Download Charge transport across ultrathin semiconducting molecular layers

Workshop on Research Collaboration FAPESP - Trinity
Charge transport across
ultrathin semiconducting
molecular layers
Carlos Cesar Bof Bufon
Functional Devices and Systems Laboratory
Research scope
• Materials Science
• Strain-Engineering
• Nano/microfabrication
• Self-assembly
Smart
Architectures
Novel Functional
Devices and
Structures
Top-Down
Inorganic
Materials
Hybrid
Organic/Inorganic
Metamaterials
Organic
Materials
Bottom-Up
Research Activities on
Hybrid freestanding nanomembranes
Ultra-compact sensors
a)
b)
c)
Synthesis of hybrid freestanding nanomembranes.
Fabrication and characterization of hybrid molecular heterojunctions.
Fabrication and characterization of nanomembrane based elements.
Ultra-compact capacitors
Bof Bufon C.C. et.al , Nano Lett. 2010
Sharma R. et al. Adv. Energy Mater. 2014
Hybrid molecular heterojunctions
Hybrid molecular heterojunctions
Bof Bufon C.C. et.al , Nano Lett. 2011
Bof Bufon C.C. et.al , J. Phys. Chem. C 2014
Bendova, et. al, J. Phys. Chem. C 2016
Vervacke, C. et al. RSC Advances 2014
Grimm, D. et al. Nano Lett. 2013
Supporting Innovation
Sensors and detection systems for Brazilian strategic fields
Fuel quality control
- production
- storage
- transport
- end user
Food quality control
- processing.
- storage.
- transportation.
- end consumer.
Environmental and heath monitoring
- medical and health screening.
- industrial residues in rivers and lakes.
- evaluation of the water contaminants by:
- biological contaminants;
- heavy metals;
- agricultural defensives.
Research Activities on
Hybrid materials and devices
Patterning of PPy thin films
a) Synthesis of organic thin films on novel substrates.
b) Micro- and nano-fabrication processes of organic thin films:
i) incorporation of organic films in inorganic platforms;
ii) patterning of organic thin films;
iii) scaling-up.
c) Fabrication of organic/inorganic hybrid functional elements.
d) Characterization of organic/inorganic hybrid functional elements.
PPy Schottky-Barrier FET
PPy film as oxygen gas sensor
- I (µA)
Paper-based in-flow sensors
Drain-source current (µA)
In-flow acid detection
T=300K
Drain-source voltage (V)
Time (103 s)
C.C. Bof Bufon et al. Appl. Phys. Lett., 2006
C. Vervacke, et al. Anal. Chem. 2012
Patent pending, 2014
C.C. Bof Bufon et al. Phys. Rev. B., 2007
Introduction
Hybrid Molecular Electronic Junctions
James R. Heath and Mark A. Ratner, Physics Today 2003
Metal
Metal
Insulator
L
Semiconductor
X
R
Semiconductor
Insulator
Introduction
from organic to molecular electronics
Bridging the gap between organic electronic devices (thicknesses of 10-100nm)
and molecular electronic devices (at least 1 dimension smaller than 10nm).
McCreery, Yan and Bergren, Phys Chem. Chem. Phys. 2013
Introduction
from organic to molecular electronics
Bridging the gap between organic electronic devices (thicknesses of 10-100nm)
and molecular electronic devices (at least 1 dimension smaller than 10nm).
From thin- to ultra-thin organic semiconductors
Z. H. Xiong et al. Nature 427, 821 (2004)
Technological challenges
x
x
x
x
x
x
x
Substrate
Substrate
Short-circuit via pinholes
Metal interdiffusion.
Haick et al., Acc. Chem. Res. 41, 359 (2008)
Delicate materials require new contacting methods
Vertically contacting molecular layers: some examples.
Evaporation of contacts
Lodha et al, J. Appl. Phys. 2006
Hg droplet
Evaporation of contacts
Haick and Cahen, Acc. Chem. Res. 2008
Bonifas and MacCreery, Nat. Nanotech. 2010
