Synthesis and Characterization of TMDs for Space Applications

Roger C. Walker IIAdviser: Dr. Robinson

10/16/15

Cosmic Ray-diation

Lunar gamma rays due to cosmic raysD. J. Thompson, D. L. Bertsch (NASA/GSFC), D. J. Morris (UNH),

R. Mukherjee (NASA/GSFC/USRA)

Highly-energetic ionizing radiation from beyond

the solar system!

Electronics in The Final Frontier

Two types of errors:• Hard (fatal)

• Soft (non-fatal)Cosmic Radiation degrades

space-based electronics

There is a need to radiation-harden micro- and nano-electronics!

There is a need to study radiation effects on 2DLMs!

Radiation Interaction with 2DLMsHow do high radiation environments influence the

electronic properties of 2DLMs and the performance of 2DLM-based transistors?

Main focus in literature has been graphene![With some hBN (not shown) and MoS2…]

Radiation Interaction with Graphene

Back-gated GFET subjected to electron beams – M. Foxe et al

Back-gated GFET X-ray sensor – A. Patil et al

Exfoliated SLG transistor exposed to 1.14 GeV Uranium-238 – O. Ochedowski et al

Radiation Interaction with Graphene

Radiation Interaction with TMDs

SL Exfoliated MoS2 transistor exposed to 1.14 GeV Uranium-238 – O. Ochedowski et al

SL Exfoliated MoS2 transistor exposed to 1.14 GeV Uranium-238 – O. Ochedowski et al

Radiation Interaction with TMDs

Our Experiments

I. Synthesis / Exfoliation of TMDsII. Initial Characterization

I. Surface sensitive techniques: AFM, XPS, etc.III. Device Fabrication

I. This has recently split off into additional investigations on plasma-based oxidation and dielectric integration with TMDs

IV. Radiation ExperimentsI. In development with Jovanovic group (PSU NucE)

WSe2 Synthesis and Characterization

S. Eichfeld et al

Substrate: Sapphire

S092315A

S100715C

WSe2 Synthesis and Characterization

Great for growth, but our initial experiments require TMDs only=> use for oxidation and dielectric experiments

WSe2 grown on epitaxial graphene

(S092315A)

1 2

3 4

Se/W ratios:#1 = 1.817#2 = 1.863#3 = 1.895#4 = 2.11

Dielectric Integration

Rq < 0.3 nm

Rq < 0.2 nmRq ≈ 0.4 nm

Rq ≈ 3 nm

Image Rq = 2.63 nm

Dielectric Integration

Rq ≈ 0.2 nm

Rq (0.5, 0.8) nm∈

Rq (0.5, 0.7) nm∈

Image Rq = 0.965 nm

Rq ≈ 0.8 nm

Device Fabrication

Complete top-gated device

Known issues:• Uniformity of WSe2

• Schottky barriers• Dielectric integration

• Unintentional oxygenation (plasma/ambient)

Device Irradiation

Features:• Vacuum/gas-filled environment• Irradiation with internal source (through

source holder) / external source (through optical window)

• Measurement of the electrical properties (I-V measurement) of 2D materials

• Two-axis translation with high precision

Irradiation Chamber Construction

No leakage found with helium leak detector

Ultimate achievable pressure:

less than 0.1 mtorr (1.3E-4 mbar)

Pulsed laser testing for simulating single-event transient induced by heavy ions

Motivations to use lasers:1. Accessibility and cost of ion beam facility: Particle accelerator is needed for ion beam

testing. It is difficult to be set up in a regular laboratory. It also doesn’t comply with industrial demands for radiation hardness assurance.

2. Laser beam exhibits higher temporal and spatial resolution compared with heavy ions. It causes less damage to the material and is therefore more repeatable.

Figure courtesy of Pease et al.

Example of transient pulses induced by ion beam, laser and simulation: What can we learn from pulsed laser testing:

1. Single transistor level study:Study the transient voltage and current produced; Understand the charge generation, transport and collection mechanism; Understand the impact of defects on the charge transport …This is the aim of our current research!

2. Circuit level study:Identify the most sensitive (vulnerable) node in an IC and determine the device failure cross section

Ion micro-beam testing

Image: Michigan Ion beam laboratory

Motivation: For space and defense applications. (Defense against cosmic rays!)

What can we learn from ion beam testing:1.Displacement damage induced by heavy ions;2.Transient charge collection induced by heavy ions;3.For ICs, we can learn various device failure cross sections (Single Event upset, single event latchup, single event burnout…) as a function of particle energy or LET (linear energy transfer: energy deposition per unit distance)

Laser testing vs. Ion beam testing

Buchner et al. NRL laser setup

Summary

• We want to investigate radiation interactions with TMDs for space applications

• We can fabricate, irradiate and characterize 2DLM-based devices to test this claim

• Irradiation experiments will soon be underway

• Carrying out additional experiments to support

Thanks for your time!

Questions?Suggestions?