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ELLIOT YOUNG – LYDING GROUP

UNIVERSITY OF ILLINOIS

OCTOBER 20 T H , 2015

Characterization of Low-Dimensional Tantalum Trisulfide using Scanning

Tunneling Microscopy

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Where I Work

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Where I Work

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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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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

b

a

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Background

Roucau et al. Phys. status solidi 1980

a = 36.804 Åb = 15.173 Åc = 3.340 Åb

a

c

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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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Step Height

11.7 Å 12.5 Å

Histogram analysis shows a step height of approximately 12 Å

Roucau et al. Phys. status solidi 1980

Image taken at 0.1 nA, -3.5 V

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Row Spacing

Average row spacing: 15.5 ÅLocal modulation: 4.48 Å

Lyding et al. Phys. Rev. B 1989Image taken at 0.1 nA, -3.5 V

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Row Spacing

Row spacing: 16.88 Å Local modulation: 4.15 ÅShows three secondary peaks instead of just two and with peak spacing ~0.3 Å smaller

Images taken at 0.1 nA, -3.5 V

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Row Spacing

Images taken at 0.1 nA, -3.5 V

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Measuring Modulation Along Row Axis

Measured spacing between features along row axis ~ 12.1 Å

Meerschaut et al. J. Less Common Met 1975Images taken at 0.1 nA, -2.5 V

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Measuring Modulation Along Row Axis

Image taken at 0.1 nA, -2.5 V

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Small Flake Analysis

Image taken at 0.1 nA, -3.5 V

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Band Gap for Small Flake

Images taken at 0.1 nA, -2.5 V

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Spectroscopy for Small Flake

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

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Spectroscopy for Small Flake

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Spectroscopy for Small Flake

1.1 eV

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TaS3 Row Intersection

Images taken at 0.1 nA, -3.5 V

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TaS3 Flake

Images taken at 0.1 nA, -3.5 V

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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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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 forall sizes and arrangements larger than 10 nm

Lyding et al. Phys. Rev. B 1989

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Acknowledgments

Professor LydingLyding Group