Holmlin et al. J. Am. Chem. Soc. 2001
Lift-off Float-on
Cahen et al, Nature 2000
Haick and Cahen, Acc. Chem. Res. 2008
Nanomembranes:
the third wave of works on nanomaterials
Nanomembranes are structures with thicknesses of less than a few hundred nanometers and with
minimum lateral dimensions at least two orders of magnitude larger than the thickness.
Thin
Flexible
Strain engineered
Geim, Nat. Mater. 2007
Kim, Science 2008
Zhang, Nano Lett. 2006
Deneke, Appl.Phys.Lett. 2007
Patternable
500µm
Thurmer, Nano Lett. 2010
Sun, Nat. Nanotechnol. 2006
Bof Bufon, 2010
Rolled-up nanomembranes
Some features of interest.
a) Mechanical flexibility (transition 2D – 3D):
Impact on the device’s footprint area.
b) Quasi-2D nature:
Sensors with improved performance and novel functionalities.
c) Patterning and integration capabilities:
Allows the creation of a variety of 3D devices and hybrid organic/inorganic
heterojunctions.
Nanomembrane technology:
strain engineering
selective
removal
Strained Layer
Sacrificial Layer
Substrate
Patterning of regular arrays of rolled-up nanomembranes
500µm
Bof Bufon, 2010
Experimental conditions:
1) Substrate: Si/SiO2
2) Sacrificial layer: GeO2
3) Strained bilayer: Ti/Cr
4) Rolling media: H2O
Ø = 5µm-100µm
Concept of hybrid capacitor based on nanomembranes
Max. 50nm
C.C. Bof Bufon, Nano Lett. 10, 2506 (2010)
@DSF-LNNano 2016
Zooming in and out
STEM-EDS map
R. Sharma, Adv. Energy Mat. 4 (2014)
C.C. Bof Bufon, Nano Lett. 10, 2506 (2010)
Design, yield and dielectric material
Sharma R. et al., Large-area Rolled-up
nanomembrane
capacitor
arrays
for
electrostatic energy storage”.
Advanced Energy Materials - Volume 4, Issue
9, June 24, 2014
Capacitance of the rolled-up capacitor
RC 
C 3D 
1
  2  
C 2D 
N
Capacitance per foot print area ~220 µF/cm2
C.C. Bof Bufon et al., Nano Lett. 10, 2506 (2010)
State-of-the-art for Al2O3: ~100 µF/cm2
Barnerjee et al., Nat. Nanotech. (2009)
Hybrid organic/inorganic capacitor by SAM incorporation
Current and capacitance dependence on the chain length
C.C. Bof Bufon, Nano Lett. 10, 2506 (2010)
Soft but robust electrodes based on nanomembranes
“crossbar-like” structure
• Pinhole-proof;
• Soft contact: low damage to film (SAM, etc)
• “Large scale” production and integration;
• Versatile material composition;
• Self-adjusting gap.
• Geometrical contact area < 1µm2
Soft mechanical contacting method: Self-adjusting contacts.
Haick et al., Acc. Chem. Res. 41, 359 (2008)
Contacting ultra-thin CuPc layers (Au/CuPc/Au)
Releasing of the nanomembrane in H2O
Submittend
J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279
Electrode gap ~ 3nm to 110nm
CuPc
model molecular system
Water-gated CuPc transistor
DST calculation: Nita, P. et al., Nanoscale, 2014.
X-Ray: Hoshino, A, et al. Acta Crystallogr. Sect. B: Struct Sci, 2003.
Furlan, Merces, Vello and Bof Bufon,
Organic Electronics 31, 2016
Organic Electronics, 2017
10.1016/j.orgel.2017.06.041
Knupfer, M. and Peisert, H., phys. Stat. sol.(a), 2004
4 µm
J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279
Transport properties of CuPc thin films: IV and It traces
Yan, H et al, PNAS 2013
The Journal of Physical Chemistry C, 2017
10.1021/acs.jpcc.7b02528
Transport properties of CuPc thin films: IV and IT traces
for t = 6.5nm
1) For V < 0.15V and T > 100 - 140 K, hopping conduction dominates;
2) At T = T1: transition from thermally activated transport to tunneling;
3) Strong temperature dependence for T > T1 associated to impurity/defect (ID) sites;
For T > T1:
 Ea 
Submittend
I  V exp  

