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Novel device behaviors at low dimensional heterojunctions in 2-D materials Lincoln J. Lauhon Department of Materials Science & Engineering October 5, 2015 12th U.S.-Korea Forum on Nanotechnology 2-D Geometry Produces New Functions Hersam,

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Lincoln J. Lauhon

Department of Materials Science & Engineering October 5, 2015

Novel device behaviors at low dimensional heterojunctions in 2-D materials

12th U.S.-Korea Forum on Nanotechnology

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2-D Geometry Produces New Functions

Hersam, Marks, Lauhon et al, PNAS USA, 110, 18076 (2013). 1D + 2D Concept generalized in Hersam, Marks, Lauhon et al, Nano Letters 15, 416 (2015).

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Degrees of Freedom to Explore

Explore, Understand, Control Mechanical Interfaces Optical Defects Spin Electrical

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SiO2 Si Monolayer MoS2 Grain boundary Au

4 μm 1 2 3 4

Hysteretic I-V curve with low and high

resistance states  memristor.

Switching ratio (ON/OFF) ~ 103
Observed in devices with grain boundaries

and sulfur vacancies.

Hersam, Marks, Lauhon, Nature Nanotechnology 10, 403 (2015)

Grain boundaries lead to memristive behavior

Unique opportunity for neuromorphic computing

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A new type of heterojunction in MoS2

Thickness-dependent bandstructure results in fundamentally new type of semiconductor junction.

Type II Type I

SPCM of 1L-ML Junction

Howell, Jariwala, et al., Nano Lett., 15, 2278 (2015)

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SPCM modeling extracts band profiles

Simulations reproduce bias dependence assuming a type-2 band offset. FE modeling based on material parameters determined from uniform thickness devices.

Measured Simulated

Howell, Jariwala, et al., Nano Lett., 15, 2278 (2015)

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Degrees of Freedom to Explore

Explore, Understand, Control Mechanical Interfaces Optical Defects Spin Electrical

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Atom Probe Tomography of a 2D Material: Ag doped (PbSe)5(Bi2Se3)3m

PbSe Bi2Se3

1.65 nm

NIST: Singh, Tavazza

NU: Mercouri Kanatzidis

Ren, Lauhon et al, unpublished. Ag Se Bi Pb

10 nm 10 nm 10 nm 10 nm

Ag doping changes m=1 phase from

metallic to superconducting.

Ag is expected to dope only the

PbSe layer. Can dopant location be resolved by APT?

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Atom probe shows Ag dopes both Pb and Bi layers

PbSe Bi2Se3

Ag in Bi-Se Ag in Pb-Se

Significance: Validation of ability to predict and measure dopant locations in 2-D materials.

First Principles Calculations: Defect Formation Energies

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Degrees of Freedom to Explore

Mechanical Interfaces Optical Defects Spin Electrical

Explore, Understand, Control

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Mechanical Properties of MoS2 Membranes

ACS Nano 5, 9703 (2011)

Nonlinear force vs. displacement Sensitive to small forces

Adv. Mater. 25, 6719 (2013)

Piezoelectric Monolayer

Nature 514, 474 (2014)

𝑔 = 2.4048 𝜌𝑒 𝑈 𝜍𝑢

Annalen der Physik 527, 27 (2015)

Membrane-like below ~6L

ACS Nano 7, 6086 (2013)

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Modes identified from thermal fluctuations

Thermally excited vibrational modes

are observed and identified.

Nominally degenerate modes are split.

– Could indicate mode-coupling.

(2,2) (1,3) (3,1) (1,2) (2,1)

SIM

(1,1)

EXP Liu and Lauhon, Nano Lett ASAP.

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Distribution of thermal energy in mechanical modes depends on modulation frequency

(1,1) sidebands VISIBLE OFF ON

Liu and Lauhon, Nano Lett ASAP.

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Normal-mode splitting is observed

Strong coupling enables coherent energy exchange.

(1,2) (2,1)

150 uW 350 uW

Peak splitting  coupling rate g.
g is 10 X the decay rate γ.

Liu and Lauhon, Nano Lett ASAP.

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Degrees of Freedom to Explore

Mechanical Interfaces Optical Defects Spin Electrical

Explore, Understand, Control

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Degrees of Freedom to Explore

Mechanical Interfaces Optical Defects Spin Electrical

Explore, Understand, Control

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Challenges in 2-D Materials & Devices

Functional Imaging Synthesis of New Materials Device Modeling Nanostructural Analysis

Integrated approach to 2D MSE

Doping & Defects Integration of Quantum & Continuum Models Heterogeneity at Multiple Lengthscales Reproducible Processes & Interfaces

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Lauhon Research Group

NUCAPT, NUANCE

Group: Sarah Howell (G-4) Nari Jeon (G-4) Spencer Park (UG) Ryan Paull (G-1) Xiaochen Ren (G-3) Zhiyuan Sun (G-2) KunHo Yoon (G-5) Deep Jariwala (Hersam, Marks) Cited Alumni: Chung-Chiang Wu (PD) Vinod Sangwan (PD) In Soo Kim (PhD) Collaborators: Mark Hersam Northwestern Tobin Marks Northwestern Teri Odom Northwestern

M. Kanatzidis

Northwestern Gregor Koblmuller TU Munich Yossi Rosenwaks Tel Aviv University Arunima Singh NIST Francesca Tavazza NIST