Summary of research in solid state spectroscopy on variety of material

Walker, W. C.

English

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J 
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FINAL REPORT 
Research Grant NGR 05-010-001 
National Aeronautics and Space Administration 
and 
0 
University of California,  Santa Barbara 
ULTMVIOLET SOLID STATE Sl3CTROSCOPY 
IN THE SPECTRAL REGION 3309 - 300 A 
Grant Period: October 1, 1960 - December 1, 1969 
Pr inc ipa l  Investigator 
William C. Wzlker 
Professor of  Fhysics 
https://ntrs.nasa.gov/search.jsp?R=19700008218 2020-03-12T01:44:20+00:00Z
INTRODUCTION 
Heseazch G r a n t  NGR 05-010-031 began October 1, 1960 and terminated 
December 1, 1969. 
out i n  the area of so l id  s t a t e  spectroscopy on a var ie ty  of materials 
of i n t e r e s t  t o  both u l t r av io l e t  op t ics  and so l id  s t a t e  physics. 
During t h i s  period experimental research was car r ied  
Studies 
were aimed pr inc ipa l ly  a t  obtaining a de ta i led  knowledge of fundamental 
e lectronic  spectra and o p t i c a l  propert ies  from near-normal incidence 
reflectance measurements obtained over a broad range from 3000 - 300 A 
(4 - 40 eV). I n  the course of  the  research, o ther  techniques involving 
-photoemission, 1-dnescence ,  thin-f i lm transmission, and modulation 
spectroscopy were also employed. This research vas  among the  f i rs t  t o  
obtain l o w  temperature highly resolved exciton and interband spectra  
f o r  strongly ion ic  insu la tors  and cor re la te  them with spec i f ic  e lec-  
t ron ic  s t a t e s  i n  the solid.  The most s igni f icant  r e su l t s  of the 
research were: 
a. 
b. 
C. 
d. 
e ,  
A deta i led  understanding o f  the  interband spectra of several  
alkali halides and alkal ine ea r th  oxides f o r  which the f irst  
cor re la t ions  were made of  spec t ra l  data  and empirical psuedo- 
po ten t i a l  band s t ruc ture  calculat ions i n  ionic  sol ids ,  
Observation of exciton-phonon bound s t a t e s  i n  a lkal ine ea r th  
oxide spectra., 
The f i r s t  observation of  valence band, spin-orbit  s p l i t t i n g  
i n  metal oxides, 
The development and ea r ly  use of' po lar izers  fo r  far u l t r av io l e t  
spectroscopy, and 
Evaluation of  the op t i ca l  constants of a var ie ty  of u l t r av io l e t  
o p t i c a l  materials above the fundamental absorption edge. 
-2 - 
S W R Y  OF REXEARCH 
The i n i t i a l  e f f o r t  i n  the  research was a t h i n - f i h  transmission 
study of  plasmon e f f e c t s  i n  I n  and Pb undertaken with the help of A. 
Alkezweeny. Plasmon induced transmission bands i n  both materials were 
observed and used t o  determine both plasmon energies and d-band 
exc i ta t ions  i n  these m a t e r i a l s .  The r e s u l t s  were reported i n  J. Phys. 
Chem. Solids,  V o l .  - 24, 1667 (1963). 
Simultaneous with the above, J. Osantowski studied the fundamental 
spectra of CdS and ZnS i n  normal incidence reflectance.  Both spectra 
were found t o  be r i c h  i n  s t ruc ture  which was l a t e r  ident i f ied  with 
density-of-states maxima and interband edges. The r e s u l t s  were reported 
t o  the  American Physical Society i n  March 1964 and published i n  J. Phys. 
Chem. Solids,  Vol, - 25, 778 (1963) and J. O p t .  SOC. Am., Vol, 53, 399 
(1963) 
X-ray i r r a d i a t i o n  e f fec ts  near the absorption edge of LiF were 
studied by E. Schpansky. An i r r a d i a t i o n  induced absorption band a t  
11.1 eV was discovered and i t s  r e l a t ion  t o  o ther  color centers  i n  LiF 
determined through bleaching experiments. The r e s u l t s  were reported a t  
the  F i r s t  In te rna t iona l  Conference on Vacuum Ul t rav io le t  Physics, Apr i l  
1962 and published i n  J. Quant. Spectrosc. Radiat. Transfer, Vol. - 2, 
613 (1962). ' 
One of the  irrportant r e s u l t s  of t h i s  research emerged from a 
comprehensive study of the fundamental spectrum of diamond begun by 
J. Osantowski and completed by R. A. Roberts. For t h i s  work, a lo!.; 
-3- 