 kT 
J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279
Physisorbed vs. chemisorbed molecules
Au/CuPc/Au
Yoram Selzer et al. J. Am. Chem. Soc. 2004, 126, 4052
Transport properties of CuPc thin films:
Activation energy for T > T1
- Ea < EF - EHOMO: hopping into the molecular layer;
- Impurity/defect sites work as charge localization
centers where:
 temperature enhances the hopping process.
 applied bias lowers the potential barrier
between such sites.
Region B
q3
Ea  E0 
V
 r 0 d
*in accordance with the in-plane ε calculated for CuPc thin layers:
Shi, N.; Ramprasad, R. Phys. Rev. B 2007, 75, 155429.
Ramprasad, R.; Shi, N. Appl. Phys. Lett. 2006, 88, 222903.
Shi, N.; Ramprasad, R. Appl. Phys. Lett. 2006, 89, 102904.
εr = 13*
Low temperature transport
For T < T1:
• the charge carriers are trapped into the ID sites;
• the transport across the CuPc layer occurs either:
 via the molecular levels or;
 by a non-resonant tunneling across the thin barrier.
V < 0.26 V: non-resonant direct tunneling
(DT) across the CuPc barrier.
  2d 2meΦ 

I  V exp 





V ~ 0.40 V: “resonant tunneling”
V > 0.75 V: Fowler-Nordheim tunneling
(FN).
  4d 2m  3 
e
2

