Black phosphorus and phosphorene: From 3D to 2D and back

Transcription

1 Black phosphorus and phosphorene: From 3D to 2D and back Scott C. Warren October 27, 2016

2 Acknowledgements Students Graduate Adam Woomer Tyler Farnsworth Jun Hu Kaci Kuntz Dan Druffel Anginelle Alabanza Suzanne Setti Jacob Pawlik Undergraduate John Darges Frank Alcorn Eleanor Brightbill Jon Thompson Elena Kovalik Ryan White NSF DMR NSF DMR NSF GRFP (x4) UNC start-up funds Funding Beckman Young Investigator Award ACS Petroleum Research Fund UNC Office of Tech. Development An unnamed company Collaborators: David Tománek, Andy Moran, John Papanikolas, Joanna Atkin

3 Solution-processed materials for electronics & photonics 0-D Materials Synthesis Assembly Devices Bawendi, JACS, 115, 8706 (1993). Murray. Nature, 439, 55 (2006). Nozik. Phys E, 14, 115 (2002). 1-D Materials Synthesis Assembly Devices Heeger, MacDiarmid, Shirakawa, JCSCC, 16, 578 (1977). Heeger, Nature, 357, 477 (1992).

4 Phosphorene: a tunable 2-D building block? Band gap (ev) 3-D black phosphorus: 0.35 ev 2-D black phosphorus 1.8 ev M.P. of black 2.6 GPa = 980 C P-P bond enthalpy = 50 kcal/mol P oxidizes easily Takao, Asahina, Morita. J. Phys. Soc. Jpn. 50, 3362 (1981).

5 Forms of elemental phosphorus White Nanotubes Red Fullerenes amorphous Violet Other 2D Blue phosphorus

6 Black phosphorus phase diagram orthorhombic rhombohedral Phys. Lett. A. 122, (1987)

7 Black phosphorus structure Unit cell Top view 5 mm Interdigitation of lone pairs Cartoon of lone pairs 3.1 Å

8 Survey of mechanical exfoliation Using a Bruker FastScan in an inert atmosphere, we acquired 500 images and assessed ~2000 flakes. Yield of sub-5 nm pieces = 0.1%

9 Liquid exfoliation of BP 5 mm Solvent Sonicate/ Shear mix Adam Woomer 1 μm

10 Solvent selection Solvents: 1) Benzonitrile 2) 1,3-Dimethyl-2- imidazolidinone 3) 1-vinyl-2-pyrrolidinone 4) N-methylformamide 5) N-methyl-2- pyrrolidone 6) Dimethylformamide Patent pending. Liquid exfoliation of black phosphorus. (2014). ACS Nano, 9, (2015).

11 Fractionation of 2-D phosphorus Centrifuge, Dialysis Re-disperse Patent pending. Liquid exfoliation of black phosphorus. (2014). ACS Nano, 9, (2015).

12 Frequency Thickness analysis 3-layer Δ = Contrast change Patent pending. Liquid exfoliation of black phosphorus. (2014). ACS Nano, 9, (2015).

13 101:002 Confirmation of thickness by HR-TEM 002 {002} {101} 101 {200} nm -1 5 nm Layers

14 Transfer function Transfer function Intensity ratio depends on microscope lens {101} {002} Ratio = 2 Ratio = 24 Spatial frequency (1/nm)

15 Large scale production and isolation of monolayers Jun Hu Patent pending. Liquid exfoliation of black phosphorus. (2014).

16 Optical spectroscopy of black phosphorus Y. Kondo, M. Ikezawa: Physics Monthly (in Japanese) 6, 395 (1985) Exciton binding energy in bulk black phosphorus = 7.9 mev

17 Phosphorene: an anisotropic 2-D material (z) armchair (x) Mirror symmetry in plane perpendicular to y No mirror symmetry in plane perp. to x Absorption of photon (parity = -1) is forbidden in y.

18 Measuring the fundamental band gap Tyler Farnsworth ACS Nano, 9, (2015).

19 Band gap (ev) A new method for quantifying the absorption edge Thickness (layers)

20 Measuring the fundamental band gap Tyler Farnsworth ACS Nano, 9, (2015).

21 Comparison to previous reports ACS Nano, 9, (2015).

22 Analysis of lifetimes L Recombination site Band gap engineering in a 2D material for solar-to-chemical energy conversion. Nano Letters, 16, (2016).

23 Control of edge and surface chemistry Oxygen water both Kaci Kuntz Interpreting core-level spectra of oxidizing phosphorene: Theory and Experiment. T. Yang, B. Dong, J. Wang, Z. Zhang, J. Guan, K. Kuntz, S. Warren, D. Tomanek. Phys Rev. B. (2015).

24 Conclusions & Announcement (1) 2D phosphorus is an exciting new building block for solar energy conversion. Excited state lifetimes are fairly long and transport characteristics are good. (2) Quantum-confined 3D solids can be built from 2D materials. (3) Passivating recombination sites on 2D materials is necessary for extended lifetimes of carriers. Phosphorene-meeting.com

25 Acknowledgements Students Graduate Adam Woomer Tyler Farnsworth Jun Hu Kaci Kuntz Dan Druffel Anginelle Alabanza Suzanne Setti Jacob Pawlik Undergraduate John Darges Frank Alcorn Eleanor Brightbill Jon Thompson Elena Kovalik Ryan White NSF DMR NSF DMR NSF GRFP (x4) UNC start-up funds Funding Beckman Young Investigator Award ACS Petroleum Research Fund UNC Office of Tech. Development An anonymous company Collaborators: David Tománek, Andy Moran, John Papanikolas, Joanna Atkin