1. InAs
Nanowires
substrate preparation
&
growth dynamics

2. nano-fabrication
structural-characterisations
thermodynamics
& kinetics
ME
+
coffee
+
sleep
deprivationnanowire
growth
growth
kinetics

3. Outline
• Introduction
• Substrates
• Growth Dynamics*
3
* in progress

4. Nanowires

5. Nanowires
200 nm

6. WZZB
III-As
nanowires
only!
growth
direction
[111]c
[0001]

7. Vapor Liquid Solid
mechanism
As As In
room temperature growth temperature≅420℃
Or, in thermodynamical language:

8. molecular beam epitaxy
(MBE)

9. • 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

10. Substrates
• Fabrication process overview
• Position control & size control
• Substrates for NW network
• Novel InAs -SiO2
10

11. 20 μm
Positioned gold catalyst
Cleaning

12. Size control
30 kV
100 kV

13. • Catalyst volume -> NW diameter & growth rate
• NW diameter -> NW properties!
• Catalyst position -> creation of NW networks
why care about volume and position control ?

14. Kinking eventStraight stem growth Merging event
substrates for NW networks

15. [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

16. SiO2 Substrates
• Novel SiO2 and InAs
100 nm
SiO2
InAs

17. • 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

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

19. in-stu
X-ray diffraction
BL11XU
@
SPring8
*Preliminary results

20. the set-up

21. Scattering from a crystal
a

22. crystal truncation rod

23. demo time
♥ reproducibility ->code on Github
https://github.com/giulioungaretti/sp2014

24. Icrystal truncation rod
Iwurtzite
Itwin
In Flux
On
In Flux
Off
[10l]s
11.52
l
TWWZZB
overview-growth interruptions

25. [0 1 0]s
direction (r.l.u.)
[−210]
s
direction(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(Intensity)
0.5
0.55
0.6
0.65
0.7
0.75
0.8
s s
[1 0 l]
s
Log(Intensity)
0.5
0.55
0.6
0.65
0.7
0.75
0.8
[1 k 1.5]s
l
k
l
k
k
h
image credit: Tomas Stankevic

26. 2
1.5
1
l
[10l ]s
CTR dynamics
In on In off

27. HRTEM images taken
Sriram Venkatesan
Max-Planck-Institut
Düsseldorf
100 nm
2 μm

28. ZB
TW
1 1.5 2
l
log(dI/dt)
{111}
SiO2
InAs substrate
t1
t2
t3
parasitic growth

29. 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