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Light simulation of molecular beam epitaxy
42/number Printed in Great Britain
Vacuum/volume
12ipages
735 to 739/l
Light simulation Leszek Michalak L ublin, Poland received
6 June
and
Bogdan
991
0042-207x/91 $3.00+.00 @ 1991 Pergamon Press plc
of molecular Adamczyk,
1990 and in final form 14 November
Institute
beam epitaxy
of Physics, Marie Curie-Skfodowska
University,
20-031
1990
On the basis of the experiments described in their previous papers, the authors have presented the analogy between an effusion molecular beam applied in epitaxy technology and a light beam. A molecular beam is formed by the longitudinal channel of a molecular oven and a light beam is formed by a similar channel, lined inside with corrugated aluminium foil with a high reflection coefficient. The transverse intensity distribution of modelling beams formed by channels of different shapes is presented.
1. Introduction
The authors see an analogy between a molecular beam and a light beam (Figure I). This analogy was found to be especially close in the case of a molecular beam emitted by an effusive cell fitted with a flat round hole and a light beam emitted by a flat round ground-glass plate illuminated at the back’. In the case of longitudinal channels. this close analogy was found too’.‘. In the simulation system, the light from a bulb was introduced into the channel via a diffusing ground-glass plate. The inside of the channel was lined with corrugated aluminium foil with a high reflection coefficient. Due to the corrugation, the light was reflected from the foil in a chaotic way, just like molecules (adsorption and dcsorption) from the wall of the actual channel. The light beam intensity distribution was measured with a pho-
todctector. It means that the high vacuum processes are investigated under normal pressure. The idea of simulating an effusion molecular beam with a light beam was reported by Fedorenko in 1967’. His model of ‘light etrusion channels’ with round and rectangular cross-sections had been painted inside with a white paint. The analogy between the scattering gas atoms reflected by a surface and the scattering of clcctromagnetic radiation by a randomly rough surface was also reported by Williams5. Dunham and Hirth in their theoretical paper have discussed the effusion of molecules from conical channels of various gcometrical combinations and surface propcrtiesh. Monte Carlo calculations for effusion molecular beam generation with conical channels have been presented by F&t&s’.
(a)
/
gloss plate
---
/
----‘-m-Y__
3,
Figure I. (a) Cosine shaped Intensity distribution distribution formed by the round flat ground-glass and an ‘effusion’ light beam formed by the channel
Jo
photcdetector (b)
of the molecular beam formed by a round effusion whole in the Knudsen’s cell and the light plate illuminated with the bulb at the back. (b) Molecular beam formed by the effusion channel with the diffuser inside. 735
L Michalak
and B Adamcryk
Light
slmulatlon
of MBE
photodetector \
ground -gloss plate \
_
L Michalak
and 6 Adamczyk:
Light simulation
of MBE
lb)
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1
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1.5
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Figure 6. (a) Normalized transverse results presented in Figure h(a).
distributions
of the ‘eft‘usion’ light beams
generated
by three dillerent
I
1
of
channels.
11
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Figure 7. (a) Normalized transverse presented in the Figure 7(a).
of
distributions
position
of ‘efl’usion‘ light beam generated
by three different
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channels.
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(b) Not normalized
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Figure IO. (a) Transverse distributions results prcscntcd in the Figure IO(a).
I‘or the case where the plate is cxposcd
In analogy with Figure 6, Figures 7,8 and 9 show cross-sections of the layers presented in the Figures 3, 4 and 5. respectively. Figure 10 presents the situation where the plate is exposed to an ‘effusion’ light beam diagonally under the angle of 25 As a result of such exposition the thickness of the layer on the plate would be very in-homogeneous.
by a beam dugonally
of
detector
under the angle 25
(b) Not normalized
values 01
Acknowledgements The authors wish to thank Prof M A Herman and Prof J Marks for helpful suggestions and co-operation. This work was carried out under the Polish Central Program of Developmental Research CPBR 8.3.6. References
4. Conclusion The analogy obtained between the ‘effusion’ light beam and the effusion molecular beam intensity distributions from previous experiments ’ ’ seems to enable the use of the light simulation in the MBE cast. It must be taken into account, however, that the light reflection coefficient of the aluminium foil is less than I. moreover. that it must be corrugated. This is as if a fraction of the molecules effusing through the channel in the oven were permanently adsorbed by the wall. However, the method may give preliminary information about the parameters of effusion molecular beams gcncratcd by a possible MBE system. This method may be further improved.
