scanning probe microscopy of dendrimer monolayers · scanning probe microscopy of dendrimer...

Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering Center

Scanning Probe Microscopy of Dendrimer Monolayers

Jia Sun, Kye-Young Kim, Silas C.Blackstock, and Greg J. Szulczewski


N

N N

NMeO

N

OMe N

OMe

MeO

MeO OMe

OMe

OMe

OMe

3PD 4AA/PD

TAPD

N N

OMe

OMe

MeO

MeO

N N

N

N

MeO

OMe

N

N

MeO

MeO

MeO

MeO

OMe

OMe

OMe

OMe

S-TAPD


20nm 3PD/HOPG

Bias –3V,set point 10pA Bias –2V,set point 10pA

Bias 0.656V,set point 5pA Bias 1.59V,set point 5pA Bias 2.59V,set point 5pA

Bias is positive

Tip

Bias is negative

Tip

Electron flow

Electron flow

sample

sample


STM images of 20nm 3PD/HOPG1st image Zoomed in once and zoomed out

Scanned 6 times and zoomed out Image of small area


124000

126000128000

130000

132000134000

136000

155160165170

binding energy(ev)

coun

ts

192000194000196000198000200000202000204000206000208000

155160165170

binding energy(ev)

coun

ts

138000140000

142000144000146000

148000150000

155160165170

binding energy (ev)

coun

ts

118000

120000

122000

124000

126000

128000

155160165170

binding energy(ev)

coun

ts

X-ray photo spectra in S(2p) region of S-TAPD/Au

10 S 2 Hr

3Hr50min 26Hr


0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

0.005

0 200 400 600 800 1000 1200 1400 1600 1800

immersion time(min)

ratio

of x

ps p

eak

10s

35min

2hr3hr50min

26hr

Ratio of XPS peak area for Thiolate S(2p) and Au(4f) atvarying immersion time


Au(111) S-TAPD/Au(111)

1.3nm


Micro contact printing S-TAPD on HOPG and Au(111)

Fabricate master Cast PDMS prepolymer Cure and peel off

Ink stamp in S-TAPD/toluenesolution and dry

Printed S-TAPD lines

HOPG/Au(111)HOPG/Au(111)

Print and release on substrate


Printing S-TAPD on HOPG

9.7Х10-4M 3.2Х10-4M 9.7Х10-5M


AFM image of S-TAPD printed on HOPG


AFM image of S-TAPD printed on Au(111)


• Conclusion• To image 3PD on HOPG, bias voltage is important for

STM image contrast. There is a threshold bias of ~2.5V require for imaging.

• Dendrimer with thiol group has been synthesized, becausethiol groups have a strong affinity for Au surface, stable STM images S-TAPD/Au(111) have been acquired.

• Future work• Redox gradient dendrimer with “core” and “shell”structure

will be studied later.• The size of STM image should be decreased in smaller

size(below 50nm)• Apply pulse voltage to STM tip to change redox state.

scanning probe microscopy of dendrimer monolayers · scanning probe microscopy of dendrimer...

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