temperature, vacuum reflectometer was constructed for use i n  the range 
4 - 30 eV at 300 K a.nd 4 - 12 eV a t  80 K. 
three main diamond types (I, I I a ,  and I I b )  were obtained and the 
Reflectance spectra of the  
spec t r a l  s t ruc ture  associated with spec i f ic  c r i t i c a l  points  by com- 
parison with band s t ruc ture  calculations.  The r e s u l t s  of this study 
which both substaniated and corrected vsrious aspects of' previously 
published spectra  were published i n  Phys. Rev. Let ters ,  Vol. I 17, 302 
(1966) and Phys. Rev., Vol. - 161, No, 3, 730 (1967). 
I n  about 1964, improvements i n  band s t ruc ture  ca lcu la t iona l  
techniques and theo re t i ca l  advances i n  the in te rpre ta t ion  of fundamental 
spectra  showed t h a t  a de ta i led  determination of e lectronic  s t a t e s  i n  
insu la tors  was feasible,  provided accurate, low temperature ref lectance 
spectra  could be obtained from clean s ingle  c rys ta l s .  From 1354 u n t i l  
the  termination of the grant ,  the research was focussed on t h i s  problem. 
Measurements were undertaken on a var ie ty  of  a l k a l i  halides (KI ,  RbI, LiF,  
NaC1, and KC1)  and alkal ine ea r th  oxides (BeO, N g O ,  and CaO). New 
techniques, such a s  a pi le-of  p l a t e s  po lar izer  fo r  the f a r  u l t r av io l e t ,  
an improved low temperature (10 K)  reflectometer, and a pulsed high- 
energy l i g h t  source were developed t o  car ry  out  the research. 
\ 
The explanation of t he  MgO s p e c t r m  by comparison with the 
empirical  psuedo-potential calculat ion of M. Cohen and P. J, Lin proved 
t o  be the key t o  the problem and i n  r q i d  succession data  taken by D. 
M. Roessler 0.n NaCl and K C 1  were in te rpre ted  i n  terms of t he  MgO band 
s t ruc tureo  Later, de ta i led  band s t ruc ture  calculat ions by Cohen and 
Fong agreed i n  t h e i r  major aspects with our assignments. 
The exci ton.spectra  of the  alkal ine e a r t h  oxides (BeO, MgO,  and 
-4- 
CaO) proved t o  present one of the most i n t e re s t ing  problems of a l l .  
I n  addition t o  providing the f i r s t  measurement of the spin-orbit  s p l i t t i n g  
of the  oxygen ion valence band, they showed addi t ional  doublet s p l i t t i n g  
wi th  spacings near the o p t i c a l  phonon energy of the c rys ta l .  
suggestion by Toyozawa and Hermanson t h a t  these were exciton-phonon 
bound s t a t e s  opened up a new, f r u i t f u l  f i e l d  of research t h a t  i s  current ly  
of considerable in t e re s t .  
The 
The r e su l t s  of  the work since 1964 were published i n  several  
journals,  co-authored with D, M. Rogssler, E. Loh, and R.  Whited. 
PUBLICATIONS 
A complete l i s t  of publications resu l t ing  from t h i s  research i s  
attached. Reprints of most of these papers have already been submitted; 
those for the  one outstanding paper w i l l  be submitted a s  soon a s  they 
a re  received by the author. 
CONCLUSION 
The present research pro jec t  made fundamental contributions t o  . 
so l id  s t a t e  physics i n  general  and t o  the f i e l d  of  u l t r av io l e t  o p t i c a l  
materials i n  par t icu lar .  
of plasmon and d-band energies i n  metals t o  a de ta i led  understznding of 
e lectronic  s t a t e s  i n  ionic  insulators .  the course of the experiments, 
These contributions range from the determination 
new u l t r av io l e t  spectroscopic technique s and i n s t  rwaent a t  ion we re  
developed which ,\:ill provide the bas i s  f o r  continuing ;cork i n  the f i e ld .  
The alkal ine ear th  oxides were sho-,-m to be among the bes t  materials f o r  
s tudies  of the exci t ing new phenomena of exciton-phonon bound s ta tes .  
-5 - 
PUBLICATIONS 
Wi1lia.m C. Walker, author 
Extreme Ul t rav io le t  Reflection Spectrum of  LiF ,  J. Opt .  Soc. Am,, V o l .  
52, 223 (1962) with J. Osantowski -
Reflection Spectrum of Cubic Zinc su l f ide  i n  the  Interband Transi t ion 
Region, J. Opt. SOC. Am., Vol. 53, 399-400 (March 1963) with J, 
OSantO!?Ski  
-
Vacuum Ul t rav io le t  Optical  and Photoelectric Ef fec ts  i n  Solids,  J. 