’ B Adamczyk and L Michalak, A b’r?ircr.vit~a Mrrric C’uric,-Sklo~/o~l,sku, Section AAA, XXVIII. 15, 179 (19X3). ’ B Adamczyk and L Michalak. Int J MU.FS.‘$c,c/r 10/z Proc~c,s.\. 69, 163 (1986). ‘B Adamczyk and L Michalak. It?/ J A4rrs.c Spe(,tr ion P,ocrss, 71, 21 I (1986). ‘A I Fedorenko. Prihoul_ Tekh Eksp. 6, 123 (1967). ‘N M R Williams, J Ph~s D: Appl P/IJ~.c,4, 1315 (1971). “T E Dunham and J P Hirth, J Chun P/ITS. 49, 4650 (1968). ‘L Fiist(iss, Vucuum. 37, 75 (19X7). ‘8 R Pamplin, Molecular Bwm Epita.x~. Pergamon Press, Oxford (1980). “T Yamashita. T Tomita and T Sakurai, ~q~rm J Appl HIICY. 26, II92 (1987). ‘” M A Herman and H Sitter, Molecular Beam Epitaxv (Springer Series in Materials Science), 7 (1988).
739
Vacuum/volume
12ipages
735 to 739/l
Light simulation Leszek Michalak L ublin, Poland received
6 June
and
Bogdan
991
0042-207x/91 $3.00+.00 @ 1991 Pergamon Press plc
of molecular Adamczyk,
1990 and in final form 14 November
Institute
beam epitaxy
of Physics, Marie Curie-Skfodowska
University,
20-031
1990
On the basis of the experiments described in their previous papers, the authors have presented the analogy between an effusion molecular beam applied in epitaxy technology and a light beam. A molecular beam is formed by the longitudinal channel of a molecular oven and a light beam is formed by a similar channel, lined inside with corrugated aluminium foil with a high reflection coefficient. The transverse intensity distribution of modelling beams formed by channels of different shapes is presented.
1. Introduction
The authors see an analogy between a molecular beam and a light beam (Figure I). This analogy was found to be especially close in the case of a molecular beam emitted by an effusive cell fitted with a flat round hole and a light beam emitted by a flat round ground-glass plate illuminated at the back’. In the case of longitudinal channels. this close analogy was found too’.‘. In the simulation system, the light from a bulb was introduced into the channel via a diffusing ground-glass plate. The inside of the channel was lined with corrugated aluminium foil with a high reflection coefficient. Due to the corrugation, the light was reflected from the foil in a chaotic way, just like molecules (adsorption and dcsorption) from the wall of the actual channel. The light beam intensity distribution was measured with a pho-
todctector. It means that the high vacuum processes are investigated under normal pressure. The idea of simulating an effusion molecular beam with a light beam was reported by Fedorenko in 1967’. His model of ‘light etrusion channels’ with round and rectangular cross-sections had been painted inside with a white paint. The analogy between the scattering gas atoms reflected by a surface and the scattering of clcctromagnetic radiation by a randomly rough surface was also reported by Williams5. Dunham and Hirth in their theoretical paper have discussed the effusion of molecules from conical channels of various gcometrical combinations and surface propcrtiesh. Monte Carlo calculations for effusion molecular beam generation with conical channels have been presented by F&t&s’.
(a)
/
gloss plate
---
/
----‘-m-Y__
3,
Figure I. (a) Cosine shaped Intensity distribution distribution formed by the round flat ground-glass and an ‘effusion’ light beam formed by the channel
Jo
photcdetector (b)
of the molecular beam formed by a round effusion whole in the Knudsen’s cell and the light plate illuminated with the bulb at the back. (b) Molecular beam formed by the effusion channel with the diffuser inside. 735
L Michalak
and B Adamcryk
Light
slmulatlon
of MBE
photodetector \
ground -gloss plate \
_
L Michalak
and 6 Adamczyk:
Light simulation
of MBE
lb)
Aox
1
BXX
1.5
CA,
C,2
A,A-AAAAAAAAAAAAAAAAAAAAAA~AAAA-A
n
C
0
250
“In
poshion
Figure 6. (a) Normalized transverse results presented in Figure h(a).
distributions
of the ‘eft‘usion’ light beams
generated
by three dillerent
I
1
of
channels.
