InAs Nanowires

substrate preparation &

growth dynamics

nano-fabrication

structural - characterisations

thermodynamics & kinetics

ME+

coffee+

sleep deprivationnanowire

growth growthkinetics

Outline

• Introduction

• Substrates

• Growth Dynamics*

3

* in progress

Nanowires

Nanowires

200 nm

WZZBIII-As

nanowires only!

growth direction

[111]c [0001]

Vapor Liquid Solidmechanism

As As In

room temperature growth temperature≅420℃

Or, in thermodynamical language:

molecular beam epitaxy (MBE)

• High purity materials -> High purity atomic beams

• Ultra high vacuum : 10-11 Torr -> keeps high purity

• Control of atomic beam fluxes -> control of growth parameters

Substrates

• Fabrication process overview

• Position control & size control

• Substrates for NW network

• Novel InAs -SiO2

10

20 μm

Positioned gold catalyst

Cleaning

Size control

30 kV

100 kV

• Catalyst volume -> NW diameter & growth rate • NW diameter -> NW properties! • Catalyst position -> creation of NW networks

why care about volume and position control ?

Kinking eventStraight stem growth Merging event

substrates for NW networks

[11-2]c

[1-10]c[1-21]c

[2-1-1]c

NW facets:{112}c

{010}h

[111]c

10 μm 10 μm 10 μm

SiO2 Substrates

• Novel SiO2 and InAs

100 nm

SiO2InAs

• Novel family of substrates

• Changes dramatically the dynamics of surface diffusion

• May allow X-ray studies only on NWs by altering the signal from the substrate

SiO2 Substrates

wouldn’t it be cool to see the nanowire as they grow ?

in-stu X-ray diffraction

BL11XU @

SPring8

*Preliminary results

the set-up

Scattering from a crystal

a

crystal truncation rod

demo time♥ reproducibility ->code on Github

https://github.com/giulioungaretti/sp2014

Icrystal truncation rod

Iwurtzite

Itwin

In Flux

On

In Flux

Off

[10l

] s

11.5

2l

TWWZ

ZB

overview-growth interruptions

[0 1 0]s direction (r.l.u.)

[−2

1

0]s d

irect

ion

(r.l.

u.)

Contourplot of the [0 0 1] plane, through [0 1 1.473]

0.94 0.96 0.98 1 1.02 1.04 1.06

−0.05

0

0.05

Log(

Inte

nsity

)

0.5

0.55

0.6

0.65

0.7

0.75

0.8

s s

[1 0 l]s

Log(

Inte

nsity

)

0.5

0.55

0.6

0.65

0.7

0.75

0.8

[1 k 1.5]s

lk

lk

k

h

image credit: Tomas Stankevic

2

1.5

1

l

[10l ]s

CTR dynamicsIn on In off

HRTEM images taken Sriram Venkatesan Max-Planck-Institut

Düsseldorf

100 nm

2 μm

ZB

TW

1 1.5 2

l

log(dI/dt)

{111}

SiO2

InAs substratet1

t2

t3

parasitic growth

Conclusion and acknowledgements • Substrates can be fabricated with high control over

both size and position

• Promising results in fabrication on NW network

• Insights on growth dynamics

♥Jesper and Peter ♥all QDever’s and in particular yesterday’s night crew ♥DNRF-DANSCATT - Japan Trips funding ♥DNRF & Microsoft station Q - General lab funding and espresso