Quant. Spectrosc. Radiat. Transfe?, Vol. 2, 613-620 (1962). 
given as an inv i ted  paper at the "Fi rs t  Iz te rna t iona l  Conference on 
Vacuum Ultraviolet  Radiation Physics", April ,  1962 
Also 
a-Band Transi t ions i n  Solids,  J. Phys. Chem. Solids,  Vol. 24, 1667-1669 -
(1963) 
The Ul t rav io le t  Reflection Spectrum of Cadmium Sulfide,  J. Phys. Chem. 
Solids,  Vol. - 25, 778-779 (1963) with J. 0santo:rqki 
Ul t rav io le t  Optical  Propert ies  of Diarnond, Phys. Rev., V o l .  - 134, No. 
U, A153-Al57 (1964) with J. Osantovski 
Polar izat ion Dependence of the  Far Ul t rav io le t  Optical  Transit ions i n  
CdS, Phys. Rev, Let ters ,  Vol. - 13, 51 (1964) 
Pile-of-Plates Polar izer  f o r  t he  Vacuum Ul t rav io le t ,  Appl. Opt . ,  Vol. 
- 3, 1457 (1964) 
Fine Structure i n  t he  Direct Absorption Edge of Diamond, Phys. Rev. 
Letters, Vol. 17, 302 (1966) with R. A. doberts and D. M. Roessler 
Spin-Orbit S p l i t t i n g  of t h e  r Exciton i n  MgO, Phys. Rev. Let ters ,  V o l .  
17, 319 (1966) with D. M. Roessler 
Ultra-Violet Optical  Propert ies  and Electronic Band Structure of  
Magnesim Oxide, Phys. Rev., Vol. -, 155 IJo. 3, 992 (1967) with M. L. 
Cohen, P. J. Lin and D. PI. Roessler 
Exciton Structure i n  the  Ultraviolet  Spectra of K I  and RbI, J. Opt.  Soc, 
Am., Vol. 57, No. 5, 677 (1967) with D. M. Roessler -
Electronic  Spectrum of Crystal l ine Lithium Fluoride, J. Phys, Chem. 
Solids,  V o l .  I 28, 1507 (1967) with D. 121. Roessler 
-6 - 
Publications (continued) 
W i l l i a m  C. Walker, author 
Electronic Spectrum and Ultraviolet  Optical  Properties of Crystal l ine 
NO, Phys. Rev., V o l .  - 159, No. 3, 733 (1967) with D. 14. Roessler 
Optical  Study of the Electronic Structure of Dia,mnd, Phys, Rev., V o l .  
161, No. 3, 730 (1967) with R. A. Roberts -
Optical Constants of MgO and L i F  i n  the Far Ultraviolet ,  J. Opt. 'SOC. 
Am., V o l .  57, iqo. 6, 835 (1967) with D. M. Roessler -
Electronic Spectra of Crystall ine N a C l  and KC1,  Phys. Rev., Vol. -, 166 
No, 3, 599 (1968) with D. M. Roessler 
Phonon-Induced Sp l i t t i ng  of Exciton Lines i n  YgO and BeO, Phys. Rev. 
Let ters ,  Vol, - 20, 847 (1968) with D. M. Roessler and E. Loh 
Optical  Constants of NaCl and K C 1  i n  the Far Ultraviolet ,  J. Opt .  SOC. 
Am., V o l .  - 58, No. 2, 279 (1368) with D. 14. Roessler 
Electronic Spectrum of Crystal l ine Beryllium Oxide, J, Phys. Chem, 
Solids, Vol. - 30, 157 (S$9) with D. M. Roessler and E. Loh 
Exciton Spectra of CaO and MgO, Phys. Rev. Let ters ,  Vol. - 22, 1428 (1969) 
with R. Whited 
Exciton and Interband Spectra of Crystal l ine CaO, Phys. Rev., Dec. 15 
(1969) with R. Whited ( t o  be published) 
-7- 
€ESE-ARCH PARTICIPANTS 
Both postdoctoral  and graduate research assistance were employed 
on the  grant. A b r i e f  account of these personnel i s  given below i n  
tabular  form. 
Name 
A. Matsui 
D. Zoessler 
R. Roberts 
R. Whited 
J. Osantorsski 
L. Hughey 
E. Bchpanslcy 
A. ALkezweeny 
Posi t  ion 
Po s tdoc tora l  
Fellow 
.I 1 
Re search 
A s s  i s  t ant 
I1 
I? 
11 
If 
ir 
Degsee Awarded 
i 
Ph.D. 
Pn.D . 
M.A. 
M.A. 
M.A. 
MOA. 
Present Po s i t  ion 
Sano Electronics 
Tokyo, Japan 
B e l l  Laboratories 
Naval Research 
China Lake 
Goddard Space F l igh t  
N.B.S. 
Colorado Sta te  
University 
Meteorological 
Research, Inc. 
-8 - 
DISSERTATION AND THESIS TITUS 
Name 
Ph.D. Disser ta t ions 
T i t l e  
Exciton and Interband Spectra. of Crystal l ine C a O  -- - _I R. Whited 
Optical  Study of the  Electronic  Band Structure' of 
Diamond 
--- I R. Roberts 
M.A. Theses 
Photoelectron Energy Distr ibut ions i n  the Far 
Ult rav io le t  
--_c 
L. Hughey 
J. Osantowski Ref lec t iv i ty  of Solids i n  the  Vacuum Ultraviolet  - --
E. Schpansky Ul t rav io le t  Color Centers i n  X-irradiated Lithium -- -
F l o  w i d e  
A. Alkezweeny Extreme Ultra.violet  Photon Absorption - i n Metals 
-9- 


Ultraviolet solid state spectroscopy in the spectral region 3000 - 300 A Final report, 1 Oct. 1960 - 1 Dec. 1969

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