11
(b)
de!ecior
I
(b) Not normalized
I
1
values 01
I1
I
,o-00000000000000,
0
“\
A
1 0
Or
A
1
B x x 1.6 c
A ”
1.6
A\
A
/I
\
“\
\ A
r:no
\ h
0 position
Figure 7. (a) Normalized transverse presented in the Figure 7(a).
of
distributions
position
of ‘efl’usion‘ light beam generated
by three different
mmn
0
250 detector
channels.
of
detector
(b) Not normalized
values of results
737
L Michalak
and6
Adamczyk: 1
(a)
Light slmulatlon T
I
of MBE
IT-l,
/
,AXAXgXAOXAOxAOXAO~~~~ do000
1
03
\ i
i 0
"1
PI0
0
1,8
B
x
I
c
‘4
x 2.1
0
0
/
X
,~XXrXXXXXXXXXXXXXXXX~
x
B
x
\
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i” AA
\
c
I A’ / J I
‘A”\
i x
x
’
x
A
!
\
A
A ‘s
A
250
250mm
0 ~os’t~on
of
detector
1
r
7
I
I
1
1
oQ~OOOOOOOOOOOOOOOOOOOOOOOOO~o.o A
i
20 -
A0.1
BX
x 2.9
CI
.2
detector 10 -
positjon
of
detector
,
6
L Michalak
andB I
Light simulation
Adamczyk: I
,
,
I
,
,
of MBE ,
(a)
,
,
,
.OF.,
o A“
oiSO
(b)
X
x
oA
00°
XOA
oA
Ax
‘O\
oOOO” 0
06’
oo”
\
A
0
O0
oAxo A0
xl
B x
x 1.7
CA
x i,9
0’ 0
00
\
00°
xx xx xx XXX
3-
detector
xXxX
XX iXAbaA /
0
/
B
A
0
00
XX
xXxXx ‘X
AAA
AAA~ XXX AA~ AAA~
AAAA
C
A’
“”
“\
”
vmtion
Figure IO. (a) Transverse distributions results prcscntcd in the Figure IO(a).
I‘or the case where the plate is cxposcd
In analogy with Figure 6, Figures 7,8 and 9 show cross-sections of the layers presented in the Figures 3, 4 and 5. respectively. Figure 10 presents the situation where the plate is exposed to an ‘effusion’ light beam diagonally under the angle of 25 As a result of such exposition the thickness of the layer on the plate would be very in-homogeneous.
by a beam dugonally
of
detector
under the angle 25
(b) Not normalized
values 01
Acknowledgements The authors wish to thank Prof M A Herman and Prof J Marks for helpful suggestions and co-operation. This work was carried out under the Polish Central Program of Developmental Research CPBR 8.3.6. References
4. Conclusion The analogy obtained between the ‘effusion’ light beam and the effusion molecular beam intensity distributions from previous experiments ’ ’ seems to enable the use of the light simulation in the MBE cast. It must be taken into account, however, that the light reflection coefficient of the aluminium foil is less than I. moreover. that it must be corrugated. This is as if a fraction of the molecules effusing through the channel in the oven were permanently adsorbed by the wall. However, the method may give preliminary information about the parameters of effusion molecular beams gcncratcd by a possible MBE system. This method may be further improved.
’ B Adamczyk and L Michalak, A b’r?ircr.vit~a Mrrric C’uric,-Sklo~/o~l,sku, Section AAA, XXVIII. 15, 179 (19X3). ’ B Adamczyk and L Michalak. Int J MU.FS.‘$c,c/r 10/z Proc~c,s.\. 69, 163 (1986). ‘B Adamczyk and L Michalak. It?/ J A4rrs.c Spe(,tr ion P,ocrss, 71, 21 I (1986). ‘A I Fedorenko. Prihoul_ Tekh Eksp. 6, 123 (1967). ‘N M R Williams, J Ph~s D: Appl P/IJ~.c,4, 1315 (1971). “T E Dunham and J P Hirth, J Chun P/ITS. 49, 4650 (1968). ‘L Fiist(iss, Vucuum. 37, 75 (19X7). ‘8 R Pamplin, Molecular Bwm Epita.x~. Pergamon Press, Oxford (1980). “T Yamashita. T Tomita and T Sakurai, ~q~rm J Appl HIICY. 26, II92 (1987). ‘” M A Herman and H Sitter, Molecular Beam Epitaxv (Springer Series in Materials Science), 7 (1988).
739