ofthe decays and a 0.514 MeV gamma

0.38% of the decays), or it can be in the form of a solid (e.g., a thin film, embedded in a

fiber, or as an aerosol--See Figure 1). The types of solid radioisotopes which can be used

in the mobile power system are: S~0 with a half life of 29 years which emits only a 0.67

MeV beta; Po210 with a halflife of 138.4 days which emits a 5.305 MeV alpha 100% of the

decays and a 0.803 MeV gamma 0.0011% of the decays; and Pu238 with a half life of 86.4

years which emits a 5.5 MeV alpha 100% of the decays and a 0.77 MeV gamma 1x10-5%

of the decays. The Pu238 source was used to power the RTG used in the Voyager spacecraft.

Three RTG units produced 7200 watts of thermal power and 540 watts of electricity regu­

lated to 30 volts from 12,900 grams of the isotope. Using the PENS concept, 12,900 grams

of Pu238 could produce 2,616 Watts of electrical power.

0

2

0

8

6

50

25

00

75

75

so

25

00

75

FigureS.

fficiency ~rystal is

terials uminum

i. For ex-Pu239(n,-

.g.~9. use ofra-

lfce life-ld Pu238_

ystem's iring that

138% of r y5xlo-

de from life of

gamma led in a

be used y a0.67 )%ofthe

'e of86.4 lxlo-5%

>acecraft. city regu­

OOgrams

il

fot

rso 25

00

75

50

75

50

25

00

75

~I Kr-85 15 ye. useful life

em

10

7.sl 0.1 0.2 o.J o.4

Sr-90 ... oo 20 yearlso useful life 60

0

473

Figure 5. Estimation of PENS mass, scale, and decay are shown for Kr85, s~0• Po210, and Pu238. The geometry is assumed to be spherical with a diameter equal to the sys­tem scale estimation. Photovoltaic cells are assumed to surround the fluorescer media and the vessel is shielded with lead.

474

Making an integrated system which produces a significant power density and remains op­

tically thin is a challenge. The use of thin films, fibers, or aerosols along with thin alumi­num or silver coatings have been examined in Prelas, Boody, Kunze, and Miley 1988. With solid materials, an average atomic density of approximately 5x1019 atoms cm-3 can be

achieved for a reasonably optically thin system. The optical transport properties of films, fibers, or aerosols can be enhanced by a thin coating of reflective material [12]. Charged particles can penetrate the thin reflective coating without losing significant energy or sig­nificantly effecting the coating [12].

References

1) M.A. Prelas, "A Potential UV Fusion Light bulb for Energy Conversion", Bult. of the Am. Phys. Soc., 26(1), 1045, 1981: See also Inside R&D, Vol. 10, Number 41 (Oct. 14, 1981).

2) M. A. Prelas, F. P. Boody, M. Zediker and M. Rowe, "A Direct Energy Conversion Technique Based on an Aerosol Core Reactor Concept", 1984 IEEE Int. Conf. on Plas­ma Sci., IEEE Publication Number: 84CH1958-8, 38, 1984.

3) M.A. Prelas, E. J. Charlson, F. P. Boody, and G. H. Miley, Prog. In Nuclear Energy, 23 (3), pp. 223-240 (1990).

4) D. J. Mencin and M.A. Prelas, "Low Temperature Gaseous Core Reactors Using Ura­nium Particles Trapped in C60 Cages," Proceedings of Nuclear Technologies for Space Exploration," Sponsored by the Idaho Section of the American Nuclear Society, Snow King Resort, Jackson Hole Wyoming, August 16-19, 1992.

5) Zhou K, Charlson E. M., Charlson E. J., Meese J., Stacy T., Popovici G., and Prelas M, Appl. Phys. Lett., 61 (9), 1119-1121 (1992).

6) C. K. Chen, B. Nechay and B. Tsaur, IEEE Trans. on Electron Dev. 38, 1094 (1991).

7) T. Stacy, et. al., "Rectifying Contact Formation with Indium on Polycrystalline p-type Hot Filament CVD Diamond Utilizing Molecular Ion Implantation," Accepted for Publication in Journal of Applied Physics (February, 1993).

8) Galina Popovici, T. Sung, M. Prelas, and S. Khasawinah, "Evidence for n-type Dia­mond," Gordon Conference on Diamond Films, June 1994.

9) W. M Yirn, E. J. Stofko, P. J. Zanzucchi, J. I. Pankove, M. Ettenberg, and S. L. Bilbert, J. Appl. Phys., 44, 29 (1973)

10) R. F. Davis, Proc. IEEE, 79, No.5, 702 (1991).

11) M. Prelas, E. J. Charlson, E. M. Charlson, J. Meese, G. Popovici, and T. ~tacy, "Dia­mond Photovoltaic in Energy Conversion," Second International Conference on the Applications of Diamond Films and Related Materials, M. Yoshikawa, M. Murakawa, Y. Tzeng and W. A. Yarbrough editors, MYU, Tokyo (ISBN 4-943995-07-1), 329-334 (1993)

12) M.A. Prelas, F. P. Boody, G. H. Miley, and J. Kunze, "Nuclear-Driven Flashlamps", Lasers and Particle Beams, 6(1), 25, 1988; also, M.A. Prelas, and S. Loyalka, Progress in Nuclear Energy, 8, 35-52, 1981

13) M.A. Prelas, E. J. Charlson, E. M. Charlson, J. Meese, G. Popovici, and T. Stacy, "Di­amond and Diamond Like Substrates as First Wall Materials in Inertial Confinement Fusion," Lasers and Particle Beams, 11(1), 65-79 (1993).

CON NI~

T. Sl Depa MOt *Rd

Abstr

initial issue~

dism rectif'

1. In

seven withir persp a laq contir direct eV). for o ultrav both mater exper meas1 signifi in dire Zincb Eg=6 Howe in bo

M.A. 1 © 199