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Arsenic trisulfide
Sample preparation
As2S3 films
were
deposited on silicon substrate by thermal evaporation (Pressure < 2.10
-5 Torr, deposition rate ~ 100 Å/s). They were annealed
for 2 hours at 180 oC under vacuum before measurements.
As2S3 glasses were synthesized in our laboratory by
Dr. Mehmet Bayindir and Nicholas Orf.
Measurement and analysis
We performed a three-angle measurement at
71, 72 and 73 degree incident angle. To extract the thickness
of the deposited film, the ellipsometric parameters were fitted
using the Levenberg-Marquardt regression method with a Cauchy-like
dispersion relation:
n=A+B/λ2+c/λ4
k=D/λ+E/λ3+F/λ5
where λ is
the wavelength and A,B,C,D,E,F
are fitting parameters. The deduced dispersion relation was
used to generate starting values in the Levenberg-Marquardt regression
method to calculate the n and k values at every wavelength (independently
of any model). The standard deviation of the fit was ~ 10-3 and
the corresponding film’s thickness equal to 107.3 nm.
The n-k curves reveal that the edge of the absorption band due to
the material large electronic bandgap is at ~ 2.5 eV. The n values
are lower by ~ 1.4% than the literature values (ref.1), which can be
attributed to variations in the glass stoichiometry and/or in the
melting and deposition conditions, resulting in a different density of
the film, and tend to 2.734 in the infra-red. No significant absorption
was measured above 0.9 microns as sometimes exhibited by chalcogenide
glasses between 1 and 6 microns and 8 and 13 microns due to traces of
H2O, H2Se and other oxide impurities (ref.2).
1.
Handbook of Optics, Fundamentals,
Techniques, & Design, eds. Bass, M., Stryland, E. W. V., Williams,
D. R. & Wolfe, W. L., McGraw-Hill, INC., 1995
2. Savage, J. A., Optical properties of chalcogenide
glasses Journal of Non-Crystalline Solids 47, 101-116 (1982).
Results
Wavelength
(microns)
|
n
|
k
|
0.251
0.2672
0.2834
0.2996
0.3158
0.3319
0.3481
0.3643
0.3805
0.3967
0.4129
0.4291
0.4453
0.4615
0.4777
0.4939
0.5101
0.5263
0.5424
0.5586
0.5748
0.591
0.6072
0.6234
0.6396
0.6558
0.672
0.6882
0.7044
0.7206
0.7368
0.7529
0.7691
0.7853
0.8015
0.8177
0.8339
0.8501
0.8663
0.8825
0.8987
0.9149
0.9311
0.9473
0.9634
0.9796
0.9958
1.012
1.0282
1.0444
1.0606
1.0768
1.093
1.1092
1.1254
1.1416
1.1578
1.1739
1.1901
1.2063
1.2225
1.2387
1.2549
1.2711
1.2873
1.3035
1.3197
1.3359
1.3521
1.3683
1.3845
1.4006
1.4168
1.433
1.4492
1.4654
1.4816
1.4978
1.514
1.5302
1.5464
1.5626
1.5788
1.595
1.6111
1.6273
1.6435
1.6597
1.6759
1.6921
1.7083
1.7245
1.7407
1.7569
1.7731
1.7893
1.8055
1.8216
1.8378
1.854
1.8702
1.8864
1.9026
1.9188
1.935
1.9512
1.9674
1.9836
1.9998
|
2.249
2.395
2.547
2.679
2.781
2.863
2.923
2.945
2.966
2.968
2.952
2.924
2.889
2.849
2.805
2.759
2.719
2.684
2.656
2.631
2.604
2.587
2.571
2.557
2.545
2.535
2.525
2.516
2.508
2.501
2.495
2.490
2.485
2.479
2.474
2.471
2.467
2.461
2.458
2.456
2.454
2.452
2.451
2.449
2.447
2.444
2.443
2.441
2.439
2.437
2.435
2.434
2.433
2.432
2.431
2.429
2.427
2.425
2.425
2.424
2.423
2.420
2.417
2.415
2.415
2.415
2.415
2.414
2.412
2.411
2.409
2.406
2.404
2.402
2.401
2.401
2.401
2.401
2.401
2.399
2.397
2.395
2.393
2.391
2.391
2.390
2.390
2.390
2.390
2.389
2.388
2.387
2.386
2.385
2.384
2.383
2.382
2.381
2.380
2.380
2.379
2.378
2.378
2.377
2.377
2.377
2.377
2.377
2.378
|
1.355
1.324
1.255
1.151
1.034
0.916
0.794
0.645
0.543
0.437
0.339
0.243
0.159
0.0994
0.0507
0.0237
0.00783
0.00511
0.00369
0.00252
0.00158
0.000948
0.000729
0.000516
0.000426
0.000323
0.000223
0.000126
0.000077
0.000023
0.000023
0.000013
0.000005
0.000003
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
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