I  V exp 


3qV


Summarizing Au/CuPc/Au
• We precisely set/map the transport
properties of a model molecular system (CuPc)
controlling
the
external
parameters
(temperatures and voltage) over a wide range.
• The contributions to the conductance related
to the impurity/defect states and those due to
the CuPc molecular levels were isolated.
• At low temperatures the sequential
transitions from DT to resonant-tunneling to
FN tunneling was observed.
• The Au/CuPc/Au heterojunctions can mimic
the behaviour of molecular wires over a certain
temperature/voltage range.
Submittend
J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279
Acknowledgements
TU-Chemnitz
Dietrich R. T. Zahn
Georgeta Salvan
Michael Fronk
Iulia Korodi
IFF, IFW-Dresden
Martin Knupfer
Susi Lindner
IIN, IFW-Dresden
Celine Vervacke
Dominic Thurmer
Martin Bauer
Oliver G. Schmidt
LNNano/ CNPEM
Jeferson Bettini
Christoph Deneke
Angelo Gobbi
DSF/ LNNano /CNPEM
Davi Henrique de Camargo
Cátia Crispilho Corrêa
Murilo Santhiago
Leirson Daniel Palermo
Leandro das Mercês Silva
Tatiana Parra Vello
Paula Andreia Petrini
Mariane Peres Pereira
Isabel Emperatriz Loayza
Andreia da Silva Chagas
Rafael Furlan de Oliveira
Geovana dos Santos
Priscila G. da Costa
Kleyton Torikai
Ricardo M. L. Silva
Thank you for your attention
2014/25979-2
[email protected]
Au/SAM/Au heterojunctions
Contacting sulfur terminated alkanes
Non-resonant tunneling transport
C.C.Bof Bufon et al., Nano Lett. 11, 3727 (2011)
Au/nanoparticles/Au
STM tip
Dorogi et al. Phys. Rev. B. 1995
Andreas et al. Science 1996
n-dodecanethiol Au nanorparticles (2-5nm)
Sato et al. J. Appl. Phys. 1997
Au/NPs/Au heterojunction
J. Phys. Chem. C, 2016, just accepted
Summarizing
1) Rolled-up nanomembranes can gently contact ultra-thin (3 - 110nm) hybrid
organic-inorganic layers from the top;
2) No interdiffusion of metallic atoms was detected.
3) The charge transport across hybrid heterojunctions can be investigated.
Additional possibilities
Submittend
Transport across the hybrid junctions
Simmons model for
conductance [1] :
Field-emission [2] :
VT=160mV
[1] Simmons, J. G. Journal of Applied Physics 1963, 34, (1), 238 -239.
[2] Gadzuk, J. W.; Plummer, E. W. Reviews of Modern Physics 1973, 45, (3), 487-548.
C.C.Bof Bufon et al., Nano Lett. 11, 3727 (2011)
SAMPLE: Ag tube/Organic Semiconductor/Au electrode
D#S7#JM4@F1_Ag_11 nm (AFM)
dI/dV (6K)
dI/dV (8K)
dI//dV (10K)
dI/dV (13K)
dI/dV (15K)
dI/dV (20K)
dI/dV (25K)
dI/dV (30K)
dI/dV (40K)
dI_dV versus V for different T_CB 15:47:42 03/03/2016
0.6
5.0
10 K
4.0
0.4
4.0
0
2.0
dI/dV (nS)
3.0
dI/dV (nS)
I (nA)
0.2
3.0
2.0
-0.2
1.0
1.0
-0.4
-0.6
-0.4
-0.2
0
0.2
0.4
0
0
-0.4
-0.2
0
V (V)
V (V)
0.2
0.4
differential resistance around V= 0V
According to Mesoscopic Electronics in Solid
State Nanostructures, by Thomas Heinzel:
“The Coulomb gap manifest itself in an
increased differential resistance around V= 0
V, compared to that observed at larger
voltages”
D#S7#JM4@F1_Ag_11 nm (AFM)
3 10
12
2.5 10
12
2 10
12
1.5 10
12
1 10
12
i) 𝐸𝐶 = 2𝐶 > 𝑘𝐵 𝑇
ii) RTunnel >> RQuantum (25.8 kΩ)
At 10K (the temperature we’ve observed a gap in the
conductance) the thermal energy is 0.86 meV, so:
C < 9.3 x 10-17 F (at 10K)
The gap from the conductance plot is ~ 100 mV, thus,
considering the Coulomb blockade energy (EC), we have:
10 K
dV/dI (Ohm)
The requirements for observing Coulomb blockade are:
𝑒2
𝑒2
𝐸𝐶 =
2𝐶
𝑒2
𝐶=
2 . 100 𝑚𝑒𝑉
𝐶 = 8 𝑥 10−19 𝐹
Thus, from the conductance gap, the obtained capacitance
satisfies (i). In addition, the measured resistance is ~1 GΩ,
which satisfies (ii) as well.
We can consider the charged “site” having a disk-like geometry
with a self-capacitance given by: C0 = 8εra, whereas εr is the
dielectric constant of CuPc and a the disk radius.
9
500 10
According to the literature εr of CuPc varies from 2.1 – 7¹ (for
polycrystalline layers), thus a = 5.3 – 1.6 nm
0
-1
-0.5
0
V (V)
0.5
1
If εr = 13² (in-plane dielectric constant), then a = 0.87 nm
¹ Jarosz, G. et al, Thin Solid Films (514), 2006, 287 - 291
² Bof Bufon, C. C. et al, Journal of Physical Chemistry (118), 2014, 7272 - 7279
IxV (T)
IxV (T) 13:22:27 12/02/2016
0.6
10
-7
10
-9
ABS (6K)
ABS (10K)
ABS (15K)
ABS (20K)
ABS (30K)
ABS (40K)
ABS (50K)
ABS (60K)
ABS (80K)
ABS (100K)
ABS (120K)
ABS (140K)
ABS (160K)
ABS (180K)
ABS (220K)
ABS (240K)
ABS (260K)
ABS (280K)
ABS (300K)
0.4
-11
I (10K)
0
I (A)
I (A)
0.2
I (13K)
10
I (15K)
-13
I (20K)
-0.2
10
I (25K)
I (30K)
-0.4
-0.6
I (40K)
-15
10
-0.4
-0.2
0
V (V)
0.2
0.4
-17
10
-1.5
-1
-0.5
0
V (V)
0.5
1
1.5
+0.16 V ± 12% V (peak)
+50 mV ± 12% V
+500 mV ± 12% V
-0.16 V ± 12% V (peak)
-50 mV ± 12% V
-500 mV ± 12% V
G vs T for peaks in the forward scan
-9
1 10
-6
-9
100 10
-9
10 10
1 10
10 10
-9
-9
1 10
-9
Mean G (S)
Mean G (S)
G vs T for peaks in the forward scan
100 10
-12
100 10
-12
10 10
-12
100 10
-12
10 10
-12
1 10
-12
1 10
-15
100 10
350
-15
300
250
200
150
T (K)
100
50
0
100 10
350
300
250
200
150
T (K)
100
50
0