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The Last of Carbon Nanotubes andMore on 1D Systems: Synthesis,
Characterization, Electronics and Optics of
Semiconductor NanowiresLecture #9 ESE and MSE 525
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Separation is identified by opticalabsorbance spectra
SWNTs of decreasing diameter areincreasingly more buoyant
Observed variations in buoyant densityare believed to be a direct result ofdifference in diameter
Non destructive and scalable Most effective for separating SWNTs
of smaller diameter (< 1 nm)
M. S. Arnold et al. Nano Lett., 5 (2005), 713Green, Hersam, Materials Today 10, (2007), 59
Carbon Nanotube Separation
Density Gradient Centrifugation
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Flow and Electric Field alignment
S. Huang et al, JACS, 2003 (125), 5636, NanoLett. 2004 (4) 1025
Control gas flow during NT growth
C. Bower, APL 2000 77, 830
H. Dai, APL 2001 79, 3351
Electric field during growth
Plasma during growth
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Hydrophobic monolayerpreventsCNT adhesion
Trimethylsiyl (TMS) monolayer
Hydrophyllic (amine-terminated) monolayer promotesadhesion
aminopropyltriethoxysilane (APTS)
Well-known surface chemistry for SiO2
Images from: Liu et al, Chem. Phys.
Lett. 303 (1999) 125.CNT aligned to a narrow APTS line
Using Molecular Self-Assembly toControl CNT Placement: Example 1
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Exploit hydrophyllic/hydrophobic interactions Solvent wets RED, CNTs adhere to RED (COOH- terminated SAM)
Wang et al, PNAS 103 (2006) 2026.
Using Molecular Self-Assembly toControl CNT Placement: Example 2
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Carbon Nanotube Placement and Alignment
G. S. Tulevski et. al. in press
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Application of Selective Placement to CNT Transistors
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Substrate
Gate
Insulator
Source Drain
VDS
(V)
-100-80-60-40-200
ID(
A)
-500
-400
-300
-200
-100
0
VDS
(V)
-100-80-60-40-200
ID(
A)
-500
-400
-300
-200
-100
0
VDS
(V)
-100-80-60-40-200
ID(
A)
-500
-400
-300
-200
-100
0
VDS
(V)
-100-80-60-40-200
ID(
A)
-500
-400
-300
-200
-100
0
VDS
(V)
-100-80-60-40-200
ID(
A)
-500
-400
-300
-200
-100
0
VDS
(V)
-100-80-60-40-200
ID(
A)
-500
-400
-300
-200
-100
0
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
Electrical Probes of Charge Transport:Two and Three Terminal Structures
Accumulation
-100 VG
-80 VG
-60 VG
-40 VG
-20 VG
0 VG
carrier mobility current modulation (ION/IOFF) threshold voltage subthreshold slope
curve shape
inter- and intra- molecular chargetransport
interfacial charge transport doping
traps
All the
Action isat the interface
~ 1 cm2/V-sec
ION/IOFF ~ 107
VG
(V)
-100 -50 0 50 100
-ID(
A)
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
-(-ID
)1/2
(A1/2)
-0.025
-0.020
-0.015
-0.010
-0.005
0.000
VDS=-100V
OFF
ON
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Carbon Nanotube Transistors
drain
Yu-Ming Lin, IBM
Ti Ti
nanotube
10-5
10-4
10-3
10-2
10-1
100
101
Id[A]
2.01.51.00.50.0-0.5-1.0
Vgs[V]
Vd
-0.9 V
-0.5 V
-0.1 V
Output Characteristics
10
8
6
4
2
0
Id[A]
-1.2 -0.8 -0.4 0.0
Vds [V]
Vgs = 0.4 to -1.6 V
Step -0.4V120 mV/dec
Transfer Characteristics
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Different nanotube diameters Different metal contacts
Contacts
How do we make contact between dissimilar materials?This problem is the same in nanostructured and molecular materialsas it has been in new electronic materials for decades
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Schottky Barrier Contacts
Chen, Z., et al., Nano
Lett. (2005)
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CNT Transistors
20
15
10
5
0
Id[A]
-1.2 -0.8 -0.4 0.0
Vds[V]
+0.4 V
-0.4 V
-0.8 V
-1.2 V
-1.6 V Pd contactL ~ 600 nmdt ~ 1.8 nm
gm ~ 11 S
Vgs
to be published
3.5 S11 S26 Sgm
260 nm300 nm50 nmL
8-nm HfO2
1.7 nm
15-nm SiO210-nm SiO2gate oxide
1.4 nm1.8 nmtch
Javey et al. Lin et al. Wind et al.
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transconductance
threshold voltage
channel length
gate oxide thickness
p-MOSFET a) p-CNFET
50nm
1.5nm ~15nm
2300mS/mm650mS/mm
-0.2V -0.5V
subthreshold slope 70mV/dec 130mV/dec
IOn
/IOff
~106106 - 107
260nm
drive current 2100mA/mm650mA/mm(Vg-Vt=-1.0V)
a)R. Chau et al. Proceedings of IEDM 2001, p.621
Comparison between Si and CNT Transistors
P. Solomon, IBM
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Semiconductor Nanowires
Samuelson group
L. Lahoun
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Growth of Whiskers
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Semiconductor NW Growth
L. Lahoun
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Vapor-Liquid-Solid Growth
Growth typically at 850-950 oC
C. Lieber group
catalyst particle that forms a
liquid alloy with material ofinterest choose a composition andtemperature for synthesis wherethe liquid alloy and nanowire solidcoexist as long as catalyst remains aliquid, its preferentially absorbsreactant (versus solid nearby) andprovides site for 1D nucleation
Nanowire size proportional tocatalyst size
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http://www.youtube.com/watch?v=cFgGtTGUR2o&NR=1
Links to Semiconductor Nanowire Growth Videos
http://www.youtube.com/watch?v=iQBw8TP6fFE
http://www.youtube.com/watch?v=5uzUMEUcF-s
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In-Situ TEM Observation of VLS Growth
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Examples of NW Materials
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Building Complexity Into NWs
C. Lieber
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Nanowire Heterostructures
L. J. Lauhon, M. S. Gudiksen, C. M. Lieber, Phil Trans. R. Soc. Lond. A 362, 1247 (2004)
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Axial Heterostructure Growth and Characterization
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Semiconductor Bandgap vs Lattice Constant
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Type I and Type II Heterostructures
lowest energy forelectron and hole are inthe same region
lowest energy forelectron and hole are in
different regions
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Examples of III-V and IV heterostructures
Samuelson Group Lieber Group
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Interfaces and Dopants in NWs
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Branched NW Growth