Lecture 9 Fall 2011v1

8/3/2019 Lecture 9 Fall 2011v1

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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


14/29Phillip Kim, columbia


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Semiconductor Nanowires

Samuelson group

L. Lahoun


16/29

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

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Lecture 9 Fall 2011v1