1. E L L I O T Y O U N G – L Y D I N G G R O U P
U N I V E R S I T Y O F I L L I N O I S
O C T O B E R 2 0 T H , 2 0 1 5
Characterization of Low-Dimensional
Tantalum Trisulfide using Scanning
Tunneling Microscopy
1

2. Where I Work
2

3. Where I Work
3

4. Introduction
 Tantalum trisulfide (TaS3) and other transition metal trichalcogenides have
unique electronic properties
 Approach material limits as silicon-based devices continue to shrink – look to
alternative materials to continue improvement in integrated circuits industry
 Hard to use CNTs due to difficulties with CVD fabrication techniques,
especially size differences in the nanotubes
 TaS3 retains one-dimensional structure with same dimensions every time
Meerschaut et al. J. Less Common Met 1975
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5. Background
 Orthorhombic TaS3 deposited via DCT on H-passivated p-type Si (100)
 Bulk crystal grown via physical vapor transport
 Planar arrangement of crystal chains thought to
resemble structure of ZrSe3
 Previous work gives lattice constants a = 36.804 Å,
b = 15.173 Å, and c = 3.340 Å (Bjerkelund et al. 1964)
 Metallic at room temp. in bulk and at nano scale
T.B. Kilpatrick thesisLyding et al. Phys. Rev. B 1989
5
b
a

6. Background
6
Roucau et al. Phys. status solidi 1980
a = 36.804 Å
b = 15.173 Å
c = 3.340 Å
b
a
c

7. Goals
 Measure step height, row spacing, and modulation
along row axis and compare with previously reported
lattice constants
 Investigate band gap for different flake sizes TaS3
 Obtain high-resolution images of two-dimensional
TaS3
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8. Step Height
11.7 Å 12.5 Å
Histogram analysis shows a step height
of approximately 12 Å
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Roucau et al. Phys. status solidi 1980
Image taken at 0.1 nA, -3.5 V

9. Row Spacing
Average row spacing: 15.5 Å
Local modulation: 4.48 Å
9
Lyding et al. Phys. Rev. B 1989
Image taken at 0.1 nA, -3.5 V

10. Row Spacing
Row spacing: 16.88 Å
Local modulation: 4.15 Å
Shows three secondary peaks instead of just two and
with peak spacing ~0.3 Å smaller
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Images taken at 0.1 nA, -3.5 V

11. Row Spacing
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Images taken at 0.1 nA, -3.5 V

12. Measuring Modulation Along Row Axis
Measured spacing between features along row axis ~ 12.1 Å
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Meerschaut et al. J. Less Common Met 1975
Images taken at 0.1 nA, -2.5 V

13. Measuring Modulation Along Row Axis
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Image taken at 0.1 nA, -2.5 V

14. Small Flake Analysis
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Image taken at 0.1 nA, -3.5 V

15. Band Gap for Small Flake
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Images taken at 0.1 nA, -2.5 V

16. Spectroscopy for Small Flake
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Spectroscopy data shows band gap of 1.1 eV on silicon and no band gap (metallic)
on flake with modulation corresponding to the row spacing (~1.2 nm)
Image taken at 0.1 nA, -2.5 V

17. Spectroscopy for Small Flake
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18. Spectroscopy for Small Flake
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1.1 eV

19. TaS3 Row Intersection
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Images taken at 0.1 nA, -3.5 V

20. TaS3 Flake
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Images taken at 0.1 nA, -3.5 V

21. Future Goals
 Peel off rows from flake using tip (ideally single row)
 Further investigate variances in row structure
 Collect spectroscopy data on single layer flakes
smaller than 10 nm
 Develop definitive model for crystal structure of
orthorhombic TaS3
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22. Conclusions
 Step height of approximately 12 Å, about 1/3 of the lattice constant (36.804 Å)
 Row spacing of approximately 15.5 Å, which is in agreement with the lattice
constant (15.173 Å)
 Modulation along the chain axis with spacing 12.1 Å, which is approximately 4x
the lattice constant (3.340 Å)
 Rows appear to have either two or three local peaks, which could be due to how
sharply zig-zagged the rows are or the orientation angle between rows
 Spectroscopy data shows metallic behavior for
all sizes and arrangements larger than 10 nm
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Lyding et al. Phys. Rev. B 1989

23. Acknowledgments
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 Professor Lyding
 Lyding Group